[navcom]

I can't think of anything that would cause haze if it wasn't there. Usually if something is wrong with your lens, camera, or sensor, it will be apparent in the entire image. In yours, the trees up front are fine.

The only thing I can think of is that there really is haze and you are not realizing it. As the saying goes, the eyes tell you what you want to see and the camera tells it like it is. I can't count the number of times I've framed up a shot and then when I got back to the office realized it looked nothing like I was "seeing" it when I was there or noticed things I completely missed that ruin the shot because my brain saw around them.

Only thing I can think of. And also, as Elmo says, get rid of the UV filter if you are using one.