Re: [APML] Question on vignetting

["Jim Vineyard" <deepskyphotos@hotmail.com>]

Hello Bradley,
  If shooting a 10" f/10 SCT, check out the page(s) below, especially for a 
vignetting comparison near the page end, you'll want to look over his whole 
site too for high quality info:

http://www.astrocruise.com/geg.htm


And Clear Skies,

Jim Vineyard
www.deepskyphotos.com


----- Original Message ----- 
From: "Bradley" <bhope@thorngarden.net>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Tuesday, March 15, 2005 7:03 AM
Subject: [APML] Question on vignetting


> Morning, everyone;
>
> Got a chance to go deeper with the Orion Nebula and now, for the first 
> time,
> I'm seeing a lot of vignetting I've never noticed before. Perhaps not the
> best image to use to demonstrate it due to the trailing, but it shows the
> vignetting the best.
>
> I've checked the RA drive at a few steps above guide rate after putting 
> the
> scope back in approximately the same position and listened carefully...and
> heard faint little crunchie sounds...so I get to take the scope down and
> tear into the RA drive. Only seems to do it in one section of the sky so 
> I'm
> hoping it's just an "illegal alien" in the worm gear. And "DUH ME", I 
> didn't
> think to check polar alignment after hanging an extra 20lbs + on the scope
> (Orion ED80, piggyback setup, 7 lbs of counter weight, Pixcel 237) so I 
> got
> a bit of field rotation going on as well. Also, the framing within the
> vignetting is off a bit, M43 could have been a bit higher and I'd a 
> brought
> up more of the nebulosity beneath M42. I'm learning, and dealing with
> issues..but, sadly, this will probably have been my last chance at M42 
> this
> year. I'll be able to salvage some of what I shot night before last, but 
> it
> isn't going to be as good as it could have been...if I hadn't had the
> trailing.
>
> What I'd really like to ask is if the amount of vignetting I'm seeing is
> normal?? Optical train is 10" SCT (2500mm at f/10), Meade microfocuser and
> rear cell adapter, Meade .63 focal reducer, Meade T-adapter, 35mm camera.
> Can the vignetting be reduced some by reducing the optical train..ie, by
> removing the Microfocuser perhaps? Or by a different placement of the 
> focal
> reducer......or is this about what I should expect?
>
> Clear, dark and steady skies
>
> Bradley
>
> Thorn Garden Observatory
> http://astronomy.thorngarden.net
>
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