Grab and Go

One key to enjoying the telescope hobby is to know how to set up and tear down your equipment quickly. This is especially true around Pittsburgh where the weather can change instantly from perfect to disastrous. Over the past couple of months I have developed a reasonably systematic routine in the deployment of the telescope. With it I can set up my full video rig with automatic pointing and tracking in about 20 minutes. While not instantaneous, this is pretty quick, and I would say that it approaches what reasonable people can call “grab and go.” The following is my reference checklist and there is no reason in the world for anyone else to read it except to be bored. But I already wrote it down, so I might as well post it. These setup instructions will work for any of the Celestron equatorial mounts. They can work for other mounts too, but a lot of the details will be different.

1. Put the mount outside. I have a spot on the patio behind my house that I use every night. This patio spot gives me a good view of most of the sky to the west and south and a reasonably good view of the north and east. The house and trees behind the house block the lower parts of the eastern sky. A large tree in the yard blocks the northwest. Otherwise things work pretty well.

2. Point the mount roughly north. If it’s already pretty dark, use the hole in the polar axis of the mount to sight Polaris, which sits right over the roof of the house.

3. Set up the Telescope. Go and get the telescope and put it on the mount. Also fetch all the accessories you’ll be using. I use my scope in two general configurations. For visual work I use a 1 1/4″ diagonal and various Televue eyepieces. For video work I use my Mallincam with a light pollution filter and focal reducer on it. In addition I’ve been using the Celestron F6.3 focal reducer on the back of the scope lately. So I attach that as well. The camera goes straight into the telescope without a diagonal. This is more convenient. I attach it with a Televue 2 inch visual back because I had the camera fall out of the crappy Celestron visual back with the tiny little useless hateful set screws. The set screws failed to hold the camera, and it just fell out of the tube an on to my concrete patio. This sucked. The Televue is a 2 inch tube that holds the camera solidly using a compression ring. Highly recommended.

So my setup goes: telescope, F6.3 reducer, 2 inch visual back, a 2 inch to 1 1/4 inch adapter tube, then the camera.

4. Balance the telescope. This takes two steps. Set the mount up so that the right ascension axis is horizontal. Now you release the clutches on the declination axis of the mount. This is the one that points north and south and runs parallel to the axis of the telescope. Then while holding the scope, put it in various positions. Let go slooooowly and make sure that the scope mostly stays in place. I try to balance the scope when it is horizontal and when it is mostly vertical. Tracking and pointing near the zenith is a lot better if you get this right.

5. Now balance on the right ascension axis. This is the one that is orthogonal to the body of the telescope. This is easier. You want to position the weights on the counterweight shaft so that when you release the RA clutch and let go of the telescope (slooooooowly) the scope does not move. This is the simplest mechanical task that there is in astronomy, as far as I can tell.

Some people tell you to purposely set the balance to be a bit heavy on the east side of the mount because it smooths out the behavior of the tracking motors. Depending on what part of the sky you are looking at this means either you want the either the scope side or the counterweight side to be heavier. I have never had any luck trying to do this because it means you need to shift the counterweights whenever the mount flips, and I hate touching the mount in any way after I am done aligning it. Maybe you’ll have better luck with this.

6. Put the scope in its “home” position. For my mount this is the one where the counterweights point straight down and the scope points straight north. Peer into the finder scope and look for Polaris. It should be at least in the field of view. When the scope is in this position I turn the video camera so that later on I know which way north and east will be oriented in the field of view. This turns out to be handy later.

7. Power. Now go get your power supply. I had been using a big 12V battery, but it started to fail recently, so I bought a couple of 12V power supplies that I can plug into an outlet on the outside of my house. This has proven to be more reliable the last few times out.

8. Now wire everything up for video. The camera gets a control cable, an s-video cable and 12V power. The control and video cables go back into the house through a sliding door. The video cable goes into the USB capture widget and the into the laptop. The control cable ends at the big Mallincam control box. The largest box ever built for holding five buttons and a knob.

Then I plug the telescope controller into a 25 foot cable and run the other end out to the mount. Finally, a second 12V power cable goes into the mount itself.

9. Initialize the Mount. Work your way through the Celestron setup menu. Enter the time and date and then tell it you want to do a “two-star” alignment. This alignment will let the hand controller learn how to point at things in your sky. What you will do is pick two stars on one side of the meridian (either the eastern part of the sky or the west) and then 3 or 4 stars on the other side. I tend to start in the west and then move to the east because I tend to be impatient to go and look at things that are still rising. The eastern sky is also somewhat darker than the south and west, since the PIttsburgh light dome is primarily to the west and south of me.

For most of the summer the first star that I’d pick was Arcturus. The scope will attempt to point at the star, but it will usually miss. If the scope were already perfectly polar aligned and set up in exactly the same place as the last time I was on the patio, it might hit perfectly. But, these things are never true. So, it will miss by a bit. Use the arrow keys on the hand controller to point the scope and get the star in your favorite sort of finder. I use a 9×50 optical finder, because I’ve never figured out those red dot things. YMMV.

10. Focus. The start should now be in the field of the camera. If it is not, then that means your finder scope and telescope are not aligned. If that’s the case, remove the camera and put an eyepiece into the telescope to fix that. Assuming it is, I then go inside and fire up the video capture software. If I have not disturbed the focus too much, the star will be in the video feed and mostly in focus. Still, it’s best to go and get your Bahtinov mask to make sure.

The Bahtinov Mask is an insanely clever device that creates a diffraction pattern on bright stars that will tell you exactly when you have them in focus. Just follow the instructions and you can’t miss. After I’m done I remove the make and put on the dew shield. I’ve gotten away with just using a shield, for now. If I were smarter I’d use those heated strips as well but it’s only been an issue twice in a year.

11. Star Align. Having focussed the telescope we’re ready to finish the star align. First grab the camera controller and turn on the cross-hairs. Making the cross-hairs is a bit of a chore that is too complex to describe here. Maybe I’ll make a separate page about that. With the cross-hairs set up, use the mount controller to center the star. It will look like this when you are done:

In this picture the horizontal lines point roughly east/west and the vertical lines indicate north/south. The actual directions might be reversed, but the important thing is that I’ve oriented the camera so that the arrow keys on the controller are predictable. This is a small touch that makes life easier later.

Anyway, when you have centered the star hit “Align” on the hand controller to tell it that you want to go to the next star. The hand controller will suggest another star in the western sky. You can use the menu keys to pick one that you can see that are not too close to the horizon. Center it in the finder then in the video camera, then hit Align.

11. Calibration Stars. Calibration stars refine the pointing model of the mount to compensate for its mechanical limitations. The hand controller will ask if you want to add “calibration” stars. Hit Enter to say yes and it will suggest a star in the east to use for further alignment. Pick a star that is well placed and hit Enter. The mount will then flip around and try and point there. As before, it will miss by a bit. Center and align the first star, and the hand controller will ask you about another calibration star. Hit enter to say yes and repeat. As you add more stars you’ll notice that the pointing will get more and more accurate. Usually the third and fourth stars will be in the field of the view of the camera. If this does not happen, you probably missed with one of the previous stars which means you should just start over.

12. If you have to start over, don’t be frustrated. This happens from time to time especially as the sky changes and you need to pick different stars for alignment because the ones you were using before have moved to the wrong side of the sky or behind a tree. Don’t panic. Just unplug the mount and do the whole routine again. Pretty soon you’ll end up with a new set of stars that you can use for a month or so and everything will run smoothly again.

13. Notes on Pointing. At this point, let’s review. We’ve set up the mount and we’ve told it to point at six points in the sky. Each time we’ve corrected pointing errors by hand, allowing the computer in the hand controller to build a pretty detailed model for how to point at things. My experience is that this pointing model works very well, especially if you avoid meridian flips. This is why I try to stay in the eastern part of the sky after doing all of this. If I cross back over to the west, the mount has to flip over, and this invites the creation of pointing errors. I’ve had it work pretty well, and I’ve also had results that were so bad that I unplugged the mount and started over. In one worst case, I had to wipe reset the firmware in the hand controller after some bug corrupted it. But, these are outliers. In general things work very well at this point and the total time I’ve spent from putting the mount on the patio to having good pointing is about 10 minutes. But, for video good pointing is only half the battle. In order for the mount to track over even short time exposures, we have to make sure the polar alignment is good. Luckily, this is not hard.

