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  1. #21
    markbarendt's Avatar
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    Chan,

    Even in the digital world there is a native rating rating for any given camera, all the other settings are essentially the processing being adapted. People tend to think of the setting as a real change but it is not, the sensor does not change.

    It is like switching channels on your radio, some stations are louder than others, we use the volume control to adjust. Digital shooters use the ISO knob to similarly dial up or down the gain.

    Our analog equivalent is our enlarger exposure settings.

  2. #22

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    Quote Originally Posted by Christopher Walrath View Post
    And ASA stands for the International Standards Organization.

    Or is that the other way around...
    You're both wrong. It's Deutsche Industrie Norm that ISO stands for. Sheesh.

  3. #23

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    I once went to the trouble to look up the actual definition of the ASA/ISO value for photographic materials (I think it was in the collection of ANSI documents at Chicago Public Library). Since the true ISO value is a function only of the film, it relates to the "toe" of the exposure curve, since the slope of the curve above that depends on development. Ansel Adams' careful description of the Zone System is consistent with that definition. "EI" generally relates to a midpoint up the curve (where one would normally expect 18% grey), and therefore depends on development. I have no idea how the digital camera manufacturers define the "ISO" value on their cameras, but I suspect it is closer to "EI". If you change the "ISO" setting on a film camera, it only effects the setting on the internal light meter (with or without auto exposure based on that meter).

  4. #24

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    You all missed my point! The amount of exposure doesn't change by changing the film sensitivity. The film will have different densities depending on its ISO (or sensitivity) but if you don't change the aperture or shutter speed or the subject brightness the film is receiving the same amount of exposure no matter what. Although for the same amount of exposure one film may be underexposed and the other overexposed as they have different sensitivity or ISO rating.

  5. #25
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    I actually understand your point and I don't disagree that there will be a difference in density between films of different sensitivities.

    But, comparing Film ISO and Digital ISO is an apples and oranges comparison.

    The digital ISO standard doesn't care what the sensitivity level of the sensor is, the "developing" process is included in the standard. The ISO standard for digital cameras uses the output of the camera, specifically a JPEG image having specific qualities (essentially a digital print), to define the camera setting that created it.

    The film ISO standard doesn't care about the print. (edit: yes the original standards were based on judging prints, but it is now a mathematic formula.)

    If I use the idea behind the digital ISO standard and include my printing process in my film ratings (my EI) I can better compare the mediums.

    I can, and regularly do, adjust my printing process with Delta 400 (to do the equivalent of spinning the digital ISO dial) from about 1250 to about 25 (first excellent print to last excellent print). FP4 roughly from 250 to 8.
    Last edited by markbarendt; 01-05-2014 at 06:45 AM. Click to view previous post history.
    Mark Barendt, Beaverton, OR

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

  6. #26

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    It sounds like you are speaking of "exposure" in terms of the amount of light the subject is exposed to, where in still photography, most of us think of exposure in terms of the amount of light allowed to strike the film.

    Still photographers have a lot of flexibility in adapting to the light hitting the subject, we have both duration of exposure (to the film/sensor) and intensity to work with. OTH, cinema photographers have a fixed shutter speed, and so control exposure by the amount of light placed on the subject, which is why even when shooting in daylight they have truckloads of lights, reflectors, and shading panels to exercise that control.

    In both cases, the ISO of the film is a "tweak", that is, we can choose a faster or slower film, which then influences the other choices. A faster film will allow the use of small lens apertures, or shorter shutter speeds, to yield increased depth of field or reduced movement blurring, for example.

    Does this address the point you are making?
    Last edited by bdial; 01-05-2014 at 08:03 AM. Click to view previous post history.

