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depth of field

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All images on this website are copyright 2004 Gary & Anna Ayton. Contact me if you want prints from the originals.

see depth of field examples using the C8080

DEPTH OF FIELD IS NOT PURELY A FUNCTION OF LENS FOCAL LENGTH AND F/RATIO BUT IS VERY DEPENDENT ON HOW MUCH THE RESULTING IMAGE WILL BE ENLARGED AND THUS IS DEPENDENT ON ALSO ON FILM SIZE OR SENSOR SIZE.

DEPTH OF FIELD HAS NOTHING TO DO WITH DEGREE OF BACKGROUND BLURRING OTHER THAN SOMETIMES IT WILL EXTEND TO INCLUDE THE BACKGROUND.

WARNING: traditional DOF calculations such as those below and lens markings only apply to 4-8x enlargements which is OK for film, but for small digital sensors when we are often looking to make enlargements of A4 and larger, these DOF calculations will give increasingly soft images as enlargement size increases, and nothing impacts more on an image than lack of sharpness when you want it.

There is a lot of mis-information and misunderstanding on the internet when it comes to depth of field, hopefully, I won't be contributing to it. Firstly, many people state that DOF is purely a function of the lens - its native focal length (not its 35mm equivalent focal length), camera to subject distance and aperture and if that lens is used on a full frame camera you will have the same DOF as when it is used on a cropped sensor. This would be true if you used the same subject distance, native focal length and aperture AND you printed an enlargement with the SAME amount of magnification AND viewed it from the same distance - ie. the cropped sensor print would have a cropped print size, so the prints would look pretty much identical other than the cropped sensor print being smaller with the outer parts of the image missing. 

In reality, when one uses a cropped sensor, one usually would print to the same size as if it were not cropped and thus the magnification of the print becomes greater and when viewed at the same distance, the amount of acceptable depth of field becomes shallower.

It is complicated further by what people mean - many people concentrate on the degree and quality of background blurring so that the subject is then emphasised and has more impact, but this is actually due to a mix of different factors:

Depth of field:

The N-times-F rule for digital cameras:

A comparison of calculated depth of fields:

Depth of field in view camera scenarios:

Image resolution:

Image magnification: