Hi,
> Would this mean that opening up the lens to widest apeture would increase
> the bokeh possibilities of that particular lens because the diaphram would
> then be round? (Maybe I should burn through some film and find out) :)
Well, as goes for any lens, the further you open up the diafragm, the
shallower the DOF. As for your question whether this increases bokeh
possibilities: it may not increase the _quality_ of the lens' bokeh perse
(or maybe it does), but what it will certainly do is blur the background
more because of the shallow DOF, so the bokeh does become more pronounced.
As for rounder diafragms when shot wide open: the "roundness" of diafragms
most likely is one of the main reasons why lenses with more blades (100/2
has 9 vs. 6 of the 50/3.5) have better bokeh overall. When you close the
diafragm of the 50/3.5 (say at f16) it is still very clearly a hexagon,
whereas closing the diafragm of the 100/2 at f16 much more approximates the
shape of a circle. I don't know from memory if the diafragm of the 50/3.5 at
f3.5 represent a better circle shape than at f16 though, so I can't answer
that question with certainty... It should be interesting to test the
difference in the diafragm shapes between the 50/3.5 @ f3.5 and the 100/2 @
f4, as these are the setting which with the pictures in question have been
taken. Actually, I just verified the difference at f4 between the 100/2 and
the 50/1.8 (as I don't have the 50/3.5 over here now), and at these the
settings the diafragm of the 100/2 indeed looks much more like a circle than
the 50/1.8's (clearly hexagonal) diafragm.
> Yes, the background in badbokehbells is distracting, to the point of over-
> powering the foreground. In Giles' picture, the background is an almost
> smooth blur. In yours, there is some texture in the background, but very
> muted. Your backgrounds are very much "in the background".
Exactly, do note however, that it's not only the bokeh determining this
effect, it's also heavily influenced by the focal length of the lens and the
lens-to-subject distance. These two factors (along with the used aperture
setting) are what determine the DOF. Long focal lenghts with short subject
distance and a large aperture (as you'll undoubtedly know) make for very
shallow DOF, hence strong blurring; the "bokeh quality" of the lens then
blurs the background in a nice way or in a not so nice way...
IOW: The DOF determines the _amount_ of blurring of the background, and the
bokeh determines the _quality_ of it.
> But, I wonder. how much of 'bad bokeh' is the lens, and how much is the
> fact that the composition has out of focus bright highlights in it? Or
> are back-grounds with light coming through leaves (as in Acer's and my
> cases) just a tougher background to tame, requiring better bokeh from the
> lens to get a pleasing result?
I'm not certain if these "light-through-leaves" situations are more likely
to be rendered with bad bokeh, but as another bad bokeh example I would like
to show: http://members.xoom.com/olaf_greve/ojg_holl02.html which was almost
certainly taken with the 65-200/4 @ f4. Over here on the right you also have
these light-through-leaves highlights with very harsh bokeh, but on the left
the bokeh is equally harsh, and there wasn't a lot of light coming through
those leaves at the time. Either way, both this picture, as well as the one
with good bokeh (using the 100/2) were taken with an aperture setting of f4,
just look at the differences!
Cheers!
Olafo
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