13. Polar Alignment. The Celestron hand controller has a wonderful piece of software in it that allows you to use the pointing model that you just worked so hard to build to polar align the mount. First, tell the hand controller to point the telescope at a star that is near the meridian and also near the “celestial equator”. All this means is that the star should not be too far north or too close to zenith. The hand controller will complain if you pick a bad star, so study your planetarium program to find a good one. I used Altair for most of the summer, and have recently switched to Enif in Pegasus after Altair wandered to the western sky. Remember, I try to stay on the eastern side of the meridian for all of this.

Now go into the Align menu and pick Polar Align and then Align mount. Hit Enter and the scope will point back to the star you just picked again. Repeat the center/align dance on the video screen. You’ll get another message from the hand controller about starting the All Star Polar alignment. Hit enter to start. The scope will now point to a different spot in the sky. This is where it thinks the star would be if you were polar aligned. At this point you put the controller down and you use the altitude and azimuth knobs on the mount to re-center the star in the field of view your finder scope and then the camera. When you are done, hit enter. Then find Undo Sync in the Align menu and hit enter on that too.

14. Polar Alignment Notes. There are a few things to keep in mind with this Polar Alignment scheme. First, you always want to end your alignment by moving the altitude of the mount up. You want to do this because the knob in the back that changes the altitude gets tighter when you push the mount up, which means it will stay in place better when you are done. I loosen the knob at the start end give the mount a shove downward so I know I’ll have room to move up later.

Second, it’s really handy to have a remote version of the video feed near the mount while you are playing with the knobs. I use VNC on my iPhone so I can see my laptop screen without needing to run back to the laptop. It’s also handy to use this trick when focussing.

Finally, the Undo Sync is important. The first part of the Polar Align routine “syncs” the mount to the star you picked. This messes up the pointing model to make pointing near the star accurate. But, as you move away from the star the mount points less and less well. Also, if you move the mount a large distance while finishing the alignment you may find that your pointing gets way off. In that case, unplug the mount and redo the star align. In my experience this hardly ever happens. The one time thought I needed to do it, my pointing didn’t really get any better and then it turned out that a cable snag was the reason the mount was pointing half a degree too far south all the time.

15. Final Notes. I’ve just described my setup process in about two thousand words. But you should not be discouraged by this. With practice I can do all of this setup in about 20 minutes. While this seems like a lot of up front work, remember that the guy that just goes in the house and grabs his manual alt-az on a tripod will then probably spend 5 minutes star hopping to each dim deep sky object that he wants to look at. Meanwhile, when this process works well, you can spend the next three or four or five hours with objects that are invisible in the eyepiece hitting the tiny chip in that video camera dead center every time.

Using this setup routine I’ve been able to get the Celestron CG-5 mount to do the two basic things you need an compuerized equatorial mount to do:

1. Point at things accurately.

2. Track objects in the sky for time exposures.

I use two telescopes on the mount, an 8 inch Celestron SCT and a new 85mm Televue refractor. I run the 8 inch scope at a focal length of between 1000mm (F5) and about 700mm (F3.5). On the best nights, the mount will point this scope so that every object I ask for is just about dead center on the Mallincam’s small chip. This means that we are hitting a field of view that is at most half a degree wide and about 22 arc minutes tall every time. That’s similar to the field you would get using a 100x eyepiece, which is pretty good.

The refractor has a native focal length of 600mm and I can also run it with a focal reducer and extension tube to get to about a 400mm focal length. This gives me slightly more than a degree of field of view so I can fit bigger things, like

or

or

The main complaint I have about this mount is that it does not track smoothly. I’ll sometimes get 4 frames in a row at one or more minutes that are perfectly sharp and then right after that I’ll get 4 frames in row where the object jumps 3 or 4 pixels to the east or west. I could try using a guider to clean this up, but I get the feeling that the guider will not be able to deal with these large jumps over relatively short exposures.

In the future I plan to spend a ludicrous amount of money on a mount that will track much more smoothly. But I predict that when I do so I’ll miss the relative sophistication of the Celestron software. Being able to use the video camera in the main telescope to do polar alignment can’t be beat. Hopefully the other guys will decide to try and catch up.

At this point I am morally obligated to end this post with yet another picture of M27. So here you go.

Clear skies to you all.

Deep Sky Projects

Astronomy is an endeavor that is full of catalogs. And I don’t mean the ones that are on the Internet that are designed to separate you from your hard earned cash. For much of its history, astronomers did little else than catalog what was in the sky. Before the telescope, this meant just what you could see with your eyeballs: the brighter stars, the planets, the moon, sun, and their various activities and relationships. With the advent of the telescope, more larger and more elaborate lists of esoteric objects could be created. The most famous of these was the one created by the French astronomer Charles Messier.

Messier was a comet hunter by trade, but he is much more famous for his catalog of interesting “deep sky” objects. The term “deep sky” in this context generally means non-stellar objects that are now known to be outside the confines of our solar system or, indeed, our galaxy. These objects are “deep” because they tend to be small or faint or both. The idea is that you have to look deep into the sky to detect them. This is not universally true, of course. Many of the brighter Messier objects are easily visible to the naked eye under darker skies and if you know where to look. But the term sticks.

So how did a comet hunter get into the deep sky catalog game? Well, in his scans of the heavens, Messier kept running to objects that looked liked comets in his small telescope (small, fuzzy, non-stellar). However, to his annoyance, the objects did not move with respect to the background stars. This meant that they were something besides the comets that he was interested in. In order to help out his fellow comet hunters he decided to make a catalog of these objects. Over time this list expanded to contain about 100 various nebulae, star clusters, and what we now know to be galaxies outside of our own. Later it was expanded and corrected to contain a final tally of 110 objects. You can look up the list in various places.

The Messier catalog is significant not only because it happens to contain some of the nicest objects that there are to look at in the sky, but also because everyone who becomes interested in deep sky observing eventually needs to find every object on the list. This activity serves as a benchmark of sorts; a common ritual that we can all share.

So of course one of the first things that I did when I broke out my new telescope about a year ago was to start working through the Messier objects that I thought would be practical to see from my yard. It’s good to have a project to work on. Keeps the obsession focussed. I actually did better under the light pollution than I thought I would. All of the showpiece objects were easy to find (M42, M31, M45, etc). I managed to sniff out some dimmer objects and to find hints of low contrast extended star clouds like M33. Still, there were obvious boundaries, especially for objects that sit in the sky glow to the south and west of my house. I never managed to find M74, and have only ever seen the faintest hint of something as bright as the Lagoon Nebula (M8).

When I got the video camera this all changed. Even relatively short time exposures with the CCD puts all of the Messiers well within reach of an observer of modest skill using a modest telescope. To illustrate this for myself, I set out to take “snapshots” of every Messier object as I encountered them with the camera. My goal is to just collect a recognizable rendition of the object that is representative of what you can do with short exposures (a few minutes total) with the Mallincam. I can’t draw, so I think of this as the closest that I will come to sketching what I see like a traditional observer might do. The most esoteric image processing technique that I’ll get into here is stacking multiple short exposures to reduce noise and get a bit of detail enhancement. I’m not going to go out and collect 50 hours of “data.”

Here’s a link to the first 85 images: http://www.flickr.com/photos/79904144@N00/sets/72157627091459246/

There are a few there that I would go back and redo. But for the most part I’m happy with what I have. I’m especially satisfied with the summer stuff. The fact that the camera can reach into the skyglow and get this picture of M8:

or this of the Eagle Nebula (M16):

or this of the Trifid (M20):

never fails to amaze.

