Correct Distance Between Stops on a Copal 0 Press Shutter?

[Whir-Click]

Can anyone please tell me the correct distance between full f-stops on a Copal 0 Press shutter? I just bought one off e-bay and the existing aperture scale looks wonky: the stops aren't equidistant.

Thanks!

[Leigh]

Equidistant stops are a relatively recent improvement.
Many (?most?) old shutters were not designed that way.

I don't know whether or not that is true of the Copal Press.

- Leigh

[Whir-Click]

These should be equidistant, the existing marks are just badly placed, ranging from about 3 to 4.5mm between stops on the scale on the side of the shutter.

If someone has a Copal 0 Press, could you take a quick measurement of the distance between stops on the side scale? I would be much obliged.

Thanks, Bill

[Jim Jones]

The distance between stops should vary with different lenses.

[Dan Fromm]

The distance between stops should vary with different lenses.

No. Stopping down one stop decreases the aperture's area by 50%. This is independent of the lens' focal length and pupillary magnification. These two affect the f/ number with the lens wide open, after than one stop down (marked) is one stop down ...

W-C, I just measured a Copal Press No. 0. This is an early #0 Copal Press. The full-stop tick marks are equidistant, at the rim they're 3.70 mm (subject to a little measurement error) apart.

[djdister]

It would seem that older shutters were not so good on having equidistant f/stop scales:


compared to newer shutter assemblies:

[Whir-Click]

Dan Fromm- thank you very much for the measurement info. That is exactly what I need for an interim solution until I can send it off to SK Grimes to have proper scales engraved.

Best regards,
Bill

[ic-racer]

The "Helinski" font on my label maker was just right to make 5mm-apart numbers for a Copal #1. You may be able to do something similar at 3.7mm.

http://www.largeformatphotography.in...l=1#post285641

[Jim Jones]

No. Stopping down one stop decreases the aperture's area by 50%. This is independent of the lens' focal length and pupillary magnification. These two affect the f/ number with the lens wide open, after than one stop down (marked) is one stop down ...

W-C, I just measured a Copal Press No. 0. This is an early #0 Copal Press. The full-stop tick marks are equidistant, at the rim they're 3.70 mm (subject to a little measurement error) apart.

The aperture scale of a wide angle lens will be compressed in comparison to a long lens on the same shutter unless the scale is linear. This is conspicuous on convertible lenses.

[Dan Fromm]

Jim, get out your calipers and a convertible lens and measure the aperture's diameter at two adjacent stops for each of the two (or three) scales. You should find that the ratio of adjacent full stops diameters' step is 1.4 (lousy approximation to sqrt(2), but if the stops you choose are small your measurments will, like mine, be lousy too).