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Because a video camera can not build up a weak image by long exposure or stacking, it is best suited to bright objects like the moon and major planets. It's major forte is that it can take 30 snapshots per second and therefore thousands in a very short period of time. As seeing is a time dependent variable, even under very poor conditions there are instants when the image can be quite good. It is simply a matter of taping a few minutes of an image and then later going through the tape, one frame at a time, looking for those instants.
There are a number of commercial products on the market that will convert single frames of video into digital images that can be displayed and enhanced on a computer.
The major piece of equipment needed is a CCD video CAMERA that is light and small enough to be used on a telescope. There are many inexpensive models on the market in the category of "security" cameras that are well suited to the task. The one I purchased is Topica TP-505D. It is sold by Super Circuits for around $130. They are on the web and can be found through the search engines.
There are two major problems with this camera. The first is the usual unintelligible Pigeon English manual that is nearly worthless. The other is the fact that it assumes that you can stop down the lens to reduce the light level. Needless to say, we don't pine for large telescopes so that we can stop them down so the only option is to use very dark filters when there is too much light.
Video camera installed in 2" focuser of small telescope.
Although shown in a helical focuser, I actually use it in a rack and pinion type to
avoid rotating the image as it is focused.
The camera has a CS mount thread but included is an adapter that converts it to a C mount. In either case, another adapter is required to allow it to fit into a telescope focuser. I am not aware of a C mount to 2" adapter and I have a lathe so I made up an adapter out of polyethylene. The only problem I had was that the material is translucent and has to be painted black to exclude stray light. The led "cue" light on the front wiped out the image and drove me nuts till I figured out what was going on.
The C Mount to 2" adapter.
The threads on top screw into the C Mount adapter on the camera. The large black diameter slides into a 2" focuser.
The smaller bottom step fits inside a 2" OD tube that contains a projection lens when doing hi-resolution work.
Camera, Adapter and Projection Tube
For "wide field" imaging, the adapter goes directly into the focuser without the projection tube. The CCD chip is rather small so on a typical amateur scope, only a small portion of the moon can be imaged at a time. However, as the monitor or computer screen is much larger, the effective magnification comes as a shock. Unlike film photography, a prime focus video image of the moon is measured in inches instead of millimeters. Wonderful images of the Moon, Jupiter and Saturn can be produced in this mode.
For higher resolution, you will need some form of eyepiece or lens projection to expand the image. This can be solved with many off the shelf items. I made an adapter for a 10X microscope objective that fits into a 2" brass tube. This easily provides a magnification of 1000x or more.
Once the opti/mechanical problems are solved, the next item required is a video tape recorder. Virtually any format or style will work but to fully utilize the seeing-busting capability of video, you will need one with single frame stepping ability. In VHS format, these are not particularly exotic or expensive and if you are lucky, the one under your TV set may have it.
There are several inexpensive products on the market that convert video to digital. The one the manufacturer claims is the most sophisticated and highest resolution on Earth, is the Snappy. Contrary to Rush's commercials, the Snappy does not "snap" .. About what I would expect from him.
Aside from that and all the hours I spent trying to make it work because of lousy docs and just plain computer nonsense, it seems to work quite well. It plugs into the printer port of the computer and for gross stuff, you don't even need a monitor. For finding that best frame, however, a monitor must be plugged in to evaluate the image. When a good one is found, you click on "Snap" and it digitizes the images and provides lots of tools to enhance or fix it.
The following images were some of the first made and give a good idea of what a beginner can do with video. The first one was taken at prime focus and the second set with projection.
The following two images demonstrate the power of video in dealing with poor seeing conditions. The procedure is to compose the image at the scope on the monitor and roll tape. Focus can be tweeked while the tape is rolling in hopes of getting it just right.
The image was formed with the 10X microscope objective for an EFL of about 50 ft. The visual image was a boiling blur and the view on the monitor was even worse.
After acquiring about 5 minutes of tape, it is brought to the computer and single stepped, one frame at a time, looking for a good frame. Most of the tape looks just like it did in the scope, just a boiling mess but out of the 9000 odd frames taken in 5 minutes, there are bound to be a few that just happened to catch that rare moment of good seeing. As a video frame is only 1/60th of a second, that is all the time needed to capture that moment. Not enough for the eye or film. CCD can form an image in that time but there is no way I am aware of to get thousands to choose from in just a couple of minutes.
The frame on the right represents a typical bad frame and the one on the left a particularly good one.
The small crater between the two rills is approximately one mile in diameter.
Not So Good
Video technique can also be applied to planetary imaging to pick moments of good seeing.
Since the above monochrome work was done I have added a color camera to the equipment roster. These images of Jupiter represent what can be done on a night of fair seeing.
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