Page 100 - (DK) Advanced Photography Guide

98 EXPLAINING | FOCAL LENGTH

Sensor size and the crop factor IMAGE CIRCLE Full-frame Full-frame
If you attach a lens to an APS-C camera, it will
appear to have a longer focal length than it would Cameras don’t record the
when attached to a full-frame camera. The apparent entire image “seen” by
a lens; lenses project a
difference is due to the crop factor of the smaller circular image, with the
sensor on the APS-C. The crop factor is the ratio of edges usually outside
the size of a sensor compared to full-frame; APS-C the area captured by the
sensors have a crop factor of 1.5 (or 1.6 on Canon sensor. Lenses for APS-C
cameras project a small
cameras). To calculate the equivalent focal length circle that, when used on a
when a lens is attached to a camera smaller than full full-frame camera, shows APS-C crop APS-C image
frame, multiply the focal length of the lens by the noticeable vignetting. This ▲ The large full-frame image
crop factor—for example, a 28mm lens attached to is why full-frame cameras circle can be adapted for
crop photos when they
an APS-C camera has the same angle of view as a detect an APS-C lens. use on almost any current
full-frame or APS-C CSC.
42mm lens on a full-frame camera. To determine the
lens that matches the angle of view of a lens fitted to SENSOR SIZE KEY
a full-frame camera, divide the focal length by the
crop factor—so, to match a 15mm lens, you would Full-frame 36x24mm APS-C Canon 22.2x14.8mm
need to attach a 10mm lens to an APS-C camera. APS-C Nikon 23.6x15.7mm Four-Thirds system 17.3x13mm

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