Aperture and DOF

[cadd]

wow.

 

[Alex_B]

didn't read it all, but looks like most is said already so I will keep it short. just to come back to the DOF-preview button:

if your cam has got one, it actually stops down the aperture to the set value, hence the images you see gets darker (less light) and, with a sharp eye, you can see the DOF/estimate the DOF from what you see. It can be a bit tricky since the viewfinder images is rather small. but in principle it worls.

(sorry if this info was already hidden in what was said above )