stelin

Antoine

Thanks for the link -- very intersting.

Do you know whether for the 1D series the same basic principles apply just with (presumably) much smaller tolerances?

Steven

Antoine

Thanks for the reply:-

I don't know the figures, but presumably the acceptable circle of confusion would be significantly smaller for the 1 Series cameras which would explain why I had the "problem" with the 24-70 on my old 10D, but haven't had anything using the same lens on my 1D2 and 1D3.

You noted a difficulty in reproducing AF calibration tests. Presumably now with the 1D3 the camera's acceptable circle of confusion is sufficiently small to negate the prior focusing distance effect and make it worthwhile putting the ability to calibrate individual lenses into the camera for the user as they have?

- Steven

In addition to Mark Chappell's comment also consider that the cropped image will still have been shot with a 24, thus any wide-angle distortions will still be present (although admittedly reduced if you crop to the centre of the image)

Get the 24-70 -- It is superb. The rare occasions where you require the extra 2 stops of the 24 yet don't require more than that and are also unable to use a tripod will be vastly outweighed by the greater versatility of the zoom.

I went from the Sigma 105 f2.8 to the Canon 180 because I wanted the longer distance to "things with stings". The Sigma (which you weren't considering) is very sharp. The Canon sharper, faster to focus (by a long long way) and better built. Basically I love it.

http://www.pbase.com/stelin29/image/83994744 is a typical shot of mine with it if you want an example.

When you were doing your focussing tests -- I presume you were using "one shot" focussing. The question I have is were you just focussing once?

Sounds strange but I found the following when I used a 10D and the Canon 24-70L

Focussing once often gave a missed focus shot. -- Usually to the other side from where the focus was originally. -- ie If the lens was on infinity and I focussed on an object at 3m, it would front focus, and if it was on say 1m, and I focussed on an object at 10m it would back focus.

Basically the camera/lens combination was overshooting initially and not coming back.

I got into the habit of double or even treble focussing, and that cured the problem -- razor sharp every time. I don't have the same problem with the lens on my 1DMk2 or 1DMk3 so I guess it was a camera fault which I never bothered to get "repaired"

Hope this helps -- Steven