Quote Originally Posted by Dave Throgmartin View Post
One lens I've seen that sparks debate on the forums is the TDP ISO crops of the Tamron 70-300. My father in law owns both the Canon 70-300 IS and the Tamron. His A1 goto tele lens is the Tamron. When you compare the IQ results on various review sites these two lenses are basically the same.

The ISO crops for the Tamron 70-300 are abysmal on the long end. It appears something was wrong with Bryan's copy when you compare versus images people capture and some of the other review sites.

Some people cry bias, but I think they don't understand that not all copies are the same. In cases like this where something appears wrong testing a 2nd copy could be worth considering.

Dave
I don't use 70-200 f/4 L USM a lot so given that I'm cleaning house a bit (have sold EOS M, EF-M 22mm, 135mm f/2) it made sense to do a comparison with the Tamron 70-300 VC that brings more features to the table for a lot less money, but figured to lack on image quality.

I did a quick test at a local camera store taking pictures of a store front across the street from the sidewalk outside the shop. I used hand held phase detect AF on my 60D primarily because of the 60D not having AFMA capability and that if I was using 300mm there'd be a decent chance I would be using the crop body. I used my normal 60D JPG picture style settings of 5, 1, 2, 0.

I understand this is not a great of a test for a variety of reasons, but if you're interested read on. If not please don't flame I was trying to work within the constraints of testing at a camera shop.

70mm @ f/5.6 - Normal viewing is a push, Tamron is a fair deal better at 1:1.
135mm @ f/5.6 - Normal viewing is a push and 1:1 viewing is nearly a push as well. Slight edge to Tamron.
200mm @ f/5.6 - Canon clearly wins in normal viewing.
Tamron @ 300 f/5.6 vs f/8 - The wide open shot does not look very good and the f/8 shot is a lot better. I think if I had my 1.4 extender for the Canon it would have been better at either aperture.

For me the deal breaker was autofocus. The Canon is significantly faster when going from near to far and then from far to near. I did not buy the Tamron.

All of that said, it is not an unusual occurrence when going on group photo trips (eagles, etc...) to see the Tamron 70-300 images better my Canon + extender setup. But, the sample I used at the camera shop today likely would be a very close match for Bryan's ISO crops. Especially if the interpretation of the 300mm f/8 ISO crops is a bit soft, but usable.

Dave