Moose,
The shutter may be open for 10s of minutes in order to register
the sparse photons coming from very extended items, but in the
view will also be stars, which will register almost immediately.
Besides vibrations from the mirror - which are easily handled
by covering the lens for the first seconds of the exposure,
vibrations from touching the lens, wind gusts, walking near the
telescope, bad tracking, etc will leave the picture with star
images that zig and zag.
Ah yes, go home thinking you have a roll of great shots
after hours of "careful" guiding... only to have the roll
developed and stars look like a flashback to some 60s party.
Tom
>Date: Tue, 15 Jul 2003 14:20:34 -0700
>From: Moose <olymoose@xxxxxxxxxxxxx>
>Subject: Re: [OM] Which OM is best for astrophotography
>
>OK, I 've had a question for some time for you astrophotogs. In
>exposures measuring from 10s of minutes to hours, what difference does
>mirror lock-up make? Mirror, aperture and shutter crash-bang all damp
>down in maybe a second or 2. So out of all the light that makes up even
>a 2 min. exposure, less than 1 0s disturbed. How can that affect the
>image? None of that light which is in the wrong place, and a moving
>wrong place at that, will even register on the film.
>
>Moose
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