Re: [APML] SCT mirror lock

["John Boudreau" <jeboud@mediaone.net>]

Hi Tom,

> Do you ever attempt to re-adjust focus in the middle of a long exposure?

No, that's not something I'm really concerned about. Usually I just check
focus before each shot. And since I usually shoot with the SCT at f/11, it's
not as sensitive to temperature related focus shift as if I was using a
reducer.

While what you describe could be done, it just "pries the lid off the can of
worms" a little more to other things that could go wrong. Clear nights are
at a premium in New England, and I try to reduce the possibility of problems
that could crop up and play it safe. When I do check focus after a shot,
it's very seldom off noticeably. I knife edge with a Ronchi grating for
film, and for CCD I diffraction focus in combination with a JMI motofocus.

John Boudreau
jeboud@mediaone.net
http://people.ne.mediaone.net/jeboud/astro.htm
----- Original Message -----
From: "Tom & Lou Krajci" <krajcit@3lefties.com>
To: <astro-photo@seds.org>
Sent: Friday, September 21, 2001 7:49 PM
Subject: Re: [APML] SCT mirror lock


> From: "John Boudreau" <jeboud@mediaone.net>
>
> > Now if only I still didn't have to worry about thermal focus shift ;o)
>
> Do you ever attempt to re-adjust focus in the middle of a long exposure?
> Perhaps using a dark slide to cover the film while you adjust...get the
> OAG/autoguider tracking again at the same location...and continue the
> exposure?
>
> Tom Krajci
>
>
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