PIXPHATIC wrote in post #17757076
Also would you please enlighten us more on the fact that,if an image from 400mm DO is cropped to the extent so as to match a 500mm image.....how would you rate it as far as sharpness is concerned.
Cropping will give you less pixels on subject, so in that way, it is always inferior, if you value natural texture. If pixel-level "sharpness" (the highest contrast possible between neighbor pixels) is your goal, the bare lens is limited only by the AA filter on the camera. The lens is far too sharp for the lens itself to be the limit to sharpness without a TC. I see almost no difference at the pixel level with the bare 400 DO II and with a Kenko Pro 300 1.4 DG TC on a 7D2 (DGX does not report properly with this lens - the DGX tricky magic gets it into trouble). On a 5Dsr, the lack of AA filter might allow more difference to show, but personally, I don't think I'd be happy with the aliasing with the bare lens on a 5Dsr on perfectly stable and focused shots. You may be less particular than me about natural texture, though.
I almost always use the 400 DO II with the 1.4x TC. When I need more magnification, I use the 2x if it does not lose too much AF speed (such as when it is dark, or you are shooting in deep branches or weeds where hunting is likely). Loss of AF prowess is the only reason I would choose cropping over TC use. I only take the TCs off completely when I need to "zoom out" (at which times I often wish I was using my Tamron 150-600 instead, or had a 100-400 II).
Going by the Kenko DG 1.4 and the Canon 2xIII on the 7D2, I would say that all three focal lengths (400/560/800) are very good at AF in open spaces with little depth confusion, and moderate light. That is center-point-only, of course at 800, and therefore almost useless for BIFs, even in great light. Make it a little darker, and/or choose a scenario with more depth confusion, though, and the TCs start to impede AF, the 2xIII failing first, of course. Even when the system is hunting-prone at 800mm, though, when it does lock on, it still focuses perfectly. I never find that when focus is achieved, that focus is not right, and that is with 0 MFA.
