Crop factor is a number that compares a camera’s sensor with a full frame sensor. It tells you how much tighter a lens will look on a smaller sensor. Multiply the lens focal length by the crop factor and you get the full frame equivalent view, which makes it easy to compare lenses across different cameras.
The Basic Idea
A lens projects a circle of light. A sensor records a rectangle inside that circle. A smaller sensor records only the middle part, so the scene appears magnified. Nothing about the lens changes. You are simply seeing less of the picture.
Crop factor is the ratio of the diagonal of a full frame sensor to the diagonal of your sensor. A sensor half that size has a crop factor of about two.
Common Values
| Sensor type | Typical crop factor | Example |
|---|---|---|
| Full frame | 1.0 | A 50 mm lens gives a 50 mm view |
| APS-C | About 1.5 to 1.6 | A 50 mm lens looks like about 75 to 80 mm |
| Micro Four Thirds | 2.0 | A 25 mm lens looks like about 50 mm |
Exact values vary a little by maker, so check the camera’s specification page.
Working It Out Yourself
- Find your camera’s crop factor in the maker’s guide.
- Note the focal length printed on your lens.
- Multiply the two numbers.
- Compare the result with full frame lenses to picture the view.
For example, a 35 mm lens on a body with a 1.5 crop factor gives a view similar to a 52 mm lens on full frame.
What Crop Factor Does Not Change
- The lens still has its own focal length and its own maximum aperture.
- Perspective depends on where you stand, not on the sensor.
- Depth of field and low light behavior do differ by sensor size, but those effects are separate from the field of view.
Some people also multiply the aperture by the crop factor to compare depth of field. This is a handy rule of thumb but not essential for beginners.
It helps to remember that crop factor is just a convenient comparison tool. Photographers who grew up with film use full frame as the reference, so the numbers feel familiar. Newer shooters can ignore the multiplier and simply learn how each lens frames a scene on their own camera. Experience with your own gear is the best teacher.
FAQ
Does crop factor make my lens zoom in more?
It narrows the view, which looks like more zoom. The lens itself does not change, and you also lose the edges of the scene.
Do I need to think about crop factor with a phone?
Phone makers often quote equivalent focal lengths, which already include the crop factor, so you can compare them straight away with full frame lenses.
The Short Version
Crop factor is a simple multiplier that shows how a lens will frame a scene on a smaller sensor. Multiply it by the focal length to find the equivalent view, and remember that it describes framing rather than any change in the lens.
