Creating lens aperture scales - what a project!

[Robert A. Zeichner]

I have been wanting to mount a 203mm Ektar in a modern Copal 1 shutter for some time now and just assumed that adapters would have to be machined to accomplish this. Fortunately, the lens I had was mounted in a GRAPHIC branded Synchro-Compur 1 shutter and upon removing the front and rear groups, discovered that it would screw directly into a Copal 1 shutter I had sitting around from another project. Of course I had to make certain that the front/rear spacing was the same and so I measured the thickness of the mounted lens with my caliper. I got 35.4mm with the Compur set up and much to my amazement, got the same thickness when mounted in the Copal. Great! No machining or shims needed. All I needed to do now was to make some aperture scales.

I removed the two scales which were marked for a 210 f5.6 lens and applied some white flat back tape which I then trimmed carefully with an x-acto knife. I then reattached the top scale.
I first needed to make some light measurements with the old shutter. I remounted the lens in the Compur and installed in my view camera and aimed it at a softlight. Even a way out of focus setting of the camera resulted in a mottled, uneven illumination of the ground glass, so I fabricated an extreme diffusion filter out of frosted drafting film, cut to fit a filter adapter. That did the trick. So then I got out my Pentax analog spot meter as that one has a scale marked in 1/3 stops. Much to my disappointment, the readings I got were unreliable as it was difficult to center the meter against the ground glass. Undeterred, I thought perhaps an old Gossen Luna-Pro F I had with an accessory fiber optic probe might work better. I got out the Gossen and discovered the battery was dead. In the process of trying to remove the 9v battery clip, I managed to snap one of the connectors off. So changing direction, I got out my soldering station and a spare 9v battery clip and did a transplant. So now the Gossen works with a fresh battery and I was all set to make my measurements. The fiber optic probe appeared to work very well and the Gossen's scale was marked in 1/3 stop increments, so I was able to make some repeatable measurements. I decided to use f22 as my starting point as that would be the aperture I would most likely use with this lens most of the time. I set the Compur to f22 and took a measurement. I checked the other apertures and much to my satisfaction, the meter tracked them perfectly.

I remounted the lens in the new Copal shutter and without changing the setting on my meter, I was able to find an aperture that gave me the same reading as f22 on the Compur shutter. I marked that spot with a .3mm mechanical pencil and proceeded to go up and down the scale marking all the other aperture settings, using the meter and probe to confirm the incremental changes. I then removed the aperture scale and inked in the lines with a 00 reservoir pen from one of my many Leroy lettering sets. As long as I was at it, I figured I would letter in the apertures with a size 60 Leroy template. Once I had one scale done, I remounted it as well as the second scale and simply transferred the info to the blank scale using the marked scale as a guide. I then removed the second scale, inked it in and reinstalled on the shutter. Not as fancy as an engraved scale, but a lot cheaper. I now have one of my favorite lenses mounted in a modern reliable shutter. Please forgive the iPhone photos.

[BetterSense]

Can you share more details on the "white flat back tape" you used?
I
Ineed to do this sort of thing a lot for other projects. In particular, for years I have been looking for a good way to mark rotary knob scales, like enlarger timer knobs. Professional products have screen printed scales, but I would love a permanent way to label either linear or rotary controls that looks decent.

[Robert A. Zeichner]

Can you share more details on the "white flat back tape" you used?
I
Ineed to do this sort of thing a lot for other projects. In particular, for years I have been looking for a good way to mark rotary knob scales, like enlarger timer knobs. Professional products have screen printed scales, but I would love a permanent way to label either linear or rotary controls that looks decent.

White flat back tape is simply artists tape, similar to masking tape, but thicker, a true white color and without the crepe texture of masking tape. Here's a link to a source http://www.dickblick.com/products/ar...FVU7gQodXNILFg

[Randy]

I have done something similar (though I like your method of determining the correct f/ marks) in photoshop and then printing it out. My ability to write small and easy-to-read numbers is lacking.

[David Karp]

This is great Robert. Thanks for the tips.

[Bob Salomon]

Except for one problem. Your gg and, if mounted, your Fresnel, absorb light. So unless you compensated for that loss then your markings are off by that absobtion factor.
To do what you did properly you first take a reading directly off a gray card with your meter. Mark that reading down. Know read that same gray card through the gg with your diffuser on the lens and see what that reading is under the same light. Write that down. The difference is the amount of light absorbed by the gg, Fresnel and your diffuser.
Note the difference and set that difference on your meter as the filter factor.
Now repeat and mark your scale at each f stop as your meter indicates. Then your scale is properly adjusted.

[Graham Patterson]

I don't think so. Any absorbed light or scatter should be a constant at a particular aperture on the same camera. With the lens mounted in one shutter and using the (presumably) correct aperture markings, the meter is measuring a transmission value, not an exposure EV. Mounting the lens in the other shutter, the aperture is adjusted to deliver the same EV as measured on the ground glass. One variable - the physical aperture on the second shutter. That gives the equivalent aperture as the original shutter. There are a lot of things to watch for: getting the meter in exactly the same position and alignment, even and constant subject lighting, and masking extraneous light from the ground glass. It cannot be better than the nearest 1/3 stop if that is the best the meter can resolve, but should be close enough. Laboratory precision, no.

I have done it this way successfully, in that the film is exposed as expected.

[Dan Fromm]

Hmm. Not to be a complete idiot, but was the Compur unfixable?

[Bob Salomon]

I don't think so. Any absorbed light or scatter should be a constant at a particular aperture on the same camera. With the lens mounted in one shutter and using the (presumably) correct aperture markings, the meter is measuring a transmission value, not an exposure EV. Mounting the lens in the other shutter, the aperture is adjusted to deliver the same EV as measured on the ground glass. One variable - the physical aperture on the second shutter. That gives the equivalent aperture as the original shutter. There are a lot of things to watch for: getting the meter in exactly the same position and alignment, even and constant subject lighting, and masking extraneous light from the ground glass. It cannot be better than the nearest 1/3 stop if that is the best the meter can resolve, but should be close enough. Laboratory precision, no.

I have done it this way successfully, in that the film is exposed as expected.

Have it your way, I gave the instructions for calibrating a Linhof Focus Metering Bellows with a Gossen with the Microscope adapter attached.

Just blindly reading through a gg/Fresnel does not accommodate for the light loss from the gg/Fresnel and, since they are behind the film, the film does not see that light loss when it is exposed.
On the other hand, film has latitude and shutter speeds are up to 30% off from their marked settings when they are in factory specification.
So, depending on what you shoot and how technical you are, you may get away without calibrating your meter for gg/Fresnel loss.

[Robert A. Zeichner]

First of all, I removed the fresnel as this was simple in that it was mounted between the gg and my eyes. Since I was not taking any sort of an absolute measurement of light, but rather was using the meter simply to compare the amount of light passing through the lens set at known f22 aperture with that of a shutter for which I had no calibrated scale, I don't think the absorption of light by the gg was of any consequence. Once I was able to meter the light from the known aperture, all I had to do was to remount the lens in the unmarked shutter and move the aperture lever until the reading I got on the meter was the same. From there, it was only a matter of moving the lever an amount that would increase or decrease the meter reading by 1/3 stops and marking the scale accordingly.