Page 11 of 11 FirstFirst ... 91011
Results 101 to 104 of 104

Thread: Film vs. Digital

  1. #101

    Film vs. Digital

    Actually Jerry,

    That's not quite correct. The star trails are affected very much so by reciprocity failure. Tests that I did a long while ago with hypered Kodak PPF400 and well as Ektachrome in a cold camera showed that reduced reciprocity failure greatly increases the number of stars you see in a star trail photo. By reducing reciprocity failure, you end up with better contrast in the image between the stars and skyglow. Of course, what many people do to avoid the skyglow issue altogether (as it is a problem for both film and digital users) is to take multiple exposures of say 15 minutes each. That way sky glow is avoided, and the digital sensor will dig deeper than film possibly can and you keep the nice star trail effect.

    Believe me, after doing this for more than 25 years, I've got a pretty good handle on the limitations for film in astronomical imaging. Star trail shots are an extremly testing type of photography for both film and digital. As most shots are much shorter in duration, I will reitterate that film holds no advantages here....including resolution.

  2. #102

    Film vs. Digital

    Dave,

    I don't immediately see what you mean by "reduced reciprocity failure" in this:

    Tests that I did a long while ago with hypered Kodak PPF400 and well as Ektachrome in a cold camera showed that reduced reciprocity failure greatly increases the number of stars you see in a star trail photo. By reducing reciprocity failure, you end up with better contrast in the image between the stars and skyglow.
    Would you please elaborate? I don't immediately understand this.

    Also, are you saying that reciprocity failure darkens stars trails and light pollution equally? Or would you concede that it darkens star trails significantly less than than it darkens light pollution?

    There is also the area of black and white imaging, where film may have an advantage, yes?

  3. #103

    Film vs. Digital

    Jerry,

    One can reduce reciprocity failure in films through two methods:

    1) Gas hypersensitization. A mixture of 92% nitrogen & 8% hydrogen is used to purge all air & moisture from the film. Normally this involves film baking in a chamber for a 1/2 day to 3 days at 30 to 40 degrees centrigrade in the forming gas at about 15psi. This is different depending on the film used. Testing is by trial and error. Overdoing it increases base fog to a level that starts to reduce contrast.

    2) Cold camera. Film is placed into a chamber that is purged with nitrogen to remove moisture. The film rests against a thin glass optical window. On the back side, the film rests against a cold plate that has crushed dry ice placed on the other side. This chills film to approx 80 degrees below zero. This reduces reciprocity failure and limits the sensitivity difference between the color layers....thereby locking in color balance.

    Film lost it's advantage in B&W imaging as well as soon as Kodak discontinued it's Tech Pan emulsion. This B&W film hypered extremely well. However, it still paled in comparison to CCD cameras where the quantum efficiency was better and spectral response dug deeper into boths ends of the spectrum.

    As to star trails, the issue is that as long as the base fog levels from the skyglow stay below that which can be adjusted in the digital file later, the greater quantum efficiency of the CMOS or CCD sensor will record more stars than film....without skyglow impacting on the image.....and will do it with less noise.

  4. #104

    Join Date
    Dec 2005
    Location
    Eugene, Oregon
    Posts
    127

    Film vs. Digital

    I mostly agree with Dave here. The first thing I did when I got my Canon 20D last year, was go out and shoot star trails. Noise is pretty much non-existent at ISO 100 & 200, but I can see some (very very little) noise at ISO 400. After that it becomes much more visible.

    One thing that I did noticed however, even at ISO 100 and 15 minute exposures, is that my 20D produced at least 4 dead pixels in every image. Sometimes it was as high as 10. These were very noticable red dots on my images. Of course, I could easily correct them in photoshop.

    I still think 4x5 is nice when doing long exposures, but the depth of field becomes a problem, not to mention focusing in darkness. I never use film above ISO 100 because I don't like the grain. So when I'm using 100 speed film, I have to make sure my lens is wide open or else everything will come out too dark, no matter how long I keep the shutter open. And of course...when the lens is wide open, not everything is in focus (i.e. if I want mountains and trees to be in focus along with the star trails).

    With my 20D on the other hand, I just set the aperture to f/2.8 focused at infinity. Works really well.

Similar Threads

  1. High-End Digital Vs. 4x5 Film
    By Eric Leppanen in forum Digital Hardware
    Replies: 130
    Last Post: 21-May-2006, 18:11
  2. Post why film is better than digital, a dare!
    By Ed Burlew in forum Darkroom: Film, Processing & Printing
    Replies: 70
    Last Post: 27-Jan-2006, 09:13
  3. Digital or Film?
    By Percy in forum Digital Hardware
    Replies: 58
    Last Post: 29-May-2005, 02:51
  4. Another 'digital vs. film' thought
    By Ben Calwell in forum Digital Hardware
    Replies: 30
    Last Post: 22-Jun-2004, 09:49

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
  •