Sorry if this is a duplicate, I think the first one got lost.
Paul,
Interesting results. The early VS1`s just always seemed bright to me. I
think
the lens manufacturers in the old days did not "fudge" the f values as much
as they do today, and the old VS1`s used some big gnarly glass. Thanks
for checking it out.
Steve Larson
Redondo Beach, California
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Friday, April 13, 2001 9:45 AM
Subject: Vivitar Series 1 vs. Pentax 135 and 200mm telephotos: f/stop,
brightness shootout
> Steve,
>
> At Steve Larson's request, I compared my Vivitar Series 1 135/2.3 and
> 200/3.0 screwmount telephotos against my Pentax K-mount f/2.5s at the same
> ISO and f/stop. It appears that the Vivitars are "brighter"--that is, they
> delivered a faster shutter speed at the same f/stop.
>
> For the 200s, I used ISO 1000 and f/4. I aimed at a variety of targets in
> my basement. About half the time, the Vivitar beat the Pentax by 1 stop in
> my Super Program readout. The other half the time, the readouts were the
> same. That suggests the Vivitar is a half-stop brighter, f/stop for
> f/stop, so that its f/3 is as bright as a Pentax 2.5, since f/2.5 is 0.33
> stop faster than f/2.8. For the record, the Vivitar uses a 72mm filter;
> the Pentax, a 77.
>
> For the 135s, I probably didn't use as reliable a method. ISO remained at
> 1000. But I set each lens to its maximum f/stop. Result? About 80 percent
> of the time, the Vivitar delivered a shutter speed that was 1 stop
> faster. It would be difficult to account for this by an f/2.3 vs. f/2.5
> alone. The Vivitar uses a 72mm filter; the Pentax, a 58mm.
>
> I repeated the tests by switching cameras. Results were the same.
>
> I suspect that the Vivitars' brightness owes in part to the fact that they
> are only single-coated, and in part to a conservative f/stop claim.
>
> Paul Franklin Stregevsky
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