Telescope Reviews: Summary--VideoCAM Use on Non-guiding Mounts

I ran enough tests to present a few results. Some others have said they would post some photos soon. The question comes up on this forum about using astro video cameras on telescopes without tracking in order to see Deep Sky Objects...can you do it and what kind of scopes can you do it with?

My experiments have been with an alt-az mount or a tracking mount with tracking turned off. The telescope that I have worked with the most is an 80mm f/7 refractor but I believe the results are generally applicable to a host of f/7 or shorter focal length refractors from 4 inches of aperture on down to about 60mm or so.

Someone else can give their results for a typical f/10 SCT, but I do not think the results will be very good judging from my use of an early MallinCAM with the tracking on the C8 SCT turned off. Star trails were too noticeable for the scene to be worth it to me....unless the integrations are less than 1/4 second (less than 32X). I did not test where the views would be tolerable; someone else may want to do this.

While my camera was an older B&W MallinCAM, I have worked with a STELLACAM EX and regularly use a MallinCAM Hyper Color. I have seen enough results so I am quite confident that the results pertain to any of the MallinCAM/STELLA CAM series as long as one can use the shorter integation times (less than 128x or 2.1 seconds).

I always used a focal reducer; and mine was an older version of Rock Mallin's, although I have used others and I know there are several that deliver good results. Essentially, the lower the net focal ratio, the wider the field, the less star trailing one sees.

Before I give results, understand my definition of a good view on the screen: (1) very little star trailing or blurring of a nebula and (2) the view must be substantially better than a premium eye piece view with twice or three times the aperture. Otherwise, why bother?

My test objects were M92 and M8 on a night where viewing varied dramatically from average to terrible.

RESULTS/CONCLUSIONS FOR NON-TRACKING SMALL SCOPES (ESTIMATED TO BE APPLICABLE TO THOSE WITH FOCAL RATIOS OF F/7 OR SHORTER AND APERTURES OF 4 INCHES OR LESS):

1. Standard non-extended integration times (2.1 seconds or 128 frames of information integrated) are NOT suitable for deep sky objects. The trailing stars look like rectangles and, while nebula and clusters can still be discerned, the view is disconcerting to me.

2. At 64X (about 1 second integration time) the views of M8 and M92 were tolerable. 50% gain (AGC) was sufficient to get a good view; near full or 100% AGC gives you the same picture that 128X or 2.1 seconds of integration delivers but without the star trails. There is a bit of trailing at 64X but it was not that noticeable. The quality of the view for both objects was MUCH BETTER than a view I could obtain with the 12.5 inch Dob with a 22 Panoptic at the same test time and location.

3. At 32x or 1/2 second integration times, the results with 50% AGC produced a steady picture to the eye, not including the movement of the scene across the monitor, which one expects with a non-tracking scope situation. I could not detect star trailing at all at 32X. With full AGC, the view is better than the 64X view at 50% AGC. 32x or 1/2 second integration is actually very easily usable as long as the brightness of the object is enough for the camera to work with. Any faster integration is a no-brainer...it works but you lose more of the integration benefits so you see less on Deep Sky Objects.

4. Limiting magnitudes for using ALT AZ mounts with fast integration times {1 second to 1/2 second or 64X to 32x} is a question of type of object and what one wants to see. Globular clusters are generally beautiful with these integration times. While one does not see the star density or the depth when using these faster times, one still sees MUCH MORE than 4 times the aperture of scope with a good Eye Piece. That is not a guess: I went from the 80mm screen view and compared it to the 12.5 inch Dob view with the 22 Panoptic. So for primary Messier objects and other bright sky objects as defined by the TelRad books: the faster integration times still deliver much better than a lot bigger scope. Note, however, when surface brightness is pretty low for a galaxy or the nebula is pretty faint, the result, while better than an EP view on somewhat larger scope, is not going to blow your socks off.

5. Ease of use of an alt-az mounted scope with faster integration times: This is dependent on a person's ability, of course. I am a relatively recent observer (less than 10 years) and I consider the sky foreign to me except for major stars, bright objects, and significant constellations. I can star hop...sort of. After using a non-tracking mount with a Camera in place of the eyepiece for about 1/2 hour, I was pretty confident that I could find anything as easily as if I want looking through an eye piece. Furthermore, once the object was found, moving the alt-az scope to readjust the target to the center or to one side of the screen was pretty easy. The biggest problem with these smaller refractors on an alt az mount is not moving them around too quickly so you pinch or pull out wires. One does have to be a little more careful.

Bottom Line: would I buy a decent astro video camera (new or used) if all I had was an alt-az mount and a small refractor with a focal ratio of f/7 or better? For me, the answer is yes, because the view is better than what I can see with my 12.5 inch Dob with a good EP. Does the monitor have to be special or expensive? Nope. The standard B&W high resolution security monitors are available by a number of vendors for about $100. High resolution means 800 to 1000 TVL. Mine is 800 and did just fine. I have a 5 inch TV; it works, too. DVD players work too. In other words, the monitor is not a variable that makes or breaks the issue.

Bottom Line Two: Would I buy a used scope (fast and perhaps with some chromatic abberation) and a used camera? This is kind-of a worse case but not uncommon because there are a lot of relatively small refractors out there with a lot of chromatic abberation. The answer is yes, because a B&W video camera on fast integration times does not care how much CA is present...it will deliver a decent B&W picture of the object. As long as the scope has a short enough focal ratio and is somewhere between 60 and 102 mm, the picture I will see on a monitor with 1/2 to 1 second integration times and middle to high AGC will still be better than a telescope with 4 times the aperture and a real good EP. I used the STELLACAM EX on an old Vernon 80-mm f/6 refractor very successfully. It works.

Last item: how much time can you see the scene on the monitor that is showing the output to one of these cameras that is mounted on a small refractor? The answer is simple to measure and probably calculate. On my setup, side to side motion of the object (from one side of the monitor to the other) was about 2 minutes. After about 10 cycles, it was automatic...I knew how to jiggle the scope and recenter the object quickly...all while sitting and enjoying the monitor scene. If you say that you want to keep the object in the center 50% of the monitor, then you jiggle the scope about every minute.

NOW...wait for some other results and pictures from some other participants that will hopefully follow, fill in gaps, and correct any mess-ups in what I wrote...

Clear skies.

Roland Beard
Crozet VA