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:
117582 117583

compared to newer shutter assemblies:
117584 117585

[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.info/forum/showthread.php?29267-Here-we-go-Century-8x10-Restoration&p=285641&viewfull=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).

[Jim Jones]

Dan, Of course you are right about the aperture diameter, but the OP asked about aperture scales, not aperture diameters. You are also quite right about the difficulty in physically measuring delicate aperture diameters and optically measuring small entrance pupils. The entrance pupil of my Leitz Super-Angulon 21mm is 0.65mm at the smallest aperture, not easy to measure with the 1mm graduations on my transparent scale.

[Dan Fromm]

Jim, thanks for the reply. Thing is, the distance between each pair of the aperture scale's tick marks corresponds to a one stop change. What the f/ numbers are depends on the diameter of the lens' entrance pupil and the two openings' sizes, but regardless of the entrance pupil's diameter and the openings' sizes, moving the aperture indicator from one tick mark to the next will change the f/ number by one stop.

[Jim Jones]

I agree with that.

[dahlen59]

I mounted a super angulon 90 in a copal press with starting point f 4,5.
I measured the opening for different apertures an got the following result:
F8 starts at between 5,6 and 8 on the scale, f11 was a little more than 8. F16 was 11, f22 was 16, f32 was 22, f45 was between f22 and 32 and finally f64 was f32. It is difficult to measure exactly so it can be a bit off. I used a calipers and for the smaller openings transfered measure to a pencil I carefully positioned in the hole. So i am planning to flip the scale and
Make a new scale on the back of the original scale. But fir now I can roughly use f16-f32 just by using one less fstop on the
Scale scale.