PPT on Dark frames for star trail photography

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Dark frames for star trail photography
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What is a dark frame ?

• Long exposure photography causes noise in the
  pictures. Especially while shooting star trails.
  In Star trail Photography there are multiple long
  exposure images which eventually will be stacked
  upon each other to create one composite image. To
  tackle the noise issue, Digital cameras have a
  long exposure noise reduction on/off option in
  the settings.
• When you choose long exposure noise reduction to
  be On it takes more than a normal time to write
  the image on the card. Thats because the camera
  is creating a dark frame itself along with your
  long exposure photograph.  This dark frame is
  created to reduce noise caused by long exposures.

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How to create dark frames ?

• You just have to take the same exposure with the
  same settings as that of your intended long
  exposure photograph but with the lens cap on.
  Yes, that is the dark frame. How does it look?
  Have a look at the below picture.

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How to create dark frames ?

• During  star trail shooting, it is recommended to
  shoot at least 10-15 dark frames per 100
  exposures. Since your long exposure noise
  reduction will be turned OFF to achieve faster
  writing speeds on the card, the camera is not
  going to produce any dark frames on its own.
  Therefore you have to shoot dark frames manually
  to tackle noise in your images.
• Apart from helping to reduce noise, dark frames
  also help to eliminate hot pixels from the images
  resulting in good quality outputs.

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How to use dark frames ?
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How to use dark frames ?

• Software programmers' like Stars tax or
  startrails.de have an option to feed dark images
  to them directly. You just have to include your
  dark images with all your images and go with the
  stacking. Stars tax has a programme to create and
  include dark frames at a click of a button. Same
  with Adobe Photoshop.
• With Photoshop, since it is a manual process, you
  can place dark images selectively and blend them
  with your exposures the way you want it.

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