I don't think the Zuiko 40/2 is a retrofocus design. Looking at the
eSIF, it's optical design is very similar to the 50/1.8. I just looked
at a 50/1.8 and the deepest part is 10mm behind the mounting flange. The
mount to film distance for OMs is 46mm, giving a 36mm distance from lens
to film. Looking at the drawings on the eSIF, it looks like the film to
rear element distance for the 40/2 is about 38mm. I don't know where the
nodes typically are in these 6-elements designs, but I'll bet the rear
node on this one is about 2mm in front of the back of the rear element.
Nodes within the glass means not retrofocus, non?
It seems likely to me that the reason Nikon and Oly and ?? made their
most compact lenses 40mm was because that was the shortest focal length
where a non-retrofocus design could be used with thier SLRs. If 38mm
worked, we'd probably have a 38/2 pancake lens, 'cause it would be a
thinner pancake.
I suspect the same is true for the Cosina. It's simpler to get good
results with conventional design and they had proven designs already
produced by others to use as a basis for starting their own designs.The
M mount lens would be longer because the mount to film distance is about
8mm shorter than the Oly's. Leica could, of course use a non-retrofocus
design with the rear nodal point designed further forward to reduce the
length of their RF only lens.
Moose
Looking at the lenses on the site is interesting. I was wondering how
they could say that the same lens is available for the Voigtländer
rangefinder and in mounts for various SLRs. My first question was
whether the lens for SLRs had automatic aperture which I was not
really able to find. Second question that occurred to me is that
lenses for SLRs and rangefinders are usually designed differently,
especially in shorter focal lengths. Lens elements can recess into a
rangefinder body, but can't recess into an SLR because of the mirror.
Advantages in sharpness, contrast and correction are usually cited by
rangefinder makers because their lenses do not have be made into a
retrofocus design which requires extra elements and lens maker
gymnastics to achieve. Looking at the picture of the 35 mm lens for
the rangefinder it seems amazingly long - nothing at all like the
comparatively flat Leica 35mm. I wonder whether Cosina when planning
their lens line decided to design them all as retrofocus regardless of
their application so that a longer lens barrel could just be
substituted on the rangefinder. Have they really designed SLR lenses,
ignoring the advantages of non-retrofocus design, and just adapted
them to a rangefinder rather than the other way around?
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