Re: [APML] The perfect astrophoto book (Was: North American Nebula (or dodging aurora))

[Robert Reeves <reeves10@swbell.net>]

Both FR and ADR are functions of exposure time and FOV.  ADR is also
strongly influenced by local altitude.  The length of elongated star images
is also a function of focal length.  Shooting with a Schmidt Camera at f2 or
less for less than 30 minutes probably won't see ADR.  Try shooting a
piggyback camera with 180 telephoto off axis from the guide scope more than
10° for an hour below 45° altitude to the south and see what happens. It's
not very pretty.  This is why this kind of shot is not recommended.  It is
always best to have the guide star as close to the center of the target as
possible.  But then there's mirror flop, structural deflections, and .....

Don

Don,

Thanks for this eye-opener.  I have been puzzling over a roll of film I had
exposed several months ago, but just got developed (long story!).  From the
same polar alignemnt I was getting shots both with and without rotation on a
200 mm lens.  Now I see the possible culprit.  I may have some prime
examples of ADR in my hand.

Robert Reeves                      reeves10@swbell.net
520 Rittiman Rd.                   www.robertreeves.com
San Antonio, Texas 78209    210-828-9036
USA                                     29.484  98.440  200 meters



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