: I think this is because the older versions where attached to the bellows
: with only a very flat PMT- (or was it MPT, TMP, PTM, ...?) mount. This
: resulted in less extension than with the new versions. These new versions
: have normal OM-mounts (automatic aperture!) and some focusing capabillities
: of their own, extending the lens a few centimeters from the bellows or tube.
The later macro lenses 20mm/F2 and 38mm/F2.8 have both a length of 46mm, while
the earlier 20mm/F3.5 and 38mm/F3.5 have lengths of 20mm and 28mm, respectively.
The objective lens mount PM-MTob is only 6mm thick. The magnification ratio is
determined by the ratio of (a): the distance film<->optical center of the lens
and (b): the distance optical center lens<->subject. The longer (a) and the
shorter (b) the higher the magnification. The optical center of the later macro
lenses is further away and thus (a) longer.
hnz
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