Originally posted by Denis How can a 50-135 be compared to 70-200.
Image size at 200mm would have to be exactly the same at the same f ratio on the same camera. The focus travel on a macro type and DOF are totally different. Contrast is what drive the lens using the camera AF system. I think quite often that we are comparing apples and oranges when it comes to focus speed. Evaluating the situation, light and contrast available is often the cause of failure.
First assumption is failure of the equipment to meet every possible situations which is often not the case
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It is not compared, I did not compare those two lenses at this focal distance, since 50-135mm stops at eeeeerrr 135mm!
Well pretty simple, you need two bodies and shoot the same concert with both lenses.. and oh surprise, you find out that in the SAME situation (light blah blah blah) 50-135mm is faster...
Well in my case I am not asking the equipment to meet any situation, just low low light and af speed. End of story.