I have a Canon 600D with a kit 18-55 f3.5-5.6 IS II lens. Now I want to upgrade it with my not very loose budget.
Three main things I want to improve with a new lens are:
- larger aperture
- better build quality (especially more precise manual focusing)
- larger zoom
After studying a lot of reviews I have now 4 candidates, but I can't make a decision which one is really better for me. The lenses are:
- Sigma 17-70mm f/2.8-4 DC Macro OS HSM
- Canon EF-S 18-200mm f/3.5-5.6 IS
- Sigma 18-250mm f/3.5-6.3 DC OS HSM
- Tamron 18-270mm f/3.5-6.3 Di II VC PZD
Probably the main thing that bothers me is how does the image quality compare between these lenses in 18-70 range. Whether does Sigma 17-70mm have better image quality than other 3 super-zooms? Of course the fact that it has large aperture is very positive for me but the change from maximum zoom of 55 to 70 doesn't look very impressive compared to 250 or 270 mm.
Also I've seen some very positive reviews about image quality of Canon EF-S 15-85mm f/3.5-5.6 IS USM. It is a bit more expensive and has small aperture. Does somebody know if is it really that much better than Sigma 17-70?
I am also curious about the accuracy of autofocus and effectiveness of image stabilisation (vibration control) between different brands.
If somebody has some experience with any of these lenses or, even better, more than one of these, I would be very grateful to see the comments.
Update: Does somebody know anything about Tamron SP AF 17-50mm F/2.8 XR Di II VC? What is image quality, build quality, especially compared to Sigma 17-70 f/2.8-4?