Skip W. asks:
<< That's an interesting tidbit. So 180-20%=144mm, 200-20%=160mm? Do
you have anymore details on this? I'm surprised that the 50 & 90 fall
into the same category. >>
Yup. This info first showed up when Popular Photography was reporting
the actual focal length measured at the nearest focusing distance that
they tested. That is when I knew I didn't really need to use a 40 or
35mm Zuiko for copy stand work, becuase my 50mm f/2 Zuiko was at or near
to it already (= 40mm at 1:2). They still report this loss of focal
length in the text on some recent lenses.
<< If you put a 50/2 or 90/2 on a bellows focused at infinity, would it
suffer from the same focal length reduction? >>
No, it wouldn't.
<< Or is this a characteristic of the changes in relative positions of
the lens elements to accomplish close focusing in a helicoid design? >>
Exactly, the aberration correction system (floating elements) changes
focal length just like happens in internal focusing lenses and zooms. In
the case of the 50mm f/2 Macro Zuiko, its the front group distance from
the rest of the elements.
Gary Reese
Las Vegas, NV
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