f 1:2

f 1:4

At f 1:2 you have two copies of each branch of the trees in the background. At f 1:4 this is much improved. Further more illumination is much more even. f 1:2 shows strong vignetting and a hot spot. Also the textures of the stone at f 1:4 are much better, but this is sometimes hard to tell from the increase in DOF.