Re: [APML] Raw NGC7000

["Chris Cook" <ccjd@ix.netcom.com>]

Hi Steve -

It looks like the lens is just poor wide open.  I use a separate guidescope
in my setup and sometimes need to crank it way off center from the imaging
scope to find a bright guide star.  I have never had anything less than
round stars in my images.  Polar alignment does not seen to be an issue from
your description.  Try stopping the lens down.

I'll also comment on the single thumb screw on the TV85 focuser drawtube I
remember someone mentioning.  When I was shooting with TeleVue refractors
(TV85, TV102 and NP101) all these scope had a single thumb screw design.  I
had my F3 and .8x R/F attached and never had problems with rotation.  I
don't know the weight of the ST-8 you are using but it can't be that much
more......

Best,

Chris

----------------------------------
Chris Cook
Astronomical & Nightscape Photography
www.abmedia.com/astro

-----Original Message-----
From: Steve Lindsey <stevelindsey@earthlink.net>
To: APML <astro-photo@seds.org>
Date: Sunday, July 06, 2003 5:52 PM
Subject: [APML] Raw NGC7000


>Here's the raw scan (with some levels stretching since the scan was quite
>dark) so you can tell me what you think caused the arc'd stars around the
>perimeter.
>
>http://home.earthlink.net/%7estevelindsey/NGC7000raw.html
>
>My buddy Dan did the polar alignment very carefully on the TV85 with a 3X
>barlow and 12mm illum. reticle eyepiece.  He worked at this for over an
hour
>so I'm surprised if there was field rotation.  We didn't keep good notes on
>where the guide star unfortunately.  It was from the off-axis guide chip in
>the ST8 Dan was shooting with on the TV85.  His imaging chip was centered
in
>the same FOV as this 300mm lens.  Maybe just guiding off-center was the
>problem but I don't get why this should matter that much if mount was well
>aligned and I'm still thinking that maybe the lens doesn't like being wide
>open.
>
>Let the experts speak...  I'm all ears.
>
>Steve
>
>
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