Steve Balcombe wrote:
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This direct comparison is very convincing.
I've seen examples of very similar distracting bokeh from my 300 and 500 with TCs - shooting wildlife it's not uncommon to have problem backgrounds - so I've wondered whether there might be an element of confirmation bias in the examples chosen to illustrated the DO's blur quality. However yours is almost as direct as it can be.
I say "almost" - there is one key difference which is that you've used the 2x on the DO but only the 1.4x on the 600. The difference could be due to the Extender. Did you also try the 2x on the 600?
I have seen such "nervous" bokeh coming from almost all of the Canon big whites I have shot, including the 600 F/4 II. I think it is a focal length, distance to subject, and distance between subject & background type of thing. I think it is possible to demonstrate this on the bare lens by picking the above parameters correctly. I certainly would remove the extender from the equation and it is certainly unfair to compare a 1.4x to a 2x extender.
this in reply to questions raised in the '500 vs. 600?' thread that overflowed....
You are correct in that it is not optically equivalent to compare 400 DO II + 2X extender with 600 f/4 II + 1.4X extender, because of the different TC combinations. You can certainly argue that the 2X TC may have made the bokeh worse than the 1.4X TC. It is not easy to compare refractive and DO optics under equivalent TC configurations because there is no refractive 400 mm f/4 from Canon, and I do not have access to the 600 f/4 DO BR prototype that Canon exhibited in PhotoPlus Expo 2015 (I wish CPS would loan it to me!). This comparison was really addressing the practical problem of how to get to ca. 800 mm with the glass that we have now, i.e. that the 600 f/4 + 1.4X solution yields a demonstrably softer bokeh than the 400 DO II + 2X solution for the same scene.
However, I have done a more scientific (but 'non-big white') test that addresses your TC concerns. Here's a comparison between the bokeh of the 100-400 mm (Mk I) at 400 f/5.6, and the 400 DO II stopped down to 5.6. Both lenses were bare, thus removing TCs from the equation. The bokeh of the DO lens still suffers by comparison. Note the split/ doubled twigs in the right frames. They are not split in the left frames. The DO bokeh is more complex ('busy'/ 'nervous') than the refractive lens bokeh. I do not think that what i am seeing is just confirmation bias.
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