Question on Depth-of-Field Preview Button

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New Member
May 14, 2004
Pasir Panjang
I'm a Canon EOS 300v user.
Been wondering how the Depth-of-field Preview Button located just below the lens mount area can help in photo-taking.
Any advice pls?
I tried to use it but it just shows a darkening of the view-finder (when i look inside the view-finder) every time i press the button.
And the smaller the aperture (eg. f/22) the darker the viewfinder.
I guess it is trying to show me how little light goes in the lens when using f/22 compared to say f/11. But can anyone tell me how it helps me take better photos? :sweat:


New Member
Jun 27, 2004
The purpose of the DOF preview button is as the name suggests, for previewing the DOF of the photo before you take it. The fact that it is darker is really more incidental than anything else.

Normally, everytime you look through the viewfinder, the aperture is wide open at the focal length you have set. So the DOF is at its shallowest. Using this button allows you to actually "see" the DOF at the aperture you have chosen, thus you don't require the help of DOF calculation or charts.


Senior Member
Nov 9, 2003
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try stopping down in increments to the desired shooting aperture, ie instead of going straight to the shooting aperture of f22, try going to f5.6, f8, f11 to get your eye adjusted to the dark viewfinder. That way, you would able to see and gauge the sharpness better. Also, sometimes distractions which are not visible at the viewing aperture can turn up in the final photo as the DOF is different, eg a tree branch close to the lens doesn't turn up at f2.8 but can be clearly seen at f11.

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