Originally posted by henryk ....
That preset Bellows-Takumar is nice and sharp from center to corner, by the way. Seems to be a match for my 90mm Tamron macro. The Tamron does 1:1, but the Tak does 1:1.25, I believe....
The effective f-stop for exposure purposes for f:22 at a magnification of 1:1 is
f:44 (ie. f(1+m))!
Not only does this decrease brightness a LOT it also put the lens well beyond its diffraction limit. Say a lens/camera combination has a diffraction limit at F* for normal photography, then for macro photography the effective limit is F*/(1+m). For a magnification of 1X, I'd expect diffraction softness to start at around f:10.
While high f-numbers will increase apparent Depth of Field, the gain beyond about F*/(1+m) is compromised by an accompanying loss in sharpness.
Dave
PS The 100mm Bellows Tak should approach 1:1 if the bellows extends to 150mm or so. At 150mm + 45.5mm for the camera, the mag would be (195.5/100 -1) = .96X