I’ll be producing a detailed review of the Sigma 24-70mm DG DN ART but I thought I’d put together some initial thoughts between the two.

So how do the Sigma 24-70mm and Tamron 28-75mm differ?

1. The focal length – that’s pretty obvious
2. Construction – It’s difficult to put these two lenses in the same class. The Tamron has a plastic construction, while the Sigma has a metal construction. The Tamron’s construction isn’t bad per say but it’s still plastic. The only plastic part on the Sigma is the hood and the caps. It’s a little like comparing a good kit lens to a pro zoom.
3. Controls – Again, not much of a comparison. The Sigma has them, the Tamron doesn’t. The only controls you get with the Tamron are the zoom ring and manual focus ring which are the bare minimum you could get away with. On the Sigma, you get a focus lock, manual / autofocus lock and a zoom extension look along with the zoom and manual focus ring like the Tamron.
4. Sharpness – The Sigma wins pretty across the board, although, given the Tamron was close to the GM to start with, the difference isn’t that big, or not big enough to avoid buying anyone one of the lenses.
5. Minimum focus distance – The Tamron has pseudo macro so outright win there? Nope, the Sigma actually beats it which surprised me.

Given the comparison, I’d say the Sigma and Tamron are focussed at two slightly different markets:

1. The Tamron is targeted at the amateur market who want the image quality of a pro lens without the weight or durability requirements
2. The Sigma is targeted at the pro market who need the additional durability along with the conventional 24-70 focal length.
3. If you want something for travelling, I’d go with the Sony 24-105mm.

So why would you pick the Sigma over the Tamron?

1. If you need 24mm, pick the Sigma
2. If you need more robust construction and weather sealing, get the Sigma.

I wouldn’t pick on sharpness. The sharpness on the lenses (GM, Sigma, Tamron) is almost indistinguishable unless you pixel peep.