Enrico Marega Interactive photography course
About
ITEN

Sensors and crop factor

The sensor is the film of a digital camera. The bigger it is, the more light it gathers in total and the wider the framing with the same lens.

1Simulator

Compare the sensors

Tap a sensor: you’ll see how much of the scene it frames with the same 50 mm lens, the real sizes side by side and how much light it gathers compared with full frame.

The crop factor

1Simulator An APS-C sensor is about 1.5 times smaller than a full frame one, measured on the diagonal. With the same lens it frames a narrower slice of the scene: a 50 mm on APS-C frames like a 75 mm on full frame. That’s why we talk about equivalent focal length.

1Simulator With the same aperture, shutter speed and ISO, the photo is just as bright on any sensor. What changes is the total light gathered: a bigger sensor, with the same framing, gives less noise and more blur. Between full frame and APS-C the difference is a little over one stop.

Key points

  • Crop factor = how much smaller the sensor is than full frame. Equivalent focal length = focal length × crop factor.
  • Same settings = same brightness on every sensor. What changes is the total light, and so the noise and the blur.
  • iPhones and Android smartphones use lenses of just a few millimetres: a 6–7 mm on a small sensor frames like a 24 mm.

Try it yourself

Try it with an iPhone or an Android smartphone: frame a scene at 1× and then switch to 2×. The centre of the photo gets bigger and the edges disappear: that’s exactly what a smaller sensor does with the same lens. On an APS-C camera the same thing happens, but less: the framing tightens by 1.5 times.

Post the result and tag me @enrico.marega, or send it to me by DM: I’d love to see how you tackled it.

Quick check

You put a 35 mm on an APS-C camera (crop 1.5). How does it frame?
f/2.8, 1/250, ISO 400 on full frame and on APS-C. How do the two photos compare?