My Background and Imaging Techniques

I was born in 1946 and grew up on a farm in Indiana, about 80 kilometers north of Indianapolis. The night sky was very dark and I became curious enough about the real universe at the age of ten to ask my father for a telescope. The views through that 40mm refractor were wonderful, but I had to see more, so at the age of twelve I built a 115mm Newtonian reflector. It too was wonderful.

Since that time I have built or helped build dozens of telescopes, up to 815mm in diameter, and have built a CCD camera, but it has all been in the same pursuit I started at the age of twelve: to see deeper and better into that dark night and to capt ure part of it. I think this is the primary common pursuit of astronomers, particularly amateur astronomers, who are involved for the simple love of the subject.

CCD imaging has now become a mainstay for many of us who are continuing the pursuits of our youth. It is delightful in its concatenation of the most modern technology with the ancient and simple principles of capturing part of the night sky for closer inspection. Those principles have always been to use a dark, clear, steady sky; to keep your eyes as sensitive as possible; to look carefully and effectively at an area of interest; and to record what has been seen as faithfully as possible. For millenia, astronomers used their eyes, their memories, and their stones or papyrus. Over a few short decades, our eyes have become gigantic slabs of delicately hewn glass, our attention has become riveted by intricate guiding mechanisms, and our memories have been etched on fine-grain films and computer hardware. Only the cosmos is essentially unchanged.

I worked for NASA at the Johnson Space Center in Houston, Texas from 1972 to 2005. As a member of the Johnson Space Center Astronomical Society, my interests grew in the early 1980's to the construction and use of large Newtonian reflectors on Dobsonian mounts. I had also been active in film astrophotography since the late 1970's, using a Celestron 8, and was interested in ways of imaging through the larger telescopes. From about 1983 to 1987 I experimented with video imaging, sometimes using image intensifiers. Finally, sometime in 1988, I had my first experience with an astronomical CCD imaging system, a Photometrics Star I, and became an instant convert. I was fortunate enough to be able to borrow and use several other CCD cameras over the next few years, including the SBIG ST-4 and ST-6 systems.

With the publication of the CCD Camera Cookbook in 1994, the avenue was opened for me to build and own my own CCD camera. Since I am not an electrical engineer or electronics technician, I needed a book which could tell me in simple terms every step necessary to build such a sophisticated device. The Cookbook is perfect in that regard, so I completed a CB245 in August of 1994. I used the CB245 coupled to either my Celestron 8 (f10/f7.5) or one of my two large Newtonian reflectors. One of these is 445mm f4.5 and the other is 813mm f4. Until the late 1990's, the reflectors were mounted on equatorial platforms for tracking purposes (see the December, 1991 issue of Sky and Telescope for an article on one of these platforms). At present, my Newtonians use altitude-azimuth-focal plane (Alt-Az-FP) drive systems designed by Andy Saulietis.

From 1994 to 1996 I used my CB245 primarily for unfiltered monochrome imaging, learning much about image calibration, image stacking (summing and averaging), and image processing. Since I was using the 813mm f4 system on the unguided equatorial platform most of the time, I was limited to 15-second exposures and learned to really appreciate the CCD's capability to create long effective exposures from numerous short exposures. I quickly learned that Richard Berry's Cookbook image acquisition and processing software was the best for working with my images, so I obtained CB245 and MULTI245 and began to use them exclusively.

In 1996 I became more involved with tricolor CCD imaging, having done enough to know what I was getting into. I ordered a new RGB filter set from Edmund Scientific and an infrared blocking filter from SBIG. Meanwhile, my good friend Andy Saulietis was again designing something wonderful, a filter wheel which fits on the front of my CB245. I also needed new tricolor compositing software and Richard Berry once again came through, this time with COLOR245. To paraphrase Einstein, we all stand on the shoulders of giants!

Over the last few years, I have augmented my imaging equipment with a Starlight Xpress MX916 camera with a fast USB interface and S.T.A.R. 2000 self-guiding capability. I have also acquired improved RGB filters from Chet Schuler and a new filter wheel from Andy Saulietis. The primary software programs I use for image processing are now AIP for Windows (AIP4WIN) by Richard Berry and Jim Burnell and Photoshop CS by Adobe.

My imaging techniques are based on the very principles discussed earlier:

1. I go to the darkest skies I can, which is usually to my observatory about 100 km southwest of Houston. The sky there is about 6th magnitude.

2. To keep my "eyes" (the CCD) as sensitive as possible, I use a cooled CCD camera with a fast focal system (f4 to f4.5) and use filters with high transmission characteristics in their selected wavelengths.

3. In order to "look" as carefully as I can: 1) I use the excellent tracking provided by good drive systems and a self-guiding camera; 2) I obtain long integration times without saturating CCD pixels by stacking well-tracked subexposures; and 3) I make more integrations for the color bands to which the CCD is less sensitive.

4. In order to record what has been "seen" as faithfully as possible, I use processing techniques which bring out faint detail without destroying the delicate "true-color" balance of the image. In this regard, true color refers to the attempt to portray an object in the colors that the eye would see. All such attempts are doomed to some degree of failure, but the most faithful afforts seem to give the most pleasing results.

The steps I go through to produce a color composite image are as discussed in the link at the top of this page to the BASIC INSTRUCTION MANUAL.


Al Kelly -- 8/14/97 (updated on 3/12/06)

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