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If I take one photo with long exposure and dimmer lights and then another photo with short exposure but lights brighter to the level enough to compensate for the shorter exposure - what differences between the two photos should I expect to see? For example - would it affect noise level?

Would be interesting to hear both theoretical and practical answers.

  • What kind of light? If it is well controled artificial light or natural light outside affects things like color temperature. – lijat Jun 11 at 19:19
  • Easy experiment to perform, assuming that you have a light source that can be dimmed without changing its shape or its color. – Solomon Slow Jun 12 at 11:08
  • This seems to be a round-a-bout way of asking about digital noise in long exposures. There are Many questions about that on this sight with good and correct answers. – Alaska Man Jun 12 at 17:31
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Film cameras make hardly a difference between long exposure and short exposure (after all, you can store a film for years in the dark). Digital cameras have an inherent noise level that makes longer exposures trickier. Many limit their maximum exposure times to the order of a minute. A frequent phenomenon are "hot pixels" that change state without light influence over time. This may well be a temperature-dependent effect: some cameras do "dark frame subtraction" for longer photographs by taking a photograph with closed shutter and the same duration after the main photograph and then subtracting the image, but once a hot pixel becomes saturated, this of course does not work any more.

So for really long exposures, you want film, or take a number of digital photographs and average them in post-processing.

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In properly exposed photographs, the only difference you (the viewer) should see is if something in the frame was in motion during the exposure. A sufficiently fast exposure will effectively freeze the object in motion. A longer exposure will blur the object.

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  • What about noise? – Gill Bates Jun 11 at 20:09
  • Digital or film camera? – BobT Jun 11 at 20:11
  • Digital, but an answer for film would also be interesting. – Gill Bates Jun 12 at 13:46
  • There is no such thing as noise in film, noise is digital only. In film there is grain and it is a completely different animal, not related to digital noise in any way. – Alaska Man Jun 12 at 21:52
  • @AlaskaMan, they both related in the sense that they are both result of compensation of imperfect light measurements. – Gill Bates Jun 14 at 9:25
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Yes, film exposure is affected by unusually long or short exposures (but not for normal photo exposure ranges). This is called reciprocity failure, see https://en.wikipedia.org/wiki/Reciprocity_(photography)

Digital is not affected by reciprocity, but noise becomes a problem at long exposures.

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