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[OM] Fw: [OLYMPUS] Exposure metering

Subject: [OM] Fw: [OLYMPUS] Exposure metering
From: "Terry and Tracey" <foxcroft@xxxxxxxxxxxxxxxxxxxxxx>
Date: Wed, 28 Jan 1998 12:13:54 +1100
> > ----------
> > > Date: Thursday, 23 October 1997 07:33:44 
> > > From: M. Covington
> > > To: olympus@xxxxxxxxxxxxxxxxx
> > > Subject: Re: [OLYMPUS] Exposure metering
> > > 
> > > > 
> > > > 180 and 256 what? Lumens....foot candles?
> > > > -Gene
> > > 
> > > You would have to ask...  According to Kingslake, it is *supposedly*
> > > candelas per square foot, but in practice I find that it is somewhat
> > > arbitrary, depending on how we want pictures to look for a given type
> > > of subject.
> > > 
> > > > 
> > > > M. Covington wrote:
> > > > > 
> > > > > The sunny f/16 rule actually errs a little on the side of
> > > underexposure.
> > > > > 
> > > > > The formula for exposure is:
> > > > > 
> > > > > exposure time = (f*f) / (A*B)
> > > > > 
> > > > > where A is the ISO film speed, B is a brightness value, and f is the
> > > > > f-number.
> > > > > 
> > > > > The sunny f/16 rule implies B=256 on a bright sunny day.  That's
> true
> > > in a
> > > > > desert, but if your landscape consists of grass and trees, B is more
> > > like
> > > > > 180.
> > > > > 
> > > > > I've just been through all this trying to put the calculation of
> > > > > _astronomical_
> > > > > exposures on a scientific basis.  On my web page is an exposure
> > > calculator
> > > > > for astrophotography.
> > > > > 
> > > > > ---
> > > > > Michael A. Covington, Writer/Consultant
> > > > > http://www.mindspring.com/~covington
> > > > > 285 Saint George Drive, Athens, Georgia 30606, U.S.A.  <><


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