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Re. Widefield Photographs

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Posted by Glenn Mitchell on September 7, 2002 21:01:41 UTC

You will need to polar align your scope for long time exposures.

Anything more than a couple minutes will show visible field rotation, even though your eye will not detect it through an EP or the camera viewfinder.

Normally, you use one or two f/stops short of wide open. Logic would lead you to use the wide open f/stop, but your likely to run into more diffraction.

Time exposures will depend on the ISO rating of the film.

Most people use ISO 200 or 400 for color film. SOmething around 15 or 20 minutes.

It's best to take an exposure long enough for sky fog to just be noticeable and then remove the effect on the computer.

If you cannot do post-processing, then you will need to experiment to find where sky fog becomes noticeable in your area and under what conditions (since it will vary in the same location, depending on cloud cover, etc.).

Mitch

Glenn E. Mitchell II, Ph.D. (aka Mitch)
10" f/10 Meade LX-200 GPS (Big Blue) s/n 01088
Supercharged at ASO by Dr. Clay Sherrod, # 2314-2010
N 30 30' 49.2" / W 084 20' 13.8"

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