Astrophotography and the ETX by Jordan Blessing

Types of Astrophotography

There are basically 3 different types of astrophotography:

1. Piggyback -This can be the easiest type and should probably be the first type you attempt, at least for any deep sky photography. In this type the camera does not look through the optical tube, it is mounted "piggyback" on top of the tube. This allows a "fast" focal ratio (depending on camera lens used) and allows you to guide the camera (if you have a drive corrector or very steady hands!) through the optical tube at high power. The telescope in this case is used as a tracking platform.

2. Prime Focus -In this type the camera is directly coupled through the optical tube and essentially uses the telescope as a lens (no eyepiece is used). This works well for close bright objects that require only very short exposures such as the Moon, planets, and (Sun-with proper filters only).

3. Eyepiece projection -This is similar to prime focus except that the adapter also allows you to insert an eyepiece for higher magnification. As far as I know there are no ETX specific eyepiece projection adapters available, but I'm sure that some of the many standard 1.25" versions would work. This type due to the VERY long exposures required should be limited to the Moon, Sun (with proper filter), and the brightest planets. It certainly should not be attempted without considerable experience.

Note: The numbers above will be used in ( ) below to designate the applicable type of astrophotography being discussed.

These are listed in order of difficulty (and in order of magnification generally obtainable). You should understand that the lower the power, and the wider the field, the faster the picture will expose. Thus piggyback exposures can be much shorter than prime focus or eyepiece projection exposures. The additional benefit of low power wide field shots is that they are MUCH more forgiving of guiding inaccuracies. No astrophotography is easy. It all requires patience, practice, and a careful methodical approach to get good results. BUT it can be fun even if you don't get any good pictures at first, and when you DO get that first good picture it is all worthwhile. First I will discuss the ETX as an astrophotographic instrument, then I'll discuss some of the necessary equipment. Finally I will give tips and accepted procedures for making it all come together. I have been into astrophotography with my 8" LX-50 for a while now and can speak from experience. Though I have every imaginable photographic accessory for it (including an autoguider, etc.), it STILL can be difficult. The ETX presents a new challenge and as soon as this nasty Florida weather clears up I will be taking and posting some ETX pictures.

The ETX as a Astrophotographic Instrument

There are some basic requirements or at least "desirements" for a telescope that will be used for astrophotos. Some of these are:

• A solid sturdy mount.
• A short focal ratio (fast) optical tube.
• An accurate drive mechanism.
• A drive corrector (hand control) to allow minor drive corrections.

Well, the ETX certainly doesn't look like the ultimate astro scope does it? It has a fairly flimsy mount, a very long focal ratio (slow) optical tube, a drive far less accurate than a $2 watch and no stock drive corrector. Hmmm, well these are things that need to be taken into consideration. They will limit what we can do and how we can do it, but we just have to know the limitations and work around them as best we can. Don't despair, there are still great images out there for YOU to take with the ETX. The ETX does have one very desirable element for astrophotography a flip mirror. This can make focusing and setting up a shot much easier. This is usually a fairly expensive accessory for most scopes.

Accessories for ETX Astrophotography

Depending on the type of AP (astrophotography) we want to do we will need a few accessories. Typical accessories would include:

• Piggyback Mount -This accessory allows you to fasten a camera to the top of your scope. JMI makes an ETX specific unit that will do the job nicely.

• T-Adapter -This allows you to couple the camera rigidly to the back of your optical tube. The Meade #64 T-Adapter is made specifically for the ETX.

• T-Ring -This couples the T-Adapter to your particular brand of Camera. Many people sell these, Orion Telescope & Binocular Center is online and carries quite a few different types.

• Suitable Camera -I will get into this shortly.

• Remote Shutter Release Cable -This allows you to trip the shutter without inducing vibrations in the camera. Any camera shop will have these relatively cheaply.

• Drive Corrector -This is essentially a hand controller that allows you to make "corrections" during the exposure to account for inaccuracies of the drive mechanism. No drive is accurate enough for long exposures without some means of making corrections or pictures will streak, elongate, etc. I of course manufacture and sell the original and only dual axis drive corrector for the ETX (shameless plug).

