aquazi said:
Wow thanks guys a whole wealth of info here for me to digest. Some smashing pictures too... Wish i had those skills

That's great stuff, especially from Tom which I will have to admit some went well above my head
Yep its the EFS lens So basically the 7d and my 550d should be both the same 16-35mm? The pictures certainly had a wider aspect on his camera over mine.
I thinks at my problem is that I took a pic of the garden and the fence was curved .. Around the end... Which from what I am reading is unavoidable to some degree.... Unless I get my camera calibrated for it which may minimise it slightly? What about my other lens then? ... Or i may just swap the lens with another in the store in that case.
I was planning on using this lens and my zoom and leaving my 18-55 standard lens at home.
What are people's views on Sigma lenses, the 8 -16 caught my eye... Around the same price as my canon one... But has a much more spherical lens, which I guess means a lens filter won't go over it.
Yes it is the full frame equivalent of 16-35mm. If you take a like for like image with both cameras from a tripod there wont be any difference. Having the lens and camera calibrated will only help if the lens is noticeably soft in certain areas.
The distortion as said is hard to get away from, but can be combatted, you can either zoom in a little or recompose or try not to compose straight lines unless they are moving away from you like in PVRs image. If you are after a standard lens then I would sugest buying a 15-85 or the 17-55mm over the 10-22mm the 10-22mm is more a speciality lens for landscape not so great as an every day lens the short focal length is limiting. Or if you can keep it and buy a standard lens to accompany it.
Sigma lenses IMHO are worth keeping away from it is very hit and miss to get a sharp one, their manufacturing process is not as good as canons also because they are third party they may not always be compatible with your camera if you upgrade as canon continually upgrade their type of auto focus the lenses wont understand the new language it has happened on quite a few of sigmas lenses.
I suppose the best question to ask is what do you want out of the lens?
Unfortunately super telephoto lenses (covering a huge range so you don't have to switch lenses) like a 24-300mm are often very very soft, suffer from awful vignetting and chromatic aberration so you have to carry multiple lenses to achieve quality images. I usually carry:
10-22mm
17-55mm
50mm 1.4
70-200mm L
100mm 2.8 Macro L
then leave the rest at home unless I specifically need them. If i want to go light then i carry the 17-55 and the 70-200 to cover most situations.
I dont use the 10-22mm very often more for landscape or interior shots where things are tight. Like I said it is quite a specific lens, not really a standard lens.