You get degraded results stopping down too far, from diffraction, Schneider may be more defensive than other companies. If you're doing contact prints then it's far less of an issue compared to enlargements.
Try the lens at f64, f90 see what it's like.
Ian
Hmm. According to http://www.ground-glass.net/large-format/copal-shutters, a Copal 3's largest opening is 45 mm in diameter and its smallest is 2 mm. 240/45 = 5.33, so if the shutter's diaphragm is fully open at f/5.6 the front cell magnifies the aperture by a factor of 1.05. Then the 2 mm smallest opening will give an exit pupil of 2.1 mm, minimum aperture (focal length/exit pupil's diameter) of f/114.
Two dots. F-64 and F-90.Originally Posted by tgtaylor
Manufacture realizes that setting those small apertures can be problematic. If you come from high-to-low and stop at the mark the aperture size is different than if you come from low-to-high and stop at the mark. You are probably better off marking it yourself so you know if you always want to set it from high-to-low or the other way.
To me, those marks are for the experienced user that understands focal spread, print viewing distance, parallax error reading precision instrumentation, logarithmic progressions, aperture size in relation to focal length, film latitude and backlash in mechanical assemblies.
As others have noted, the absolute minimum aperture possible may not be considered acceptable for practical use, and so will not show aperture settings like f90 or f128.
One exception is Process lenses, which are often labeled down to f128 or f256. But the operational shooting parameters in a process camera setting are quite different from pictorial photography.
Don, a shot taken at f/128 will make a perfectly acceptable contact print. Enlarging is pretty much out, though.
The acceptability of such a contact print will depend on which person is passing judgement. Copacetic to some, intolerable to others.
Sal, f/128's limiting resolution is ~ 11 lp/mm. The generally accepted discernable minimum is 8. I wouldn't do it, but its been done.
Cheers,
Dan
"Generally accepted discernble" is copacetic for some. On the other hand, if I'm going to the trouble of making a contact print from a large format negative, as I do using a 240mm lens on whole plate, my ability to discern hews closer to Ctein's "perfect sharpness" criterion of 30 lp/mm. Therefore, I strive to avoid shooting apertures smaller than f/45. It's not always possible, but a worthwhile goal in my opinion.
Just the opposite with process lenses. They were intended to routinely be used at f/22, never ever at tiny apertures. What would be the point? Their primary application was much more demanding than ordinary taking photography, so their published images circles and apo design were standardized for perfect dot shape within this circle, at the published f-stop and specific recommended degree of magnification. So why do their aperture scales go way way down. Helliff I know. But that might just have been how apertures of that vintage were made in general, so that's what they employed as well. Of course, for our own kinds of applications we can bend the rules any way we wish. I often use process lenses for enlarging, and find them optically superior to most official enlarging lenses anywhere from f/11 down. And I mounted one for 8x10 camera use, and typically shoot it at f/45 or f/64 with great results. But there will be a tad of diffraction loss apparent at f/64 in a big print. I never stop a 4x5 lens smaller than f/32, for the same reason.
Sal, Ctein trumps me.
Cheers,
Dan
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