Improved T-Max 400

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

  1. UC

    Peter Irwin Guest

    I hope that means that it was mostly ok.
    I'm sure that's right, but published Kodak speeds
    from before 1939 are a different system. The Kodak
    speeds listed in the 1938 edition of "Eastman
    Professional Films" are not the Jones system.
    The pre-1939 Kodak system was based on inertia
    (Like Weston and H&D) and is equal to ten times
    the Weston speed.
    That's what you've said several times.

    But - In "Kodak Films" fifth edition 1951
    from the Kodak Reference Handbook on page 16,
    it says "For the black-and-white continuous
    tone negative materials covered by the standard,
    a safety factor of 2.5 is used."

    In "Kodak Films" seventh edition 1956, it says
    the same thing on the top of page 21.
    That's true, but I expect you have the same booklets
    I have where it says the safety factor is 2.5.
    The 1958 Ilford Manual by Horder has the date for
    revised DIN standard as 1957 (p. 284, 287).
    The older 1936 DIN system used the same minimum
    density requirement, but specified development
    for maximum speed, rather than a standard
    development representing something like
    normal use - as was used from 1957.

    I think the ASA Standard is ANSI PH2.5-1960, at least
    it is cited that way in Photographic Sensitometry
    by Todd and Zakia (1974 p.164).

    These would just be publication dates, the actual
    work would always be a bit earlier.
    That made a lot of sense given the number
    of meters already in use.
    It doesn't use the 0.3 times average gradient
    criterion though, it uses the 0.1 density
    above base + fog criterion.
    It seems to hold good within a third of a stop
    based on the ratings of films just before
    and just after the change.

    Note that the inertia based Weston speed also tracked
    pretty well with the Jones Kodak Speed and Old ASA.
    The normal relationship would be that Weston 40
    equaled Kodak 200 and Old ASA 50. Many films
    seem to have fit that relationship perfectly
    and I'm unaware of any that were more than
    1/3 stop off.

    The key seems to be normal development.
    Weston, Old ASA, and ISO (New ASA/New DIN)
    use different criteria, but track quite well.
    They all use normal development.

    Old DIN (1936) tracked the other systems very badly.
    It used development for maximum speed.
    The same criterion, but with normal development,
    works very well.
    The math in my previous post showed that
    an ISO 400/27 film has a DIN density
    point at -2.7 log lux seconds and that
    an Old ASA 200 film had a Jones Point
    at -2.9. Unless someone shows that
    my formulas or math are wrong, I'm
    sticking to those figures.

    The Jones Point for a typical film
    is thus 0.2 log units to the left
    and represents 2/3 of a stop less exposure
    than the DIN point.
    That was to get the numbers they wanted,
    but the actual difference between the DIN
    point and the Jones point for films
    where New ASA is double Old ASA is 0.2 log units,
    2/3 of a stop or a factor of around 1.6.
    True for most films.
    Yes but if the "Kodak Films" booklets are correct
    that Old ASA had a safety factor of 2.5, then the
    doubling of the speed ratings should have reduced
    this to 1.25. I agree that this has nothing to
    do with the 0.8 in the formula. The 0.8 in the
    formula just puts the scale where they wanted it.
    Yes, but changes in development time tend to affect
    the contrast in the toe and the overall contrast
    at the same time. Since the Jones method depends
    on the ratio between the slope of the curve
    at the Jones point and the overall slope, changes
    in development will have less effect on the
    Jones point than on the DIN point.

    Plus-X 35mm did vary in rated speed over the years.

    Kodak 200 in 1943 (Old ASA 50)
    ASA 50 in 1951
    ASA 80 in 1956

    But the speed of both Plus-X 35mm and Verichrome
    Pan just before the change was ASA 80 and both
    were ASA 125 just after the change and forever after.
    I'm aware that both systems round to the nearest
    1/3 stop so that a 1/3 stop difference in reality
    may be hardly anything at all.

    My impression is that Plus-X 35mm, while now
    greatly improved from the film introduced in 1938,
    never underwent any rapid obvious change from
    year to year. Every now and then the new stuff
    would be just a little better. A bunch of minor
    changes over 69 years can add up a lot.

    Then again, it was always around 100 speed
    by today's standards. It was always a double
    coated film, always type B panchromatic,
    always had a high acutance, and was always
    fine grained for its time.
    Medium speed films were actually pretty ok.
    I have some of my father's Verichrome negatives
    that he took with his Brownie in the 1940s.
    Even with department store processing, the
    negatives are still a bit finer grained
    than today's Tri-X in D-76 1:1.

    Peter.
     
