Modifying Lenses for Smaller Stops

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In the rear of the inner bay lenses there is a stationary lever that is located in a slot. I've always wondered if that lever is how the factory sets the smallest stop for the lens. Any ideas out there about how to change the smallest stop to a smaller one? There must be some sort of device to stop the diaphragm from closing all the way down. If such a modification were possible, I'll bet it would mess up the wide open metering. The lenses would probably have to be used on manual. SR

-- Steve Rasmussen (srasmuss@flash.net), April 15, 2001

Answers

I can't really comment on what effect any alteration would have on the metering capabilities of the lenses (and even though moderately priced as MF lenses go, they are still too pricey for me to play around with them), but I too think nearly every lens in the P67 line should be one more stop, maybe more. I also find it odd that 35mm lens-makers don't allow the lenses to stop down more than they do. Last time I checked, only Sigma went beyond the so-called standard on their macro line (most are 22, or maybe 32, but Sigma 50mm & 105MM can do 45, at least in some mounts - perhaps just Sigma & EOS). Also, Sigma is -I think- the only one offering a f32 on the wide angles and wide-angle zooms (Nikon, EOS, Tamron, Tokina, etc., all have a basic 17-35 or 20-35 zoom, but all end at f22). As for alterations in general, it is possible and I don't think it is all that difficult. I once read that scale modelers (model railroad people and magazine publishers, in particular) used to take lenses apart and use aperature discs with TINY precision holes instead of the blades - basically pinhole through a lens. I also know of people who have picked up older SLR's cheap, and altered the 50mm -or preferably 24mm- lens to go way beyond the f22 they were designed to handle. If you have ever taken an old manual lens apart, you begin to see how easy this is (take out the glass, then take out the Dremel tool and extend an slit or notch). Of course, there are trade-offs, but for what they were doing it was definitely worthwhile. I think it worth doing on cheap 35mm stuff, but it might not be worth playing around with on P67 stuff unless you came across a dirt-cheap, REAL ugly or mangled lens to use as a test case.

-- Michael Tolan (mjtolan@kbjrmail.com), August 07, 2001.

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