[thxbb12]

I can only speak for the Sigma 17-70 f/2.8-4.5 as it's the only lens I have among these.

Most people say it's soft at 70mm f/4.5, but I beg to differ. Maybe my copy is exceptionally good?

Judge for yourself and tell me what you think. The pic below was taken at 70mm wide open (f/4.5) with a Pentax K10D:







100% crop:





I find it plenty sharp and definitely sharp enough for portraiture.



[quote name='Lars' timestamp='1301988877' post='7384']

Hi,



I am looking for a similar lens for my D7000 and have done some researches.

I found out (not my own experince):

- IQ of Sigma 2,8/17-50 OS far better than Sigma 2,8-4/17-70 OS at 50 and 70mm wide open

- all other settings: similar IQ

- IQ of Sigma 2,8/17-50 OS better than Tamron 2,8/17-50 VC

- IQ of Tamron 2,8/17-50 (non VC) better than Tamron 2,8/17-50 VC

- IQ of Tamron 2,8/17-50 (non VC) slightly better than Sigma 2,8/17-50 OS



So its up to you:

best IQ and price, but no OS/VR and suboptimal AF: Tamron 2,8/17-50 (non VC)

very good IQ, OS, very good AF, highest price: Sigma 2,8/17-50 OS

if you want to use 70mm for dreamy portraits, good price, OS: Sigma 2,8-4/17-70 OS



Lars

[/quote]