Hasselblad Digital Camera, Manual

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236
THE HASSELBLAD MANUAL
most of these cameras are smaller than the 35 mm fi lm format that is familiar to most photog-
raphers. Most of these cameras have a sensor in the APS size of about 15
23 mm, (some are
even smaller), and therefore cover a smaller area that would be the case on 35 mm fi lm. In other
words, a lens of a specifi c focal length becomes equivalent to a lens of longer focal length. The
lens factor for the APS size is about 1.5
, which means that a 50 mm lens in the 35 mm fi lm
format becomes the equivalent of a 75 mm lens when used with the APS size digital sensor.
I consider the term lens factor an unfortunate choice and misleading as it may give the impres-
sion to the photographer that the focal length of the lens is changed. This is not the case as
focal length can be changed only by adding optical elements or moving elements within the
lens. A 100 mm lens on a Hasselblad keeps its 100 mm focal length and records the image as a
100 mm focal length whether it is used for the 2¼ fi lm format or any one of the smaller sen-
sors in a digital back. The change is only in the angle of view and the area coverage, which is
smaller on a digital sensor than it is on the 120 fi lm format. As a result the so-called lens factors
also must be considered in digital imaging with Hasselblad and are as follows:
36.7 49.0 sensor: 1.1 compared to 6 4.5 fi lm format
33.1 44.0 sensor: 1.25 compared to 6 4.5 fi lm format
36.7 36.7 sensor: 1.5 compared to 2¼ square format
With Hasselblad in some cases you may compare a rectangular format to a square or vice
versa, so you also must take the format shape in consideration. For example, the lens factor
Figure 14-2
Angle of view. (2) The diagonal angle of view of different lenses for the 2¼ fi lm
format from top to bottom: 40, 50, 80, 150, and 250 mm focal length. (3) The angle of view
can be expressed in relation either to the picture diagonal or to the horizontal or vertical
side. The three are different in a rectangular format. (1) On the 30 mm full-frame fi sh-eye lens,
the 180-degree diagonal angle of view is completely out of proportion to the 112-degree
horizontal or vertical angle. (4) The covering power of a lens is the diameter of the circle
within which satisfactory image quality and illumination are obtained.