DA* 50-135 has me puzzled...

OK, here's the thing:

I have been the owner of this lens for two weeks now but didn't get to do some serious shooting with it but playing around I found something quite strange.

I did a number of tests with it and got pretty inconsistent focusing at lower focal near infinity. At first I thought I might have BF or FF issues but the focus @135mm is perfect.


The "problem" seems to manifest itself at or near infinity (>5-10m) and here is an example of my test results.


Test procedure:
Camera in AF-S, Tv, 1/500s and f2.8, auto ISO. Center point focusing.
1st photo: Focus @50mm, lock and take the shot.
2nd photo: focus @135mm, lock, zoom back to 50mm and take the shot.

The test target (ugly as it should):

http://farm3.static.flickr.com/2047/2110906572_537e140965_o.jpg

Focusing is on the house's number.

Center 100% crops:

Direct 50mm focusing:
http://farm3.static.flickr.com/2316/2110906574_4a4d59ce49_o.jpg

Focused at 135mm and zoomed back:
http://farm3.static.flickr.com/2397/2110906588_d96a0bce25_o.jpg



Pretty obvious differences. So I thought, I might have BF or FF issues, let's try to find the point of focus on both shots.

Now it gets really tricky...

100% crop of the upper left of the photo (close objects):
Direct 50mm focusing:
http://farm3.static.flickr.com/2384/2110906584_b94425dc9c_o.jpg

And 135mm focused and zoomed back:
http://farm3.static.flickr.com/2004/2110906590_07e112a597_o.jpg

The 135mm focused picture is STILL sharper...

A 100% crop of the opposite corner (far away objects) shows the same result.

Conclusion: the shot taken after focusing at 135mm and zooming back is sharper all across the board. It's as if the 50mm shot had no real point of focus!!

There I must admit I am puzzled (and not in a good way...).

I suspect that this has something to do with floating elements not doing what they are supposed to do (ie optimize image sharpness all across focal length and Af range) but I would really like the one of you who have this lens to take the test and tell me if this is a faulty unit or a "normal" behaviour.

Thanks for looking, any advice is appreciated.