Improved T-Max 400

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

  1. UC

    UC Guest

     
    UC, Oct 28, 2007
    #41
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  2. Do you? Because you referred to a H&D curve you had, purportedly,
    generated yourself, but then when I challenged you to post it, you said
    to look at the published Kodak curve (which does not appear to show
    anything like the effect you originally claimed). So. Let's see some of
    this data from the testing you supposedly do of the materials you supposedly
    use.

    Oh, I forgot, you just like to hang around here and _talk_ about all the
    photography you do. One wouldn't expect less from a famous Usenet kook,
    I suppose.
     
    Thor Lancelot Simon, Oct 29, 2007
    #42
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  3. UC

    UC Guest

    I never said I generated any H&D curve myself. The curve that Kodak
    publishes supports what I say about the film. If you don't understand
    that, too bad. Tri-X shoulders off in teh highlight region. T-Max 400
    does not. It's that simple. For outdoor work, a curve like that of Tri-
    X is preferable.
    Famous? Hardly.
     
    UC, Oct 29, 2007
    #43
  4. UC

    UC Guest

    I said I had tested the films. I did not say I generated H&D curves.
    You need special equipment for that.

    Here is the curve for TMY:

    http://www.kodak.com/global/en/professional/support/techPubs/f4016/f002_0507ac.gif

    Here is the curve for Tri-X Pan:

    http://www.kodak.com/global/en/professional/support/techPubs/f4017/f009_0490ac.gif

    Do you see the difference?
     
    UC, Oct 29, 2007
    #44
  5. Special equipment like, oh, I don't know, a densitometer? Heck, you
    could get a perfectly functional one from eBay for about $100, if you
    only need it for monochrome transmission sensiometry.

    And to think, you like to throw around one-liners about how others have
    "clearly never done critical testing of materials". I guess now I get it:
    your "critical testing of materials" doesn't actually involve sensiometry
    per se (it can't, since you evidently don't own the basic tools for the
    job). Instead, you shoot some film and decide if you, personally, can
    get the results you like without changing your technique any. If not, you
    pop over here and spew some more about how the materials in question are
    useless for everyone, all the time.

    You really don't get it about why most people consider you a kook, do you?
     
    Thor Lancelot Simon, Oct 29, 2007
    #45
  6. The curves are quite interesting. Kodak does not appear
    to smooth their film curves, otherwise there would not be
    the slight uneveness exhibited by several of them including
    those for 400T-Max above. Neither of these curves shows
    much shouldering, it would appear that both films are
    capable of considerably greater density than the log 3.0
    shown as a maximum on the curves. The question is how much
    the contrast is falling off at high exposures and high
    densities. Note that the curves show a large range of
    contrast indeces. What shouldering there is seems partly
    dependent on the degree of development as one would expect.
    Also note that the range of exposure is quite wide. Assuming
    the minimum usable gradient is somwehere around log -2.5 the
    arithmetical range is around 1:400 or a bit less than nine
    stops. If we assume an average scene brightness range of a
    little less than this both films are pretty linear. For the
    most part highlight compression in both B&W and color is due
    to the limitations of the printing medium and method of
    illumination, that is reflected light. Transparencies can be
    illuminated at levels much exceeding the ambient so can
    reproduce very bright highlights, reflection prints do not
    have this advantage unless illuminated in a light box and
    printed especially for that purpose. In general reflection
    prints have more shadow detail than can be seen by reflected
    light but highlight detail is compressed because the print
    is made to make the mid-tones right by reflected light. One
    can usualy see some additional shadow detail in a print by
    looking at it with transmitted light. A print can have a
    range similar to a transparency if its illuminated by extra
    bright light in a light box and printed to the right
    contrast and density for the purpose.
    The point is that film is seldom responsible for lack of
    highlight detail. The eye generaly judges the "correctness"
    of tone rendition by the reproduction of mid gray values. In
    some cases there will be more detail in both shadows and
    highlights than can be accomodated on a reflection print if
    the contrast and overall density is chosen to meet this
    criterion.
    Getting valid characteristic curves for film is not
    trivial. The method used by manuacturers uses a special
    device for exposing called a sensitometer. This gives a
    known and controlled exposure and uses a method suited to
    the end use of the film. Processing must be done precisely
    to eliminate as many errors as possible and the resulting
    film is read on a densitometer, again matched to the use of
    the film.
    It is quite possible to get useful curves by simpler
    means but they will include variables other than the
    emulsion. Sometimes this is desirable, for instance, testing
    in a camera will yield a curve showing the effects of flare
    _in that camera_.
    In any case, the developer will also have some effect on
    the curve shape and presence or lack of a shoulder because
    the maximum density possible with a given emulsion will vary
    with the developer. For instance, active developers like
    T-Max and Microphen (which is similar) will yield quite high
    maximum densities, generally higher than can be used in
    practice.
     
