Re: Aperture calculations; 6.3 or 6.7???

[P3D <PTWW@xxxxxxx>]

DrT, who must have gotten out his slide rule, now wonders:

>Thus, the half f-stop between 5.6 and 8 is either 5.6 x 1.19 or
>sqrt (5.6 x 8).  Both methods give 6.7.  So, why is it assumed that
>6.3 is the f-stop half way between 5.6 and 8????

BobH asked us to be sure we noticed he calls them "in-between" stops,
not half-stops, and mentions something about them being 1/3 stop
shifted.  I didn't understand what he meant, especially after reading
an earlier post that said f/6.3 is exactly half-way.  After a little
more thought and examination, it appears that maybe the two scales,
Continental and English that BobH told us about, are not true mid-points
to each other, but rather have a 1/3, 2/3 stop stepping pattern.  I
guess that is what BobH was trying to say.  Can anyone confirm?

Paul Talbot


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