The summer Messier objects also brought a few surprises. I had never seen the cluster M11 before, and seeing this in the camera motivated me to get the eyepieces out and take a look too:

I think the one weakness of the video camera is on star clusters. Stars all take on a square-ish pixelly look in video rather than the pinpoint sparkles that appear in the eyepiece. M11 is well worth seeking out and is easy to see.

The globular cluster M22 also surprised me:

I knew all about M13, of course. But the fact that there was this other huge ball of stars in the same sky never occurred to me.

As the summer progressed, it became pretty clear that filling out the last holes in my Messier image catalog would not be difficult. The winter objects that I had missed before would soon come back around and I’d get another shot. So it was time to look further afield for more things to find. Here, another legendary catalog stepped up to provide a longer term project.

In the late 18th and early 19th century the astronomer William Herschel (and his sister Caroline) not only advanced the art of telescope building to various new heights, but also discovered and cataloged an unfathomable number of deep sky objects. Herschel’s list eventually reached some 2500 objects and formed the basis for the modern “New General Catalog”, or NGC for short. In addition, there are two collections of the more notable Herschel objects called the “Herschel 400″ and the “Herschel II” lists which are a good place to start to explore this larger frontier. Over the last year or two the noted Internet Astronomy personality “Uncle Rod” has been working his way through these lists and chronicling his efforts. I figured if he can try for the whole thing, I can try for the brighter stuff from my house. So that’s what I’m doing, starting with the H400 list of the brighter stuff. If nothing else it will answer the question “just how much light pollution is too much for this camera?”

Here’s what I have so far, as far as I know: http://www.flickr.com/photos/79904144@N00/sets/72157627409712613/. Favorite surprises so far?

NGC6946:

The fact that I can see this much of the Veil (NGC6995):

And, the occasional great planetary nebula (NGC6781):

Anyway, as I said before, it’s good to have a project to work on. Keeps the obsession focussed.

I have to end this piece with a shot of M27, The Dumbbell, because it never fails to look good. So here you go.

Tens of Dollars

A guy at the office and I have a running joke about the amateur astronomy business. I will opine that the market is just begging for some great product to solve problem X for every telescope user in the world. And then we both snicker that one could make tens of dollars by building and offering such a product for sale. This is a marketplace where selling thousands of units a year makes you a massive player. It’s a market that is in a permanent niche.

Now, to some people, this is a feature. There is always that class of hobbyist whose idea of sheer hell is that their interest would somehow blossom into something generates a genuine mass market interest. Even back in the 80s there were already people who thought that computers had been dumbed down too much when people started putting them into boxes for you instead of making you build a wire wrap board. These people must be really pissed off now.

Astronomy serves as a case study in what happens when the mass interest never hits. Let us be realistic. This is a hobby that is primarily enjoyed by a few tens of thousands of users almost all of whom are male and aged between around 41 and 67. As a result, the market has the following odd characteristics:

1. The market is small. There will never be a product here that has the psychological impact of something like the iPhone. Or the Apple II for that matter.

2. The market is conservative. These people really hate change. I’ve mentioned this before, but I can’t think of a single consumer device besides a commercial telescope mount that still uses RS-232 for anything. The only other uses I’ve seen are for esoteric industrial control applications. This is also a market that isn’t quite sure that eyepiece designs from the 19th century still don’t have some technical advantages. I could go on and on.

Because the market is small, there are very few players in the market that can scale their operations to modern levels. The largest companies by far are the ones based in China. Orion Telescope and Celestron are the two most well known names here. They both source all of their products from the same large optical company in China. But, as you move up the food chain cost and quality, you move into smaller and smaller companies. The most well respected maker of refractor telescopes and telescope mounts is Astro-Physics. They make at most few dozen instances of each of their products a year. If you are lucky you can get a mount almost immediately (like now) but usually you’ll wait around a year. If you are unlucky and want a telescope be ready to wait 10 years.

Here is another example: there is a guy who used to work for Astro-Physics who now makes what I hear are bitchin’ tripods for the mounts. But the only way you can hear about him is in a forum post, or a classified ad. You can only order one of his tripods via email, and you will have no idea when the thing will actually be delivered.

You see this over and over again. More than half the time you go to any large dealer of astronomical products and look up something you want to buy, the words “pre-order” or “out of stock” or “back ordered” will be right next to the “buy” button. It’s almost easier to just look at the astronomy equivalent of ebay and wait for used stuff to show up. It will often happen faster than the new stuff. This is an infuriating state of affairs. People (by people I mean me) are now programmed to expect to just go to Amazon and buy anything with one click. The astronomy world destroys this expectation completely.

The issue of scale also comes up in the software business. Several of the most used pieces of astronomy software are primarily developed by one person. Not a small team led by one person: one person writing all the code (off the top of my head I can think of Skytools, PHD guiding, Nebulosity, the Astro-Physics mount software, and Equinox). While all of these tools are certainly functional, they will not win any design awards, and they are limited in the rate at which they evolve (c.f. the market is conservative). It’s just now occurring to folks that wireless control of equipment might be neat. Or that user interfaces might want to evolve past the Visual Basic Forms sort of look and feel.

Of course, there is an upside to all of this smallness. If you are lucky you will find small groups of people making just what you want and doing a really good job with customer service. Every single one of these small companies that I have mentioned (except the tripod guy) runs a mailing list on Yahoo where questions are answered by the people who run the company. Not some customer support staffer in India. The actual guy who runs everything. This is pretty neat. It’s too bad that they can’t hook up with that Amazon commerce engine though.

It’s good that you can find good support because you are going to need it. The combination of the small size and conservative nature of the audience means that there are not a boatload of companies breaking down doors to make telescopes and other astronomical equipment easy to use. I don’t think the industry has ever really gotten past assuming everyone buying telescopes has a little DIY streak in them and enjoys constructing custom wiring harnesses by hand, or hacking marine battery packs, or any number of other little construction projects. Let’s just say that product packaging is not necessarily a great concern. For example, you can buy a $10,000 Dobsonian telescope and then find out that you have to wire up the cooling fans to a power supply on your own because it’s too much trouble for the company to do that in its “factory”. In fact, you can go to manufacturer A’s web site and read about how one of their best features is that they don’t make you wire up the fan by hand, like manufacturer B does. It would be comical if it were not so sad.

Although I have learned to adjust to the strange ways of this industry, I still find myself wishing that it would move from the darkness of an obscure DIY niche into the light of a true mass-market retail industry. I’d like for things to be in stock, and I’d like to not have to worry about knowing whether I am using the right god damned power connectors between my battery and my telescope.

Side note: the power connectors on all this equiment are universally awful. It’s pathetic that you can buy an equatorial mount that costs as much as a used car and someone will still tell you that it order to get a clean power connection you might want to “spread the pins” of the power connector just to be sure. I mean come ON people.

I dream of a day when people will realize that spending hours calibrating a CCD camera just isn’t fun, and they should figure out how to automate the process. Or the day when I’ll be able to 1-click purchase a filter with confidence instead of having to call around to fifteen small-time dealers before I find one. But, I think I’ll just have to make the best of the here and now, because I don’t see that day coming. If anything, the industry is shrinking and what we have now may be the best it will ever be. After all, there can’t be that many people waiting in line to make those tens of dollars.

Odds and Back Ends

Back in part 2 I promised a short piece on all the other fussy details related to using the Mallincam. Instead I got into an extended tangent on the subject of telescope mounts, focal length and image scale and various other things. The final missing piece is what you actually do to see the pictures. After some experimentation, I have a scheme I’m comfortable with.

The defining aspect of the Mallincam which makes it different than other astronomical cameras is that its output is an analog video signal. A more traditional CCD or digital camera captures light into the wells of its sensor and then when the exposure is done, the voltages are read out of the sensors wells one at a time and converted into discrete digital values. These are then sent over a wire to a storage card (digital camera) or your computer (CCD). To actually see a picture you have to do some post-processing on the file to convert it into an image format that you can display and then parse with your eyeballs.

