copal 1 shutter - can I swap lens sets?

[bill_1041]

I've got a nice Copal 1 shutter that came with a lens (Caltar II, 210 mm). The shutter is marked for f-stops from 5.6 to 64. Having come across a G-Claron 305 lens set (no shutter), I've discovered that the elements are threaded so they fit the Copal 1 perfectly. My question: Just because the f-stop markings indicate a maximum opening of 5.6, does that mean that any lens set that fits the Copal 1 shutter will also have a maximum opening of 5.6?

My sense is that the G-Claron is actually more like an f9, so I'd simply make a chart that starts with "marked" 5.6 = 9 "actual" and work the remaining f-numbers from there. Then a quick test shot or two would confirm I'm in the ballpark.

Looking forward to hearing your thoughts.

[Ted Harris]

Yuo are correct that the lens elements of yoru G Claron should fit directly into a Copal ! shutter with no modification. As for the aperature you are also correct that the maximum is f9. You can use your approac or send the lens off to someone like SL Grimes or richard Ritter and have them swap out the aperature scale for the correct one. A simple and relatively inexpensive job.

[Bob Salomon]

Also you may find that the new lens may or may not require shims for the front and rear cells to be spaced properly.

[bill_1041]

Bob - What would I notice in my images that would indicate a spacing problem?

[Jim Galli]

Bill, They will fit and work fine. You can measure the distance front to back with a caliper while the set is in the barrel and then double check to see that it is the same in the shutter. Modern stuff is awfully good. The land machined on both the lens barrels and the shutter are micro tolerances and it's very rare to find any difference in spacing. Your aperture scale is useable as is if you remember that you are one full stop off from what it's telling you. Not the best idea but useable in a pinch. IOW when the scale says f16 you are actually at f22 for the 305. The Caltar 210 is too nice of a lens to make it a sacrifice. Why not use both sets in the single shutter sort of like a casket set. Have your cake and eat it too so to speak.

[Bob Salomon]

"What would I notice in my images that would indicate a spacing problem?"

Not as sharp as you would expect at optimal aperture.

[bill_1041]

Thanks Jim - hopefully I'll have something to share for the next print exchange!

[neil poulsen]

By my calculations, assuming that the distance tolerances work out and that you can use your shutter with the 305mm lens, you would be very close to a stop off. So, if you set f5.6 on your shutter (designed for a 210mm lens), this would equate to an f8 if you are using the 305mm lens elements. f16 on your shutter would equate to f22, etc.