Sigma 85 f/1.4 EX DG Available Soon

[Flake]

Because all FF lenses perform better on crop bodies which take advantage of the sweet spot

[neuroanatomist]

Why do would the Sigma 50mm/1.4 be better on a crop?

For equivalent framing to use of the lens on FF, the depth of field on the crop body would be deeper.  So, f tihere are AF issues, they would be masked on a crop body by the deeper DoF.  It's the same reason you may never know if your body/lens has AF issues if you're only using variable-aperture (=slow) consumer zoom lenses (and that's why many 60D users who stick with the 18-135mm kit lens will not miss AF microadjustment).

[epsiloneri]

Because all FF lenses perform better on crop bodies which take advantage of the sweet spot

That's true, but the FF optical performance of the sigma is not much in question. Its border resolution is as good or better than the Canon EF 50mm f/1.2 USM L (which itself is not very good in the border resolution department; see photozone.de, or the review by dpreview.com). The problem with the sigma is its AF. And I cannot see how AF issues would be less on a crop body.

For equivalent framing to use of the lens on FF, the depth of field on the crop body would be deeper.  So, f tihere are AF issues, they would be masked on a crop body by the deeper DoF.

Hehe, I think we've covered this topic before. Actually, AF issues get worse, if anything, with crop. I'm not going through the crop vs. FF lens/image equivalence thing again, but will merely give you an example that will make you immediately understand why. Imagine you have a focus error with a FF camera, such that the de-focused resolution is 1/160 of the image width (0.6%). Then the equivalent image in a crop camera, would be to crop that exact FF image with a factor 1.6x. The AF error would now be 1/100 (1%) of the image size - which is clearly worse. Resolution in terms of resolved minimum angle would of course be the same (the crop image is, after all, the central part of the same image as the FF).

[Jamesy]

I was at camera show today in Toronto and Sigma had a booth with both the 50/1.4 and the new 85/1.4. I tried them both on an XSi body. The bokeh seemed nice at first glance but it can be hard to tell by chimping. The 85 is smaller than I thought it would be - it is bigger than my 85/1.8 but not the 85L grapefruit.

The only odd behaviour I noted was the infinity focus to close seemed quite slow but close to infinity was pretty snappy. They mentioned it is in the neighbourhood of $1100 CDN.

[Grendel]

Because all FF lenses perform better on crop bodies which take advantage of the sweet spot

Only if the lens offers good resolution to begin w/ -- even a 10MP 40D has a higher pixel density than any FF camera today. Hence the recent upgrades to MkII lenses, catering to existing APC-C/H densities and preparing for future MP increases on FF...

Reasonable in what way?  Fair?

Well executed and fair, yep.

[AJ]

I'm sure it'll be an awesome lens.  I just hope they get the AF thing correct from the start this time.