The Mallincam is different. There are two outputs on the back of the camera: one for S-video and one for composite video. You hook a regular analog video cable to these ports and then to a monitor and you can look at images directly from the camera. It’s as if you hooked up a camcorder from the 1990s to the back of your telescope. This is a great convenience if you want to just look at the pictures and not bother with any computer-based post-processing. Viewing with an old CRT security monitor gives you images that are as good or in some ways better than you can manage in a computer. The CRT has a luminosity to it that images confined to LCD screens lack. Believe it or not you can still find some CRTs for sale… but there are also people who use small and very expensive professional LCD video monitors.

Me, I use a computer. I actually ran a CRT screen side by side for a couple of nights as well, but didn’t see too much advantage in it. Anyway, I always have my laptop nearby since it’s running my planetarium and observation logging software. So naturally I’d want to use it to capture pictures. This leads to the question of how to capture video frames in the machine. On my Macintosh laptop, I tried two different schemes:

1. Firewire capture device, some Mac software for image adjustment. I bought a relatively expensive Canopus capture device. S-video goes in one side and Firewire goes into the Mac. Very high quality. Sadly, I was never happy with the capture and processing end. There is a tool called Camtwist with a lot of nice features, and even some filters specific to the Mallincam. Unfortunately it the basic tools it has for adjusting contrast, gamma, color and brightness are hard to use and much too fussy. The astronomy filters are pretty cool, especially if you are limited to shorter exposures. But the lack of a good set of basic controls killed this tool for me. The other worry with this tool is that it’s essentially written by two guys who have stopped working on it, so new versions of MacOS are sure to break it.

2. USB capture device under Windows. Again, the device has an S-video (or composite) input and then hooks up to your computer with a USB cable. For very little money you can pick up a “Dazzle” video capture box on Amazon. The quality is not as good as the Canopus, and you need special drivers that may or may not work on your Windows system. I had to buy and install Parallels to make this work. The drivers did not work in VMWare. In a strange bit of turnabout, once you get the device working there is a basic capture program that is much better than the Mac stuff in the “just works” department. I refer to AmCap.

AmCap doesn’t look like much on the outside. It has your basic shitty Windows XP layout and various modal dialog boxes. But, it does a couple of critical things right, which I will now explain. All of the Mac video capture progams assume that your goal is to capture a huge stream into a movie and then import it into Final Cut or iMovie or something. What this ends up meaning is that it’s hard to find software that has the video feed in one window and the adjustments in another window and lets you make adjustments to the video while seeing the feed change in real time. This is exactly what AmCap does.

When you fire it up, the main window has the output from the video feed. You can then open an adjustments dialog and drag it off to the side and push the brightness, contrast, saturation and other knobs around to fix up the picture. The sliders have an effective range of adjustments and a good “scale” in that they don’t change too fast which was my complaint about the Camtwist adjustments.

I should put a screen shot here to show you what I mean, but I don’t have my camera running to do so, so you’ll have to wait for later.

In practice the main adjustments you end up making are brightness and contrast. In a relatively light polluted environment like my back yard, you are always fighting the brightness of the skyglow and trying to beat it down without losing detail in the object that you are looking at. So the scheme is to drive the brightness down as much as you can and push the contrast back up to get some detail back. All the while you want to keep and eye on the noise. In the best cases, you can get good object detail and a nice dark background with acceptable noise, like this:

In the worst cases, I’ll have the brightness slider bottomed out and still have a huge glowing ball of noise in the frame, like in this shot:

I was looking at this object low in a very hazy sky, thus all the awful noise. This is about the best you can do with just AmCap. You could, and people do, use additional devices to adjust the signal before it hits the capture device. The Mallincam has spawned a large amount of interest among telescope geeks in archaic analog video processing devices to try and fight the dual problems of background brightness and noise. The most popular of these are based on old time base correctors that you used to use to copy old VHS tapes. These are hard to find since the main use for them was pirating VHS video tapes that no one cares about anymore. But if you snoop around you can still find them. Rock Mallin used to sell a modified one that he called the “DVE”, but he ran out. You can even find versions of these devices that allow you more sophisticated adjustments in color, brightness and contrast. I have not as yet experimented with anything like this, mostly because of the cost and also because I don’t want to add yet another box to my chain of complexity. But, if I ever run longer exposures that I do now, I’ll look into it more carefully.

AmCap also lets you capture single frames out of the video feed into a bitmap image file that you can then look at later. I’ve gotten into the habit of making a folder for each object that I look at on a given night and capturing 5 or 10 good frames into the folder. “Good” here is defined mostly by the quality of the tracking during the exposure. The mount is not always perfect, alas.

For a while I’d go over my screen shots at the end of the night and pick one that I liked for each object and throw them up on flickr. Here is a favorite object out of the southern summer sky, the Eagle Nebua:

It’s a bit noisy and washed out because it is relatively low in the southern sky. This puts it right in the worst sky glow that I have in my yard. On a bad night you can’t even see many stars with binoculars in that part of the sky, and it’s supposed to be filled with the rich star clouds of the Milky Way.

Anyway, a week or so ago I discovered that if I had five or ten good frames that were fairly well aligned, I could use some code in the Nebulosity application to “stack” the frames together and smooth out the noise and detail. What you do is tell Nebulosity how to align the pictures, and then just tell it to chew on the frames. The result, after a 5 minutes of Curves adjustment in Photoshop, looks like this:

This is really fantastic in my opinion. It’s about ten minutes of work above and beyond staring at the original video and capturing a few good exposures. But the stacking makes a big difference in the final quality of the picture. If you are interested, the tutorial I used to figure out Nebulosity’s stacking feature is here. Skip the parts about pre-processing and go right to the explanation of how to align images and do Standard Deviation stacking. It’s actually possible to do some dark frame subtraction with the Mallincam as well, but if you start down that road pretty soon you’ll find yourself running 8 hours of LRGB data collection when you should sleeping. I’m not sure I want to go there yet.

If you are observing at this point that all of this seems a bit similar to CCD imaging, I don’t think you are off base. There are similarities, but there are also differences. I think the Mallincam still does more pre-processing of the image than even one shot color CCD cameras do. The result is that you can can both observe the object in “real time” and then later post-process the images in a limited way to make them prettier. I like doing both.

That said, it’s not hard to imagine someone building a more streamlined CCD capture application that did some of the work that the Mallincam’s video hardware does. It should not be beyond the realm of possibility to quickly capture data from a short CCD exposure and process it into a color image in real time without all of the baggage of a long winded traditional CCD calibration and image processing workflow. Imagine an iPad app that can talk to one of the new eyepiece-sized CCD guider cameras, capture an image and show it to you instantly while you stand next to the telescope… maybe even over wifi. You could then save the individual files to your computer later to do stacking and other processing. All things being equal I’d buy that app.

To close, here are two more shots from my recent nights out. First, M8, the Lagoon nebula:

This is five stacked frames. Next, M17, the Swan. This is also around five stacked frames.

The best part of summer is coming. Hopefully the skies will be clear enough to see what’s up there.

Spring To Summer and The Nexus of All Things Dorky

As spring has turned into summer we are up against our last few chances to look at the really faint fuzzies in the spring sky. I refer of course to the mega-clusters of galaxies in Virgo and Coma Berenices. This week in Pittsburgh has been miraculously clear from summer haze, and my telescope mount has been miraculously clear from strange mechanical hiccups, which means I have spent a last few quality hours with the galaxies this week.

My first stop for the night was M64. I had found that the only image I had of M64 was a bit of a blurry mess because the focus of my telescope had gone off as a I captured it. So I took another shot at it, and it came out better:

This is about a 1 minute exposure. I also used the opportunity afforded by a well behaved mount to take 5 separate frames at 1 minute, and also a “dark” frame with the telescope covered up. I then used a cool program called Nebulosity to combine all these images and use the dark frame to clean up warm pixel noise and generally smooth things out. The result is this:

Noticeably nicer, without a whole lot more work.

After M64, I hopped over to the nearby NGC 5005 to add a new object to my “observed” list. The main reason people buy telescopes is to collect objects into an “observed” list. Anyway, this proved to be a nicer object than some of the smaller “M” galaxies in the area, with a pretty compact spiral:

From there, I then jumped into the Coma Berenices cluster and got the surprise of the night. I centerd my frame on the galaxy known as (I thought) NGC 4889. But, as you can see from the picture, the object is really small. I wasn’t really sure what I was looking at. To make things more confusing, Skytools did not think that there was any object named NGC 4889. It only knew about NGC 4884. Well, it turns out that one of many bugs in the NGC catalog is that these two objects are the same. There is only 4884. This mystery solved I stared at the field of view for a while, and noted a ton of little “stars” that looked suspiciously fuzzy. What could those be?

Since we live in the future there is an oracle in the sky that can tell us what these things are now, and all you have to do is send it a simple picture. I refer, of course, to the Astronmetry blind plate solver. I have mentioned this engine before, but at the time I did not give it enough extended credit. This system is as close to magic as we can get in the modern world. Best of all, it combines all three major dork passions into one glorious nexus of geekdom: it’s a computer that processes photographs and tells you what astronomical objects you telescope is pointing at.

Here is the picture I sent it:

The astrometry bot extracts everything out of the frame that looks like a star, and then compares the star patterns with a huge index that has been built from one of the more comprehensive catalogs of all stars down to some ridiculously faint magnitude. If it can find a strong enough match in this index, then with no information other than a noisy image, the system can tell you:

1. The exact celestial coordinates of the center of the picture.

2. The size of the field of view.

3. The name of every interesting object in the field.

4. Which way points north.

And so on. This used to take hours of painstaking work comparing your picture against a paper atlas. Now you send a picture to a web site and wait about 45 seconds, and you get back something like this:

The only thing more magical would be if it ran natively on an iPad (ha ha).

What the astrometry bot told me was that I had wandered in to a huge cluster of galactic bodies. The frame contains seventeen island universes each made up of hundreds of millions of stars. Truly a fantastic sight.

I rounded out the night with a reminder of what is to come over the next couple of months. I sent the telescope over to one of my favorite objects, the Trifid Nebula (M20). Images of this object through a six inch scope were what convinced me to take the plunge at the Mallincam in the first place, and the camera did not let me down. Here is a set of five frames, 45 seconds of exposure in each:

It should not be possible that this looks this good. Especially since the area of the sky this sits in is in the worst of the light pollution in my yard (to the south and west).

I’m looking forward to shifting from galaxy hunting to looking at the great nebulas of the summer. As another teaser, here is the Dumbbell (M27).

I think I’ll go to bed early tonight.

Fine Tuning in the Virgo Cluster, Plus a Surprise

Somewhat uncharacteristically Pittsburgh has had five reasonably clear nights in the last two weeks. In fact, we’ve had so many nights that I actually skipped one due to fatigue. On the other nights, I have taken the opportunity to try and fine tune setting up my little observational “system” for maximum efficiency. I hesitate to say that I succeeded since the device still regularly confuses me. But with my captured images as evidence, I will say that I’ve managed to improve what I can see by a substantial margin over the last couple of months. All this, plus a surprise.

There are three parts to the puzzle:

1. Mount setup, especially polar alignment.

2. Picking the right effective focal length.

3. Setting up the computer for image capture.

Mount and Alignment

The first two go hand in hand. So we will cover them in an interleaved fashion. It is axiomatic that the performance of the mount determines the focal length you can use. Since I am cheap, I bought an inexpensive Celestron mount (the CG-5) with relatively crude mechanics. This means that it has rather large tracking errors which would be magnified greatly by a long focal length. In addition, I am lazy so I have not set up an autoguider to correct those tracking errors. This means:

1. I should use the shortest focal length that I can get away with.

2. I should set up the mount as well as possible (within the constraints of not having a permanent position) to minimize tracking errors created by misalignment and such.

My telescope has an aperture of 200mm and a native focal length of around 2000mm (F10). After playing with many combinations, I decided that for my telescope while the image scale at F5 (1000mm) was pleasing, especially with smaller objects, the mount just could not track well enough. So, I finally settled on a setup that gives me F3.5 (around 700mm).

The following images of the galaxy M51 illustrate the difference in image scale and tracking quality:

First, at F3:

Second, at F3.5 to F4:

Finally, at F5 or a bit more:

The shot at F3 has way too much vignetting to really be usable. At F3.5 things are a lot better. The tracking is a tiny bit worse, but still tolerable. You can see a lot of detail in the object. Finally, at F5 the object is a nicer size, but we are right on the edge of what the mount can manage without guiding. The stars are a bit fat and the detail in the object can get blurred.

The second half of the mount performance equation is how well we set the mount up in the first place. Recall that the general scheme goes like this:

1. Set up the mount on the patio. Point the leg of the tripod under the polar axis roughly north.

2. Put the scope on the mount and balance.

3. When it is dark enough, turn the telescope sideways so you can look through the hole in the polar axis. Adjust the mount until you can see Polaris in the hole.

4. Plug the mount in and do a pointing alignment. The mount will point at 2 stars in one side of the sky and up to 4 on the other side.

5. Try to end step four on a star near the meridian and fairly high in the sky. Use this star to run the polar alignment software in the mount.

While this seems simple enough in principle, the mechanics of the mount and the temperamental nature of the software make every night a new adventure. Here are my tips for making your setup a less stressful experience. Note that these tips are by no means a complete method for foolproof setup. I still find that every other time I go out something weird happens and I throw my hands up in frustration. I find that it’s better to go out expecting the to do the alignment twice, because you will anyway.

So, things to watch out for when setting up a Celestron CG-5:

1. If you are doing the 2+4 star alignment and the mount does not seem to be getting any better at pointing, you probably aligned on the wrong star a couple of steps back. Unplug the mount and try again. Don’t try to fix it, just start over. The UI on the handbox is not really set up to effectively replace alignment information. I have tried to do this a few times when I realized that everything had gone wrong, and it just makes it worse.

2. The accuracy of the initial pointing will vary widely based on how the mount is feeling or whether you got lucky on your initial rough polar alignment. Don’t be surprised if the first couple of stars don’t even make it into a wide field finder scope. My finder is 5 degrees across and yesterday I spent the whole night missing. But, this does not really effect the final accuracy of the pointing system. After all my frustrations, I got the best pointing I have ever had last night. Good tracking too.

3. Don’t start aligning the mount too early. Without other stars as references, you are likely to guess badly and then you need to go back to step 1.

4. If you have a sequence of stars that works, milk it for as long as possible. Whenever you change the stars you use for alignment you are just asking for the mount to change up on you and go nuts. This happened to me when I decided to toss Dubhe into my list one night. Two problems: the mount did not seem to point at Dubhe, and I don’t really know where Dubhe is. Needless to say I started over again.

5. Try and arrange for the +4 part of the 2+4 to be on the side of the meridian where you want to be working for most of the night so you avoid doing a meridian flip. Also, I have had weird problems with the mount pointing off into la-la land if I do a meridian flip just before or right after finishing the polar alignment. So beware. Generally I try to end up in the West, because the sky to the West is not blocked by my house.

6. Plan ahead with the alignment stars to avoid areas of your sky blocked by trees, or houses. This is why aligning in the Eastern half of the sky doesn’t work for me.

7. When adjusting the latitude of the polar axis with the awful hand screw, always miss too low on purpose so that you hit alignment while tightening the screw. This way it won’t loosen later.

8. Occasionally, usually when everything has gone perfectly and you are polar aligned in 10 minutes, your first GOTO will send the scope pointing into the ground. At this point you should power down and go inside and have a beer. Since you are setting up a video camera, you don’t need to worry about wrecking your dark adaption. This is the best thing by far about using this camera, by the way.

Finally, I like to align with a high power eyepiece and switch to the camera after. This calibrates the pointing system with a smaller field of view, which in my experience means you get better pointing.

