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| p.4 #8 · Carl Zeiss Apo Sonnar T* 2/135 |
wayne seltzer wrote:
If I remember right, I thought it is to do with the ratio of entrance pupil to exit pupil size.
My ZA seems to have rounder bokeh circles and smoother bokeh.
It has a lot "to do" with the pupil ratio, but for secondary reasons - it's not the ratio in it self, but rather other mechanical limitations that cut off the ray bundle. A lens with a high positive pupil ratio will have less trouble with mechanical restrictions behind the aperture, but often more in front of it (if we're talking about at least 50mm lenses, on a DSLR BFD distance from the sensor and a mirrorbox in the path...). But in front you can increase the lens diameters - you can't do that in the back, where you have a small square mirrorbox to fit the ray bundle through.
See the new 55mm distagon as a sample of this.