RMS of Kodak Portra 400 film

Discussion in 'Color: Film, Paper, and Chemistry' started by lmurillo, Sep 28, 2011.

  1. lmurillo

    lmurillo Member

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    So recently I found out about RMS on film and I'd like to know a bit more about it.

    I tried doing a bit of research a so far I have that

    1. The lower the rating the finer the grain of the film
    2. The size of the frame will result in a higher or lower RMS value
    3. The RMS number does not represent the sharpness of the film

    I've also found a couple of tables for RMS values of different stocks of film but most of them if not all haven't been updated in about 6 years. Anyone know of any updated RMS tables?

    I read the technical documentation from Kodak for the Portra 400 film but they only mention the PGI rating.

    Any other piece of information that would be useful in learning more about RMS? Or how to test the film stock at home?
     
  2. Photo Engineer

    Photo Engineer Subscriber

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    Luis;

    RMS = Root Mean Square. It is a measure of the average grain read from a microdensitometer across each density of a step wedge and then plotted against Log Exposure. Fine grain films are slow and coarse grain films are fast. Grain size may vary from 0.1 microns to 10 microns, but most films are a blend of 3 different sizes.

    RMSG does not vary with frame size. RMSG is a constant with a given material, but the apparent grain goes down as frame size increases due to the magnification needed to view it.

    RMS is not sharpness.

    PE
     
  3. EdSawyer

    EdSawyer Member

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    Sadly, I don't think Kodak publishes that info on their new films, which is a pain in the ass as it makes it difficult to compare newer films to older films.
     
  4. lmurillo

    lmurillo Member

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    Yeah, also read that in one of the tables I saw, but is it possible to test it at home? Maybe not as exact as the one done by real labs but an approximation?
     
  5. Photo Engineer

    Photo Engineer Subscriber

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    Yes, you can test it if you have a microdensitometer.

    PE
     
  6. lmurillo

    lmurillo Member

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    So...yeah...no...hehe :confused:

    Well they sell one on the electronic bay for US$900... :laugh:

    So...besides for comparing the new stock to the old stock...is there any other critical uses that knowing this would yield? Afterall it doesn't establish the sharpness of the film