Calibration after a new Copal shutter?

[cyron123]

Hello,
Is it important to calibrate the lens shutter system after changing a copal shutter?
I heard that depends on the focal length?!?!
Thank you.

[Leigh]

Is it important to calibrate the lens shutter system...

I don't understand what that means.

The only "calibratable" component is the shutter mechanism itself, specifically the speeds.

These can be set as a group, but not individually.

The "best practice" in shutter repair is to adjust it to minimize the overall error, so some speeds might be slow and some might be fast. Speed tolerances are quite wide, on the order of 20 to 30 percent.

The aperture ring markings should be correct if the scale is made for the lens being used.
Note that f/5.6 (for example) may be in different places for different lenses.

- Leigh

[Doremus Scudder]

If you mount a lens in a shutter that already has an aperture scale for a different focal length lens, you will have to "calibrate" the aperture scale or find an aperture scale for the lens you have mounted.

There a lot of info here on exactly that: search.

best,

Doremus

[cyron123]

Hi,
I have talked to a rodenstock guy one month ago and he told me that there is a tolerance in every copal shutter. Like in every part. And you need to calibrate with shims the lens system. They make this at rodenstock. But I don't know if this is necessary for every lens copal combination..

[Bob Salomon]

Hi,
I have talked to a rodenstock guy one month ago and he told me that there is a tolerance in every copal shutter. Like in every part. And you need to calibrate with shims the lens system. They make this at rodenstock. But I don't know if this is necessary for every lens copal combination..

No, it isn't. And Rodenstock shims come in a variety of thicknesses and if you have two lenses of the same series and focal length with consecutive serial numbers the shim required for one may be different then the shim/s required or not needed on the other. The shorter the focal length the more critical this becomes. And since Rodenstock makes view camera lenses as short as 23mm, 28mm 32mm, 35mm, 40mm, 45mm, 50mm, 55mm, 60mm, 65mm, 75mm 90mm, etc. these are all very carefully done. It also isn't really a DIY project if the lens is to perform to factory specifications. Rodenstock does sell their lenses in just front and rear cells only. But the page in their distributor price list that has these lenses listed has this statement at the bottom of the page:

" The prices shown in our price list are for mounting of the front and rear cells in shutter delivered by our customer. (that means you send your shutter to the factory).
The assembly can only be done at Qiotpiq Phototonics Feldkirchen. We will NOT deliver front and rear cells unmounted. We insist that the lenses will go through our quality control department." (once mounted in shutter)

[Leigh]

The cell seating dimension on Copal shutters has a tolerance of +/-0.025mm, which is 0.001 inch.

Lens manufacturers match front and rear cells so that their spacing matches the shutter for which they're made.

Amateurs do not have the optical equipment required to properly position the cells in the shutter.
Doing so requires a sophisticated optical bench.

- Leigh

[IanG]

Lens manufacturers match front and rear cells so that their spacing matches the shutter for which they're made.
- Leigh

I think they are matched for other reasons as well particularly with symmetrical designs. The manufacturers know which cells give the best results combine.

The cell seating dimension on Copal shutters has a tolerance of +/-0.025mm, which is 0.001 inch

In the 50's & 60's Compurs tolerances were way out with some shutters which lead to poor quality 90mm f6.8 Angulons ( the had inconsistent spacings).

Ian

[Leigh]

I think they are matched for other reasons as well particularly with symmetrical designs.

I didn't say that was the only reason. I said it was A reason.

In manufacturing, the technique is called "binning". You measure the critical parameter, then put the item in various boxes depending on the measurement. For example, all those that are .01" oversize go in one box, those that are nominal in another, and those .01" undersize in another.

You do the same for both cells.
Then you match one that's .01 oversize with its opposite that's .01 undersize.

This keeps the internodal spacing constant, but shifts the nodal points within the shutter by a small amount.
That's where shims come in, attempting to reposition the cells properly relative to the diaphragm.

This technique has been used for a couple of centuries.

- Leigh