Potential Long Exposure Problems

If you shoot digital, you can skip to the final topic below (Digital).
Reciprocity is a fancy term for the reciprocal relationship between aperture and shutter speed –

  • Open the shutter wider, and
  • Compensate with the correct faster shutter speed, or
  • vice versa, and
  • Your exposure remains the same

Film shooters have to worry about something called reciprocity failure.

  • This term describes the situation where the aperture/shutter reciprocity trade-off no longer works.
  • Reciprocity begins to fail when exposure times get long
    • “Long” depends on the film used
    • Typically 1-10 seconds and longer
    • Corrections are provided with each specific film
  • Digital cameras (no film, duh!) don’t suffer from reciprocity failure

Digital cameras don’t suffer from film reciprocity failure. However, they have their own long exposure problem – noise. If you aren’t familiar with digital noise (details aren’t vital), here are two articles-

The most important thing is to realize that noise can be a problem and plan for it in the following cases –

  1. When using long exposures (say 5 sec. or longer – depends on the camera sensor).
  2. When using high ISO values (“high” – camera dependent)
  • In Camera – Cameras offer approaches to deal with both noise sources at the time of image capture
    • Again, make & model dependent – check your manual
    • Like everything else, it is always better to get things as close to perfect as possible in the camera (& not depend on Photoshop)
    • Camera example, my Nikon D300 –
      • High ISO noise reduction menu options
        • Options like on/off and high/normal/low reduction for ISO of 800 & up
      • Long Exposure noise reduction (over 8 sec.) menu options
        • A 2nd shot is made with the same shutter speed but with closed shutter, after the 1st . The 2nd shot is subtracted from the 1st pixel by pixel to create the final image.
        • Realize that the 2nd (closed shutter) would be pure black if there were no noise. What is subtracted is the non-black pixels, i.e. the noise.
        • There’s a cost for doing this – your exposure time (time between shots) doubles.
    • Check your manual for similar options
  • Post Processing – Both types of noise can be addressed (to varying degrees of success) in software where there are many options
    • I use Noise Ninja – highly regarded, free trial available
      • That said, I almost never use noise reduction software because
        • My style of photography (read, tripod) rarely requires high ISO
        • For long exposures I normally use my camera’s Long Exposure Noise Reduction option (see in camera above)

Bottom line – Noise is a real problem only when you don’t anticipate it and plan for it (mostly).

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