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  1. #1
    marciofs's Avatar
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    Box ISO rate and Real ISO

    Hi,

    So, I shot and develop a roll of 35mm Fomapan 400 with Rodinal following the data in digitaltrhth.com.
    But later on I founded out the real ISO of fomapan 400 is 250 with Rodinal.
    So I wonder of the data in digitaltruth.com, dispite it says ISO 400, is indicating the development time for its real ISO which is 250?

    I god a good result from development but I usually over expose a bit.

  2. #2
    AgX
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    The "real" ISO speed with Rodinal would mean applying ISO standards on estimating the film speed of this combo.

  3. #3
    Ian Grant's Avatar
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    You really mean your personal EI (exposure index). I don't use the 400 but do use the 100 & 200 both at half the box speed with great results.

    Ian

  4. #4

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    Marciofs,

    A film has only one ISO speed based on a set of strict criteria. If this film is ISO 400, that is its speed under ISO test conditions. However once you depart from those conditions, the effective working speed, usually defined as Exposure Index (EI), may or may not change. Some of the factors are objective (perhaps Rodinal does not yield full ISO speed), and others are subjective.

    Here is a good summary from Kodak. It will apply to any film.

    http://www.kodak.com/global/en/profe...185/cis185.pdf

  5. #5
    markbarendt's Avatar
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    The ISO rating of a film is done per ISO specs by the manufacturer. Probably not done with Rodinal.

    If you follow the manufacture's instructions and use the same developer, agitation, temperature.... then you should find the speed very close to what the manufacturer found.

    If you do anything else it's no longer going to match the ISO and the new number is better referred to as EI or exposure index.

    Your EI is "personal" and reflects your processes, biases, metering practices, your equipment's vaugarities, the quality of water used, and more.

    Finding an EI other than box speed and different than others find, that works good for you for any given combo of equipment and materials, is perfectly normal.
    Last edited by markbarendt; 04-28-2014 at 08:37 AM. Click to view previous post history.
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  6. #6

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    Quote Originally Posted by markbarendt View Post
    The ISO rating of a film is done per ISO specs by the manufacturer. Probably not done with Rodinal.
    Correct. The developer is specified in the standards. It is not related to Rodinal.

    We should also mention although unlikely, Rodinal may or may not produce a curve with this film which meets the standards for ISO 400. A recommended EI on digitaltruth could still be any other number.

  7. #7

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    I have also wondered about whether or not to use the 'box speed' development time quoted in guides like Digital Truth for the EI I have calculated. I have normally done that and then adjusted the development time, if necessary, for future films. I think the quoted time for a particular film/dev combination at 'box speed' generally comes from the manufacturer of the film or developer.
    If you got good results with the method you tried, I would stick with that speed and time.
    Alex

  8. #8

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    Usually a film manufacturer will give developing times and film speeds for a variety of developers. The more common developer information is usually included as an insert or printed on the box. Don't use Foma film so this may not be the case for them. Developer manufacturers provide similar information. I usually take information given by third-party sites with a certain amount of scepticism.
    Last edited by Gerald C Koch; 04-28-2014 at 09:26 AM. Click to view previous post history.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  9. #9
    marciofs's Avatar
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    I am saying that because wherever review I find in the internet they say Fomapan 400 is actually ISO (or better perfomaced) at 250 to 320 depending on the developer (250 for Rodinal). And I have read many posts complaining about issues with this film exposure and replies explaining it is because 400 is not the real ISO.

    After reading that (in different pages) I was surprised I got a good exposure. And I was wondering if the data in digital truth is actually adapted to develop it at ISO 250, or if it was because I am used to over expose a bit so I just got luck.

    This is a example of what I got: http://www.marciofaustino.com/upload...08865_orig.jpg

  10. #10
    Bill Burk's Avatar
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    Possibly your shutter is "slow" which allows you to get good results using EI 400 settings, even if processing in Rodinal might give you an actual film speed closer to 250.

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