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Thread: Shutter speed sequence: when did it change?

  1. #11
    Foamer
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    Re: Shutter speed sequence: when did it change?

    Didn't film speed rating also change about 1960? I seem to recall that what was called "ASA 200" became "ISO 100" somewhere around then.


    Kent in SD
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  2. #12

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    Re: Shutter speed sequence: when did it change?

    My recollection is that the ISO adopted the existing ASA film speeds straight across, in the mid-70s. I worked in the camera and film departments of a now-defunct membership store from '76 to '77. The film boxes were labelled "ISO" by then but everyone still asked for film by its ASA speed.

  3. #13
    Cor's Avatar
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    Re: Shutter speed sequence: when did it change?

    More than you ever wanted to know, perhaps...;-)..

    FWIW, the current version of the ISO standard for B&W still film allows the use of any desired developer provided its specified along with the results. Older versions specified particular developers the formulas for which were included in the standard. Two developers were described, a "standard" and a "fine grain" one, neither of which were much like any commercially available developer.
    The ISO standard requires a lot of stuff that is probably not necessary for practical testing such as a waiting period between exposure and development to account for latent image stability. Note that the ISO standard measures speed with certain assumptions about minimum shadow detail. It is based on an average gamma or contrast index with corrections for other indexes but does not measure or characterize any other film properties such as tone rendition or grain. A practical evaluation would include both. Tone rendition is pretty much a property of the H&D curve shape. A formal measurement requires a calibrated sensitometer meeting certain requirements as to lamp color temperature etc. The curve should be measured with a calibrated densitometer with illumination matching the method to be used in printing or viewing. However, a less formal practical evaluation can be done using step wedges but one still needs a densitometer of some sort. Rough measurements can be made from the projected image from an enlarger using an enlarging exposure meter. In any case the plotted curve will give a good indication of what sort of tone rendition the film will have. Grain is another matter and must be evaluated visually. Kodak uses at least two methods of measuring graininess and makes a differentiation between what they call graininess and granularity. Such measurement is not trivial.
    While the H&D curve shape is mostly determined by the properties of the emulsion it is affected to some extent by the developer so that any evaluation of tone rendition must be done noting the specific developer used. Probably a useful evaluation would be done using two or three common developers.
    There are some properties of film such as latent image stability and rate of increase of fog with time, which are need to be measured in a controlled way so can not really be measured in a meaningful way by casual methods. There are other properties but these are generally not of great interest to the working photographer.
    FWIW, the current ISO method is based on the later DIN method. It was modified to put the speed point higher on the toe to about the same point as would be established by the older Jones/Kodak/ASA method when used without the ASA fudge factor. Jones found that for good tone rendition the minimum exposure had to be on a point on the toe where the gamma was 1/3rd of the overall gamma. Increased exposure would do no harm but less exposure would result in a loss of shadow detail and inferior tone rendition. The DIN method is based on a minimum density but this is below the density of the Jones point. When the ASA adopted the DIN method it did extensive research on existing films and found a nearly constant ratio of 1.4X between the two points so that factory is built-into the standard. This is _not_ the same as the 2X "safety" factor used in the original ASA standard which went against Jones' idea of keeping the negative as close to minimum density as was consistent with "excellent"
    tone rendition. Minimum density is desirable because it maximizes sharpness and minimizes grain.

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    Richard Knoppow

  4. #14

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    Re: Shutter speed sequence: when did it change?

    Thank you for this Cor. I wish Richard posted here.
    David

  5. #15

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    Re: Shutter speed sequence: when did it change?

    Quote Originally Posted by Two23 View Post
    Didn't film speed rating also change about 1960? I seem to recall that what was called "ASA 200" became "ISO 100" somewhere around then.


    Kent in SD
    I bought my first 35mm camera in 1982. I remember because I bought it for a vacation to Knoxville Tennessee for the 1982 Worlds Fair. At that time Kodak was still marking their boxes in ASA. It wasn't long after that though that Kodak dropped the ASA and used ISO. I can't remember the exact year they did that though.

  6. #16
    Jac@stafford.net's Avatar
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    Re: Shutter speed sequence: when did it change?

    Quote Originally Posted by Two23 View Post
    Didn't film speed rating also change about 1960? I seem to recall that what was called "ASA 200" became "ISO 100" somewhere around then.
    For B&W an ASA 200 film became a 400 speed film because the so-called safety factor was removed. The film did not change.

  7. #17

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    Re: Shutter speed sequence: when did it change?

    I'm confused.

    I thought this thread was about when the shutter speed sequence marked on shutters changed, not about when ASA film-speed designations were was absorbed into ISO system. These are two separate things, right?

    Doremus

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