If all of this seems like a lot of work, it is. Last night I spent about 90 minutes doing trying to make sure that I could repeatably get a good polar alignment in a systematic fashion. I can’t really say I succeeded, because I was still confused about a few things. Also, I only got to spend an hour actually looking at anything. But The M51 capture above made it worth it.

The Rest

Now that the scope is set up, here is the rest of the checklist.

1. Connect the control and video cables to the camera.

2. Plug the video camera into the USB capture box. I use a cheap Dazzle DVC100. I have also played with a Firewire box and it is better, but the post processing tools, strangely, are better on Windows. So I’m using USB for now.

3. Fire up Parallels on the Mac. I use this because VMWare would not talk to my video capture widget. After the capture device connects, run AMCap to capture video. This is a .NET example program that does video capture. I use it because the brightness and contrast controls are much better than anything I’ve found on in MacOS for adjusting the video in real time. There are a few video processing applications for MacOS, but the native brightness/contrast/color controls are all awful. Clearly someone needs to fill this void.

4. Put the focussing mask on the telescope and go outside with the iPhone and focus the scope using the iPhone to watch the video feed via VNC. This is the future baby.

5. Take the mask off and go back inside with the hand controller for the mount. Now you can sit inside and point the telescope at what you want to see. Adjust the video with AmCap. Do screen captures to record your conquests.

I use Skytools to make lists of things to see. Skytools is very useful, but I find the UI clunky. I would like someone to take his databases and make a leaner planning program for the iPad. You could make tens of dollars doing this.

Lately, I’ve been working in the Virgo Cluster of galaxies because it’s almost summer and this is my last chance until next year. A month ago I was happy to get this out of focus and not so detailed shot of M87 and some companions. I was just amazed that there was anything there at all:

Last weekend, I managed to do this:

This has the nice feature that it’s actually in focus. The tracking is also a lot better. Good enough to capture this small detail in M87: the famous jet. Here is a slightly closer look:

Here are a few other favorites from this area and close by:

M94:

M101:

NGC 4631:

and M88:

Finally, a Surprise

One thing I’ve been doing to make myself feel better is to revisit objects I looked at last month and try to do better this month. Along these lines, I’ve taken a bunch of pictures of that old favorite, the Whirlpool Galaxy M51. Here is my first one from two months ago:

Here is the one I took yesterday:

I’m fairly happy with the progress.

Having taken so many pictures of the same object, I came across the following cosmic surprise. Here is a shot of the galaxy taken on May 30:

And then again two days later:

If you study the two pictures you will note that there is a “new” star in the second one that is not in the first. To the left of the core there is a straight line of three stars. The middle one is the new one. If you don’t feel like finding it, go to the Flickr image and it’s already marked there.

It turns out that this is a supernova that had been discovered by some amateurs in France just the day before. A single star 35 million light years away explodes with such violence that a little video camera in my sky-glow-filled suburban back yard can pick it up as a new point of light in a 45 second exposure. I never would have imagined that this would be possible 25 years ago.

I guess I’ll have to get a guider.

A Subject for Yet Another Cloudy Night

Pittsburgh is on its way to about the tenth day in a row where the dusk brings a bank of clouds and haze from the west. So I'm going to talk about field of view, image size, focal length and image size and a cool photo-related astronomy service. Anyway, we'll start with a horribly dry and boring technical discussion having to do with optics.

Focal Length and Focal Ratio

The focal length of a simple telescope the distance the light must travel before it comes to a single point of focus in the optical system. In lens-based systems this is a property of the main objective lens. Light enters the system through the front of the lens and comes to focus somewhere in back of the lens. The distance from the focal point to the center of the lens is the focal length. Similarly with mirror-based systems the light hits the front of the mirror and then comes to focus somewhere in front of it.

The focal ratio of a simple telescope is the ratio of the focal length of the scope to the size of its aperture. So, if your Newtonian telescope has an 8 inch mirror and a 80 inch focal length, then its focal ratio is 80/8 = 10. For some reason we write this "F10" to make sure everyone understands what is going on.

Many telescopes are made up of multiple lenses, multiple mirrors, or some combination of both. My Celestron C8, for example, uses an optically neutral lens, a concave mirror and a convex mirror. The concave mirror is around F2. The convex mirror has a "negative" focal ratio of F5. I'm not sure how this is computed, since convex mirrors don't focus the light at all. In any case, this arrangement stretches the effective focal length of the primary resulting in an F10 telescope.

Why Do We Care?

The short answer is: the focal length of the telescope determines, to a large extent, the apparent size of the objects that you look at with that telescope. The general rule is this: longer focal lengths make things bigger.

If you are using your eyeballs to look through the telescope, you can't just look into the back end of the scope and see an image. You actually need a second lens to put the image on your eyeball. This lens, or set of lenses is called an eyepiece. Eyepieces come in various sizes and shapes, and since they are lenses, they have focal lengths. In general eyepieces with long focal lengths are for looking at large fields of view at low power. On the other hand, eyepieces with short focal lengths are for looking at small fields of view at high power. In other words, the final object size in your field of view is determined by a combination of the characteristics of the telescope and that of the eyepiece.

This turns out to be handy. You can carry a bunch of different eyepieces around with you and pick which one to use based on how big the object is that you want to look at. This is how things worked for hundreds of years, until someone invented cameras.

Cameras are different

Here's an unexpected annoyance when you switch from using eyepieces to using a camera: the camera always sees the same field of view. The field of view of the camera is completely determined by two measurements:

1. The effective focal length of the telescope.

2. The size of the sensor in the camera. Ok, so you might be using film, so the film size would matter instead of the sensor size. But chances are you are not, so let's forget about that.

Since the size of the sensor in most cameras is fixed, if you want to change the size of the field of view covered by your pictures, the only thing you can do is manipulate the effective focal length of the telescope. Another way to put this is that the only way to change the scale of the objects in your pictures is to change the focal length of the telescope. If you want to take a picture of something really small, you want a long focal length. If you want to take a picture of something really large, you want a short focal length.

At first this seems sort of inconvenient. Carrying multiple telescopes around is a lot harder than carrying a small bag of eyepieces. Luckily, those clever optical designers have again come to our rescue. It turns out that you can buy any number of special lenses that attach to the end of a telescope and manipulate the effective focal ratio.

Some lenses flatten the light cone and therefore stretch the focal length. We call these barlow lenses. On the other side of the coin, focal reducers make the light cone steeper and make the effective focal length shorter. Thus, as a general rule Barlows make things bigger, and focal reducers make things smaller.

Focal Reduction is Your Friend

For Mallincam use, it turns out that we are generally more interested in shorter focal lengths than longer. There are several reasons for this:

1. The chip in the Mallincam is small. In addition, the camera's strengths lie in capturing images of deep sky objects, which tend to be more extended in size than (say) double stars or planets. Therefore, generally the case that you are trying to fit relatively large objects on to the relatively small chip, so reducing the image scale is a good thing. Now, this is not always true. If you are hunting tiny planetary nebulas, you'll need to be working at a relatively long focal length.

2. Short focal lengths usually mean smaller F-ratios. From our lessons in photography we will all remember that smaller F-ratios mean shorter exposures. This is true in astrophotography too, at least for the extended deep sky objects that we tend to use the Mallincam for. Shorter exposures are always a good thing.

3. In addition to shortening exposure times, short focal lengths mean that you can get away with sloppier tracking in your telescope mount. This is because you are effectively working at a lower level of magnification, so tracking errors will not be as evident.

So Now What?

There is no lack of advice on how to combine various focal reducers with the Mallincam. Just consider this PDF file with dozens of different combinations. The available hardware for this can be summarized in the following list:

1. Reducers that attach to the back of your telescope using the standard Schmidt-Cassegrain threads. These tend to be designed specifically for SCTs, but who knows, maybe they can work elsewhere. Celestron, Meade, Antares and others all make an .63x reducer that hooks up this way. Meade also makes a .33x reducer that is designed only to be used with small CCD cameras. Conveniently, the Mallincam is just such a camera. I have a Celestron .63x which I also use with my eyepieces.

