150-400 depth of field

[Geo]

Now that more of these lenses are available so, presumably more users, I wonder how everyone is getting on with choosing an appropriate aperture for small birds at max fl. Obviously focus is so much more critical at 1000mm (equiv) focal length, do you find your camera AF up to this? Do you just shoot wide open or stop down for more depth of field? Has anyone tested just to see how much dof there is at 1000mm?

[Walti]

I'd suggest this isn't a problem! Given the following calculation:

[Geo]

100m is a long way for small birds! How about 20m?

[shakyHands]

400mm @ F4.5 at 20m gives a total depth of field of 33cm (8cm DOF at 10m);
at 500mm and f5.6 (using the inbuilt 1.25 TC) at 20m give 26cm DOF (6cm DOF at 10m);
at 700mm and f8 (in-built 1.25 and external 1.4 TC) at 20m gives 19cm DOF (5cm DOF at 10m);
In all cases the DOF is roughly symmetric around the focus point .
I reckon that these numbers are roughly inline with what I see.

[Geo]

Thank you, very useful..

[shakyHands]

I reckon I was about 6m away from these tawny frogmouth, shot at 700mm wide open at f8 (internal 1.25 and external 1.4 teleconverters)
The first image is unprocessed raw,
The second is after DXO pureraw3 deepprimeXD and some exposure adjustment.
Both are the full frame exported to jpeg with 1600 longest side.

[wanderer]

Generally, I don't stop down. As shown above the DOF is sufficient to catch a bird. It may be necessary to stop down a bit to catch a butterfly at close quarters but as with all these winged beasties, they move that fast that, for me, shutter speed is the driving factor followed by ISO then aperture.