Depth of field preview button: try it yourself

1. DoF Preview

Press DoF button; see background blur live (may darken viewfinder).

2. Aperture Check

At f/16, preview; see if foreground/background both sharp.

3. Blur Confirmation

At f/2.8, preview; confirm background melts away.

4. Low-Light Challenge

Preview in dark; hard to see, but confirms DoF.

5. Alternative

If no DoF button, take test shot; review on LCD instead.