Sigma 17-50 vs Sigma 17-70 f/2.8 OS...

I have been looking back and forth between these two lenses for several weeks and I have to order now if I want it in time for my vacation. I mostly like shooting birds with my 400mm but want a good walk-around lens. I can't afford the Canon lenses after buying the 400, so I thought I would go with the Sigma. Wondering why the 17-70 is so much cheaper than the 17-50. Either is within my budget. I just want to get a lens with a good image quality. Will the 20mm difference be missed by going with the 17-50? I already have a nifty-50, so that's why I was thinking the 17-70 might be the better choice. Your thoughts? The lens will be used on both a 7D and an xTi.

And if you have an alternative lens I should consider, let me know.

The 17-70 is much cheaper because it has a variable aperture, and optically is not as sharp as the 17-50.

It is however, still a very good lens, especially for the price. I chose the 17-70 because I didn't really need constant 2.8 as I have my sigma 30 1.4, and the 17-70 does 2.8 at the wider end anyway, so I opted for more range and cheaper price.

If you don't think you'll need the constant 2.8, which you very well may not, since the 50 1.8 can cover the longer end where the 17-70 has a narrower aperture, you should be very happy with the 17-70.

Agreed. I find myself using the telephoto end of my 17-70mm so the extra 20mm is somewhat useful. As a "general walkaround lens", it's to have the most convenience in terms of reach. The main difference between the two (besides the 20mm difference) is variable aperture in the 17-70mm, and lack of a distance scale (no FTM).

Thank you both for your replies. I just ordered the 17-70 and it will be here Thursday. I'm looking forward to adding it to my camera bag!

Elvin wrote in post #13097304
and lack of a distance scale (no FTM).

The 17-50 doesn't have FTM or a distance scale either.

Well, they both have a "painted" on distance scale.