page_title: Crop factor
section_title: Digital lenses
hierarchical_section_title: Crop factor / Digital lenses
caption_attribution_description: English: Comparison of the Rebel XT and 5D Mark II CMOS sensors. The Rebel is a "crop body" while the 5D Mark II is a full frame DSLR.
context_page_description: In digital photography, the crop factor, format factor, or focal length multiplier of an image sensor format is the ratio of the dimensions of a camera's imaging area compared to a reference format; most often, this term is applied to digital cameras, relative to 35 mm film format as a reference. In the case of digital cameras, the imaging device would be a digital sensor. The most commonly used definition of crop factor is the ratio of a 35 mm frame's diagonal to the diagonal of the image sensor in question; that is, CF=diag₃₅ₘₘ / diagₛₑₙₛₒᵣ. Given the same 3:2 aspect ratio as 35mm's 36 mm × 24 mm area, this is equivalent to the ratio of heights or ratio of widths; the ratio of sensor areas is the square of the crop factor.
  The crop factor is sometimes used to compare the field of view and image quality of different cameras with the same lens. The crop factor is sometimes referred to as the focal length multiplier since multiplying a lens focal length by the crop factor gives the focal length of a lens that would yield the same field of view if used on the reference format.
context_section_description: Most SLR camera and lens manufacturers have addressed the concerns of wide-angle lens users by designing lenses with shorter focal lengths, optimized for the DSLR formats. In most cases, these lenses are designed to cast a smaller image circle that would not cover a 24×36 mm frame, but is large enough to cover the smaller 16×24 mm (or smaller) sensor in most DSLRs. Because they cast a smaller image circle, the lenses can be optimized to use less glass and are sometimes physically smaller and lighter than those designed for full-frame cameras.
  Lenses designed for the smaller digital formats include Canon EF-S and EF-M lenses, Nikon DX lenses, Olympus Four Thirds System lenses, Sigma DC lenses, Tamron Di-II lenses, Pentax DA lenses, Fujifilm XF and XC lenses, and Sony Alpha (SAL) DT & E lenses. Such lenses usually project a smaller image circle than lenses that were designed for the full-frame 35 mm format. Nevertheless, the crop factor or FLM of a camera has the same effect on the relationship between field of view and focal length with these lenses as with any other lens, even though the projected image is not as severely "cropped". In this sense, the term crop factor sometimes has confusing implications; the alternative term "focal length multiplier" is sometimes used for this reason.
caption: An APS-C format SLR (left) and a full-frame DSLR (right) show the difference in the size of the image sensors.
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