    Richard Knoppow, Oct 29, 2007
    #46
  7. When I look at Kodak's graph for Tri-X 4164, I get only a hint of a
    shoulder, and that begins at a density of 2 or more (depending on how
    you develop it). Most photographers I know of would never want printable
    highlights as dense as that. They either want them to go pure white,
    or they adjust the contrast (if possible) in the field or in the
    darkroom.

    And furthermore, depending on how you develop it, the toe
    starts at a density of 1 (though more likely, at a density of 0.7.
     
    Jean-David Beyer, Oct 29, 2007
    #47
  8. UC

    Peter Irwin Guest

    I had been under the impression that the Jones
    point for a 200 old ASA film was at log -2.9.

    I'm not really reliable at math, so I'd be glad
    if someone would show me if I've gone wrong.

    If the old ASA speed definition is:

    old ASA speed = 1/(4xE)

    then E = 1/(4x old ASA)

    E = 1/(4 x 200)
    E = 1/800
    Log (E) = -2.903


    The curve probably would continue as reasonably linear
    a fair bit to the right of what is shown on the graph,
    so the actual range of the film is pretty huge.

    The slight bend at the right of the tri-x graph might
    have some effect on tone reproduction, if you actually
    gave the film that much exposure, but it hardly looks
    like a major departure from linearity.

    Peter.
     
    Peter Irwin, Oct 29, 2007
    #48
  9. I think you are refering to log exposure. I am going to
    have to research this because I don't remember if the
    ASA/Jones method used the same units (lux seconds) as are
    currently used. In any case, the Jones method was based on
    an exposure giving a minimum toe gradient of 1.3rd of the
    overall straight line gradient. I think the ASA standard
    required a contrast index about the same as the current ISO
    standard, that is, approximately right for contact printing
    or diffusion enlarging. I just looked at the Kodak curves on
    their web site and estimated there the log exposure
    intercepted the toe. In any case, moving a little one way or
    another would not make much difference in overall exposure
    range. You are probably right that the exposure I found for
    these ISO-400 films are about what you will find for ASA-200
    films due to the 2X safty factor the ASA applied to Kodak
    speeds in its 1943 standard.
    The current ISO method includes a multiplier of
    1.4x. This is not a safety factor but rather to adjust the
    speed gotten from the exposure for a density of log 0.1
    above gross fog and support density to the point where the
    toe gradient is about 1/3rd the overall straight line
    gradient. When the ASA adopted the new DIN method to replace
    the Jones/Kodak method in 1958 it found by extensive survey
    that for nearly all pictorial films the ratio between the
    log 0.1 density point and the Jones speed point was about
    this ratio, so the DIN speed is divided by 1.4 to obtain the
    equivalent Jones/Kodak speed. The reason for changing the
    method was that the Jones method proved very hard to use in
    practice.
    Jones and his associates at Kodak Labs conducted
    extensive experimentation to find the practical mimimum
    exposure needed by a film to deliver good tone rendition. He
    found that the minimum shadow exposure had to be on the toe
    no lower than where the toe gradient (or contrast) was 1/3
    of the straight line gradient. Increased exposure had little
    effect on tone rendition but perceived quality fell off very
    quickly if the exposure was reduced from this point.
    Jones chose to find the _minimum_ exposure because
    films of the time had optimum grain and sharpness when at
    minimum density. Modern films still have this property but
    its much less now than in the period of the 1920's through
    1940's when Jones did his work.
    Kodak's approach to tone rendition was to standardize
    the development of the negative so that a constant contrast
    was obtained and to adjust print contrast, if necessary, by
    choice of paper grade. This is about the opposite of the
    Zone System which attempts to adjust negatives so that they
    all print on the same grade of paper.
     
    Richard Knoppow, Oct 30, 2007
    #49
  10. Mis typed, should be 1/3rd.
     
