Improved T-Max 400

Discussion in 'Darkroom Developing and Printing' started by UC, Oct 10, 2007.

  1. Nicholas O. Lindan, Oct 31, 2007
    #61
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  2. UC

    pico Guest

    pico, Oct 31, 2007
    #62
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  3. UC

    pico Guest

    :) Life is short, Richard. What's two rolls in a lifetime if it settles the
    question?
     
    pico, Oct 31, 2007
    #63
  4. UC

    UC Guest

    Well, that's what I have done. I have shot several rolls of each film,
    adjusting developing times to give similar overall contrast with each
    film. It's expensive and time-consuming, but teh developing times
    given by manufacturers are often excessive and inconsistent.
     
    UC, Oct 31, 2007
    #64
  5. UC

    UC Guest

    When you use the film, the differences appear. I develop much less
    than the longest time shown. The point is that you CAN easily see the
    differences. Kodak brought out Polymax paper specifically to combat
    the problem. Now that Kodak is out of the paper business, they may
    have adjusted the curve of TMY to work better with other papers. After
    all, Tri-X Pan does sell better. TMY is 20 years old!
     
    UC, Oct 31, 2007
    #65
  6. UC

    Peter Irwin Guest

    I think this is getting a little confusing for me.
    I will state what I understand as clearly as possible,
    and you can tell me if I'm going wrong somewhere.


    Kodak Speed
    -----------
    In 1939 Kodak introduced a new speed system based
    on the results of extensive psychophysical research.
    This research showed that the minimum useful exposure
    Required to yield an 'excellent' print was at a point
    where the gradient of the H&D curve was 0.3x times the
    average gradient of the slope over a range from the
    exposure point to log 1.5 above the exposure point.

    Finding this point called the "Jones Point" requires
    a recursive operation. One has to first guess the point
    to find the average gradient, and then refine your guess
    on the second try.

    Kodak speed is given by the formula:

    Kodak Speed = 1/E

    Where E is the Jones Point in Metre-Candle-Seconds.
    (Same as Lux Seconds).

    If you had such a thing as a exposure meter
    calibrated for Kodak speeds, there would
    be no safety factor. Kodak Speed didn't catch
    on because few if any people owned such meters.


    OLD ASA Speed 1943
    ------------------

    In 1943 the ASA adopted the Kodak speed system
    with one important change.

    The formula was now

    ASA Speed = 1/(4 x E)

    This was intended to give numbers usable with
    both Weston and GE meters. The new ASA standard
    meters were to be calibrated midway between the
    old Weston and GE calibrations. With an ASA
    meter, old ASA speed had a safety factor of
    2.5 (1 1/3 stops).

    I don't think there was a particular level
    of negative contrast required by the old ASA
    standard, because the Jones point remains in the
    same place over a fairly wide range of development
    contrasts. Development contrast is supposed
    to be typical of photofinishing practice.

    DIN Speed
    ---------
    The original DIN speed system (1936) was
    very unsatisfactory. Sometimes it would
    even get the relative speeds of films
    in the wrong order. The reason for this
    was that the original DIN standard required
    films to be developed for maximum speed
    rather than according to normal use.
    Old DIN speeds are indicated by the presence
    of "/10" so 24/10 degrees DIN is an old
    DIN speed.

    In the 1957 DIN standard, the "optimal
    development" was replaced by a rigidly
    specified development more typical of
    real practice. People soon noticed that
    the new DIN numbers actually made sense.

    New ASA Speed
    -------------
    Since the new DIN system was easier for
    film manufacturers in practice and
    actually worked pretty well, the ASA
    decided to adopt a new system based on
    DIN speeds. It was also decided to
    abandon the rather large safety factor
    and have speeds roughly twice that of
    the old while keeping meter calibration
    unchanged.

    The 2:1 relationship is typical, but is
    not exactly true of all films as the following
    table shows.

    Film OLD ASA NEW ASA
    ---- ------- -------
    Plus-X 35mm 80 125
    Verichrome Pan 80 125
    Tri-X Pan Sheet 200 320
    Tri-X Pan 35mm 200 400

    ISO Speed
    ---------
    The current ISO standards for B&W film
    are essentially the same as the New DIN
    and New ASA standards.

    Where Hm = the 0.1 above base + fog point in lux seconds.

    Arithmetic speed S = 0.8/Hm

    Log speed S degrees = 1 + 10 x log10 0.8/Hm

    The Log ISO is in fact the same as the
    DIN speed.

    DIN Speed = 10 log10 1/Hm

    Because 10 log10 0.8 = -1
    (at least very very nearly).

    So Log ISO and DIN are both equal to
    the log exposure of the 0.1 above base + fog point
    divided by minus 10.

    The 0.8 denominator in the arithmetic speed
    makes 1 ASA equal to 1 DIN and places the
    New ASA or ISO arithmetic speed where it
    was wanted.

    example:
    Tri-X pan 400
    ISO 400/27 degrees
    New ASA 400
    New DIN 27
    OLD ASA probably still 200

    0.1 above base fog point (Hm) is -2.7 log lux seconds

    This is true from all formulas.

