Interactive
Sensor sizes & crop factor
The same lens projects the same image, but a smaller sensor only captures the middle of it. That is crop factor. Pick a format and watch how much of the scene it keeps, and how that changes a 50mm lens.
Full frame
36 × 24 mm · 1.0× crop factor
Used in
Crop factor is just sensor size and framing, so it applies the same to infrared-converted bodies. Converted cameras come in all of these formats.
Why medium format is bigger than full frame
"Full frame" just means a sensor the size of a 35mm film frame, 36 by 24mm. Medium format is bigger because it comes from a different, older film size: 120 roll film, about 61mm wide, which Kodak introduced in 1901, well before 35mm became the popular format. Today's digital medium format (for example Fujifilm GFX at 43.8 by 32.9mm) keeps that larger-than-full-frame lineage.
A physically larger sensor gathers more total light, which means lower noise and wider dynamic range at the same final image size. It also tends to give a shallower-looking depth of field, because you reach for a longer lens to fill the bigger frame. The trade is cost, size, weight, and usually slower lenses.
Sensor size and lens size are separate things
A lens projects a circle of light (its image circle) and the sensor sits inside that circle. The two are sized independently, which is why you can mix them, with caveats.
- Full-frame lens on a crop (APS-C) body: works fine. The sensor uses the center of an oversized image circle, so there is no vignetting. The view is tighter by the crop factor, so you lose some wide angle.
- Crop (APS-C) lens on a full-frame body: the image circle is too small to cover the sensor, so you get dark corners. Many full-frame bodies handle this by switching to a smaller center crop automatically, which lowers the resolution (a 45MP camera can drop to around 17MP).
- Either way you still need a compatible mount or an adapter. A full-frame lens is the more future-proof buy if you might move up to a bigger sensor later.
Two things people get wrong
- Crop factor does not change the lens. A 50mm is always a 50mm. On a 1.5x body it simply frames like a 75mm would on full frame. The focal length and the aperture (f-number) do not change.
- Sensor size is not a depth-of-field setting. Bigger sensors look shallower only because you use a longer lens or move closer to fill the frame, and that is what reduces depth of field.
Sources
Full-frame sensor size; 120 roll film history; Crop factor; Cambridge in Colour, sensor sizes; Mixing crop and full-frame lenses. Reviewed June 2026.