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Depth of Field |
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Some would have you believe that you cannot understand depth of field without first understanding 'Circle of Confusion'. Whilst the mathematics behind depth of field requires the circle of confusion figure for your camera / format, no prior knowledge is required. However, if you are interested in this subject click here to read the article. |
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Precise focus is only possible at one particular distance. As we come away from that point, elements of the image will become progressively more out of focus. In reality however more of the image (in front of and beyond the point of precise focus) will 'appear' sharp due to the limitations of the human eye. This area of 'acceptable focus' is called the depth of field. |
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The actual depth of field is governed by a number of elements, namely Lens Focal Length, Aperture, Object Distance (Point of Focus) and the infamous Circle of Confusion for the camera used. The diagram below shows how the depth of field is affected by Aperture and Object Distance, given a lens of focal length 50mm and a Circle of Confusion of 0.019 (Canon EOS 400D). |
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Looking at the graph we can see that for an aperture of F2, focussing on an object 50m away we have a nearside focus limit of 28.42m and a farside focus limit of 207.67m. This gives a depth of field of 111.58m. |
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The graph also shows how the depth of field increases as the aperture is reduced (f number increases). At f32 the range increases to; nearside = 3.8m, farside = infinity. A PDF table for the graph above can be found by clicking here. |
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Formulae |
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Sould you want to try things for yourself, the formulae are given below. For information on Hyperfocal Distance, click here. |
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