FOV stretching?

When I'm looking at object x in the center of my FOV and then turn (without moving) so that object x is in the corner of my FOV it jumps closer to me and stretches out. Please take a look at those screenshots and tell me what's going on. Is it supposed to look like this??? What do I have to set the FOV slider to in order to make this stop?

My resolution is 1920x1200 and the FOV slider is pretty much in the middle right now.

Thanks.