2. Reducers that attach as eyepiece filters. The best example of this is the Antares .5x reducer. There are a few others. But I have this one so I'll talk about it.

3. Special reducers made specifically for the Mallincam that thread on the front. These can be hard to come by. I have an MFR-5, which is a two piece device which I will talk about in a bit. Rock Mallin has also made an MFR-3 which was a single lens. The use of this lens is covered in the PDF I linked to above.

4. If you use Celestron telescopes, you can look into the Hyperstar system. This device lets you run your SCT at around F2, which is pretty cool. This works particularly well for larger apertures. For smaller scopes, the image scale gets to be too small to be useful.

5. Finally, various optical companies make custom reducers/field correctors just for their telescopes, usually refractors. You can find these devices made by Vixen, Astro-Physics, Televue, Borg and others. I don't have any of these (maybe soon!).

For my purposes below, I'll cover some experiments that I have done with devices that fall into the first three buckets above, since I actually own them.

Computing Effective Focal Length

This turns out to be harder than you think. You would naively hope that when you buy a focal reducer, somewhere on the box it would say something like "when you attach this to your telescope, it will cut the focal length in half." Unfortunately, it's not that simple. The effective focal length your telescope with the focal reducer added depends on the optical qualities of the reducer and on the spacing between the reducing lens and your eyeball, or the CCD in the camera. The Celestron/Meade/Antares "F6.3" reducer is specified as being a .63x reducer, but this is only actually true if the spacing is just right. If you are closer to the lens than the assumed distance (around 90-100mm, I think), then the final reduction is a bit smaller. If you are further away, then you get more reduction.

This effect is why you see so much traffic on the Mallincam groups about putting "spacers" between the camera and the focal reducer. Note that while you can get some mileage out of changing the spacing, if you get too far outside of the optimal range you will experience various optical maladies, the most obvious of which will be light fall-off in the corners of your picture. The more you push the reduction the worse this gets, since the steeper light cone will inevitably can only cover a smaller image area. This is why reducers like the Meade .33x can only be used with small chip CCDs. Put anything bigger behind it and you get dark corners.

In addition, you may have trouble focusing your telescope and you may find that the image at the edges of the field of view are distorted in strange ways. These issues all reflect the fact that the focal reducer is working against the laws of physics and trying to get you a free lunch.

Now, there are some optical formulas that let you plug in the focal length of the focal reducer and the spacing and compute the effective focal reduction. However, these are of limited use for two reasons:

1. Focal lengths tend not to be specified, and measuring the spacing is hard.

2. The formulas go out the window if you use multi-lens systems. This is because you can manipulate the spacing in multiple places and wen you do that who knows how the reduction factors combine. The MFR-5 has this problem since you can put spacers between the two lenses or just after them. You can also end up confused if you combine the Celestron .63x reducer with another lens.

A better way to figure out what your effective focal length is is to just use the camera to take a picture and then compute the field of view of the picture. If you know the field of view covered by the picture and you know the size of the CCD you used to take the shot, then you can solve for the effective focal length. Now, you might ask, how do you compute the field of view covered by a picture? Here the Internet comes to the rescue. All you do is this:

1. Join Flickr.

2. Joint the astrometry Flickr group.

3. Take your screen gran and add it to the group's pool.

4. Wait.

If your shot is clean enough, the bot that watches the pool will grab it and compare it against a huge database of star and object positions. Usually it will then tell you what part of the sky you took a picture of and the size of the field of view covered by your photo. I have a few examples here in my Flickr page. This one is the best:

Note the comment from the Astrometry bot. It tells you the coordinates of the center of the photo, the size of the field, and even all of the interesting objects in the picture, in case you didn't know. This is fantastic. Anyway, I take the field of view and then use Skytools 3 to match it with the right effective focal length. Skytools has an engine that will show you the field covered by your camera at a given focal length, so you can just plug values into that until you get something that matches. If you don't have Skytools there are any number of other package that do this, including some handy web pages.

Using this scheme, I have tested the following configurations of focal reducing lenses, and computed the efective focal length for each one:

1. The Antares 1.25" .5x reducer. This one is designed to be used with around 50-60mm of extension. I did not have quite that much, so in my pictures the effective F-ratio (with my C8) is about F5.5 instead of F5.

2. The MFR-5 with a 5mm spacer between the lenses. This gives you F5.

3. The MFR-5 with a 10mm spacer behind the entire assembly. This gives you F3.5 or so. This combination also produced obvious vignetting.

4. Finally, the Celestron .63x combined with the front lens of the MFR5 the standard 1.25" diagonal. This also gave me around F3.5. I used this odd combination because I fit in my diagonal without bottoming out on the mirror. Since I switched to the GEM I stopped using the diagonal so this is not that critical anymore. Still, it's a nice combination.

The next test I plan to run if I ever get a clear night is to combine the .63x reducer with the Antares. I expect to get to around F3.5 or hopefully a bit less. I might also try the Meade .33x focal reducer.

In my telescope, I find that F3.5 is nice because everything is a bit brighter, but the image scale at F5 has been better for the smaller galaxies that you tend to look at in the Spring. Your mileage will vary according to the aperture of your telescope and the quality of your mount.

I will note here that my measurements of the MFR-5 do not match what appears on the various Mallincam web sites, in the Internet forums and in the camera's documentation. I have no insight into why what I found was different, but my numbers are consistent and I'm fairly confident that they are right.

Summary

1. Focal length determines field of view and therefore image scale in the camera. For the Mallincam, shorter focal lengths tend to give you a better image scale.

2. Shorter focal lengths also reduce your focal ratio and therefore your exposure times.

3. Focal reducers can do their job well, but only under certain constraints, like spacing and the size of the final image circle.

4. With an 8 inch SCT telescope, working at F5 to F3.5 is a good range of focal lengths. Any shorter and stuff gets too small. If you need to go wider, it's probably wiser to get a wider field telescope.

Late Night with the Mallincam

If there is one thing that I have learned in my now medium-long lifetime it's that in Western Pennsylvania you cannot count on clear skies lasting. So when the clouds parted last Friday night at 11:15pm, I had a short quandry. On the one hand, it was 11:15pm and I should be in bed. On the other hand, it might be the last window of clear sky for another month. April to this point had been nothing but gray skies, cold, and rain. After considering this for about 45 seconds, I started to set up the telescope.

As this was my second time out with the new mount and as the first time had gone pretty well (got set up and aligned in about 20 minutes) this time things went less smoothly. To make this work well, you need script and a list. And I forgot a few parts of the script. Here is how you set up.

First, we need short tangent on what we want the mount to do for us when we are done. By convention we keep track of the position of every cataloged astronomical object that we deal with using something called the equatorial coordinate system. This coordinate system is similar to the one we use on the Earth, with the longitude and latitude, except it that it's projected on the sky. The east/west coordinate, similar to longitude, is called Right Ascension or RA. I don't know why. RA is measured like time, in hours, minutes, seconds and so on. This turns out to be convenient because you are often interested in the time at which objects are visible or not. If you know the time of year and the RA of the object, you can compute whether or not you should be able to see it.

The North/South coordinate, similar to Latitude is called Declination, or DEC. This coordinate is measured in the familiar degrees, minutes, seconds, and so on.

Our equatorial mount, unsurprisingly, has two axes that go by these same names. The right ascension axis is also called the polar axis of the mount.

The eventual goal of the setup is to align two things. First, we want to align the polar axis of the mount with the polar axis of the Earth. This alignment is called polar alignment and allows the mount to track objects in the sky while only driving the telescope along one axis.

Second, we want to give the mount's computer an accurate picture of what is where in the sky so it can point the telescope automatically. I call this star alignment to distinguish it from polar alignment. When we are done, we should be able to tell the mount to point the telescope anywhere we want in the sky, and it can do some quick calculations to figure out exactly how to run the motors to pull that off. Then we sit back and watch the object come into the field of the eyepiece, or camera. So, here we go.

