Originally posted by UncleVanya A fair point. I'm not sure what to call this but I'm certain it isn't bokeh as normally defined and discussed.
Both you and Sandy are correct - and that's why I talked about amount of "blur" and not amount of bokeh. Biz's thread's
title is in that regard incorrect, but the body of the post, mentioning "amount of blur" is using the better term.
---------- Post added 03-11-20 at 05:12 AM ----------
Originally posted by BigMackCam For the same subject-to-camera and background-to-camera distance, the 70-200mm lens - shot at 100mm (assuming it actually is 100mm, allowing for focus breathing) - and the 100mm prime will both produce the same depth of field when shot on the same camera, at the same aperture. The quality or "character" of the bokeh may differ, though. Whichever lens produces the smoothest-looking bokeh (which, in this example, has nothing to do with depth of field) might be the better choice for your "melted" background, but that's going to be subjective...
The only way to test the amount of blur here (otherwise the visual aspects of bokeh will confound it) would be to force a specular highlight ("bokeh ball") from a point-like light source near the center of the frame. In this test, the diameter of the ball should be the same (admitting some slight inaccuracies because, of course, nothing is ever dead accurate. We are still talking about an art with imperfect* optics).
*And that's, at least partially, the beauty of it all, innit?