    ISO Artith or New ASA = 0.8/Hm
    = 0.8/10^-2.7
    = 0.8/0.002
    = 400

    ISO Log Degrees = 1 + 10 x log10 0.8/Hm
    = 1 + 10 x log10 0.8/10^-2.7
    = 1 + 10 x log10 400
    = 1 + 10 x 2.6
    = 1 + 26
    = 27

    DIN Speed = 10 x log10 1/Hm
    = 10 x log10 1/10^-2.7
    = 10 x log10 501
    = 10 x 2.7
    = 27
    Same Answer!

    DIN Speed of 27 means Hm is -2.7 log lux seconds.
    - neat - all you have to do is divide by negative 10.

    If Old ASA 200 then Jones point E = - 2.9 log lux seconds

    ASA Speed = 1/(4 x E)
    = 1/(4 x 10^-2.9)
    = 1/(4 x 0.00126)
    = 1/0.00504
    = 198.41

    Close enough.

    Peter.
     
    Peter Irwin, Oct 31, 2007
    #66
  7. UC

    UC Guest

    It is my opinion, and that of many others, that the 'new' ASA speed
    sytem introduced in 1959 gives numbers that are too high, by about 2/3
    stop.
     
    UC, Oct 31, 2007
    #67
  8. UC

    Peter Irwin Guest

    I think the primary reason for this is that the question
    you want the ISO rating to answer is a different question
    from the one it was designed to answer.

    The question the speed rating is designed to answer
    is "what is the minimum exposure required to produce
    a negative from which a print judged to be 'excellent'
    can be made?"

    The question you probably want answered may be
    something like "What exposure meter setting will
    consistently give negatives that are easy to print
    well?"

    The answer to the second question is going to generally
    be a lower exposure index than the ISO standard.

    Peter.
     
    Peter Irwin, Nov 1, 2007
    #68
  9. UC

    pico Guest

    I use the film. And are you not aware that Tri-X has changed again?
     
    pico, Nov 1, 2007
    #69
  10. UC

    pico Guest

    MOST EXCELLENT observation. Kodak set the metrics. Those are the same folks
    who conducted a hugely expensive and detailed survey of average customers
    (largely of automatic processing) and Kodak set their metrics to those
    standards, as abysymal and utterly tasteless as they were, they still
    represented the drug-store processing majority. (Imagine the Bell curve -
    who wants to live on top?) Oh, and what camera did Kodak come out with in
    response to that study? The wholly embarassing failure, the Disc Camera!

    But to add a contemporary data point - with so many people scanning
    negatives, a whole new scale must be developed (no pun). Me, I'm still
    scanning prints. So shoot me already. :)
     
    pico, Nov 1, 2007
    #70
  11. UC

    Peter Irwin Guest

    Thanks, but I think you misunderstand me. I didn't mean
    anything sarcastic when I used "excellent" in quotes.

    I just meant that the two questions:

    "What is the highest EI setting I can use and still
    get excellent quality prints?"

    and

    "What is the best all-round EI setting to use in practice?"

    are different questions with different answers.
    The ISO speeds for negative film provide good answers
    to the first question, but not necessarily to the second.

    The important detail to remember is that the ISO speeds
    are intended to get you very near the minimum exposure
    that will work well with negative film. The maximum
    exposure is generally much higher.

    The optimum setting for your purposes is something
    you have to find for yourself. All film manufacturers
    including Kodak actually say this.

    Peter.
     
    Peter Irwin, Nov 1, 2007
    #71
  12. UC

    pico Guest

    Of course. So shoot short rolls or sheet film and custom expose and develop.
     
    pico, Nov 1, 2007
    #72
  13. UC

    UC Guest

    Well, I don't think the shadow contrast is as good at ISO as it is at
    about 2/3 ISO. This is based on many thousands of negatives.
     
    UC, Nov 1, 2007
    #73
  14. UC

    UC Guest

    No, it has not changed, other than 'normal' manufacturing
    improvements. I got this from Kodak themselves a couple of years ago.
     
    UC, Nov 1, 2007
    #74
  15. UC

    UC Guest

    That's not necessary or practical for 35mm users. Just set your meter
    at 2/3 ISO and usually you will have near-perfect negatives.
     
    UC, Nov 1, 2007
    #75
  16. UC

    UC Guest

    No, I don't think so.

    It was "What index will produce the greatest number of correct
    exposures without losing definition through overexposure on automatic
    cameras".

    You have to remember that the late 50s saw the introduction of
    numerous compact, semi-automatic and meter-coupled 35mm cameras with
    primitive meters.

    The way these cameras metered resulted in overexposure errors more
    often than underexposure errors, if I recall correctly. It was felt
    that a reduction in exposure was warranted because of this.
     
