‘What is crop factor?’ is probably the most commonly asked question in photography. In this quick guide we’ll explain everything you need to know about focal length magnification in photography.
Because photographers shot on 35mm film for so many years, and because full-frame cameras boast a sensor that’s the same size as a 35mm frame of film, lens focal length is often talked about in terms of 35mm equivalence.
This can be a little confusing at first, but in short, all you have to remember about crop factor is that it’s the ratio of a camera’s sensor size to a 35mm frame of film. Once you get your head around it, you’ll find it starts to make sense. Here’s how it works in practice…
What is focal length magnification?
A lens designed for a full-frame camera produces an image circle that is slightly larger than the sensor. When you mount this same lens on an APS-C-format camera, the image circle will be much larger than the sensor, so the image looks like a cropped version of the full-frame picture, or like a longer lens has been used on the larger sensor.
This is why a camera with a sensor that’s smaller than full-frame is typically called a ‘crop’ or ‘focal length magnification’ factor.
Crop factor for Nikon & Canon
With Canon APS-C format DSLRs this crop factor 1.6x. Nikon DX-format cameras have a crop factor of 1.5x. In real terms, this means that if you were to mount a 100mm full-frame lens on a Nikon APS-C format camera it will produce images that look like those you captured at 150mm on a full-frame camera.
Of course, the lens’s actual focal length is 100mm, but when you’re using it on that Nikon camera with a smaller APS-C-size sensor its effective focal length then becomes 150mm. Likewise, the Canon would be 160mm.
Crop factor for Fuji & Sony
Crop factor for Micro Four Thirds
Micro Four Thirds cameras have a focal length magnification factor of 2x. And if you’re quick with your maths, you’ve already realised that your 100mm lens has just become a 200mm optic!
In the early days of DSLRs, there were few lenses with short enough focal lengths to make their effective focal length wide or super-wide on APS-C format. Happily this is not an issue today.
The focal length magnification factor of APS-C and Micro Four Thirds cameras is often seen as an advantage because it enables you to frame subjects more closely without the expense – or weight – of long telephoto lenses.
In particular, it’s advantageous to sport and wildlife photographers who may not be able to get very close to their subjects.
Common focal lengths and their crop factors
Nikon, Fuji, Sony
Micro Four Thirds
Small sensors vs large camera sensors
Advantages of small sensors
- Smaller cameras
- Lots of depth of field
- Long effective focal lengths
- Central section of full-frame lenses is used and this is usually the highest quality area
Advantages of large sensors
- High image quality
- Depth of field can be limited for creative effective
- Full-frame lenses give their ‘true’ focal length