Is my DA*50-135 broken?

Hey!

Does anyone have a DA*50-135.

I'm experiencing a lot of missed focus. The images tend to be very soft at f/2.8, it's like shooting with a kit lens :O
I have calibrated my lens 3 times, the focus should be spot on, but most pictures look out of focus.
I have to stop down to like f/4 to get anything useable. Yet sometime f/2.8 comes to life again.
I don't know what to make of it. Am I hallucinating?

Does anyone have the same lens? Share your experience!

This has really left a bad taste in my mouth.
I'm currently trying to find someone locally to help and check my lens.

:P

*maybe I should start buying new gear instead of second-hand :D

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My gear:

Camera: Pentax K-50
Lenses: DA*50-135 / DA-L 18-55 WR / Cosinon 1.8 50mm
Flash: Yongnuo YN660
Tripod: Zomei Q555

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