"George M. Anderson" <george@xxxxxxxxxxxxxxxxxx> moved upon the face of the
'Net and spake thusly:
> > Stars are a point source---f/stop is irrelevant
>
> Have to disagree. F/stop very relelvant due to lens imperfections at
> wide open apertures.
Allow me to rephrase.
"When calculating exposure, the usual relationship of f/stop to
exposure does not apply. For normal images, a 300mm lens at, say, f/4
and a 28mm lens also at f/4 give the same exposure. For point sources
this is not the case---exposure is proportional to diameter of
aperture, rather than ratio of focal-length-to-aperture-diameter."
Concern for minimal aberration is why I shot my starfield slides at
f/8 rather than wide-open f/2.5.
cjb
--
Christopher Biggs -- chris@xxxxxxxxxxxxxx -- Stallion Technologies Australia.
There's a bug in my mailer that mangles my sig but V guvax V'ir svkrq vg abj.
Uneqyl jbegu qrpbqvat, jnf vg? Rznvy zr "Fhowrpg: fraqctcxrl" sbe zl CTC xrl.
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