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  1. #1
    Scheimpflug's Avatar
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    Opacity of undeveloped vs developed film?

    Hello.

    Off hand, does anyone have any knowledge of wether fully-exposed and developed negative film is more or less opaque than undeveloped film? I would be interested to know for both C-41 color and B&W film, if they happen to be different.


    At a glance, the developed film which is solid black (instead of the undeveloped orange/brown/grey) *looks* like it would block more light, but I suspect this is just an illusion based on the color. Unfortunately I don't have the right equipment to test it to know for sure.


    Also, am I correct in my thinking that developed but un-fixed film would be more opaque than the same film after fixing?


    Thanks.

  2. #2
    Photo Engineer's Avatar
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    Fully processed color and B&W films have less turbidity than unprocessed film due to the emulsions themselves. Fully opaque films use a rem jet backing to prevent antihalation, but other films are just cloudy until processed. Opacity is also caused by the presence of dyes which sharpen films by reducing internal reflections caused by the emulsion grains acting as tiny mirrors.

    This is much more complex than the average person thinks, but basically, all of the materials that cause this effect are removed at the end of the process.

    PE

  3. #3
    Scheimpflug's Avatar
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    Thanks, Photo Engineer.

    I'm not sure that I fully understand your explanation, so let me double check some things.

    Are you saying that only rem jet backed films can be *fully* opaque, and that other films (developed or not) will always be slightly transparent?

    Also, does higher turbidity equate to higher opacity?

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    Amongst the many freaky characteristics of Kodak's 5360 Direct MP film (or 2360, the Estar-based variant I've been playing with) is the fact that the unexposed film looks like a translucent red filter. You can see right through the stuff! I haven't measured it with a densitometer but it sure looks like the developed film is denser. While the black areas aren't quite as densely black as a normal negative film (some of which might just be from the clear base), they certainly look denser than the unexposed film. The red is just a dye that washes out.

    Duncan

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    Photo Engineer's Avatar
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    Quote Originally Posted by Scheimpflug View Post
    Thanks, Photo Engineer.

    I'm not sure that I fully understand your explanation, so let me double check some things.

    Are you saying that only rem jet backed films can be *fully* opaque, and that other films (developed or not) will always be slightly transparent?

    Also, does higher turbidity equate to higher opacity?
    Only rem jet backed films are totally opaque. Light does not pass through.

    Other films are translucent or near opaque. They vary from a color such as the post by Duncan to varying degrees of being "frosted" in appearance to "passes light but no apparent image". You can see shadows through these films at the minimum.

    PE

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    Erik Petersson's Avatar
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    I always wanted to ask what the colour of unexposed film is, just because the question seems to be logically impossible. (Colour implies that light is hitting the film, and it would not remain unexposed.)

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    Pure unexposed panchromatic film emulsion is gray and is about the consistency of heavy cream when melted. Other addenda change the colors. Pure orthochromatic emulsion is red and about like cream. Pure blue sensitive emulsion is white and looks just like cream.

    When cold, the emulsion is like cream mixed with jello. You can break it with your fingers or a knife.

    When coated, the addenda such as acutance dyes and trimmer dyes alter the color to what you see when you look at the exposed leader of 35mm film.

    PE

  8. #8
    Erik Petersson's Avatar
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    You make me hungry, Engineer!
    And thanks for the answer to this tricky question!

  9. #9
    Scheimpflug's Avatar
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    Hmm, ok. So how then do the "Daylight Spools" work for the films that don't have rem jet? Is it just assumed that the combination of several wraps of film are going to block "enough" of the light so as to not fog the whole roll when being loaded?


    Quote Originally Posted by frobozz View Post
    Amongst the many freaky characteristics of Kodak's 5360 Direct MP film (or 2360, the Estar-based variant I've been playing with) is the fact that the unexposed film looks like a translucent red filter. You can see right through the stuff! I haven't measured it with a densitometer but it sure looks like the developed film is denser. While the black areas aren't quite as densely black as a normal negative film (some of which might just be from the clear base), they certainly look denser than the unexposed film. The red is just a dye that washes out.
    Interesting! Perhaps Photo Engineer would know if it is possible that the film really is more dense after the developing? You might be in the same situation I am in... Where the subjective perception of the color makes it hard to judge by eye what is actually happening with the amount of light transmission through the film.

  10. #10
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    With unprocessed film, the density goes up as it is wrapped onto a spool, such that about 2 or 3 layers block all light, but loading instructions do specify "dim light" or "away from direct sunlight", and the loading assumes that the edges are completely protected. See a spool of 8mm film for an example.

    After development, film has the density that results from the effects of: exposure + sliver halide quantity coated + development + the form the developed silver takes when developed. The maximum density is usually about 3.0 but is rarely used.

    PE

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