[adifrank]

Hi. I'm reading through the manual of my new Canon 5D mark ii.



In the chapter on Av camera mode there is a short and not so clear explanation on something called a Depth of Field Preview Button. I found the button. When I press it the image in the viewfinder gets a bit darker.



The manual says:

Press the depth-of-field preview button to stop down the lens to the current aperture setting. You can check the depth of field through the viewfinder.

What does it mean by - "stop down the lens to the current aperture setting"? And how exactly do I check the depth-of-field through the viewfinder?

I just can't figure out what exactly this preview is and what it has to do with depth of field.



Can anyone please explain this to me?



Thanks!