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When I tried to do long exposures of the sky with my entry level DSLR I noticed a lot of hot or dead pixels. Will shooting with my old cheap film SLR be better? Will film be better for long exposures without hot pixels? Will film have any disadvantages when shooting long exposures?

  • Film obviously won't have any hot pixels. – Philip Kendall Jul 10 '16 at 6:46
  • @philipkendall Of course ! – Janardan S Jul 11 '16 at 10:10
  • @PhilipKendall That's not strictly true. High ISO film will show graininess, which is the equivalent of hot pixels. The detective crystals in all films are quantized, so there can be nonuniform response. – Carl Witthoft Jul 11 '16 at 11:18
  • you can NOT shoot film in a an "old DSLR" the D stands for digital. Old film cameras are SLR. Just sayin. – Alaska Man Jul 11 '16 at 19:25
  • @CarlWitthoft i disagree. Grain could possibly be considered the equivalent of digital noise but not hot pixels. – Alaska Man Jul 11 '16 at 19:31
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The problem with film is that it's sensitivity reduces with the reduction of power of light source. This means that if you need exposure time x to get a satisfactory photograph, the light source with small power (i.e., magnitudes dimmer than day sky) y, you will need much more than N*x exposure time if you decide to photograph the same light source with power y/N. This is called reciprocity failure and its magnitude varies between film models. It is described in datasheets.

So, even a digital camera with a smaller sensor may be better than a film camera for astrography. There are special films sensitive in the IR range which may indeed be better but I do not know whether any such film is still produced and I am not very competent in this sphere.

Various defects of digital images may be sorted out with different tricks which astrophotographers use: black frame subtraction, exposure stacking, multiple exposures noise reduction.

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No, digital will be still better than film, because of its higher sensitivity and ease of use. All serious astronomy work moved to digital even before amateur dslr cameras appeared.

Dead or hot pixels are usually not a problem because they can be eliminated during the processing - unlike regular photography, astrophotography is almost always a result of merging multiple exposures and advanced image processing.

Not exactly a true test, but interesting - Andres Symes comparing his 1 sec iPhone exposure with 50 minutes 19th century astrophotography enter image description here

Film cameras might be still reasonable for special and artistic purposes, like taking month-long exposures.

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You'll have to deal with reciprocity failure, otherwise known as the Schwarzschild effect. You'll also be limited to lower sensitivities (ISO) with most readily available film than with most digital cameras. With film you won't have any hot pixels, but faster film is grainier than slower film.

Unless you're willing to invest in a fairly expensive sidereal tracking mount that compensates for the earth's rotation with respect to the celestial sphere you will be limited on your exposure times unless you're looking to make images that include star trails.

With digital you can take the equivalent of long exposures by taking many shorter exposures and combining them. This usually works out much better than a single long film exposure.

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