You may get a few opinions here but if you really want an exhaustive discussion of this lens, do a search at Rob Galbraith's forum:

Rob Galbraith Forums

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Hi Transall,

What Camera do you Have? If it is a 1V or 1Ds then yes if not no. These are the only cameras which have on the Center AF point the ability to focus at f8.

All other Canon bodies do only focus down to f5.6, this means the 1.4x extender.

The EOS3 will quite happily focus @ f8. This means you could use the 400F4 and a 2x. You will only have access to the centre focus point with an f8 combo.

However reviews on this lens would suggest that it is not one you would want to use a 2x on, even though it will autofocus. Personally I would be looking at the 500 with a 1.4x

Gordon

Nobody answered the portion of the original question about whether other DO lenses have been announced. To the best of my knowlege, no.

I haven't used the 400/4 DO so I can't speak from experience about combining it with the 2x extender, but I would go out on a limb to make two predictions based on my experience with my 300/2.8 and the 1.4x and 2x extenders (on an EOS 1N):

First, autofocusing with the 2x is significantly slower than with the 1.4x. Second, I toss out a much larger percentage of the 2x shots as unsellably soft. So much so that I almost never use the 2x any more. For my purposes renting a 400/2.8 to use with the 1.4x would yield much quicker and more accurate focusing when I need the extra reach.

I recognize that the size and weight difference between the 400 DO and the 400/2.8 may be a big issue if you need to carry the rig very far. On the other hand, the 400 DO is one of very few lenses that let one use the words "400/2.8" and "less expensive" in the same sentence!

One last thought. My 10D gives a field of view with the 300+1.4x equivalent to 720 mm on a full frame body. (Only 10% different from the 400 DO+2x on that full frame body.) So, if reach without bulk is the priority, consider going with one of the non full frame cameras.

Rick

Hi,

Can anyone share some experiences with the Canon 400mm DO lens, please?
Does the autofocus function work if you use the Canon EF 2x extender with the DO lens?
Have other DO lenses been announced now?

Thanks in advance,  Transall.

Thanks for the reply, Gimpy.

I've posted the questions there too, and I've got some answers already. I'm not sure about the 2x extender, though.

Cheers,  Transall.

Thank you very much for the clear answer, Rainer.
Currently, I have an  EOS3. Yes, I'm still not digital!  

Cheers,   Transall.

My own rule-of-thumb for MTF cutoff is that I can expect "satisfactory" performance on a DSLR if the MTF is >70%. From the Canon book EF Lens Work III, a number of the Canon lenses meet this criterion wide open, with the 2x extender axially, but when we go out to, say, 12mm off axis (required by the 1.6x crop factor DSLRs) then most lenses drop out. The best behaved, wide open, with the 2x extender seem to be the 300/2.8, 400/2.8, 500/4, 600/4. From the MTF curves I'd expect that these 4 lenses should satisfy most people used with 2x extender if the subject is central, and anywhere if closed down one stop. All the other Canon lenses would seem to require even further closing down, reducing drastically their utility, IMHO. In particular the 400/4 DO looks like it would require closing down 1.5 to 2 stops, ie shooting at f11 or 16 to get good behaviour off axis. These views are simply from the Canon-supplied (some call them optimistic?) MTF curves. Personally I find them an excellent guide.