    Peter Irwin, Nov 2, 2007
    #81
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  2. UC

    pico Guest

    The study I am familiar with was a market study; it strove to find the kind
    of print most people like so that they could recommend processing and
    materials to their mass processing clients. Market means the typical
    purchaser.
     
    pico, Nov 2, 2007
    #82
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  3. UC

    Peter Guest

    I was wrong about this. I looked up official Weston
    speeds from 1940 and compared them to Kodak speeds
    from 1943 - and they just aren't always that close.
    The Weston speed system was ok, but it
    wasn't that good. Weston speeds quoted by Kodak
    in the 1943 book are just converted Kodak speeds
    - so of course those match.

    I was also wrong about the date of the original DIN
    speed standard. DIN 4512 was 1934 not 1936.

    Peter.
     
    Peter, Nov 2, 2007
    #83
  4. UC

    UC Guest

    Everything I have ever read says the safety factor before 1959 was
    2.5. It was reduced to 1.25 in the new system. The right factor is
    about 1.75.
     
    UC, Nov 2, 2007
    #84
  5. I don't know what you mean by the "right factor" the
    numbers 1.75 do not exist in the standard.
    Also, the 0.8 or 1.25 factor in the new standard is
    _NOT_ a safety factor as I explained in my long previous
    post. It is meant to adjust the value gotten from the
    straight DIN method to the speed which would result from the
    Jones/Kodak minimum usable gradient method.
    The ASA adoption of the Jones/Kodak method did include a
    safety factor of 2.5. This was done to insure that there
    would be a developable image when applied by amateurs.
    Unfortunately it resulted in quite dense negatives. Jones
    worked on the basis of determing the minimum practical
    exposure for good tone rendition in order to obtain the best
    sharpness and grain characteristic from a film. He also
    found that increased exposure made little difference to the
    tone rendition but that underexposure by even a small amount
    resulted in poor rendition, so, the ASA and Kodak decided to
    lower the film speed by about a stop to make sure people
    would get acceptable results. Tone rendition was considered
    more important than optimum grain and sharpness.
    Again speeds _reported_ by the current method are about
    double those obtained by the original ASA method and about
    half of those obtained by the method used by Kodak
    internally. the division of the Kodak speed by a factor of
    two fits the resulting speed to the calibration of the
    exposure meter calculators current in the United States in
    the 1940's, i.e. Weston and General Electric. Weston had
    their own system of determining speed and all measurements
    were made, at least at first, by Weston, so there was no
    temptation for manufacturers to cheat, as they could with
    the earlier DIN, Schneiner, or H&D systems, all being used
    at the time. I have never found a description of the method
    used by General Electric. GE speeds were two numbers higher
    than Weston speeds and the original ASA sytem was designed
    to result in a number in-between these two so it could be
    used on either meter with insignificant error. Weston speeds
    were rounded off so that all films within a bracketed range
    had the same speed value. Probably GE did the same.
    Actually, the current ISO standard also has rounded off
    ranges so published speeds in any of these four systems are,
    and have always been, approximations.
    Again, the speed depends on the degree of development.
    The ISO and new DIN standard effectively specify a contrast
    index by specifying the density range to be obtained from an
    exposure range. Any change in the contrast will affect the
    effective speed. That's why the term EI, or Exposure Index
    should be used when a speed has not been determined by the
    ISO method.
    Also, common developers can affect speed. The range is
    around 1.5 stops overall for developers ranging from
    Microdol-X or Perceptol (low end of speed when used full
    strength) to Xtol, T-Max, Microphen (all at the high end of
    speed) with developers like D-76 being in the middle. The
    standard requires that the developer used be specified with
    the speed ratings. Kodak does this on its development charts
    but I have never seen a developer specified on a film box.

    In any case, the calculator of an exposure meter is
    designed to fit an average scene into the usable range of
    the film. Changing the film speed simply moves the exposure
    left or right along the curve. The mid gray value, which is
    often argued, is actually of little relevance, provided its
    in the linear part of the curve somewhere. More important is
    where shadows that are to have some detail fall. They must
    be recorded on the film characteristic at a point where the
    contrast is high enough to record the detail. If too far
    down on the toe the shadows become blank. Moving them up
    will improve their rendition but exposure must not be moved
    up the curve enough to make the highlights _which are to
    have detail_ fall onto the shoulder, where, again, the
    contrast is low. For modern film there is no practical
    shoulder unless the film is overexposed by a great many
    stops.
    Printing density is another consideration: overall
    density becomes higher as exposure is increased. Negatives
    which are so dense that they take very long printing
    exposures are undesirable even if they deliver good tone
    rendition.
    Worrying about small errors in exposure is useless for
    normal B&W, the important thing is to give the negative
    enough exposure for good shadow detail. Once this mimimum is
    met there is a long range of increased exposure which will
    still result in good tone rendition in the print.
     
    Richard Knoppow, Nov 2, 2007
    #85
  6. UC

    UC Guest

    The 'new' standard reduced the safety factor, but did not eliminate
    it. It was reduced from 2.5 to 1.25. I have read this somewhere. A
    factor of 1.75 (basically, lowering the speeds by 1/2 stop) would put
    the shadows up a little higher on the curve and give better separation
    of shadow detail.
     
