[APML] Exposure Question

["Brian Larmay" <astrobri@ameritech.net>]

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

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