Some of the odd maximum f #s are members of an older f stop
series that is no longer used. f/4.5, f/6.3, f/9 etc.
Most focal length, f-stop lens configurations are chosen for
marketing reasons. Some one makes a popular new design, say the
Elmarit 135mm f/2.8, and then all makers issue one. Why else did
Nikon have a 43-86mm zoom? (Same range as one of the first zooms
made.) An f/4.5 might be based on some old lens (many single focal
length designs, except internal focus ones, are decades old), with
the series 4.5, 6.3, 9, 12.5, 18, 25, 36. Later it could be made
re-marked and re-click-stopped as 4.5, 5.6, ..., 32.
Paul Farrar
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|