I rented a 300mm 2.8 IS from a local dealer last weekend for a softball game as my 70-200 was in for repair. There was some kind of issue with the lens as I could not achieve any kind of flat plane of focus. I suspected a mis-aligned or loose lens element. It seemed to get better or worse, perhaps depending on focus distance. For a time it seemed worse around home plate than in the outfield. Autofocus seemed to be struggling at times, and even when I went manual it was difficult to focus, leaving me thinking it was time for a new eyeglass prescription.
Here is an example photo:2013-04-06 at 13-02-16
by Progeny of Light
, on Flickr
Note that the webbing in the player's glove appears mostly sharp (but not perfectly so, in my opinion) and the face is less focused, and the feet are WAY out. In fact there seems to be NO area of grass in the lower third of the image that is in focus. There should be a strip of sharply focused grass right at the players feet.
Also, the blur at the outer edges appears streaked as if from motion blur, but this is virtually impossible as the photo was taken at 1/1600 sec.
I showed sample images to the dealer and they refunded my rental fee. I was doing a little more shopping in the store when the rental guy approached me and told me he'd done some test images with the lens on a 5D and they looked perfectly normal. I looked at them and agreed. He suggested there was a problem with my camera, although neither of us could come up with a logical explanation for how the camera could cause this type of image blur.
When I got back home I shot some test images with my 7D (the camera used with the rental lens) although the longest lens I had on hand was a 24-105. Therefore, I could not replicate the telephoto conditions I experienced with the 300mm. My pictures were fine.
So my question to you all is this: Has anyone seen anything like this before with a 300mm 2.8 or other lens? Anybody know of any kind of camera malfunction that could cause this?