>From: "Hugo Lopes" <[EMAIL PROTECTED]>
>
>I know this was previously discussed but, I came across an "F-stops
>Incremental Chart" taken from the "Nikon School Handbook" and found out
>that an +1/2 stop increment over f1.4 is f1.7 and not f1.8! Beeing an
>EOS "1/2 stop cameras" owner all my life (I moved to the EOS 3 recently)
>it came as a shock to me, to find out that my beloved EOS 1000FN, 600
>and 5 were displaying an +2/3 stop increment over f1.4and not an 1/2
>stop (neither does my EOS 3 in 1/2 stop increments mode, for the
>matter)! To make things more confusing, they show +1/3 stop over f4.0
>and so on. They almost never display the true 1/2 stops. I'm I missing
>something here? If there is an answer to this question in the list
>archives, please kindly tell the approximate date when this was
>discussed and I'll go search for it. If not, can someone explain this?
>Thanks
It was discussed at least around March 8-13 although we concentrated
more on the maximum apertures than to intermediate values.
I think the real answer was not found but *my* assumption is that
Canon just chose some values in early days and stick with them until
it was too late to change them to the correct ones (if they ever
even wanted to do so).
The intermediate values (e.g. in Av mode) are half-stops even if
the values shown are exactly not. The maximum apertures (e.g. 1.8
or 4.5) may or may not be half-stops. Because the lens maximum
aperture is not always the advertised value it is hard to tell the
truth even with few measurements.
By some light level testing I came to a conclusion that e.g. the
physical maximum aperture is always the same and does not depend
on if the camera is set to 1/2 or 1/3 stop accuracy.
Thus when I set aperture to 4.5 (100-400 at 100mm) the light level
was always the same when I was switching between half or third stop
scales on my EOS-3.
Vesa
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