Most sensors used in digital single lens reflex cameras have a smaller area than the surface of 35mm film but focal lengths are still expressed in the 35mm format. As a result, each camera’s effective focal length will be different than the one listed on a lens.
The effective focal length is determined by multiplying the actual focal length of a lens by a camera’s crop factor, also know as Focal Length Multiplier and Field of View Crop Factor.
Before buying a lens, it’s important to know the crop factor of your DSLR.*
Our conversion chart shows the effective focal length of a lens by crop factor.
|Crop factor/Focal length multiplier conversion chart|
* The crop factor should be listed in the specifications section of a camera manual. Entry-level cameras made by Canon usually have a crop factor of 1.6, though some higher-end models have 1.3, or none at all. Nikon, Sony and Pentax crop cameras usually have a multiplier of 1.5. Four-thirds systems such as those made by Olympus and Panasonic have a multiplier of 2.