Archived posting to the Leica Users Group, 1997/03/13

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Subject: Re: Astrophotography
From: Paul Young <pauly@sdd.hp.com>
Date: Thu, 13 Mar 1997 08:17:30 -0800 (PST)

> >The adapter would come from Celestron for about $100 bucks maybe.  They
> >usually end up in a T-mount. (about $15)  Check with your local
> 
> 
> Nah.  Hal doesn't say what sort of Celestron he has, but if it's one of the
> standard Schmidt-Cassegrains, it takes a simple Photo Adapter, which runs
> 
> 
i<snip>

I haven't read the Scientific American article, nor have I even
viewed this comet. Yet. I do have some comet photo experience.
Using your telescope as a prime lens makes it a 1000 to 2000mm
lens. This means an angle of view in the neighborhood of one 
degree. The comet's tail may span 3 degrees now, and may 'grow'
to three times that in the coming 40 days. Taking a picture
through the Celestron would only show the head, which might be
interesting, but won't show the tail(s) in all their beauty.

If the Celestron has a clock drive, use it as a mount for the
camera with a moderate telephoto lens (called piggybacking).
Celestron offers a piggyback adapter which mounts to the 'scope
and has a 1/4-20 male thread for your camera or lens. Align
the telescope (polar alignment) and run the clock motor and
the setup will track the comet pretty well for probably up to
a two minute exposure (The comet does move slightly with
relation to the background stars).

Exposure? Use an EV of about -4 (f/2 @ 20 sec for ISO 400)
to capture most of the tail's beauty. This assumes you are
at a reasonably dark site as light polution will greatly
reduce your ability to see and photograph all the details.
I have found that at 20 seconds on a tripod with 200mm
(a good focal length to try for comets) I get a bit of star
trails (due to earth's rotation), but piggyback on a clock
driven telescope will get rid of the trails. At least you can
do decently with a tripod up to about 20 or 30 seconds with
a 135 (on a Leica M!).

BTW, I like to use EV as a concise way to express the metered
light value of an object It allows one to juggle around the
aperture, shutter speed and film speed. 

HTH,

Paul.