Originally posted by YJD The Sigma 17-70 doesn't do macro, it does close up which I do like but so does the Tamron 28-75 even though the close up aren't as close. I think the sigma is 1:2.7 and the tamron 1:3.5. It's not those exact number but it should be around there.
The close up in Sigma is of much higher life size ratio over the Tamron. I don't remember the exact number, it is roughly 1:2.7 in Sigma while the Tamron is about 1:3.9.
Only you can make the right decision for your needs. No body can tell you the right thing for your needs. I end up having both as I really liked both of them.
To make things more simple, I would suggest you to stick with the Sigma and add the use of flash to help with indoor. Add a reflector as well. You won't gain much by selling the Sigma and replace it with Tamron as you may find yourself needing the wide angle especially in family outing when you want to do casual shootings with a wide to portrait zoom range.
If your purpose is t do freelance work and aim for the direction for event and portraits, then the Tamron 28-75mm f/2.8 is a good value to add to your gear but it can't replace the walk-around purpose in the Sigma. In terms of IQ, the tamron is a touch better than the Sigma. But the sigma's core strength that you won't find in the Tamron are a few
- Much more versatile from wide to portraits
- a better walk-around due to focal range
- smaller, lighter and more compact as 1-lens do it all type of zoom
- a better close up lens over the Tamron
If you plan for a K5, K-r and K-x, the sigma's weaknesses in slower aperture and vari-focal apertures is reduced by the high iso capability of the camera body. The sigma is still quite a fast lens if you use it in the range of 17-50.
When you use flash with Sigma, remember to take the lens hood off. Combined with your AF280 flash and a upgraded body in the future, the combo is hard to beat.
Hope this helps you a bit. Again, nobody thinks alike and you don't need to decide based on others' input.
Thanks,
Hin