Tamron 17-85mm or Canon

Appears to be quite a price difference between the Tamron and Canon 17-85mm Lens. Is Tamron quality in the same ballpark as Canon, which will make it a cost effective purchase?

I belive the canon 17-85 has IS feature, the Tamron does not.

the optical or picture quality goes towards the tamron 28-75. I don't think tamron makes a 17-85?

The tamron is also 2.8F, whereas the Canon is not constant F, but has IS. 2.8F is also worth a few stops over the canon.

Ive seen pictures from the 17-85, i think the optical quality is much better than people make it out to be. I have seen some VERY dynamic photos from that lens.

Sure its a little slower, but IS is a pretty nice feature too. I use a 20D, i just crank up the ISO since noise is really under control.

Its the range from 17-85 which makes that lens more tempting than the tamron for me. The tamron 28-75 is a nice lens, but i dont like switching lenses, and if you need to pack light, im only gona take 1 lens on a trip with me, the 17-85 fits the bill perfectly.

Not to mention, i dont like to buy too many 3rd party lenses, but the 28-75 2.8 is an exception.