DEPTH-OF-FIELD PREVIEW BUTTON

Normally, the lens’ aperture is always fully opened, except at the time the picture is actually taken, for looking through the viewfinder under maximum brightness conditions.

However, by pressing the depth-of-field preview button, the aperture can be closed down to the selected shooting aperture before the picture is taken, enabling you to check depth of field through the viewfinder before shooting.

DEPTH OF FIELD

When you set the focus for a particular subject, there is an area in front of and behind your subject, which will also be in focus. This is called the Depth-of-Field.

Depth of Field will increase when

Using a smaller aperture value (Larger F-number)

i.e. When you photograph the subject under the same conditions but change the aperture value from F8 to F22, F22 will show more area in focus (more depth of field).

Using shorter focal length (wide-angle) lens.

i.e. When you photograph the subject under the same conditions, changing only focal length from 50mm to 28mm, the 28mm lens will show more area in focus (more depth of field).

Photographing the subject at greater distance

When you photograph the subject with same focal length lens and aperture value but change the camera-to-subject distance, the subject at the greater distance shows more area in focus (more depth of field) compared to subject at the shorter distance.

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