LF-lenses on MF-Cams. How is register calculated?

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europanorama

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Want to adapt 125mm fujinon and 150mm Apo-Sinaron in Seiko 0-Shutter in special Bessa I with P67_mount. Yes format is also special 56 x93mm(not 88mm) and seems not altered. Front has P67-mount but register is not 85mm but 48mm, reduced by 37mm. so there is plenty of room for M65-helicoid.
so can i calculate infinity by measuring 125mm for the 125mm from shutterplane to film?
With all the possible adapters.cammount with different flanges 1, 3, 7mm and shutterthickness i get min. helicoid-sizes of 55/60 for the 125mm to 80/86mm for the 150mm. it seems 90mm would match best 17-31mm helicoid.
Since i killed aperture-blades on Seiko i would need new shutter. Or FLs which match existing Copal 1 which i have already.
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Camdesign not by me-designed for pinhole. am about to establish innovative setups incl. shift-pinhole and 18° cosmos circle shutter. universal system using existing parts.
------------------------
It seem everything answered here:
Calculating lens focal length | Photrio.com Photography Forums
 
Last edited:

shutterfinger

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Large format lens register/focus infinity at a distance from the film plane. The nominal focal length is marked on the lens trim ring, the actual focal length is measured. Some lens are designed to focus infinity closer to the film plane than their focal length.
 

Huub

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What shutteringer says: with large format lenses there can be slight differences between the actual focal length and what is stated on the lensring. A 125mm might well be 123,4 mm or 126,1 mm or something else. On top of that some lenses have a different film to focal plane distance then their focal length. For instance, my 58mm Super Angulon XL has a slightly bigger film to flange distance, which make using this lens easier in situations where there is not much room between front and back standards. The only way to actually know is to measure. Easiest way is either measuring the lens on a large format camera or using some kind of (improvised) groundglass on your own camera.
 
OP
OP

europanorama

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Joined
Aug 10, 2004
Messages
381
Location
Basel-CH
Format
Large Format Pan
Want to adapt 125mm fujinon and 150mm Apo-Sinaron in Seiko 0-Shutter in special Bessa I with P67_mount. Yes format is 56 x88mm. Front has P67-mount but register is not 85mm but 48mm, reduced by 37mm. so there is plenty of room for M65-helicoid.
so can i calculate infinity by measuring 125mm for the 125mm from shutterplane to film?
With all the possible adapters.cammount with different flanges 1, 3, 7mm and shutterthickness i get min. helicoid-sizes of 55/60 for the 125mm to 80/86mm for the 150mm. it seems 90mm would match best 17-31mm helicoid.
Since i killed aperture-blades on Seiko i would need new shutter. Or FLs which match existing Copal 1 which i have already.
------------------------------------
Camdesign not by me-designed for pinhole. am about to establish innovative setups incl. shift-pinhole and 18° cosmos circle shutter. universal system using existing parts.
------------------------
It seem everything answered here:
Calculating lens focal length | Photrio.com Photography Forums

not editabla anymore? correction above
 
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