An aspect ratio is the relative sizes of the height and width of an image.

Many different aspect ratios have and continue to be used in photography. In film photography, the 3:2 ratio became the most commonplace as it was the native ratio of 135 film. The 4:3 ratio of 645 format also saw a lot of usage. Many film cameras used a 1:1 (square) ratio, exemplified by the popular 126 film format.

Almost all digital camera models today natively use the 4:3 ratio. There are few exceptions to this rule among compact cameras but the majority of dSLR cameras use 3:2 sensors. A small number of compact cameras have had 3:2, 16:9 and 5:4 aspect ratio sensors.

An assortment of aspect ratios are used with photographic prints. This means images are often cropped to fit.

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