Is there any chance they could make it the quality of their new 70-300 IS L lens?
they tried that, it's called the 28-300L, and it's â‚¬2500, 10% above the 70-200/2.8ii, the cheapest of the lower half of the canon range (next price up is the 200f2 at â‚¬5500).
looking at the review, it's got a lot of compromises, the 'barrel' distortion at 28mm is high enough that i'd be tempted to call it 'beachball' distortion, the vignetting on FF is 1 stop or worse everywhere except 50mm and f8, in the text they talk about loss of contrast, and the MTF are nowhere near what i'd call L-quality on their own.
But to put all of those features, especially the 10x focal length range, and making it faster than f/5.6, that's what you have to put up with, it's the best they could do to keep it within the realms of affordable.
Even making the same design down to 18mm, the vignetting and barrel distortion on the wide end would be horrible. but making it efs-only would take out a hunk of extra glass, lighter, saving money there to make it 18mm wide might keep the price the same. (but who would buy a â‚¬2500 efs lens? people with that money either love their 7D to death, or would be on a 5d or 1d)
comparing to the tamron 18-270, they've got slightly less barrelling at wide, and a slightly bit better vignetting (everything's under 1-stop except 18mm wide open). for the MTF, it's a bit hard to compare FF to APS-C, but the graph-shapes look about the same rough shape, the tamron only a little bit behind. But the CA, eesh, unless you want to take pictures that look like a kaleidoscope, that's enough to put me off.
in short, the only people who would buy a super-zoom type lens like this would be:
- beginners moving up from 'superzoom' or 'bridge' whatever you call them, dslr shaped but smaller and one lens. the IQ you'd get from these would (probably) be better, the manual features would be enough to make pics better if you knew what you were doing.
- size/weight constrained people who absolutely *can't* take more than 1 lens, or can't swap it for any reason (ie, you're covering the paris-dakar rally in a sandstorm).
- people who don't know any better, and think higher number means better.
- personally, i'd go the 70-300L and 24-70L with change left for filters rather than the 28-300L, again, unless i was travelling light through the desert and couldn't change lenses.
meanwhile, it's probably too late for your salmon bbq (sounds interesting though). my decision would go on focal length, if you wanted wide or zoom. my 70-300L has hardly been off my 7D body since i bought it, it's getting to the point where i'm taking very cropped landscapes with it and finding good excuses for making 'artistic' crops instead of swapping to my wide lens.
anyway, back to the OP, just based on gut feeling, canon's version of an 18-270 would have to be as good or better than a tamron equivalent, it's almost definitely going to be more expensive (how much does the 'canon' nameplate add on?), but there's no way it'll even come close to the 28-300L, which itself is no stunner either. it'll keep the mass-market, facebook-uploaders, 4*6 printers, and compact-upgraders happy though...