to a smaller-format camera causes a photographer to move further from the subject, then the perspective will be affected. The extra amount of enlargement required with smaller-format cameras increases the blur due to defocus, and also increases the blur due to camera motion (shake). As a result, the focal length that can be reliably hand-held at a given shutter speed for a sharp image is reduced by the crop factor. The old rule of thumb that shutter speed should be at least equal to focal length (in millimetres) for hand-holding will work equivalently if the actual focal length is multiplied by the FLM first before applying the rule. Many photographic lenses produce a more superior image in the center of the frame than around the edges. When using a lens designed to expose a 35 mm film frame with a smaller-format sensor, only the central "sweet spot" of the image is used; a lens that is unacceptably soft or dark around the edges can give better results on a smaller sensor. However, since the image projected onto the sensor must be magnified more to make a print using a smaller sensor, lenses used on smaller formats must deliver a higher-resolution image to the sensor for acceptable quality and the smaller sensor must have higher SNR in order to compensate the reduced amount of light captured by the lens actually hitting on the sensor. Common crop factors Crop factor figures are useful in calculating 35 mm equivalent focal length and 35 mm equivalent magnification. Some common crop factors are: See also 35 mm equivalent focal length Angle of view Field of view Image sensor format Lenses for SLR and DSLR cameras References External links DSLR Crop/Magnification Factor on The Luminous-Landscape "Focal Length Multiplier" on Digital Photography Review Digital Crop Factor About Lens Multiplication Factors and Apparent Focal Length Increase Science of photography