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Calculating depth of Field

As a means of calculating the depth of field for any given distance lenses often have a series of markings on them that relate to the aperture setting and are read of onto the distance scale of the camera.

 

This lens has a focal length of 55mm and when the focus point is about 20 feet.

When the aperture set at f8 the depth of field extends out on both sides to the distance marked by the two red lines, in this case just over 30feet and down to just below 15feet.

If however we changed the aperture to f16 the depth of field would be extended up to infinity, and down to 10feet.

If however we changed the aperture to f4 the depth of field is reduced from below 30 feet to just over 15feet.

This lens has a focal length of 600mm. It can be seen that the focus is much more critical and the depth of field more limited than the 55mm lens above. Even with the aperture set at f32 and the lens focused at 300feet, the depth of field is reduced from about 200feet to 500feet

 

 


Three other factors play a part in depth of field:


subject distance

focal length

aperture

 

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