RE: [APML] NGC7000 - Still Trying

["Jeff Ball" <jeffball@zoominternet.net>]

Hello Steve,
I do not know the reputation of the Nikon 300mm f4.5.  To my eyes, the
stars seem to be elongated vertically across the frame in a uniform
pattern.  This could be the .jpg settings or file resolution on my
monitor.  My first guess would be flexure.  If you are shooting in humid
conditions, film creep may be considered, but I would expect a different
pattern of elongation, perhaps erratic or horizontal/diagonal or
non-uniform across the frame. I have used Televue equipment for CCD
imaging, but their focuser leaves a lot to be desired when it comes to
rigidity with a CCD camera.  I have not used the new locking ring
focusers, perhaps which is what you have and would lessen the concern
about flexure.  My experience with Provia 400F and E200 are that
exposing much more over an hour does very little good.  I did push some
exposures at f8 and really got nothing extra.  I think this stuff needs
fast lenses to get the photons on in the first hour.  I exposed Provia
and E200 at f8 for nearly 2 hours and was very disappointed with the
results.  This was on extended objects like M31 and IC1396.  I also push
processed one stop. I have some stuff coming up that was shot at f6 for
one hour on E200 and Provia and I am very happy with the results. So my
advice is to not go with longer exposures on the Provia.  I think your
Supra option sounds good.  How are you focusing the 300mm?  Focus may be
a bit soft as well.  Best wishes.  A lot to think about, but I know you
will get it down soon.  Keep us posted and keep up the good work.  I
know you are trying to get the best image you can.  Hope this info
helps.

Jeff Ball
www.astro-photography.com


-----Original Message-----
From: astro-photo-bounces@seds.org [mailto:astro-photo-bounces@seds.org]
On Behalf Of Steve Lindsey
Sent: Saturday, July 05, 2003 2:37 AM
To: APML
Subject: [APML] NGC7000 - Still Trying

I redid this shot last weekend with the 300mm lens wide open again at
f4.5.
Made sure the polar alignment was great and pushed the Provia 400F only
1
setting vs. 2 the last time.  Also got my friend to help mount a ring
for
the front of the lens to ensure no flexure in the lens mount.

Still got arc'd stars in the corner areas but they were more symmetrical
and
I think this time were just optical from vignetting vs. field rotation.
I
thought this lens could do wide open but maybe not.  This was a 60 and
45
min stack and much more cropped than the last post.

http://home.earthlink.net/%7estevelindsey/NGC7000.html

I think my options are as follows but would like your advise:

1. Stop lens to f5.6 and go 1 or 2x120 min with same film and push or
2. Stop lens to f5.6 and switch to "old Supra" and do 2x60 min shots

What do you folks think?

Steve



_______________________________________________
Astro-Photo mailing list
Astro-Photo@seds.org
http://seds.org/mailman/listinfo/astro-photo