I came across an odd note on a camera building website yesterday to the effect that the flange focal length of the 80mm lens in a 'blue dot' (later model Seiko) shutter was different to the 80mm in other shutters. This seems to be a little strange.
The shutters used with the Mamiya TLR and 80mm lenses were:
Seikosha-MX
Seikosha-S
Seiko
Seiko, late
Copal
The MX series dates to the original Mamiyaflex, the Seikosha-S had the 40.5mm filter thread 80mm, the Seikos had the 46mm filter thread 80mm, while the Copal was used with the 80mm f3.7.
To my knowledge there were four lens designs - the 40.5 threaded, the 46mm, the 80-S (also 46mm and probably 'blue dot'), and the f3.7. The Seikosha and Seiko shutters are all #0 compatible, and should be the same thickness from the back to the inner face of the front lens mount. (I assume the Copal is also #0, but it is not relevant to this discussion). This may not be the case?
I only have a 'blue dot' 80mm myself, and measuring the pressure plate to the front of the camera front plate gives my 71.3mm (+/- 0.3mm). Add in the lens mount plate, and that would come to about 72mm at infinity focus for the back of the shutter. Lenses do get shimmed in the mount or the shutter, but I have yet to see more than 0.25mm in shims used.
So, are there differences between the flange focal length (infinity focus extension of the lens panel from the pressure plate) with the Seikosha-S, Seiko, Seiko (late with older 80mm black lens) and the Seiko (late with 80mm S lens)? And are the differences due to the optical construction, or the physical shutter?
The bellows design of the Mamiya C makes minor changes quite possible, and would largely go unnoticed. But someone mounting just the taking lens would notice an infinity focus discrepancy from an expected extension.
The shutters used with the Mamiya TLR and 80mm lenses were:
Seikosha-MX
Seikosha-S
Seiko
Seiko, late
Copal
The MX series dates to the original Mamiyaflex, the Seikosha-S had the 40.5mm filter thread 80mm, the Seikos had the 46mm filter thread 80mm, while the Copal was used with the 80mm f3.7.
To my knowledge there were four lens designs - the 40.5 threaded, the 46mm, the 80-S (also 46mm and probably 'blue dot'), and the f3.7. The Seikosha and Seiko shutters are all #0 compatible, and should be the same thickness from the back to the inner face of the front lens mount. (I assume the Copal is also #0, but it is not relevant to this discussion). This may not be the case?
I only have a 'blue dot' 80mm myself, and measuring the pressure plate to the front of the camera front plate gives my 71.3mm (+/- 0.3mm). Add in the lens mount plate, and that would come to about 72mm at infinity focus for the back of the shutter. Lenses do get shimmed in the mount or the shutter, but I have yet to see more than 0.25mm in shims used.
So, are there differences between the flange focal length (infinity focus extension of the lens panel from the pressure plate) with the Seikosha-S, Seiko, Seiko (late with older 80mm black lens) and the Seiko (late with 80mm S lens)? And are the differences due to the optical construction, or the physical shutter?
The bellows design of the Mamiya C makes minor changes quite possible, and would largely go unnoticed. But someone mounting just the taking lens would notice an infinity focus discrepancy from an expected extension.
