Originally Posted by
marko
It's not the easiest button to use, but when you look through your viewfinder, you are seeing the scene through the LARGEST aperture on the lens regardless of what F stop your lens is set to. When you click the DOF preview button THEN you see the scene through your chosen aperture.
Since an aperture like F22 is small - the scene (as seen through that small hole) is darker. If you look carefully, you CAN see that the sharpness from foreground to background is SHARPER with an Fstop like F-22.
Try this during the day in bright sunlight and this will be clear. It's hard to do this in the house because it's dark.
Hope that helps
Marko