Used camera check

Sensor dust and hot pixel test

Shoot one test photo and drop it here. We mark dust spots, hot pixels and dead pixels. The photo is analyzed inside this browser only.

Sensor dust

  1. Stop down to f/16 or smaller and set focus manually to the closest distance.
  2. Fill the frame with clear sky or a white wall. About +1 exposure works well.
  3. Drop the JPG below.

Hot and dead pixels

  1. Put the lens cap on, turn off long exposure noise reduction, and shoot at ISO 100 for 1 to 4 seconds.
  2. For dead pixels, also try a defocused shot of a white wall.
  3. Drop the JPG below.

Dust, hot pixels and dead pixels

Sensor dust sits on the filter in front of the sensor. It gets darker and sharper as you stop down, and shows as soft spots in the same place in every photo. A blower or sensor cleaning removes most of it. Large faint blotches may be oil or water marks.

Hot pixels are single bright dots in a dark long exposure. There are more with longer exposures and a warmer sensor.

Dead pixels stay dark even in a bright photo. They don't respond to light, so a defocused shot of a white wall shows them best.

Reading the result

  • A few hot pixels in a 1 to 4 second exposure are normal. Most cameras can map them out with a pixel mapping function.
  • If spots also appear in the same place in photos at normal shutter speeds, talk to the seller before you buy.
  • The dust view boosts contrast heavily, so clouds or wall texture can show up. Check whether the same spot appears in two photos.

At the meetup

  1. With the lens cap on, take one shot at ISO 100 for 1 to 4 seconds.
  2. Stop down to f/16 or smaller and take one shot of the sky or a white wall.
  3. Drop both above, and check the shutter count from the same photos.

The other checks are in the used camera buying checklist.