Lens F/Stop Scale Question

[dbla]

Hey all,

I purchased with Schneider Symmar 135 f/5.6 lens with my Wista a month or two back. The aperture scale only goes to f/8... Since this is a f/5.6 lens I am making the assumption that wide open is 5.6. Is there any reason I shouldn't believe this is accurate/is there any way for me to test this out?

Thanks!!

225045

225046

[Dan Fromm]

Hold the lens in front of you with the shutter open. Open the diaphragm as far as it will go. The diaphragm leaves should be invisible. Slowly stop down until the diaphragm leaves appear. Open up very slowly until they disappear. This is the f/5.6 position. If aperture indicator will move farther towards wide open, mark the position you found "5.6"

Try the same exercise with a lens in a shutter with the correct aperture scale to gain some faith in the procedure.

[Oslolens]

The aperture scale is for another lens: could be a 90mm f8 so no need to rely on its accuracy.
I believe the distances between stops are accurate, print the scale with identical distances only start at f5.6. Place f5.6 where the aperture blades start to show and make sure to test f11 and f22 to be sure.

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[xkaes]

Ditto.
After checking for the fully open spot, you can leave it as is -- and remember that f8 really means f5.6, etc. -- or you can make you own scale, as a replacement or glue it on top. I've seen replacement scales for various lenses and shutters on EBAY -- frequently. Some (most?) large format lenses (Schneider, Fujinon) have f-stop scales with a code stamped on them for the shutter -- for Fujinon, it's like "45" or "57" (not to be confused with the f-stops). That might help you find a replacement.

[Conrad . Marvin]

I think that you will find that the distance between the stops will be different on a scale that was made for a different focal length lens.

[Dan Fromm]

I think that you will find that the distance between the stops will be different on a scale that was made for a different focal length lens.

Interesting. Why do you think so?

[Conrad . Marvin]

To find the f stop diameter for a given focal length lens, you divide the focal length of your lens by the f stop that you want. You can measure the stop carefully from the front of the lens to come up with a usable scale. It’s not the diameter of the iris, but the diameter looking through the lens…the entrance pupil? that determines the amount of light that gets to the film. Remember, f8 must let in the same amount of light on a 90mm lens as a 450mm lens and the size of the aperture will be very different to accomplish this. The scales will be quite different for each focal length, but they will have equal spacing between each stop, at least on a Copal shutter.

[Mark Sawyer]

To find the f stop diameter for a given focal length lens, you divide the focal length of your lens by the f stop that you want. You can measure the stop carefully from the front of the lens to come up with a usable scale. It’s not the diameter of the iris, but the diameter looking through the lens…the entrance pupil? that determines the amount of light that gets to the film. Remember, f8 must let in the same amount of light on a 90mm lens as a 450mm lens and the size of the aperture will be very different to accomplish this. The scales will be quite different for each focal length, but they will have equal spacing between each stop, at least on a Copal shutter.

Each diminishing stop decreases the aperture area by half, regardless of focal length. What might change is the degree of magnification of the aperture by the front element/entrance pupil, but this will be consistent across f/stops for any given lens. Except for that possibility, the OP just needs to allow for one additional f/stop. Better yet, do the measurements and see what's going on.

It looks like a new aperture scale has been mounted on the shutter. Dbla, you might try unscrewing it to see if there's another scale underneath.

One other possibility is that it might be an f/5.6 lens, but restricted to f/8 by that shutter, (I can't see what size Copal it is).

[ic-racer]

Looks like the proper scales for that shutter to me.

[Bill Poole]

Isn't that shutter, with two scales, for a convertible lens?

[Conrad . Marvin]

If a #0 Copal, then a 135mm f5.6 fits in it. If a convertible then the second scale would not start with f8 but something like f12.