    UC, Nov 1, 2007
    #76
  17. Thousands of negatives with the _one film_ you've evidently decided is
    an acceptable film for anyone to use. How... tremendously persuasive.

    I don't suppose it might have occurred to you that you could probably get
    perfectly good results with almost any film you picked up from the store
    shelf if you were willing to adjust your own technique. Well, as materials
    disappear from the market faster and faster over the next few years, I don't
    think you're going to have much choice about it, unfortunately.
     
    Thor Lancelot Simon, Nov 1, 2007
    #77
  18. UC

    UC Guest

    ??? What are you talking about? I use lots of different films. The
    point is that 2/3 ISO is better than ISO for almost every film I've
    tried. The exception was Ilford Pan-F, which works well right at 50.
     
    UC, Nov 1, 2007
    #78
  19. This is getting long but I can't find anything to snip.
    I don't know when Kodak began using Jones' method
    internally but it did begin to publish Kodak speeds around
    1939. Jones actually worked out his system much earlier.
    The ASA adopted the system in 1943 with a safety factor
    of 2. ASA speeds were 1/4 of Kodak speeds. The resulting
    number could be used with either Weston or General Elecric
    meters of the time with insignificant error. However, the
    safety factor increased the exposure by a stop over the
    Jones speed point. A film rated Kodak 400 would be an ASA
    100 film by this standard. In its data sheets of this time
    Kodak stated that the exposure could be reduced a stop if
    work was carried out carefully.
    The second ASA standard changed the method of
    measurement from the Jones minimum usable gradient to a
    fixed minimum density method as adopted by the DIN in the
    early 1950's (don't have the exact date at hand). However,
    they wanted to accomplishe two things: first was to make the
    speeds compatible with earlier ASA speeds, and secondly, to
    maintain something like the Jones idea of the minimum
    gradient. The ASA conducted extensive surveys of films of
    the time and found that there was a nearly constant ratio
    between the fixed minimum density, that is log 0.1 above fog
    plus support density, and the Jones point as found using the
    Jones method. This obviated the difficult Jones measurement.
    The ratio turned out to be about 1.25 times the exposure
    required to reach the DIN density point. So, a factor of
    0.8, the reciprocal of 1.25 is introduced into the
    calculation of the speed in the new ASA method. In effect
    the speeds were now double those measured by the old ASA
    method and half of the Kodak speed.
    I reiterate that the factor in the current speed method
    is NOT a safety factor but rather to bring measurements made
    by the method into agreement with the speed that would be
    measured by the Jones/Kodak method and reverts to Jones'
    original idea of finding the minimum exposure that results
    in good tone rendition.
    The original Kodak method does not seem to have had a
    fixed contrast, however, contrast does affect the speeds
    measured by either method. The Kodak method does specify a
    fixed exposure interval, much the same as the current
    method.
    Since the old ASA method and the new ISO method are
    compatible as to speed point even though measured by
    different techniques, its possible to translate old ASA (pre
    1958) speeds to equivalent modern speeds by simply
    multiplying by 2. Keep in mind that the speeds in both
    systems are rounded off as were old Weston speeds so there
    may not be an exact agreement. Also, even though Kodak used
    the same trade names for decades the emulsions were changed
    many times. Current Plus-X is not the same as the product
    of, say, 1948 although its broad speed catagory is about the
    same and its intended use is about the same so speed
    comparisions must be made with some care.
    What is surprizing is how fast films of the mid 1940's
    were. The difference was, of course, grain. A 1940's film
    which would measure 400 on the ISO system would be extremely
    grainy compared to a modern film of that speed.
     
    Richard Knoppow, Nov 1, 2007
    #79
  20. This is simply not true. The Kodak speed method was
    developed over a very long time by quite valid research all
    of which has been published in peer reviewed journals. Much
    of the work conducted under L.A.Jones leadership was
    published in the Journal of the Franklin Institute.
    There is a big difference between market surveys and
    scientific investigation and you are confusing the two.
    Kodak's main thrust has always been to make photography
    practical and easy for amateurs, that's what George
    Eastman's philosophy was and he built one of the most
    successful businesses in history on it. The influence is
    still there even though Kodak has moved from chemical to
    electronic photography.
    Actually, the ISO speeds are quite practical but many
    photographers do not understand how they are supposed to be
    used. The speed applies only whan the specified developer is
    used and when film is developed to the same contrast index
    as is used in the standard measurement. This is about the
    contrast for contact printing and diffusion enlarging. If
    film is devloped to a lower contrast the exposure must be
    increased.
    Also, Jones found that the quality of the prints changed
    little once the minimum exposure was reached. Minimising the
    exposure minimises the density of the negatives, which, in
    genera, is better for minimising grain and maximising
    sharpness, however, it is often the case that increasing
    exposure a bit improves tone rendition, perhaps because of
    errors in using an exposure meter.
     
    Richard Knoppow, Nov 1, 2007
    #80
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