View Full Version : Calibrating lens to a Compur shutter

26-Jun-2000, 21:02
I have 90 mm Super Angulon in a defective Compur shutter. I also have a spare Co mpur shutter in very nice condition with the same min/max aperture. If I were to exchange shutters, what kind of calibration is needed to match the lens to the new shutter? When I take the lens elements off the defective shutter, I see no s hims. Thanks for your guidence!

David A. Goldfarb
27-Jun-2000, 01:19
If the thread matches and the lenses screw into the new shutter, you could use a depth gauge to make sure the distance from the rear lens of each cell to the aperture blades is the same for the new shutter. If not, you could have the shutter modified and adapter rings made (see www.skgrimes.com).

The aperture markings might not apply to the new lens if they were originally for another lens. You could determine that either by measuring the actual diameter of the apertures for each shutter at each setting. If not, you could draw a new aperture scale and stick it on the lens (either using the formula: f-stop=focal length/diameter of the aperture, or using a light meter with a booster capable of taking groundglass readings) or you could have a new scale engraved.

David A. Goldfarb
27-Jun-2000, 01:21
For those disturbed by the unresolved "either," the second sentence of second paragraph above should end: "or with a light meter."

Michael S. Briggs
27-Jun-2000, 02:48
Most likely, you can just switch the lens barrels to the spare Compur shutter. As mass produced items, lenses and shutters are intended to be made precisely enough that they are interchangable. One exception is that the spacing of the lens elements of wide angle lenses is critical and is sometimes fine tuned with thin washers. Your lens lacks such shims, so you don't have to worry about it. Otherwise you would transfer the shims too.

If you want to be really sure, measure the distance from the back of the back cell to the front of the front cell using machinist's calipers. This distance should be the same with the lens cells mounted in either shutter.

If the aperture scales are the same, then you are also ok there.

Bob Salomon
28-Jun-2000, 06:29
It is critically impportant with wide angle lenses that they be re-collimated when remounted in a new shutter. Normally this should be done by a qualified repair shop with the proper equipment.

Additionally the aperture scales need to be re calibrated