Thomas Bantel wrote:
Shape (or number of blades) of the aperture is only part of the game.
I sure don't buy my lenses because of good bokeh, but I occasionally
notice it in my pictures.
E.g. if I compare the 200/2.8 L and 80-200/2.8 L at 200mm.
Both lenses have 8 aperture blades, the shape of the aperture should
therefor be similar. Nevertheless, the 80-200 renders out of focus
highlights not as smooth as the prime. The difference is, that the
circls of confusion are more evenly illuminated with the prime, while
the zoom is quite uneven, if my memory serves me right it's even a
little darker in the center than at the edges. Last year I have taken
one frame with it, where it really jumped out on me and where I thought:
Ouch! This would have come out much better with the 200/2.8 prime.
Ok, no big deal, I have taken a lot of pictures with it where it really
shines, so I certainly don't think about getting rid of it because of
"bad bokeh". Its sharpness and contrast is quite good, that's what
counts the most for me too.
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Thomas,
When light passes the edge of a diaphragm blade it is scattered in a
direction perpendicular to that edge. Hence, with both apertures being 8
bladed of the same size we eliminate that being a possible cause and look to
the difference to have more to do with the number of glass elements and how
they are put together. More glass adds aberrations and the need for greater
correction. This would be the potential cause for the difference you see
between the bokeh in your images.
Peter K
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