• Illuminated Reticle Eyepiece -This is really a necessity for making a good drift alignment and accurate guiding corrections during piggyback exposures. Many places sell these, they are essentially a 9-12mm eyepiece with red illuminated bullseye crosshairs. A poor mans alternative to this for doing a drift alignment or piggyback guiding would be to defocus the star image so it just about fills the field of view with a "ring" so you can easily see which way it is moving.

Suitable Cameras for Astrophotography

The ideal camera for AP will have some or all of the following features:

• Manual Shutter - This feature allows you to open the shutter via cable and keep it open for extended times since batteries are not involved, the mechanism is fully mechanical with no batteries needed (though the camera may take batteries for metering etc).

• Mirror Lockup -This allows you to manually lock the mirror up before triggering the shutter. This can greatly lessen vibrations, but is not a necessity. The "hat trick" can be used as a work around.

• "B" (Bulb) Mode -This mode allows you to hold open the shutter indefinitely, NON automatic is what you want for AP. All the fancy built in camera gizmos in the world will be lost trying to properly expose for AP.

• SLR Lens Mount -If you want to be able to couple the camera optically to the OTA the lens must be removable and a T-Ring must be available for it.

• Interchangeable Focus Screens -Things can get real dark though a viewfinder and focusing can be very difficult. If your camera can accept different focusing screens you will want to get the clearest, brightest one possible.

Probably the single best camera for AP is any one of the Olympus OM-1 versions out there. These cameras are no longer made, but they have ALL the desirable features and can be found at a reasonable price in good condition (about $100-$200 depending on condition). Check AstroMart, online camera classifieds, used camera dealers, etc. Also available for this camera is the vari-magnifier, if it has one of these included cheap you have found a real deal. This accessory allows you to swing the viewfinder all around for easy viewing and has variable magnification for finer focusing. Another popular camera that is probably much easier to find is the Pentax K-1000. It has some of the features, but is not nearly as well suited as the OM-1. The OM-1 came in chrome or black, and had designations such as OM-1, OM-1 MD (motor drive compatible), OM-1N (same as MD except for very minor changes). Do a search on the web for the OM-1 faq for a ton of information.

Suitable Films for Astrophotography

I have used many different films for AP and I think a few stand out. The main things you want from AP film is high speed and a fine grain. There are many other things involved, but I am staying fairly basic to keep things as simple as possible. My personal favorites since they work very well and are easily obtainable are Fuji G-800 (or 1600 if you can find it) for color shots and Kodak P-3200 for black and white. Take a look at my LX-50 web (http://home.att.net/~jblessin) page for a couple examples of different films.

Hints, Tips, & Tricks

• A Scientific Approach -A scientific methodical approach is best for AP. You should make yourself a checklist of all the things necessary to take the shot and follow it, this will prevent you from accidentally skipping an important step and realizing it too late. You should also keep clear and accurate notes of each picture. Things such as film speed, exposure time, subject, wind, bumped camera, cloud interference, etc will help you make sense out of what went wrong when you get a messed up picture back and plan your strategy for the next session. I find writing a pain in the field and often keep notes on a micro tape recorder and transcribe them later.

• Start off Easy -The Moon is by far the easiest object to photograph. Since it is so bright exposure times are extremely short. This means guiding inaccuracies really aren't a problem. This also lets you bump up the power and use prime focus or eyepiece projection to get close ups and still be able to finish an exposure before inaccurate guiding becomes a real problem.

• A Drift Alignment -While it can be a pain and time consuming there is no substitute for a near perfect polar alignment. Any error will compound over time and cause stars to streak or turn into little curled "Fritos". There are many articles on the web about drift alignment, but I will go over the procedure quickly. Either use an illuminated reticle eyepiece or defocus so a star about fills the field of view so you can easily see which way the selected star is moving in the eyepiece. The higher the power (use a barlow) the better as things will progress much faster.

Follow these steps...

