500mm vs 600mm?

John Sheehy wrote:

BirdShooter7 wrote:

While lighter weight and shorter length would be welcome in a 600mm f/4 DO I don't imagine the diameter of the lens will be any different from the current 600mm f4 and I expect the price to be quite high. Also though the 400 DO II is way better than the original optically I'm not 100% convinced that the DO technology is quite up to the conventional designs though it is getting closer. I have a feeling the rumored 600 DO wouldn't be a real option for me.

There are definitely some subtle compromises with DO. While the 400/4DO II is an excellent, cutting-edge lens in many ways, it handles things like small points of specular light, or sunlight coming through tiny leaf apertures in trees very poorly in terms of onion bokeh. Sometimes it doesn't, though, so I think it has something to do with wavelength composition. I think it also affects AF in marginal conditions, which would explain why cameras that support multiple f/8 AF points with the 100-400 II only support center point with the 400/4DO II.

That's the main negative thing that weighs in my mind about having the DO II; the fear that the 7D3 or whatever turns out to be the logical successor of the 7D2 only supports center-point with the lens at f/8. That will make my heart sink. Even 9-point in the center is much less hunting-prone, and quickly locks onto something close, even if you have to tap again or manually override, which is much faster than having the lens slowly go way out of focus, while your subject eludes you. F/8 AF on the 7D2 is there in the center, nominally, but it sucks unless light and contrast are good, and depth is simple.

As far as 600/4DO goes, I can't imagine that weighing less than 8 pounds, and still a tripod lens, basically.

Agreed. My experience with, and opinion of, the 400 DO II has been mixed. Its advantage is being an easily handheld BIF lens, usually with 1.4X extender. A shortcoming is inferior bokeh. If the ratio of lens-to-subject distance vs. subject-to-background distance is small 'enough', the bokeh can be fine. But if the ratio is large 'enough', the bokeh of complex backgrounds can appear harsh. The problem seems to be exacerbated by use of extenders which are often required for birds & wildlife.

400 DO II + 2X III

400 DO II + 2X III: crop showing 'onion ring' bokeh in the turtle image

400 DO II + 1.4X III: the OOF pylons and wires were rendered with crisp edges

600 f/4 II + 1.4X III: the OOF pylons and wires were rendered with soft edges

Directly comparing bokeh of refractive vs. diffractive optics, same background & aperture, at similar FL

I much prefer the smooth and pleasing backgrounds I get from 500 f/4 and 600 f/4 II. If the rumored 600 f/4 DO uses the same diffractive tech as the 400 DO II, then I would expect similar bokeh properties. As you suggested, I would not expect a 600 f/4 DO to be anywhere near as light-weight as the 400 DO II; its weight may be akin to that of a 500 f/4 II. This largely negates the very easy portability advantage. So I am not that enthusiastic to replace (at considerable cost) an outstanding refractive 600 f/4 II with a somewhat lighter DO version, considering the likely trade off for a harsher bokeh in many of my images.