Have you made any lens adjustments? May be necessary? However, we do have to keep in mind that all those high powered lenses that sell for a small fortune are not sold just for their "good looks". They perform like nothing else when it comes to sharpness, color and resolution. The more potent the MP the more it matters.....that's not a happy thought when it comes to expense, but unfortunately, it is the truth. The good news is that once you have a few and get past the expense, there are no regrets.
Anyhow, that is my thoughts.....for what they are worth?
Best Regards!