>But what about the 28-135 f/3.5-5.6 at 28mm wide open? What real
>speed did your meter readings indicate? Was it slower than
>"f/2.8 + 1/2 stop" or slower than f/3.5 (real, numerical value)?
>Anyway, 1/4 stop slower than marked is nothing special. A lot of
>lenses are speced that way. I've seen tests where the lens was 2/3
>of a stop slower than the specs wide open. Typically superzooms at
>the long end ... And that's not light falloff in the corners,
>that's the result for the central part of the image.
Sorry for mixing things up. I didn't remember (now) that the 1/3-
scale is 2.8 - 3.2 - 3.5 - 4 - 4.5 - 5 - 5.6.
It was wrong in my previous post.
28-135 was slower than "f/2.8 + 1/2 stop". In other words, the jump
from f4 to f3.5 (when EOS-3 was set for half-stops) was maybe
a quarter stop. So, according to my not-so-accurate test the
28-135/3.5-4.5 probably is slower than real 3.5.
>Back to the f/4.5-xx lenses. While its easy to imagine what will
>happen if you tell a f/3.5 lens to open up to f/2.8 +1/2 (it will
>be wide open), what will happen if you tell a f/4.5 lens to stop
>down to f/4 +1/2 (which means an f/number > 4.5)? Will it be
>wide open or closed down a little? Hmm, where's that
>100-300 f/4.5-5.6? ;-)
Sorry, I checked 100-400@100mm (f4.5) only when EOS-3 was set for
half-stop scale (it was around 2 a.m. anyway when I made the tests).
I may do (just for "theoretical interest") it once more with
1/3-scale selected and see how the jumps are between 5.6 - 5 - 4.5.
IF f3.5 is f4 + half-stop it is also interesting to see if f3.5
at 1/2 and 1/3-scales is equal or not.
Vesa
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