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  1. #51
    Stephen Benskin's Avatar
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    Quote Originally Posted by Ian Grant View Post
    Box speeds are actually just a starting point, after all Kodak actually recommended using Tmax 100 at 50 EI for greater tonality. What's more important is what EI gives you the results you require and that may not be the box speed.
    Are a starting point for exposure not film speed. I believe I made this point in my post. The ISO speed gives you information from which to make a personal EI choice.

    Doremus Scudder
    FWIW, it seems pretty well-established that reducing developing times significantly from standard (whatever that is now, since every manufacturer can decide for itself), for whatever reason (contrast control, personal EI, etc.) will reduce effective film speed. With that in mind, it only makes sense, sensitometrically, that if one develops to a lower contrast index, one's personal E.I. will be lower than ISO speed.
    It's a very common misunderstanding. Film speed isn't determined by density because negative density by it self isn't relative to print quality. Film speed is determined by gradient. The fixed density of the ISO standard is a short cut to determining the fractional gradient point. As per Nelson, the fixed density method is only accurate when the contrast falls within the ISO contrast parameters. Otherwise you need to plug ΔD and Δlog-H into the Delta-X equation because with increased and decreased negative development, the fixed density method is less accurate. You're probably conflating it with how an increase in film density usually is accompanied by a higher gradient. This isn't always the case and definitely not to the same degree in different film types. This is all explained in Simple Methods of Determining the Fractional Gradient Speeds of Photographic Materials by C.N. Nelson and J.L. Simonds. If the OP really wants to understand what the REAL ISO is about, this is the paper.

    As for a personal EI, whatever makes you happy.

    The statement that very manufacturer deciding for themselves what the contrast for the standard should be is patiently wrong. The contrast parameters are clearly defined in the standard. Any variation and the ISO prefix cannot be used.

  2. #52

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    Quote Originally Posted by Photo Engineer View Post
    I usually shoot all negative films about 1/3 stop slower than box speed so as to get better overall latitude. So, a 400 speed to me is a 320.
    Latitude on the low end, to me suggests you are giving yourself an additional safety factor because of how many variables there are in metering etc.

    This is different than why most people down-rate their B&W negative films. The common argument is they get better shadow detail - implying better overall print quality. This is where I'd repeat people likely don't know what kind of negatives they are actually making vs what they think is happening. It's an issue with how people read/interpret/mis-interpret all the various methods out there in the Zone world etc. We tend to come away from those methodologies thinking we are "smarter" than we actually are. Like "aha, now I know how to find the real speed of my film, not the BS Kodak tells me, which must be why my prints always sucked".

    So this goes back to my earlier question - how do people know D-76 doesn't produce "full rated speed"? How are they even defining "full rated speed"? Is isn't just a density above B+F. There is a required gradient over an exposure range.

    I'm not saying it is wrong to shoot at half box speed. That's fine. I just think very few people really know why they are doing it. For a long time I certainly didn't.

    I'm not saying people need to learn about any of this to make good prints either. There is enough latitude and error throughout the end-to-end process for lots of approaches to lead to excellent results. The only reason I initially brought all this up is the title of the thread: "Box ISO rate and Real ISO". Barring extreme procedures, baloney developers and stuff, if you say the real speed of your ISO 400 film is 160, you should be able to back it up.

    PS: Glad to see Stephen post to the thread!

  3. #53
    markbarendt's Avatar
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    Agreed Michael,

    It was interesting for me when I started to grasp the concept of latitude and that we didn't actually ever print everything available from a given film/frame and that our prints generally only represented a fraction of what a given negative held.

    When I came back to film I started with slides and was coming from digital where I loved shooting jpeg. It was really tough coming to grips with the thought that what I did with the camera/film only had a general relationship to the print, not an absolute one. That the print I just made was just one possible interpretation of many.

    With this realization I started testing the latitude and was amazed just how far one can stray (in EI terms) and still make nice prints, just as expected. Finding the limits of that range, for any given film/developer combo, allows for a great amount of creative freedom and spontaneity without worrying about whether or not I got something workable. It also moved me away from thinking my camera work had screwed my print, at least in most cases.
    Mark Barendt, Ignacio, CO

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

  4. #54
    Photo Engineer's Avatar
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    Michael, the same arguments hold for both B&W and color as they are generally made to the same overall aim curve shape. The big difference is that color begins to "go off" due to crossover and other effects if you go too far over or under.

    PE

  5. #55

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    Assuming your metering is accurate, make sure you're not using different ISO because you are not developing the film properly. Temperature control in the developer step is important - the solutions may be at the right temperature but if the tank/reels/film are different you won't be developing at the right temperature. Also, your thermometer should be calibrated to a color thermometer to get the right temperature.

    Since employing good temperature control (bringing the tank/reels/film to temperature and maintaing it in a water bath, and using a thermometer calibrated to a color thermometer), results shooting at box speed and developing according to instructions have been excellent.

  6. #56

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    I run my own speed tests to standardize my exposure technique n printing technique, paper/dev film/del combos, to give me the range of tones that fit my style. I never pay sny attension to box speeds or if my meter jives with another! Its my own standards to fit my equipment n methods.
    Anyone can make a Digital print, but only a photographer can make a photograph.

  7. #57
    markbarendt's Avatar
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    Quote Originally Posted by paul ron View Post
    I run my own speed tests to standardize my exposure technique n printing technique, paper/dev film/del combos, to give me the range of tones that fit my style. I never pay sny attension to box speeds or if my meter jives with another! Its my own standards to fit my equipment n methods.
    In the beginning, did you start somewhere close to box?
    Mark Barendt, Ignacio, CO

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

  8. #58
    Stephen Benskin's Avatar
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    What makes people confident that their testing method is yielding reliable results?

  9. #59
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    Quote Originally Posted by Stephen Benskin View Post
    What makes people confident that their testing method is yielding reliable results?
    I guess it's rather subjective to a point. For my serious work and non-experimentation, I mainly do reversal and follow the box speed at first. If I personally don't find the rated speed to my liking, I assign it my own EI. But, I always make it a point to follow the manufacturer's specs for processing to the letter, this way I don't introduce any other variables that may cause inconsistencies.
    "The real work was thinking, just thinking." - Charles Chaplin

  10. #60
    Bill Burk's Avatar
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    Sorry to bring up a new argument in the conclusion... But the first debate I won in high school was because I had a suprise argument.

    The Delta-X Criterion, which I use for my own speed determination (so I subscribe to it but I want to explain something)... is based on the agreement that 0.3 Gradient is the appropriate speed point... Based on the study of The First Excellent Print.

    Zone System speeds are NOT based on the study of the The First Excellent Print. So there is no reason except coincidence that the speeds even closely relate.

    The First Excellent Print is based on people who viewed prints and pointed to the ones they liked. Built into this study is a Standard Observer's Opinion that "some" of the shadow detail is not important.

    The biggest difference between this and the Zone System is... You will never hear anyone who uses the Zone System saying that shadows are not important.



 

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