  7. #27

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    Quote Originally Posted by TimFox View Post
    I have no idea how the digital camera manufacturers define the "ISO" value on their cameras, but I suspect it is closer to "EI". If you change the "ISO" setting on a film camera, it only effects the setting on the internal light meter (with or without auto exposure based on that meter).
    They do the same as Ilford: they evaluate "ISO" on a practical, rather than ISO standard form. Most (all?) Ilford films have disclaimer like this:
    "It should be noted that the exposure index (EI) range recommended for 100 DELTA Professional is based on a practical evaluation of film speed and is not based on foot speed, as is the ISO standard."

    Edit: actually I was wrong, there is ISO for digicams: http://www.dpreview.com/forums/thread/2838786

    I wonder how accurate my digital metering for film is then... :-/

  8. #28
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    Quote Originally Posted by bdial View Post
    It sounds like you are speaking of "exposure" in terms of the amount of light the subject is exposed to, where in still photography, most of us think of exposure in terms of the amount of light allowed to strike the film.

    Still photographers have a lot of flexibility in adapting to the light hitting the subject, we have both duration of exposure (to the film/sensor) and intensity to work with. OTH, cinema photographers have a fixed shutter speed, and so control exposure by the amount of light placed on the subject, which is why even when shooting in daylight they have truckloads of lights, reflectors, and shading panels to exercise that control.

    In both cases, the ISO of the film is a "tweak", that is, we can choose a faster or slower film, which then influences the other choices. A faster film will allow the use of small lens apertures, or shorter shutter speeds, to yield increased depth of field or reduced movement blurring, for example.

    Does this address the point you are making?
    No, not my point, nor I think Chan's.

    I think both of us are assuming that the scene EV would be the same for any specific comparison.

    I think Chan is suggesting that in the digital realm the ISO setting is not necessarily considered a tweak, that it has become a primary adjustment that can be used in place of/instead of time and aperture.

    I'm suggesting that we can do essentially the same thing with film, as long as we consider the adjustments that can be made in the darkroom.

    XP2 is a great example, the following was copied from the Ilford spec sheet:

    CHOOSING THE RIGHT FILM SPEED FOR THE JOB
    Best overall quality EI 400/27
    Finer grain (with easy printing) EI 200/24
    Finest grain (but with denser negatives) EI 50/18

    Note
    No matter which film speed is chosen, standard C41 processing is recommended.
    In this example essentially only the exposure of the paper need be adjusted and the ISO/EI can be allowed vary from frame to frame. Using ISO/EI as a primary adjustment allows a very different way of shooting than Adams used and taught. Yes the technical look of the print may change with the change in exposure but, the creative use; the ability to maintain a given DOF and given amount of motion blur across a range of EV's is very freeing.

    This same principle (ISO/EI being adjusted) is used in disposable cameras, Holga's, blah, blah, blah...

    In my experience normal B&W films can be used the same way.
    Mark Barendt, Beaverton, OR

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

  9. #29

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    Yes Mark! I saw posted by those folks who claim they use manual mode but with auto ISO so basically they can set the shutter speed and aperture any where they want and yet it's the meter that automatically gets the right exposure (or not). Since many times the exposure is not correct automatically the standard control for exposure is Exposure Compensation control. Therefore on their cameras it must be an easy to use control not one of those on our camera where it locks and located in place hard to use with the camera to the eye.

  10. #30
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    Quote Originally Posted by Chan Tran View Post
    I don't hear anyone in apug saying so but folks in the D forum consider ISO as one factor in exposure. They talked about the exposure triangle. But however, one control the amount of exposure by changing the subject brightness (if that is possible), changing the aperture or changing the shutter speed. The ISO doesn't change the amount of exposure the film gets.
    the analog analogy equivalent of the exposure triangle is the exposure waterbucket.the aperture is the size of the valve;time is the filling time and ISOis the size of the bucket. the object is to fill the bucketto the rim. too much waterand the bucket overflows=over exposure;not enough water and the bucket is not full=under exposure;filled to the rim is perfect=perfect exposure;so whatever you change (aperture,shutter speed orISO)just make sure to fill the bucket;anything goes,but with analog,the bucket has a fixed size.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

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