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Mamiya 645 Pro 50mm f/4 Shift

DanTidswell

New member
I'm certain that this is a stupid question, but can someone tell me what this rotating part of the lens does?



I did look for a manual before asking - honest! :)
 

ondebanks

Member
Basically it is used on the older non-electronic coupled cameras to tell the body the f/stop selected on the lens.
Sort of...more precisely, it tells the metering prism the f/stop *difference* between full aperture and the stop set on the lens for shooting. It is a relative aperture indicator, not an absolute one. For example, mount an 80/1.9 lens and set it to f/5.6; note the position of that coupling lug. Then mount a 300/5.6 lens and set it to f/11; the coupling lug rotates to the same position, as in both cases there's a difference of 2 stops.

I think the system is rather clever in its simplicity. It tells the meter what it needs to know for correct exposure; no more, no less. Feeding in an absolute aperture value would allow back-calculating of the light eV level, but would not result in a different exposure.

Ray
 

RodK

Active member
The system was developed after the old Nikon systems of the 1960's which also sported this claw type connector on the lens.
Rod
 
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