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Thread: film vs digital

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    Re: film vs digital

    Quote Originally Posted by Bob View Post
    Maybe so, but the SI version seems to be the one most used today in photographic and scientific applications.
    -bob
    A little clarification--the ONLY definition used in scientific and photographic applications today and for a long time before now--micrometre is the actual term but micron has been in use since 1876 or so. And no offense to the machinists I know that still work in inches. (I would really like to know who was making one millionths on an inch cuts or holes 100 years before the SEM. ) I think you will find a micron (or mil) in engineering referred to 1/1,000th of an inch, which is 24.5um.

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    Re: film vs digital

    Quote Originally Posted by Shashin View Post
    A little clarification--the ONLY definition used in scientific and photographic applications today and for a long time before now--micrometre is the actual term but micron has been in use since 1876 or so. And no offense to the machinists I know that still work in inches. (I would really like to know who was making one millionths on an inch cuts or holes 100 years before the SEM. ) I think you will find a micron (or mil) in engineering referred to 1/1,000th of an inch, which is 24.5um.
    Yup, micrometer is correct, but colloquially an awful lot of folks call them microns as in a 5.5 micron pixel pitch.
    -bob

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    Re: film vs digital

    I know, every scientist I work with uses "micron." "Micrometre" pegs you as a geek.

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    Re: film vs digital

    Quote Originally Posted by Shashin View Post
    I know, every scientist I work with uses "micron." "Micrometre" pegs you as a geek.
    ok, perhaps m but I keep forgetting my keyboard shortcut for it.
    -bob

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    Re: film vs digital

    Quote Originally Posted by Bob View Post
    Very cool.
    I was furiously looking for data on film emulsion thickness and found only one source for radiographic film which was listed as 10 microns(metric)
    I am guessing that the cross-section you have posted looks roughly like about a 20 micron thickness but we know that color negative film is often coated in at least 4 layers (three color and one usually thinner yellow filter).
    So unless we have more data, can we assume that the emulsion layer is on the order of 5-10 microns? I seem to recall this figure although I have misplaced my old copy of Mees and James.
    Also, can we assume that the emulsion consists of approximately 40% silver halide and 60% binder (from memory)
    I unfortunately predate tabular crustal emulsions which seem to be pretty popular, but it appears to me that these are roughly 1 micron across the base. I do not have a good reference for their thickness.
    The next step might be the estimation of the number of such grains in a volume of emulsion at nominal thickness and some area we might agree as that which effectively is a perceivable unit of area.
    For sake of argument, perhaps we have an enlarging factor of perhaps 2 (approximately a 4x5 negative enlarged to an 8x10 print) to 8 (35mm frame's 24mm enlarged to 8 inches).
    Final print observable minimum feature size of lets say 85 microns (300 per inch converted to SI) which gives us a film "observable unit" from say between 42 microns on a side for 4x5 and 11 on a side for 35mm.
    Anybody have better data for these assumptions?
    thanks
    -bob
    As far as I know, emulsion and coating thickness has been a closely guarded secret. I have found very old references to it, but are usually vague and are certainly referring to old emulsion and no T-grain technology.

    My question would be how important is this information anyway? Couldn't you get the answer from a simple densitometer? Not in terms of individual grain, which I think is not very useful, but simply the efficiency of the emulsion to pass/reflect light. You should then be able to scale to area? Perhaps not. Not sure.

    Although, right now, I can't remember what the actual question was.

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    Re: film vs digital

    If I find an old B&W neg or print, I will put it under a microscope.

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    Re: film vs digital

    Quote Originally Posted by Shashin View Post
    I think you will find a micron (or mil) in engineering referred to 1/1,000th of an inch, which is 24.5um.
    1/1,000th of an inch? You got to be joking. Inches were dumped by all but one industrialised country very, very long ago and doesn't translate to scientific measurements easily.

    A micrometre is one-millionth of a metre (or one-thousandth of a millimetre, 0.001 mm, or about 0.000039 inches). The term micron and the symbol , representing the micrometre, were officially accepted between 1879 and 1967, but officially revoked by the ISI in 1967. It's still in use in some English speaking countries though.

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    Re: film vs digital

    Quote Originally Posted by Jorgen Udvang View Post
    1/1,000th of an inch? You got to be joking. Inches were dumped by all but one industrialised country very, very long ago and doesn't translate to scientific measurements easily.
    That is in engineering. And in the US. And no, not much use in the sciences.

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    Re: film vs digital

    From what I recall reading many years ago (and for me "recall" is a relative term for me personally...LOL)...B&W emulsion is on the order of 10 microns give or take, greatly depending on the film stock. Just as Bob (and others) estimated.

    Shashin, very cool and yes, the whole world (especially the scientific community) works in metric . Just don't ask me why I have a couple of "english measurement" rulers in the draw next to me...LOL.

    Dave (D&A)

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