Re: f/6.3 or f/6.8? & Three R's

[P3D <PTWW@xxxxxxx>]

>Actually, f/6.3 is _exactly_ in-between f/5.6 and f/8 exposure-wise 
>for the same reason that f/8 is between f/5.6 and f/11 (instead of 
>f/8.3).  We are dealing with sqare roots here.

Thanks for clearing up my confusion!

> Write 1, 1.4 and then double 1, then double 1.4 and proceed to get:
>1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 44...

The doubling part is easy but square roots...geez, haven't done
them in about 20 years!  But what do you take the square root
*of* to find an inbetween f-stop value?

>The Three R's (snip) "sunny day rule" was aimed at ASA 10 Kodachrome.

I thought that might be the case, but never tried to verify it
mathematically.  I recall seeing an asa 10 based exposure guide
on a Revere camera.

Paul Talbot


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