Crop factor

If you were to put the same lens onto different camera bodies with different image sensor sizes — full-frame and smaller—you would notice that what you see through the viewfinder is a smaller physical area in the cameras with the smaller sensors, as seen in 2-9 and 2-10.

The term crop factor refers to the fact that the imaging area is physically smaller. Less of the image circle projected by the lens is used; therefore, it is in effect cropped. The image remains the same size at the film plane for a given lens and subject distance — it is in no way “magnified.” This is also why a telephoto lens appears so much more powerful — the field or angle of view has been reduced. This is great for nature and sports photographers, as the net result is more-apparent telescopic magnification with no tradeoff of maximum f-stop loss. The opposite is, true, however for wide-angle shots, because there is a lessening of wide-angle viewing.

These two images were taken from the same position with exactly the same lens and focal length, but on two different cameras: the Canon 5D and the Canon EOS-1D Mark lln. While the Mark lln is a higher-end professional camera, it does not have a full-frame sensor; the 5D does. Note how the full-frame image in 2-9, taken by the 5D, takes in more of the scene. Both shot with a Canon 100mm Macro lens, ISO 250, f/7.1 at 1/100 second.

Category: Photography System

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