On Fri, 21 Jun 2002 03:44:33 -0500, "³ª Thomas"
>"Gary Frost"
>news:3D124BEE.B9A8DF50@nospam.com...
>> Chris Quayle wrote:
>> > "³ª Thomas" wrote:
>> > > The biggest problem with external meters is that they
>can not compensate for the amount of glass used in lenses.
>The glass limits the amount of light reaching the film.
>This is a big consideration that most overlook. In camera
>meters are the best solution.
>> > >
>> > Someone else mentioned this recently. Ok, assuming the following range
>> > of lenses, for example AI Nikkors, what would you think a typical range
>> > of error would be in terms of stops ?...
>> >
>> > 24mm f2.8
>> > 35mm f2
>> > 50mm f1.4 (assume this is the zero error case )
>> > 135 f2.8
>> > 180 f2.8 ED
>> > Chris
>> I wouldn't be concerned with any of these lenses. It only would
>> become significant with 16+ element zoom type lenses.
>That's not quite true. Zooms can have many thin elements.
>It's a matter of how much glass is used. Take a Nikkor
>Ai-S 28/2.8 and Ai-S 28/2.0 and you will notice that even
>though the 2.0 is one stop faster it does not let anymore
>light in. The 28/2.0 has one element more than the 2.8 yet
>it has MUCH more glass. Glass eats light. Period.
Uhhhhhhhh.....
I just happen to have both lenses, and on an F100, reading
the same plain-toned surface at the same angle with both
wide open, the f2 gives 1/25th second, the f2.8 gives
1/13th second, both centered well at those shutter speeds
one stop apart, as one would expect... I have found very
few lenses with anomalous transmissions, regardless of
construction, though almost all are "slower" than rating
due to technical "cheats" for maximum aperture and
illumination roll-offs which are maximized at maximum
aperture (the metering pattern affects the meter reading
with this). The second accounts for the 500mm f8 Nikkor
metered TTL being off about 1/2 stop due to the mirror
"hot spot", and I'm not sure what accounts for the
Nikkor 15mm f5.6 metering being off about 1/2 stop read
TTL (illumination is remarkably even with this lens) -
perhaps it is the first (it may not be actually f5.6
wide open... As for the lenses listed in the post above,
I would expect them all to read with very little variation
between them.