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Path: utzoo!linus!philabs!ttidca!ttidcb!josephs
From: josephs@ttidcb.UUCP (Bill Josephs)
Newsgroups: net.rec.photo
Subject: exposure stop formulae
Message-ID: <254@ttidcb.UUCP>
Date: Tue, 29-Jan-85 09:26:12 EST
Article-I.D.: ttidcb.254
Posted: Tue Jan 29 09:26:12 1985
Date-Received: Sat, 2-Feb-85 22:37:14 EST
Organization: TTI, Santa Monica, CA.
Lines: 24


     I've been meaning to post this for a while and keep
forgetting...for the mathematically inclined, the following formulae
can be used for calculating the ubiquitous difference in stops between
two f stops or two guide number (first formula) or between two shutter
speeds or two ASA/ISO ratings:

                   #stops = 2*(log(fg1/fg2))/log(2)

or:

                     #stops = log(sa1/sa2)/log(2)

where:

     fg1 and fg2 are two f stops or two guide numbers,

and:

     sa1 and sa2 are two shutter speeds or ASA/ISO ratings.
			 
			Bill Josephs
			TTI
			Santa Monica, Ca.