Archive for January, 2014

PostHeaderIcon The Truth About Crop Factors

A reader wrote me recently regarding an online merchant’s ad touting the benefits of a 50mm DSLR lens on a smaller format camera. The ad claimed that due to the 2X crop factor in a Micro Four-Thirds camera like the Panasonic GH3 the 50mm lens could serve as the functional equivalent of a moderate telephoto, a popular choice for portrait photographers.  At first the reader accepted the ‘equivalency’ assertion, but now he is no longer sure. Since the narrow angle of view is due to the smaller imaging target rather than magnification, can a 50mm lens ever be functionally or aesthetically equivalent  to an 85mm or 105mm?

A 50mm lens is still a 50mm lens regardless of the camera’s target or sensor size.  While it’s true that the 2x crop factor reduces the viewing angle and field of view the foreshortening of perspective one expects from a moderate telephoto is not present. This contributes to an unnatural cropped look; this look characterized by the increased depth of field of the 50mm focal length compared to an 85mm or 105mm.

The same logic should occur to camera folks touting the virtues of 4K image capture which they say makes possible significant cropping to HD 1920 x 1080 inside the 4096 pixel frame. The cropping may indeed constrain the field of view  but the unnatural perspective inside the cropped frame may appear be potentially disturbing to audiences.

SLR portrait lenses 85mm – 105mm are effective because they help preserve a normal i.e. realistic roundness in the face of subjects when shooting at normal distances of six to eight feet (1.5m – 2.5m).  A 50mm lens at only a few feet from the subject may produce too much roundness and thus produce a look like an ogre. Maybe this is what you want. Maybe it isn’t.

Canon 50mm Prime

Given a 2X crop factor this 50mm can never be the functional equivalent of a moderate telephoto portrait lens.