1. Obtain the best polar alignment you know how with traditional methods.

2. Make sure the drive is running and slack is out of the geartrain so the scope is actually tracking during all steps.

3. Center a bright star near where the meridian and celestial equator meet (telescope approximately straight up and dec reading near 0).

4. See which way the star is drifting in Dec only (disregard RA drift). If the star is drifting down you need to shift the telescopes polar axis West. If the star is drifting up you need to shift it East. Make this adjustment by grasping the 2 rear legs and pivoting the scope very slightly on the center leg in the desired direction. Repeat until you are satisfied the drift has ceased.

5. Now center a star near the Eastern horizon still near a 0 degree dec setting.

6. Again watch for drift in Dec only. If the star drifts down the telescopes polar axis is too low (shorten center leg). If it drifts up the polar axis is too high (lengthen center leg). Repeat until you are satisfied the drift has ceased.

You are now as accurately aligned as you will ever be. While taking the exposure there will be very little if any drift in declination, almost all corrections will need to be in RA (tracking speed).

• The Hat Trick -This is a method of opening the shutter without vibrations showing up on the film and ruining your picture. Take a black piece of cardboard (the "hat") or similar object and cover the front of the telescope (or camera for piggyback). Open the shutter. Wait a short time until you are confident the vibrations have dissipated. Now quickly remove the obstruction to start the exposure. Make sure you don't touch the scope while moving it away. To end the exposure you would reverse the procedure. I like to cover it up from the opposite direction to ensure equal exposure time across the film (the way a shutter also works).

• Focusing -Focusing accurately can be one of the most difficult tasks of AP. There are a number of methods you can use to improve your focus. I won't go into detail here except to mention the methods so you can do a web search for more information.

Common focusing Methods:

Knife Edge Focusing -This is probably the single best way to focus, a pain but very accurate. Will not work on Moon or planets as they are too large. Requires that no film be in the camera at the time or that you have a "dummy" camera with a perfectly equal focal plane distance.

OTA Mask -This works fairly well and can also be used for the Moon and planets. You essentially make a cover that fits over the corrector plate of the ETX with 2 holes in it opposite each other. Now when you look through the scope you will see 2 images, simply adjust the focuser until they merge into a single perfectly focused image. Remove the mask before exposure. This method can make the image darker since you are stopping the scope down probably best for bright objects (the moon and planets).

Magnifiers -Use a small finder scope to view the image on the camera focusing screen and adjust as usual. I've never really tried this method but many swear by it.

Parfocal Lens - Since the ETX is equipped with one great AP accessory (the flip mirror) this may be the best method of getting easily repeatable results with the least hassle. You will need to buy a ring that fits over the barrel of an eyepiece and that can be fastened in place with a setscrew. You would attach the camera with a T-Adapter to the rear of the ETX. Open the camera and perform a perfect knife-edge focus. Now flip the mirror and look into the eyepiece. DO NOT touch the focuser. Slide the eyepiece in or out of the holder until it is perfectly focused. Lock it down there. Now push down and lock your barrel ring in place on the eyepiece. As long as you don't remove the barrel ring you should be able to pop the EP in, focus carefully with your eyes and flip the mirror. This will of course be fine as long as you are focusing at infinity, not for the moon or planets.

• Bracketing - At first there is a lot of trial and error involved in focusing and exposure times. "Bracketing" is simply taking more than one picture while only slightly changing either focus or exposure time to settings on either side of what you think should be correct. Look on the web for an exposure calculator as a start. Then bracket your shots to insure there should be one that is ok, remember to record all this so you know when the prints come back! Generally for deep sky focus is at infinity all over so you can focus on any nearby bright star then move to a dim object. Deep sky exposure time is limited by the accuracy or your drive, alignment, and guiding patience. Exposure times for the moon on the other hand will be very short.

Putting it all Together

So, with the right accessories, methods, and practice you too can do some darn good ETX astrophotography. You may not get pictures like Hubble, but you will have the satisfaction of knowing YOU took that great colorful shot of the Orion nebula. And when you get that first really great shot back from the developers make sure you send me a copy to post on my upcoming astrophoto hall of fame for all the world to see!

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