Giant Lens Aperture Problem

[Andrew van Bommel]

Hello all, I just purchased a giant lens on eBay (item # 3836517099) hoping to use it on a giant camera (not yet built). The aperture dial has numbers 5.6, 8, and 11 but I can only move the dial from 5.6 to 8, hitting solid stops on each aperture setting, as if they were the maximum and minimum aperture settings. Looking inside the lens, I can see that the aperture dial should move more, as seen by the extra room each aperture leaf could potentially travel. The lens is unmarked, except for the aperture settings and a "Made in Germany". It would be great if I could stop down past f/8.

I appreciate any help any of you out there could give.

Thanks.

[Jason Greenberg Motamedi]

Looks to me like you have bought a photocopier lens, or something of the sort. I have never tried one, but they are optimized for 1:1. My feeling is that you will probably have to stop down to at least f/22 to get decent results, so you may need to actually take the thing apart. Often lenses have small metal stops or tabs inside the iris scale which prevent them from stopping down. Pull the lens apart and see what you find. At worst you lost $17...

[Ernest Purdum]

Jason is probably correct, but since lenses for giant cameras are scarce and often expensive, you might want to hold off on disassembly until you have a chance to find out what it might do for you. At f8 you would at least be getting an idea of the minimum coverage (which might increase on stopping down). You then would be in a better position to decide whether or not to pay a repairperson to work on it. Sometimes screws holding a diaphragm in place are installed with "Loctite". This makes them hard to remove and one slip of the screwdriver can do a lot of damage.



I took a look at the item. You may have achieved a record for the most optical glass per dollar ever bought on eBay.

[Andrew van Bommel]

Thanks for the quick and informative responses. While attempting to take the lens apart, removing one set of screws allowed me to move the aperture ring to about f/22. However, I never did get the lens open. Putting the lens on a wooden box and using my makeshift ground glass (8x10 glass sprayed lightly with white spray paint- it kinda works!), I discovered that the coverage was only about 13 inches in diameter. It hardly changed when stopped down. Looks like it's back to searching eBay...

Thanks again.