ExpoImaging ExpoAperture2 Manual (Imperial/Standard) - Manual (Page 9)

ExpoAperture 2 Depth-of-Field Guide Manual
V 1.0
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We have included a chart with the ExpoAperture 2 Depth-Of-Field Guide which provides
the appropriate circle-of-confusion to use with your camera. Of course, you are free to use
any circle-of-confusion you wish depending on your desired final result.
1.E - The Advent of Digital Cameras
Unfortunately, the increased popularity of digital cameras has been accompanied by an
increase in misconceptions about their depth-of-field capabilities. These misconceptions
result in statements such as "the smaller the sensor the better depth-of-field" and "for the
same angle-of-view the depth-of-field increases by the crop factor of the camera."
Statements like these fail to emphasize the overall contributing reason that apparent depth-
of-field increases when using digital cameras, which is that manufacturers have had to
incorporate shorter focal length lenses on digital cameras in order to maintain the angle-of-
view typically found in lenses traditionally used for 35mm film, called ‘normal’ lenses.
Compact digital cameras have extremely small sensors, typically 2/3 of an inch to ¾ of an
inch. To compensate, the camera manufacturers use equally as short focal length lenses,
often in the range of 7mm to 9mm. Most of them do not have f/stops greater than f/8.
With these short focal length lenses set at f/8, nearly infinite depth-of-field is achieved. As a
result, achieving any sort of creative depth-of-field control with these cameras is virtually
impossible.
Normal lenses are lenses with focal lengths that approximate human vision perspectives.
With 35mm film or "full frame" digital cameras, the typical normal lens is 50mm – a 40
degree angle- of-view. On digital cameras with a 1.5x crop factor, as an example, a normal
lens with a 40 degree angle-of-view would be approximately 33mm. On a medium format
film camera a normal lens would be 75-80mm. Therefore the smaller sensor size, in and of
itself, has little to do with the better depth-of-field. The apparent better depth-of-field is
almost entirely the function of the shorter focal length lenses.
The basic rules of depth-of-field, which are based on lens optics, have not changed just
because of the introduction of digital sensors. Only the difference in digital sensor size
versus 35mm creates a difference in depth-of-field results. The truth of the matter is that
the same focal length lens and aperture setting when used on a 35mm camera and on a
digital camera will produce the same depth-of-field, when the resulting image is enlarged the
same number of times. Because images from digital cameras require greater enlargement to
achieve the same print size, the enlarged image from a digital camera will actually have less
depth-of-field given the same focal length and aperture. To have the same depth-of-field,
the circle-of-confusion needs to be smaller. The correct circle-of-confusion can be quickly
calculated by dividing 30 microns by the digital camera's crop factor. Therefore to achieve
the same depth-of-field, because of the required smaller circle-of-confusion, you need to use
a shorter focal length lens or smaller aperture.
Fortunately most digital camera manufacturers use shorter focal length lenses in order to
compensate for the angle-of-view necessary to approximate the normal lenses used on
35mm cameras. However this has a tendency to over-compensate since changes in focal