Re: [APML] Exposure Question

["Glenn Ray" <glennlray@mail.ev1.net>]

May be a bit late to jump in on this, but..

Why do you want to stop a 50mm f/1.8 lens down to f/5.6?  Is your coma really that bad @ f/4?  Your photos look fine @ f/4; I see a little coma in the edges, but nothing unattractive.  And vignetting, while apparent, is correctable digitally.

Also, you need to consider that increasing the stop will increase the star size.  This effect has been previously discussed in the APML (in fact, I asked about it:  http://astro.umsystem.edu/apml/ARCHIVES/SEP00/msg00046.html).

I say, stick to f/4 or faster, take twice as many shots and stack. <g>

Glenn Ray
Cypress, TX

---------- Original Message ----------------------------------
From: "Brian Larmay" <astrobri@ameritech.net>
Reply-To: Discussion of Film Astrophotography <astro-photo@seds.org>
Date: Sat, 20 Sep 2003 16:31:21 -0500

>Hi all,
>
>Ive been slipping on everything concerning astrophoto since spring and will
>finally be getting out tonight for some long overdue practice.
>My question is concerning exposure time...I always stop my lens to f/4 with
>exposure times of 7 mins, but this time I want to stop down to f/5.6 ...
>what would the correct exposure time be then?
>Whats the formula?
>Will this sharpen my images noticably vs @ f/4?
>Will this reduce Vignette and help me to create mosaics alot easier?
>
>All exposures are made using Kodak E200 tonight.
>
>Ty,
>Brin
>
>My Photography
>Homepage: www.astrobri.com
>
>Geographic Longitude= 88W
>Geographic Latitude= 43N
>Corrected Magnetic Latitude= 53
>
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