How do you create an aperture scale for a lens?

[sully75]

I have a 6 1/2" Voightlander Dynar lens in shutter that I'm attempting to use on 4x5(my first journey into quirky lens land). The shutter is broken but I'm using it with a speed graphic. The aperture scale has fallen off the shutter.

I was wondering how I could figure out an aperture scale? I believe the lens is f5.6 wide open. Is there a formula for figuring out different apertures?

Thanks!

[Jack Dahlgren]

I have a 6 1/2" Voightlander Dynar lens in shutter that I'm attempting to use on 4x5(my first journey into quirky lens land). The shutter is broken but I'm using it with a speed graphic. The aperture scale has fallen off the shutter.

I was wondering how I could figure out an aperture scale? I believe the lens is f5.6 wide open. Is there a formula for figuring out different apertures?

Thanks!

Each stop is a reduction in the amount of light by 1/2. If you know it is f/5.6 wide open, you can use a light meter and a steady unchanging light to find out where each stop lies on the scale. Start at wide open and move the lever until the light reading indicates one stop difference, make a mark, continue until you run out of travel. Then do the same thing backwards to confirm your readings and see if there is any slop in the lever.

While it may be possible to derive a formula for the scale, it is better to measure directly as you don't know how the internal design of how the aperture responds to movement.

[Jim Galli]

Divide the common aperture nos. into 165 to get aperture diameter in mm. ie. 165 divided by 8 is 21. A 21mm hole is your f8. 165 divided by 11 is 15. A 15mm hole is f11, and so on. I think Dynar's are f6.3

[sully75]

Divide the common aperture nos. into 165 to get aperture diameter in mm. ie. 165 divided by 8 is 21. A 21mm hole is your f8. 165 divided by 11 is 15. A 15mm hole is f11, and so on. I think Dynar's are f6.3

Hi Jim,

I'm finally actually working on this lens. By your method, do I measure the aperture with the cells in or out? The opening of the aperture with the cells out appears to be f8. With the cells in it looks more like f6ish.

Thanks
Paul

[BradS]

Hi Jim,

I'm finally actually working on this lens. By your method, do I measure the aperture with the cells in or out? The opening of the aperture with the cells out appears to be f8. With the cells in it looks more like f6ish.

Thanks
Paul

You measure with the optic in place, looking into the front of the lens.

[Jim Jones]

The Vade Mecum lists Dynars as f/5.2, f/5.5, and f/6, but none in 6". It's not a perfect reference. When measuring the diaphram to determine f/number, look through the front of the lens from enough distance to reduce parallax.

[sully75]

Hmm...I had it in my head that it was 5.6, but now I'm not sure. I believe that it is the lens listed here

I'll take a picture and post it.

[rdenney]

The diameter is not the physical diameter of the aperture, but its apparent diameter (pupil opening). That is not so easy to measure.

It is easier to measure it on the ground glass. But doing that requires a couple of things. One is that the measurement will be sensitive to a range of issues, including changes in alignment, so put the spot meter on a tripod to fix its location with respect to the camera. The second problem is that a ground glass will pick up ambient light from behind the camera, so shield all that off either with a darkened room or a good focus cloth.

You can find the maximum brightness of the lens by comparing it to a known lens. Focal length does not matter. Set up an evenly illuminated panel of solid, neutral color as the subject. Open the aperture wide on the subject lens, focus on the panel, and take a reading right in the center of the ground glass with the meter point right along the lens axis. Replace the lens with a known lens and refocus, and adjust its aperture until you get the same reading as with the subject lens. The reading on the aperture scale is the wide-open f/stop of the subject lens. Mark that, and then reinstall the subject lens and refocus. Close the aperture until the meter reads 1 EV less, and that is the next stop, and so on. You can use a piece of tape and mark the apertures with a fine pen. Then test with real photographs, and make an inscribed focus scale if that's how far you want to take it.

Or, you can send the lens to Grimes and they will make an aperture scale for you that will be very pretty (and expensive).

Rick "who prefers methods that use values important to us, such as the amount of light falling on the film plane" Denney

[Jack Dahlgren]

The diameter is not the physical diameter of the aperture, but its apparent diameter (pupil opening). That is not so easy to measure.

Rick "who prefers methods that use values important to us, such as the amount of light falling on the film plane" Denney

Yep, measuring the diameter is error-prone and all we care about is how much light gets through the lens.

[Jim Jones]

Yep, measuring the diameter is error-prone and all we care about is how much light gets through the lens.

Yes, that's why why some photographers have used T-stops instead of F/numbers. Some of us are accustomed to f/numbers for calculating DOF and other perameters, with perhaps a correction factor for the transmission of the Dynar (which might be a hundred years old). Measuring the entrance pupil with a ruler and calculating the f/stop seems easier to me, and with less probable error. It's the photograph that really counts, not the contortions we go through to get it.