Magnification Factor
The crop factor is sometimes referred to as "magnification factor", "focal length factor" or "focal length multiplier". This usage reflects the observation that lenses of a given focal length seem to produce greater magnification on crop-factor cameras than they do on full-frame cameras. This is an advantage in, for example, bird photography, where photographers often strive to get the maximum "reach". A camera with a smaller sensor can be preferable to using a teleconverter, because the latter affects the f-number of the lens, and can therefore degrade the performance of the autofocus.
A given lens casts the same image no matter what camera it is attached to. The extra "magnification" occurs when the image is enlarged more to produce output (print or screen) that matches a standard output size. That is, the magnification as usually defined, from subject to focal plane, is unchanged, but the system magnification from subject to final output is increased.
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