Of course they're important. If you have a lens that exhibits extreme halation at certain distances or apertures, or a lens that renders cat's eye or swirly bokeh etc. that's arguably a more important trait than sharpness/distortion/CA.
I had an old Canon 35mm f2 lens that had weird bokeh and I loved IT. it had many problems but It make some very unique photos.
most of the time, everything that makes a picture look more pleasing to the human eye is important.
Agreed. Everything can be measured but we certainly don't have exhaustive measurements, they can't really be made exhaustive (there are infinitely many ways to slice the baloney), and people wouldn't be able to cope with the results if they could be made exhaustive.
Hi Berni,
Set up an experiment in which some photos are taken with a lens that is supposed to "render" really well, and another lens that's merely "clinical", and see if expert photograph judges can tell the difference.
Sure they can, as long as you tell them which is which.
MTF just tells us about the contrast in the focus plane. Is it possible that some lenses have a higher contrast outside the focus plane than other lenses, even though the amount of DoF/blur should be the same? Don't know, but if so, then it becomes more difficult to distinguish between 'contrast' and 'bokeh'.
I think you misunderstand the "no" responses. "No" in this context (at least the way I interpreted it) doesn't mean that the character of a lens is not important; it only means that it is important AND measurable. Just because you can measure or quantify something doesn't mean you can't also appreciate and enjoy it. Just because we may not be able to measure such qualities now, doesn't mean we won't be able to do it someday, when we are more clever.
Very good points.
No, it tells us about contrast everywhere. A lens that is blurry in the focus plane will be blurrier than others in the OOF areas too (since the OOF blur discs will be slightly larger for a lens with poor sharpness). This in turn implies that the contrast is lower in the OOF areas as well. Ideally, however, we would like multiple MTF measurements so that we can separate global contrast (contrast at a very low resolution requirement) from microcontrast (contrast at a higher resolution requirement) since the implications of these two might be slightly different for the OOF area. On the other hand, lack of global contrast (due to flare) is hardly a problem with modern lenses so the lack of a separate measurement of that aspect is not really badly felt.
See above.
I wouldn't really say it becomes more difficult to distinguish those two. The characteristics of good bokeh that I outline in my response to tt321 here
I think that a description of "clinical" often refers to a lens that actually measures very well, whereas -- e.g., for video -- a lens described as "cinematic" may have rather poor measurables. "Artistic" bokeh is often far from what one would consider "good" bokeh. It may be swirly or busy looking.
If the qualities exist and make a difference, then expert photographic judges should be able to detect photos taken with the "better" lens. We need quantifiable research and not opinions.
I'm not sure what is classed as good bokeh is so easy to determine. I think whereas for instance no-one would want a lens with more chromatic aberration (unless they're after some ye-olde effect I guess), and it could therefore be marked on a scale of one to ten. With bokeh on the other hand I know some people like the swirly bokeh effect you get with some lenses, others don't; some like foliage to be buttery, others prefer a bit of a choppy appearance. Personally it depends on what I want from the particular photo, but my point is one type of bokeh characteristic is the best a lot less often then it is with almost any other lens characteristic.
