From: Forrest Egan (fegan_at_antispamdomain.not)
Date: Sat Jun 28 2003 - 15:38:12 EDT
Art,
Since I also have a G-11, I've got some first-hand experience here...
I guess a first question would be...what camera are you using (what's your
max BULB time)? If you're limited to less than 1 minute, the polar scope
alone (if proper care is taken) can get you close enough for imaging. If,
OTOH, you've got a 5 minute (or longer) BULB time, you may need to do a
drift to take advantage of those longer exposure times.
From my experience with the G-11, I find if I can get all three stars
properly aligned in the polar scope (don't forget to use the 2000/2005/2010
offset for the 2nd and 3rd star...that small difference can be huge when it
comes to imaging, no big deal for visual observing), that I can get 45-60
second exposures without drift. Of course, after a series of exposures the
image will typically start drifting across the LCD.
Since my camera can only do 60 seconds, I typically don't bother drift
aligning when I'm working from home. Why? Frankly, no matter how many
images I take I'll never get past the light pollution affects (a few of
those nasty mercury-vapor street lights...seven to be exact...easily visible
from North to South along my Eastern view). So, DSO imaging from home is
more of a practice session and exercise in patience (when it comes to
processing them). Hence, I typically limit myself to 20 or 30 images per
object...then, move to something else. Unfortunately, I have a lot of trees
obstructing my view to the NW and SW, and the house to the West, so I can't
just swing to the other side to get away from the street lights.
HOWEVER, when I'm at the club's dark sky site (Chiefland) I will drift
align so I can shoot more images without tweaking to re-center. When I did
M42 last November, I literally left 'theForce' controlling the camera for 1
1/2 hours as I wandered the observing field, chatting with a few group
members who were there. When I got back M42 was still nicely centered in
the LCD. IIRC the image drifted no more than 20 or 30 pixels over 90
minutes. That's the major advantage of an accurate drift alignment or a
permanent observatory...not having to guide during the imaging session.
Forrest
-----Original Message-----
From: artrosch [mailto:artsdigiphoto_.at._attbi.com]
Sent: Saturday, June 28, 2003 11:58 AM
To: digital_astro_.at._yahoogroups.com
Subject: [digital_astro] Re: Drift align without horizon?
Sorry, folks. I'm using a G11 without GOTO, and my trees block
a significant amount of horizon, up to 40 degrees Dec, as Vega
is the first bright star to clear the trees after dusk. It's even
worse in the south; there is virtually no sourthern view at all,
but some view in the West, Arcturus, for example. It's lovely
and dark here, almost Mag 5, but it's a tiny little bowl of sky.
I do have the polar scope on my G11.
art
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