    UC, Nov 2, 2007
    #86
  7. UC

    Peter Irwin Guest

    It also tended to match what the Weston and GE systems
    were already doing. The Weston and GE systems were
    actually working quite well in practice. The change
    to a unified system with a really sound theoretical basis
    was obviously a good thing, but it was probably desirable
    at the time for the new system to give people answers
    which were close to what they were already getting
    from their meters.

    Even in the 1943 Kodak datasheets, there was a sentence
    "When it is desired to reduce the exposure to a
    minimum, these meter settings can be doubled with
    little danger of of serious underexposure."
    My understanding is that a one stop increase
    in exposure typically results in an increased
    negative density of 0.2 or so. This seems to
    me to be a fairly small shift. Doubling
    the exposure time for the negative will less
    than double the exposure time for the print.
    Even then, the increased grain and loss of sharpness
    from 1 stop or so extra exposure must have been
    quite small.

    According to T.L.J. Bentley's "Manual of the Miniature
    Camera" (4th ed. 1953 page 102) - "The resolution
    obtainable with photographic film suffers to some extent
    with excessive exposure, but with a good film the effect is
    not so noticeable in practice as some statements suggest:
    it can be shown by test that, at X 16 enlargement under
    critical conditions, the deterioration with an increase
    in exposure to eight times the least exposure giving an
    enlargement of optimum quality is barely detectable
    under the closest scrutiny."

    Even if you think you might be somewhat fussier,
    it doesn't seem that the adverse effects of a single stop
    increase could have been very noticeable even in 1953.
    In the early 20th century, Alfred Watkins produced
    lists of measured speeds for plates sold in the UK.
    In theory his numbers should have been 1.47 times
    higher than honest H&D speeds, but in practice they
    are generally lower than manufacturers' rated speeds.
    When I last had a look at this it appeared to me
    that Ilford H&D used a fudge factor of two. This
    appears to have remained the case from the early teens
    through the 1940s. Ilford H&D can be converted to Weston
    by dividing by 50, and roughly to modern ISO speeds
    by dividing by 20.

    Ilford seems to have been quite open about this:
    in the 1934 Ilford Manual on page 40, it reads
    "It might be mentioned, further, that for various
    reasons the original details laid down by Hurter
    & Driffield have been departed from to some extent,
    and in consequence the H&D speed number of an emulsion,
    though correctly only about two-thirds that of a
    Watkins number, is generally given as about one-third
    higher."

    European Scheiner inflation seems to have been
    a major problem. The DIN standard was supposed
    to correct this. DIN numbers were originally
    around 10 less than the Scheiner speeds, though
    the difference seems to have grown to 11-13 by
    the 1950s.

    I've never seen one either. There is a good
    discussion of the Weston method in the
    1958 Ilford Manual.

    According to a post by David Carper of Ilford
    on photo.net:
    <http://photo.net/bboard/q-and-a-fetch-msg?msg_id=003WI4>

    Ilford HP5+ has an ISO speed of 500/28 in Microphen,
    compared to a speed of 400/27 in ID11. The speed at
    a Gbar of 0.75 is less than a third of a stop higher
    than it is at a Gbar of 0.62. The speed at a Gbar of 0.55
    is less than 1/4 of a stop slower than at a Gbar of 0.62.

    So while changing development does change the speed point,
    it doesn't appear to change it by all that much in most cases.
    A single extra stop isn't going to cause any trouble
    in the darkroom. An exposure of six stops over
    does cause a big problem: not only are the printing
    times too long - it can be hard to focus the
    enlarger. A six stop overexposed negative will
    actually print ok, but it is an absolutely ridiculous
    thing to do except as a test to prove a point.

    Peter.
     
    Peter Irwin, Nov 6, 2007
    #87
  8. UC

    UC Guest

    Peter has made some excellent points, and my experience corresponds
    precisely with what he says. One stop increase in exposure above the
    bare minimum results in hardly any change except increased shadow
    detail. I use about 2/3 stop over the ISO exposure, i.e., I rate most
    ISO 400 films at 250.
     
    UC, Nov 6, 2007
    #88
  9. UC

    pico Guest

    At one point Weston changed the calibration or setting of the dial. Was it
    when ASA was introduced? Darned. I will get the big box of old Westons and
    compare and let you know what I find.
     
    pico, Nov 8, 2007
    #89
  10. UC

    ____ Guest

    Film: You can use all of a curve that fits between .001 and 1.71
    Ha ha less image area from .001 to .15 & the 1.00 to 1.71 areas!

    Paper: You must compress all film values to fit a range between .15 and
    2.00 for a natural and real representation :)
     
    ____, Jan 1, 2008
    #90
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