Mine arrived yesterday and my initial impression is that It's well worth the money. It handles well and fits nicely on the 70d. Really big lenses dont match well with a smaller body like that but this one seems just right.The IQ is what I expected, really good to 400 and good to 600 same thing for the af. I think the sigma 120-300 with the canon tc's is still better but this lens is 1/2 the weight and less than 1/3rd the price (1/4th if you add the cost of the converters) if you are looking for a packable high quality long zoom with an attractive price then I don't see how you could do much better, I am very pleased so far.
...are you saying that the Sigma 120-300 is better than the tamron at 600 ie 600/5.6 - or 600/8?
Yes, I read that review which is not very complimetary. That goes against most other reviews and my own experience with the lens. I also looked at a lot of samples with this lens and the sigma 2x converter and by all accounts the new lens did not perform as well as the lens it replaced which is odd because the new lens is sharper.
I decided to try it with the promaster, kenko, and canon tc's. The kenko and canon 1.4x work really well. The kenko/promaster 2x is sharp but it has metering problems. The canon 2xiii gives much better results than what I saw from the sigma 2x samples?
From using both the sigma and tamron lenses I would say that using the bare lens the sigma is hands down better and its f2.8
Using the canon 1.4xiii or kenko 1.4x the sigma is better and its f/4 420
Using the canon 2xiii the sigma and tamron are pretty close and that's a plus for the tamron in cost and weight.
I still think the sigma with the canon 2xiii gives better results at 600 but its not a huge difference.
My benchmark is the 300mm f/2.8 II +TCs, and I'll compare it with the Tammy when I return on Monday and open my Tammy parcel, which was delivered yesterday. According to TDP, the Sigma with 1.4xTC at 420 stopped down to 5.6 looks as good as the Canon +1.4xTC at 420 and f/4, which is really very good. At 600mm with 2xTC, the Sigma has to be stopped down to f/11 to rival the Canon at f/5.6. If the Tammy at f/8 or f/11 at 600 is as good as the Canon at 600, I will be overjoyed.
The Tammy is meant to be for me a lighter lens for travel and when I need a zoom. The Sigma with the TC weighs about 3.7 kg compared with 1.9 for the Tammy. And is not an alternative.
420 f/5.6 vs f/4http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=844&Camera=453&Sample=0&FLI=6&API=3&LensComp=739&CameraComp=453&SampleComp=0&FLIComp=1&APIComp=1
600 f/11 vs f/5.6http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=844&Camera=453&Sample=0&FLI=7&API=5&LensComp=739&CameraComp=453&SampleComp=0&FLIComp=2&APIComp=2
5D IV, 5DS R, 7D II, EOS-M, Powershot G3 X, 400mm DO II, 300/2.8 II, 1.4xTC III, 2xTC III, EF 1.8 STM, EF 70-200/4 IS, EF 24-105, 15-85, 100-400 II, Sigma 10-20, Sigma 150-600mm C, EOS-M 18-55, f/2 22, 11-22