    Richard Knoppow, Oct 30, 2007
    #50
  11. UC

    Peter Irwin Guest

    Thanks. I think a metre-candle-second is the same as
    a lux second.

    I've been trying to get a handle on what the X axis
    on the H&D curves means in practical terms.

    Here is what I've come up with:

    For ISO 100, units are log lux seconds:

    -2.3 - Jones point (Old ASA 50)
    -2.1 - ISO B&W speed point (0.1 above base + fog)
    -1.05 - where usual light meter tries to put the average
    -0.3 - where 100% reflectance goes if meter aimed at grey card
    0 - enough to fully blow highlights on typical slide film

    A difference of 0.1 is 1/3 stop.
    A difference of 0.3 is one stop.
    Thus for 400 speed film subtract 0.6 from these figures.

    I think this (if accurate) is a fairly useful list to
    keep in mind when looking at H&D curves.

    I know there are theoretical problems with trying to
    co-relate camera exposure with the figures on
    the H&D curves, but it seems to me that we are essentially
    doing just that whenever we set our light meters
    based on the ISO value. I don't think I've seen
    such a list anywhere so I've collected one together myself.

    It would be great if someone would point out errors,
    or add anything which seems useful.

    Peter.
     
    Peter Irwin, Oct 30, 2007
    #51
  12. The ISO speed point is not actually log 0.1 density
    above fog plus base density but rather the value gotten by
    multiplying this by the factor 1.4. This is supposed to put
    the point at about the same place as the Jones point.
    Measured by the Jones method there really is not a fixed
    density point since the speed is based on the relative
    gradient of the toe vs: straight line of the film curve.
    However, the research done by the ASA when they changed over
    to the DIN method (fixed density point) showed that for the
    great majority of films the two bore a fixed relationship.
    The current ISO standard is uses the same method as the
    1958 ASA standard with some ammendments in detail. For
    instance, the old standard specified two developers, a
    general purpose one and a fine grain one, neither of which
    was much like any standard commercial developer. The current
    standard does not specify a developer but requires that the
    published speed identify the developer used for the test.
    Thus a film can have more than one speed if the manufacturer
    tested it with more than one developer.
    The current standard specifies that development be
    carried out so that a log exposure interval of log 1.30
    results in a density interval of log 0.8 measured from the
    point were the density is log 0.1 above fog plus base
    density. This is a gamma of about 0.62, not too far from
    typical practice.
    The point at log 0.1 density is called log10 Hm and
    arithmetric speed is S=0.8/Hm (note that the arithmetric
    value rather than the log value is used). For log speeds the
    formula is S (in degrees)=1+10log10 0.80/Hm
    I was in error when a stated that the correction factor is
    1.5, its 1.25, the reciprocal of 0.8. Thus the ISO speed is
    about 80% of the value that would be calculated directly
    from the 0.1 density point. If one applies the correction
    factor to the density it would be 0.125
    The standard has a chart of ranges of log10 Hm to speed
    where several samples are measured. I think this is what you
    want. Some rounded off values are:
    ISO speed Log exposure at 0.1 density point
    25 -1.5
    50 -1.8
    100 -2.1
    200 -2.4
    400 -2.7
    800 -3.0

    Note that the exposure equivalent to the Jones point would
    be about 1.25 times these values, i.e., about -2.63 for ISO
    100 film.

    Thanks for asking about this, its been educational to
    figure out the answer.
     
    Richard Knoppow, Oct 30, 2007
    #52
  13. UC

    UC Guest

    I photograph a standard subject (the houses across the street) in
    clear sunlight in the morning. It is very easy to see differences in
    shadow vs highlight contrast, graininess, color sensitivity to green,
    etc. The clear sky shows grain quite readily. The shadows under the
    awnings, and in the doorways, clearly show differences between films.

    The house numbers show sharpness. It is useless to do trails of
    materials except under conditions that mimic actual use.
    No. I'm too busy doing things correctly.
     
    UC, Oct 31, 2007
    #53
  14. UC

    UC Guest

    Richard:

    It is easy to see the differences in shadow and highlight contrast in
    Tri-X vs TMY, when developed for similar overall contrast, in
    negatives taken in the same illumination at the same time of the same
    subject matter . In Tri-X Pan, the shadows have more contrast and the
    highlights have less. If you would take the trouble to do this sort of
    test you will see it quite clearly.
     