1. Take the mount outside. Point the right ascension axis of the mount roughly north.

2. Attach the counterweight on the counterweight thingy.

3. Go back inside and grab the telescope. Attach the telescope to the mount using the quick release dovetail arrangement.

4. Balance the scope and the counterweight along the right ascension axis. To do this on my mount, you release the clutch on the RA axis. This lets you turn the mount by hand rather than with the motors. Now turn the mount until the shaft is horizontal and gently let go. If the telescope drops, move the counterweight further away from the telescope and try again. If the counterweight drops, move it closer to the telescope and try again. Iterate until the whole system is balanced.

5. Now balance the telescope along the declination axis. Tighten the RA clutch. Carefully loosen the DEC clutch turn the telescope until it is horizontal. Slooowly let go and see how the tube moves. With the Celestron telescopes you can then move the scope backward and forward in the quick release saddle until it balances.

6. Now turn the mount until the little index marks line up. When you are done doing this the scope is in its "zero" position and should be pointing North. If it's dark enough you can look in the finder scope and maybe see Polaris. Resist the urge to center Polaris in the finder. This will do you no good because the axis of the finder is not what you want to point at Polaris. I shoud know, I wasted my time doing this.

7. Instead what you want to do is look through a hollow in the RA axis and put Polaris into that hole. Then you know the polar axis is looking roughly at Polaris, which is more useful. To do this, loosen the DEC clutch and turn the tube to 90 degrees from where it was. You should now be able to look through the hole and see sky.

Get down on your knees and push the mount around and peer into this hole and see if you can see Polaris. It might take a few tries before you can see anything, depending on how dark it is. If you can't see it, use the following odd scheme to find it. First, you will note two long bolts with handles on them on the front and the back of the mount. These adjust altitude. They do not do it very well. In particular, it's hard to smoothly lower the altitude. So, on the theory that you are pointed too high, loosen the front lever and push the mount so it falls down a few degrees in altitude. Then, using the back lever raise the mount again and hopefully you'll see Polaris enter the field. If not, you might be off to the side a bit. Shove the mount sideways one way or another and try again until you get Polaris in the hole. The field of view through this hole is pretty wide so this isn't too hard.

8. Also on the front of the mount you will notice two knobs that push the mount side to side. If Polaris is not centered side to side in the hole, use these knobs to move it around. To move the mount you loosen one knob and then tighten the other one. I don't remember how things are oriented so you will just have to try yourself until you figure it out.

Starting with Polaris roughly in this hole turns out to be important. In my short experience, if you are too far off the star alignment which I will describe next never ends up working.

9. Now turn the scope back to the zero position and plug in the power cord. Answer all the questions about time and date and such that the hand controller will ask you and start the two star alignment. Tell the mount to move the scope to the first star it suggests. If you can't find that star or its blocked, hit the undo key to try other stars until you get one you like. The mount will point the telescope at the star you picked and then you will use the arrow keys on the hand control to center the star in your finder then the eyepiece. The Celestron manual tells you to always make sure the final movements of the stars are driven by the Up and Right arrow keys. This minimizes the resulting backlash in the gears. I have no reason to doubt the manual on this point, so be careful about that.

The mount will then let you repeat this process on a second star. You will notice that by default both of these stars will be chosen from the western part of the sky. After you are done, the hand controller will ask you if you want to add "calibration" stars, all of which will be chosen from the eastern part of the sky. You can add up to four of these stars. Keep adding them until the pointing gets very accurate.

There are two important things to know about this procedure:

First, the east/west breakdown is important for mounts like the CG-5. The CG-5 is what we call a "German Equatorial Mount", or GEM. The geometry of the GEM is such that you have to be aware of the relative position of the telescope and an imaginary line called the meridian. The meridian is the line that runs North/South and splits the sky in half East/West. If you have set up your mount correctly, the middle of the tripod sits right on top of the meridian, and in a GEM this means that the scope is on one side of this line and the counterweight is on the other. The thing you have to remember is that GEMs have a hard time tracking past the meridian because when you go too far either the scope or the counterweight shaft will run into the mount. Bad news.

To get around this problem GEMs flip the scope around whenever they cross the meridian. You want to be able to do this and maintain pointing accuracy, so the Celestron software does allows you to do extra calibration to make sure this works right.

The second thing to remember about star alignment is not to try to do it when there are thin clouds around. This makes it easy to guess wrong and align on the wrong stars, or stars you cannot see. Then no matter how many stars you align to, the pointing never gets any better. If you notice this happening, the best thing to do is to reboot the mount and start over. I ended up in this situation at about 11:45pm. By then the sky had really cleared, so I buckled down and tried again. I turned the mount off, made sure that I got Polaris into that damned hole, and started again. Ten minutes later I was ready to move on.

10. Having fine tuned your star alignment, you can now engage a nifty little piece of software that is unique to the Celestron controllers. It is called "all star" polar alignment. Pick one of the stars that you used for the final calibration as long as it is not too close to either due North or zenith. Hit the Align button on the hand controller and navigate to the Polar Align menu and then choose Align Mount and hit Enter. The mount will think a bit and then move the telescope to point at the star you just picked. Use the hand control to center it just like you did before. When you are done, you tell the hand controller to start the Polar alignment. The telescope will think a bit and then move to another spot in the sky. This is where the alignment star would be the mount were in fact polar aligned. Now you get to get down on the ground again and use those knobs and levers from before to push the mount around in azimuth and altitude until the star is centered in your eyepiece. When you are done hit the Align button and you are done.

By this time your knees and shoulders should be a bit sore, but your mount will be well aligned for both pointing and tracking. I managed to get to this state by about 12:15am. So then I yawned and went in and got my camera.

While the CG-5 mount is bigger, heavier and more complicated than my old 8SE mount, it does have its advantages. First, I have found that the tripod is much more solid, so the telescope does not shake and shimmy when I'm trying to focus. Second, it's a lot easier to use the camera because I can stick it into the back of the telescope without worrying about it hitting the base of the forks. On the other hand, there are some things you want to be careful about.

If you do not firmly attach your eyepiece to the telescope, you may find that the mount can make it fall out as it turns and twists the telescope at all strange angles. This is bad. You may also find that the various cables that stick our from various ports in the mount and lodge themselves between the motor housings. I've had this happen twice now and I'm not sure why, but it does make the mount upset. Try to avoid this.

Luckily, on this night, with the time nearing 12:30am, I had none of these issues and was able to happily go to my first target, the galaxy NGC 2903. There are two things to note here. First, you can see the cool spiral arms of the galaxy. Second, even with about a minute of exposure, the mount is still tracking pretty well. I have found in general that a minute works well. Two minutes is a bit too long.

Second target of the night was the "Hockey Stick" galaxy, NGC 4656. This is a pretty dim object, I was happy to get a good view of it.

I then cruised through the galaxy clusters in Virgo and Coma Berenices. There was M64, M84, M86, M87, and M91. For two hours, everything I asked for hit right on the camera and the mount tracked with relative smoothness. I was using the camera with a .5x focal reducer, which means that the effective focal length of the telescope was 1000mm instead of 2000mm. This means that the field of view of the camera is roughly 20 by 15 arc minutes, which is pretty darned small. Overall I remain impressed by the ability of a 25 cent embedded processor to accurately point a 15 pound telescope with this level of accuracy.

Somewhere around M87 I noticed the pictures looked funny, with ugly bloated stars. I didn't think about it too hard until I tried to look at M101 and it was all blurry. So, I turned the telescope to the globular cluster M3 and tried my best to refocus.

Having gotten closer, I went back to M101 and got the surprise of the night. Most of the objects I had looked at had been small with bright cores but not much in the way of larger scale detail. M101 was different. The arms spread out over the field of view with dim hints of dust lanes and other grand details.

I finally shut down for the night at 2:45, sleepy but pretty happy. I was also hopeful that with a bit more practice I'd be able to tease even more out of these objects sitting above me in the sky. Who would have thought you could see this much with relatively little work in your backyard.