Page 6 of 6 FirstFirst ... 456
Results 51 to 52 of 52

Thread: Film vs digital for long exposures

  1. #51

    Join Date
    Jul 2016
    Posts
    1,559

    Re: Film vs digital for long exposures

    Quote Originally Posted by barnacle View Post
    There are a number of points regarding digital noise which are being conflated here.

    If you add multiple images together, the light-generated signal, which is (nominally) constant increases linearly; the random electronic noise (thermal and shot noise) are added as the sum of their square root values - so when the final image is scaled, the noise is reduced with respect to the desired light. This increases the signal to noise ratio (higher is better) by 3dB for each doubling of the number of images being stacked.

    Sensor noise - pixels with a fixed non-zero dark value - require a black frame which can be subtracted from the finished image since they will act as point souces. Since they are also subject to thermal noise, you should also use multiple dark frames to average that noise down.

    Neither of these are issues with an emulsion (though it has other issues which I discussed earlier).

    Neil
    There are ways to solve all that. For planets a nice approach is using video cameras at 20 to 50 frames per second and stacking some 1000 images.

    It is explained here:

    http://www.skyandtelescope.com/astro...etary-cameras/

    I'm a user of Point Grey cameras for machine vision applications, I've been using the Flea 2 model a lot, in this example he is using the later Flea 3 model.

    This way it also allows to get a very wide dynamic range, as we can even generate a 24bit per channel image is we want, from addition of component frames, of course with much lower effective bits per channel, but with no clipped bright point.


    Film has other problems... today film is not very common in astronomy, still great photographs can be taken !!!

  2. #52

    Join Date
    Mar 2012
    Location
    Vermont
    Posts
    144

    Re: a 30 minute exposure

    Quote Originally Posted by AtlantaTerry View Post

    Every tool is different. We as photographers need to know what to use and when.
    Yes! Plus we have so many options to choose from.
    Different tools offer different approaches and shape how we work as well.

Similar Threads

  1. Replies: 5
    Last Post: 10-May-2012, 19:50
  2. Best Color Film for Long Exposures
    By David Solow in forum Darkroom: Film, Processing & Printing
    Replies: 4
    Last Post: 11-Apr-2011, 10:54
  3. Best Color Film for Long Exposures
    By David Solow in forum Style & Technique
    Replies: 18
    Last Post: 9-Apr-2011, 06:37
  4. Best negative color film for long exposures?
    By engl in forum Darkroom: Film, Processing & Printing
    Replies: 14
    Last Post: 22-Aug-2010, 19:50
  5. Best film for long exposures?
    By shannaford in forum Darkroom: Film, Processing & Printing
    Replies: 16
    Last Post: 2-Dec-2008, 02:29

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •