Copal 3 minimum aperture?

[StuartB]

I've recently bought a Schneider 240mm lens with a Copal 3 shutter which is marked to a minimum aperture of f45. However, the iris continues to close considerably after the last markings, to what I would guess is at least f64.

Does anyone have any knowledge of what the actual minimum aperture is (either from manufacturers specs or testing)?

Thanks in advance.

[Arne Croell]

I've recently bought a Schneider 240mm lens with a Copal 3 shutter which is marked to a minimum aperture of f45. However, the iris continues to close considerably after the last markings, to what I would guess is at least f64.

Does anyone have any knowledge of what the actual minimum aperture is (either from manufacturers specs or testing)?

Thanks in advance.

For a modern Copal the spacing between the f-stops is equal, so if you move it down from f/45 the same distance that you have between the other full stops, you should be at f/64, and so on. However, the smallest openings are not as accurate as the other ones, as any play or manufacturing tolerance will have a larger effect.
Note also that the f/stop is determined by the diameter of the entrance pupil, i.e. the magnification of the aperture opening by the front elements plays a role - your f/45 might be an f/64 for another lens in the same shutter.

[David de Gruyl]

For further reference, I have a nikkor-w 240 in a copal 3 that shows aperatures down to f/64, and the lever goes a bit past there.

I suspect that if it went past f/64 it would be marked, but it is all about printing / labeling.

[photographs42]

The minimum marked aperture is usually the minimum because beyond that, the image quality is degraded more than the manufacturer feels acceptable. You can go smaller but you pay the price in image quality.
Jerome

[ic-racer]

Funny that it is not marked, as f64 with that lens on an 8x10 camera is still 'safe.'
Perhaps the shutter or aperture scale are not what was originally with that lens when new.