Re: Advice needed on 180 APO with external meter

[Eric Welch <ewelch@gp.magick.net>]

At 11:56 PM 5/28/96 +0800, you wrote:
>Eric, regarding the 180 APO. I note your comments about the light
>transmission. Does this meant that if I was using an external light meter, I
>should under expose by say 1/3 stop because the 3.8 is really more like 2.8
>? Comments would be appreciated.

I would say you should test the lens (which is 3.4, not 3.8) and see what it
does. A few frames will let you know. As for that matter, every lens you use
needs to be tested like that for critical work. Why? Because no lens
actually works at the given aperture. They have f-stops, which are the
physical size of the aperture based on the focal length. Then there's the
t-stop, which is the actual amount of light that passes through the lens
after some of it has been diverted, because of the glass used, number of
lens-to-air surfaces, coatings, etc.

On the other hand, I never needed hand-held meters for anything except flah
metering. I have always trusted, and been rewarded by the accuracy of
Leica's selective metering. It takes some learning, and burning some film,
but for those of us who don't pay for our film, that's not so bad. <g>
(Within budgetary limits).

For example, I used to shoot basketball with two lenses, mostly. A 90
Summciron and a 180 Elmarit. In one particular gym (they all vary, of
course) I would set the shutter speeds of the cameras at 1/500 for 6400 ISO.
The 90 Summicron would be set at f3.5 and the 180 Elmarit would be set at
f2.8. The exposure would be exactly the same on film. Why? Because the 90
Summicron is more efficient with light than the 180 Elmarit. So test your
lenses. If you can't tell the difference, then don't worry about it. If you
can, you've gotten better control of the process. Let us know how it works
out for you.

==========================
Eric Welch
Grants Pass Daily Courier