Crop Factor

As many image sensor formats are now available and a simple comparison of lens systems would make little sense, most manufacturers provide information about the camera’s 35mm equivalent focal lengths. This is useful for photographers as it gives them a basis for comparison.

On single-lens reflex cameras the 35mm equivalent focal length can be calculated using the crop factor (often also known as the focal length multiplier). Full-frame digital cameras have a value of 1 as their image sensors are the size of a 135mm (24x36mm) film frame. On other cameras, the values can be found in the camera’s technical specifications (Canon, except full-frame, e.g. 1.6). Most brand name values of non-full-frame cameras are around 1.5 and 1.6. One exception is the Four-Thirds system which has a value of 2.

The following subject was captured using an analog 135mm film camera with a focal length of 28mm. If this lens at this focal length were to use an image sensor format smaller than the 135mm film, noticeable trimmings would appear in the image. The picture shows the trimming of a Four-Thirds sensor (crop factor 2) and a sensor in APS format (crop factor 1.5). The APS format (also known as the APS-C format) is most widespread format of single-lens reflex cameras. APS-C format is derived from the APS format in the setting “classic“. To some extent, manufacturers avoid the expression APS and use other terms to describe this sensor format. This is due to the fact that APS in analog photography is associated with poor image quality.

Crop-Faktor - Vollformat - APS - Four-Third-Sensor

Important! – When buying a camera check the optical zoom. This enables images to be captured with almost unvarying picture quality but with different focal lengths. Digital zooming happens at the expense of image quality and is ultimately just the trimming of an image. This can usually be done in higher quality in post-processing programs.

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