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 | ||||
|---|---|---|---|---|
| 1.3X | 1.5X | 1.6X | 2.0X | |
| 8mm | 10.4mm | 12mm | 12.8mm | 16mm |
| 10mm | 13mm | 15mm | 16mm | 20mm |
| 14mm | 18.2mm | 21mm | 22.4mm | 28mm |
| 17mm | 22.1mm | 25.5mm | 27.2mm | 34mm |
| 20mm | 26mm | 30mm | 32mm | 40mm |
| 28mm | 36.4mm | 42mm | 44.8mm | 56mm |
| 35mm | 45.5mm | 52.5mm | 56mm | 70mm |
| 50mm | 65mm | 75mm | 80mm | 100mm |
| 85mm | 110.5mm | 127.5mm | 136mm | 170mm |
| 105mm | 136.5mm | 157.5mm | 168mm | 210mm |
| 135mm | 175.5mm | 202.5mm | 216mm | 270mm |
| 200mm | 260mm | 300mm | 320mm | 400mm |
| 400mm | 520mm | 600mm | 640mm | 800mm |
| 500mm | 650mm | 750mm | 800mm | 1000mm |
| 600mm | 780mm | 900mm | 960mm | 1200mm |
* 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.