Copernicus, Full-Sized Alpine Valley, Full-Sized Aristarchus, Full-Sized
Other Images, Thumbnails & Full-Sized
By Charles R. Genovese, Jr., M.D.
My interest in astronomy began over thirty years ago, and during my teenage years I captured many pleasing images of the Moon and planets and deep sky objects on film. Though I never lost interest for over 25 years, there were too many distractions and never enough time to restart serious observing and photography. About three years ago I began observing in earnest again and moved up from my venerable RV-6 Dynascope, which still is in excellent condition after having the mirrors recoated about four years ago, to a 10" f/6 Newtonian. I longed to begin imaging again but I still did not have the time for conventional photography and all the associated darkroom work, and I rejected purchasing a conven- tional camera because in our humid weather, the idea of moving a computer outside was absurd (because it was my wife's computer anyway).
After an article in Sky & Telescope, I tried videotaping with a hand-held camcorder and found it worked amazingly well. My next step was an inexpensive black & white security camera known as a GBC-400. This camera is not much larger than a pack of cigarettes, weighs nine ounces, has a sensitivity of .03 lux and has 512 by 412 pixels on an interline chip and outputs over 400 lines of resolution. Videotapes of the Moon, Jupiter and Saturn were beyond my wildest expectations. Using eyepiece projection, fine detail easily visible on the screen was better than I could see directly! In fact, the first time I noticed that there was a rille in the center of the Alpine Valley was with this set-up and is only .3 arc-seconds wide!
Using eyepiece projection, the image scale can be as high as 0.3 arc-seconds per millimeter, giving 87 arc seconds across the 11 inch wide monitor screen. In addition, I was in complete comfort; I did not have to sit still and become a mesquito blood feast! Moments of of good seeing could be repeated over and over again by replaying the tape, not only that night, but for others at anytime, and a crowd could watch the monitor all at once. Mesurements could also be taken directly from the screen and events such as shadow movement on the Moon, eclipse progression, rotation of Jupiter or moon movements could be captured in real time. If I had a clear sky for comet Shoemaker-Levy's crash, I could have recorded the impact flash as it crept above the limb! Oh well, next time...
Also, in comparison to digital cameras, there is nothing more sophisticated to this than hooking up a single wire into a camcorder or TV that everyone already has! My next step was to upgrade the recorder to Hi-8 with over 400 lines of resolution. I also wanted a better camera and finally chose a Murnaghan Instruments research grade camera as it is the only analog frame transfer chip (rather than interline), therefore giving potentially higher resolution and less light loss. It also has full manual controls including exposure, gain, gamma and black level, which is only available on this particular camera. In practice, all of my expectations were exceeded. The camera output feeds into an analog video processor, which helps to decrease noise and is convenient for adjusting the overall gain. Do not use a digital processor as artifacts may be introduced which will become evident with computer processing later. For maximum resolution, eyepiece projection is used at about f/40 to f/50. Amazingly, the electronic magnification is over 50 times to my 13 inch diagonal screen giving it effective total focal length of over 20,000 inches! Jupiter is over five inches across the screen and the Moon could measure over 200 inches in diameter. I often make a continuous recording during an observing session, a moment of good seeing will never be misssed. At 30 frames per second, an hour and a half long video tape can hold over 200,000 images. At 30,000 bits per digital image, digital storage cannot begin to compete. Excellent hard copies can easily be made by conventional photography of the monitor and it is much easier to capture those moments of good seeing because you can replay them over and over again.
For color film, which can be processed at the one hour photo (near instant gratification), a Wratten 85 filter (Salman), helps balance the blue color temperature of a TV monitor; otherwise, the pictures will have a blue-greenish cast which will be difficult for automatic processors to eliminate. Contrast should be adjusted to a little lower than you would normally use for viewing, as the print papers used at the automatic photo processors are often contrasty. Exposure should be one-eighth to one-quarter second to avoid uneven illumination of the screen. Additionally, if the camera is defocused slightly, the scan lines can be nearly eliminated. Tom Dobbins (author of Observing and Photographing Observing and Photographic the Solar System) and I have spent a great deal of time experimenting with this technique and he has sent me several magnificent black and white photos. However, in the long run, frame digitizing and computer processing gives the best detail. After a review of the recording, moments of excellent seeing are chosen and individual frames are evaluated and individually digitized and stored by a Computer-Eyes RT/monochrome digitizer. (I now use the Snappy frame digitizer which gives far better results). Several frames from a dark field are also stored. The images are then pulled into SkyPro and a dark field, made of eight blended frames, is subtracted from each image. These are then carefully superimposed and then blended (one or two for the Moon will do; the more the better for planets) to decrease video noise. Conventional processing using smoothing, sharpen, unsharp masking, etc., are then used. The final results are startling as the short exposures and numerous exposures freeze fine detail in average seeing that would be otherwise blurred, and allows me to capture detail of the Moon and bright planets as go9od or better than the best published photographs taken with the largest mountaintop telescopes. Using digital CCDs, only a few amateurs with larger telescopes, excellent seeing, and a lot more effort and expense can significantly improve on these results.
Charles R. Genovese, Jr., M.D.
P.O. Box 969
Independence, LA 70443 USA
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