On Mon 2001-09-24 (07:39), [EMAIL PROTECTED] wrote:
> > I have heard remarks that a 200/2.8 prime will transmit more
> > light than an 80-200/2.8 zoom. Is this true? I thought a
> > 200/2.8 was a 200/2.8 whether it be a prime or part of a zoom.
> > Thanks for any help.
>
> I'm with you 2.8 is 2.8. Two different lenses, if calibrated properly,
> should deliver the same amount of light at the film plane when set to 2.8.
> No ifs, ands, or buts! Otherwise photography doesn't work with
> interchangeable lenses.
2.8 is NOT 2.8 - this number does not depend on real measurements, but on
physical calculations only.
Aperture is give mainly by diameters ond focal length.
Real numbers are not required: If it's not enough light, the exposure
meter will double your time, whether the selected aperture is called 2.8
or 3.5, whether it is a faked or real number, as long as you do need
double times.
Sad to say that any fake is possible. Maybe you can compare real numbers
when you take two different lenses of identical focal length and compare
the data they suggest. Which Pentax would show continous integer
numbers for times, instead of 36/60/125/... only?
Regards
Martin
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