Enrico Marega Interactive photography course
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Depth of field and background blur

Depth of field is the slice of the scene that looks sharp, in front of and behind the point of focus. Three things change it: the aperture, the distance from the subject and the focal length.

1Simulator

Blur the background

Change the aperture, distance and focal length: from 3 to 20 metres. The further back you go, the more of me fits in the photo. The diagram under the photo shows where the sharp zone starts and ends. Try the APS-C sensor too.

The levers of background blur

1Simulator Wide aperture (f/1.8, f/2.8): a thin sharp zone. Closer to the subject: an even thinner sharp zone. Longer focal length: the background more magnified and more blurred.

1Simulator There’s a fourth lever that’s often forgotten: the distance between subject and background. If the person is leaning against a wall, the wall stays almost sharp even at f/1.8. Move them a few metres away from it and the background melts.

1Simulator The sensor matters too. With the same lens, at the same distance and the same aperture, an APS-C camera frames more tightly. If you step back to get the same framing as full frame, the background comes out a little less blurred, by about one stop: a 50 mm at f/1.8 on APS-C frames like a 75 mm and blurs more or less like a 75 mm at f/2.8 on full frame.

Key points

  • For a very blurred background: wide aperture, get closer to the subject and move the background further away.
  • At normal distances the sharp zone extends roughly one third in front of and two thirds behind the point of focus.
  • To get everything sharp, from the foreground to the horizon: a narrow aperture (f/8–f/11) and a short focal length.
  • On APS-C, with the same framing, the blur is about one stop weaker: f/1.8 blurs like f/2.8 on full frame.

Try it yourself

Photograph an object on a table with the background far away. Shoot wide open and at f/11, then halve your distance and take the two shots again. Compare the four backgrounds.

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

Which combination blurs the background the most?
Portrait at f/1.8 with the person leaning against a wall: the wall is still sharp. Why?