Ok… about EF-S lenses… this has me somewhat excited, as I have 2 APS-C Canon DSLRs, the 7D and 350D.
I have the Canon 15-85mm f/3.5-5.6 USM IS and really love tat lens. I have used the 17-55mm f/2.8 USM IS, and indeed it’s great – the f/2.8 an obvious advantage. Though when I want ‘fast glass’ – I typically want faster than f/2.8 (e.g. f/1.4 – f/2).
Realising the physical compromises (i.e ‘laws of physics’), I would prefer a 15-55mm to a 17-70mm in a f/2.8. I just find the focal length of 17-55mm limiting for a ‘walk around / travel zoom’. Hence I deliberately chose the 15-85mm over the 17-55mm. My 15-85mm gives good to great IQ at all mm / aperture settings.
The 15-85mm has 4 stop IS, and great USM focus, and is built well. The size is ‘just right’ on my 7D (a tad smaller or larger would still be ok). I have a number of 72mm filters, so staying with 72mm would be a bonus!
From the UW perspective, I have the Sigma 8-16mm.. previously I had the 10-20mm Sigma. The extra 2mm (down to 8mm) really is a huge bonus. I really love my Sigma 8-16mm, it’s sharp, contrasty and handles flare quite well. Also good size and built well. AF adequate for what it is. If Canon can pull of an amazing EF-S UWA, like a 8-15/20mm – something sharp, contrasty, great detail into the corners, that would be awesome.
But I would only likely swap if it also had IS. It seems Canon is getting more 'keen' to use IS on UWAs, which I'm very happy about... e.g. they have on their EF-S 10-18mm, or EF-M 11-20mm or their EF 16-35mm f/4. I don’t need a fast aperture in an UWA, f/4 would be awesome, but f/4-5.6 is adequate too.
Then I do want a new 50mm from Canon (doesn’t HAVE to be a EF-S…), I have the 50mm STM, and really like this lens, got a good copy for a very good price just when it became available. Wide open it’s reasonable (really quite good from f/2.2) – if Canon make any good sharp, contrasty USM 50mm (whether EF or EF-S) – I’m ‘in’, especially if it has IS.
Paul 8)