New Zeiss apertures to f-stop converter

[Jim Andrada]

Just wondering if someone has a good conversion method to convert "New Zeiss" aperture sizes to today's standard system.

[roetronxoay]

Is this what're looking for?
214621

[Jim Andrada]

Thanks much. I've seen that one. What I'm wondering is whether anyone has mapped the number from say 27.36 to the nearest third or half stop between f/22 and f.32.

f 27.36 isn't a particularly useful number when using a meter calibrated in 1/3 stops

[reddesert]

Thanks much. I've seen that one. What I'm wondering is whether anyone has mapped the number from say 27.36 to the nearest third or half stop between f/22 and f.32.

f 27.36 isn't a particularly useful number when using a meter calibrated in 1/3 stops

If you know the f-number, then take the next lowest standard f-number and use this formula to find the increment in fractional stops:

increment = log [ (f-number / next-lowest-f)^2 ] / log(2)

The amount of light goes as the square of the f-number, and every stop multiplies by a factor of 2 so stops are logarithmic.

For ex, I read that table as saying new-Zeiss aperture 4 = f/25, so compare it to f/22:

increment = log [ (25/22)^2 ] / log(2) = 0.37

So f/25 is about 1/3rd stop slower than f/22.

[Tin Can]

Another example of non standardisation to keep early photography difficult and secretive

and the beat goes on