Thanks for all your pointers.

I have come to the conclusion that I want the 17-40mm and am willing to spend that extra. I will finally get my hands on an L lens. I expect not to be disappointed.

PS. If you have anything else to add, please do.

In these discussions I never see the Sigma 17-70 f2.8 mentioned. I have one it is a great lens fast focusing close focus which has to be seen to be believed and reasonable price. It is streets ahead of the Sony 18-70 kit lens which came with my A350.

I did consider it very early in my search, but very quickly discounted it largely because I decided I wanted a constant aperature, the longer focal length could be helpful but i doesnt make up for the negatives.

Sigma 17-70
 

I didn't mention in my previous post it is a very sharp lens. My logic is that at 17mm the f2.8 is good for viewing brightness but at longer focal lengths the DOF is too shallow to be a real asset. It just surprises me that less is heard of the lens, if it was no good I could understand it but it is a very good lens.

What Derek said.
J

I also think that sample variation is more of an issue in cheaper lenses - I know someone who had the Sigma 28-70 f2.8 and hated it, he changed to the Canon 24-105 and is much happer. Persumably you have a much better copy of the Sigma lens than he did.

I know when I owned the Sigma 500 f4.5 I tested it against other copies of the same lens and found mine to be a very good/sharp copy. For me the lens is the most important bit of kit (I think the lens you use has more effect on your photos than the camera), but it's still not as important as the person behind it. I've seen stunning shots taken with cheap lenses, and total rubbish taken with very expensive gear.

Yes - I think you're right there. Sigma has certainly had a reputation for dodgy quality control in the past, and I guess I have been lucky with my lenses. (If my first sigma Ex had been a duff one, I probably wouldnt have persisted with them!)
And it is definately the photographer that makes the biggest difference, despite all that the adverts would have us believe!

I'm a big fan of Sigma lenses now, as I was Tamron a while ago. Yes, build quality isn't quite as robust as Camera manufacturers equivalent, but it's not too bad.
Would echo what has already been said about getting what you pay for. Sometimes though, that price difference is a little much to stomach. Sometimes in the case of specialist lenses the choice is already made.... looking at a v fast wide (the sigma 20mm 1.8) for example.

Hmmm I seriously doubt that spending 10x more on a lens will get you a 10x better photo.

Whilst you'll see a difference in test shots where the scene is designed to show up a particular flaw in the optics, for day to day use you'll see none of it. At best you'll get a warm cosy feeling in having spent 10x more than the next guy. Mind you he's probably got a warm cosy feeling at having spent 10x less than you.

I agree that the cost/benefit ratio is not linear. Your picture will not be 10x better, it's the person pressing the button that makes that level of difference.

I don't agree that for day to day use you won't see the difference. If your pictures are all taken at say f/11 and 30mm then I agree that the differences in the final images between kit lens and one at 10x price will probably not be that that great. If that's the argument you are making, then I agree.

If you compare the final images once you start using these lenses at their extremes, wide open, then you most definitely will see differences. Whether these differences are worth 10x the cost is an entirely subjective decision that only the individual can take.

Duncan