Charlie writes:
<< Another thought, The 25mm tube loses 1 stop. >>
That is strictly due to bellows effect in a 50mm lens. Extend a longer lens
25mm and it will not loose 1 stop: it will loose less in proportion to the
focal length of the lens. I believe it would take 45mm of extension to get a
1 stop loss in a 90mm lens.
The 2x converter loses 2 stops.
Yup, and the 1.4X looses 1 stop. This isn't the same physics that are at play
in an extension tube.
> Are there lenses that are optimized for extension tubes?
In the Olympus line, not really, if I take it to mean the fixed length
extension tubes. The 135 (to a lesser extent), 80, 28, and 20 macro lenses
are optimized for the bellows. The 80 (to a lesser extent) and 135 for the
telescoping extension tube. The 25mm extension tube is optimized for the
extension necessary on the 50mm f/3.5 and f/2 to get it to 1:1, BUT the
focusing is quite restricted IF you want the close focus aberration control to
be optimized for near focus. In another words, the lens has to be racked all
the way out.
Gary Reese
Las Vegas, NV
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