i've checked that the rates of 75-300/4-5.6 II and 75-300/4-5.6 II usm are 3.1 and 4.1 respectively. i wonder if usm plays a role in optical performance???? thanks

-- legnum (legnum212@email.com), December 31, 2001

Answers

No, USM does not play a role in optical performance. It plays a role in focus speed and noise. The 75-300/4-5.6 II and 75-300/4-5.6 II usm are the exact lenses, except one has a USM motor.

-- Jake F (JakeF@nowhere.net), December 31, 2001.

thanks,this is also what i think. But then,are the ratings given by photodo reliable? i believe that those L lenses perform better(and so higher rates),i just wonder if some non-L lenses score the same rates. Can anyone here comment on this??

-- legnum (legnum212@email.com), January 01, 2002.

Go back to photodo and recheck the ratings. The 4.1 rating was for the 70-200mm f/4 L lens. If a lens has no rating beside it it has not been tested by photodo.

-- Marc Bergman (shotput8@earthlink.net), January 01, 2002.

No, photodo is not reliable.

Eg, the 300 F4L IS scores only 3.4, while the 70-200 F4L scores 4.1. I can assure you, from experience of owning both lenses, that the 300 is sharper. Either it's a typo, where someone meant to type 4.3, or they got a bad sample, or they left IS on with the lens on a tripod, all of which could reasonably explain the result.

USM does not play a role in optical performance. Not possible.

As said above, no 75-300 scores 4.1. You are probably referring to the 70-200 F4L, which is a very different lens to the 75-300 USM

-- Isaac Sibson (isibson@hotmail.com), January 01, 2002.

Thanks a lot. If photodo is not reliable,then in what other ways can i know the optical quality of a lens before i buy it??

-- legnum (legnum212@email.com), January 02, 2002.