Originally posted by Ash The important difference to me between lenses of different maximum apertures (given the same aperture, subject distance and focal length) is the OOF rendering, particularly in the highlights.
DoF should theoretically (and intuitively) be the same for instances where the variables that affect DoF are being kept constant.
I think ash has hit the point as clearly as any one.
I have, for example, 3 different 135mm lenses in M42 mount:
- S-M-C Takumar 135/3.5
- Tele-Lentar 135/2.8 Preset
- XR Rikenon 135/2.8
They all perform differently, even when set to the same aperture, the Rikenon has a color cast and is at any aperture 1 stop slower to yeild the same exposure,
I find that the Tele-Lentar has a much different Bokeh, or out of focus rendering, which I largely attribute to the 14 blade aperture that collapses to a circle at all f-stops, as opposed to the 6 blade aperture of the other 2 lenses,
AND what I think is more important, is the difference in location of the aperture blades within the lenses.
The impact of this difference in Bokeh is that the tele lentar seems to give much better separation between foreground (in focus) and back ground (out of focus) areas. The impression is that it has "less depth of field" when in fact, I think in looking closely at the images produced by all 3, the in focus area is exactly the same.