    UC, Oct 31, 2007
    #54
  15. UC

    Peter Irwin Guest

    I will try to respond at length later, but there is one
    quick thing I would like to point out.

    s = 1 + 10log10 0.8/Hm

    Is a convoluted way of very very nearly saying:

    s = 10log10 1/Hm.

    For proof of this look at the table from below
    and notice that all you have to do to convert
    DIN speed to the 0.1 density point is to divide
    by minus 10.
    DIN speed
    or ISO Log
    15 -1.5
    18 -1.8
    21 -2.1
    24 -2.4
    27 -2.7
    30 -3.0
    I don't understand how you got that number.
    When I use the OLD ASA formula for a speed
    of 50, I get -2.3. Your number looks closer
    to OLD ASA 100.
    Thanks very much also,

    Peter.
     
    Peter Irwin, Oct 31, 2007
    #55
  16. UC

    Peter Irwin Guest

    It is 2360K (The same colour temperature as the old
    acetylene sensotmetric lamps) screened by a liquid
    Davis-Gibson filter to convert it to 5400K.
    This was the standard adopted at the International
    Congress of Photography in Dresden in 1931.

    For less exacting purposes you can use a 2850K
    sensotometric lamp screened with a Wratten 78AA
    filter.

    This is book-knowledge - I have no personal
    experience with such things.

    Peter.
     
    Peter Irwin, Oct 31, 2007
    #56
  17. 1 lumen (lm) = 1/683 Watt at 555nm = 1 (non-existent) green candle (cd)
    1 lumen / m^2 = 1 lux
    1 lux-second = 1 cd-second/m^2

    Or 1 lux-second is exposing the film to the light of a standard
    candle at a distance of 1 meter for one second.

    Sensitometry is usually performed at a color temperature
    of 5,500K - a blue filter and a dim bulb (2,250K (?))
    is the usual source. The bulb is calibrated to a
    'standard' bulb.

    Lumens/Lux are defined photoptically, using the spectral
    sensitivity of the eye. Strictly speaking using lux for
    film response is horse poop unless you use 555nm light.

    The green light 'luminous efficiency' of 683 lm/watt
    incident radiation is also used for the 5,500K source
    as doing it properly opens a huge can of worms that
    wouldn't really add anything useful.

    There is no legitimate ISO speed for
    film that has a spectral sensitivity that differs
    significantly from that of the human eye.
    ISO/ASA = 0.8 lux-sec / (lux-sec required for 0.1 OD on the film)
    Correct: 100 = 0.8 / lux-sec
    lux-sec = 0.008
    log (lux-sec) = log (0.008) = -2.097
    Here it gets messy ... but it's a good enough number -
    ~3.5 stops more exposure than that required for 0.1 OD.

    Or, ~1/8 second at 1 meter from a candle - no lens
    on the camera - gives an exposure creating a negative
    that should print to 18% grey.
     
    Nicholas O. Lindan, Oct 31, 2007
    #57
  18. Oh, I munged that up.

    1 lm = 1 candle-steradian where a steradian is the solid
    angle that illuminates 1 m^2 at 1 m (or 1 ft^2 at 1 ft).

    1 lux-second = 1 cd-sr-sec/m^2
    = the illumination of 1 candle at a distance of 1 meter
    for one second.

    As if anyone cares.
     
    Nicholas O. Lindan, Oct 31, 2007
    #58
  19. The standard does not specify a color temperature for
    the sensitometer. It refers to ISO standard 7589, which I do
    not have but states that the color used for the sensitometer
    exposure may be ISO sensitometeric daylight, studio
    tungsten, or photflood and that the type of illuminant be
    specified with the speed.
    Per Nicholas Lindan's comment about the illuminant
    please note that the standard we are refering to, ISO
    6:1993:E is for black and white pictorial negative still
    film. Films which have sensitization that is not similar to
    the human eye, for instance IR film or X-ray film, are
    covered by other standards. Even B&W negative motion picture
    film is covered by a different standard.
    For peter, the 0.8 factor is NOT the same as 1, it is 20%
    different which is quite different. The density value I
    stated is the value from the charts in the standard for the
    log exposure at the speed point multiplied by the reciprocal
    of 0.8, that is 1.25 and should be the log exposure at the
    point on the toe approximating the Jones minimum gradient
    point. The 0.8 factor is in the standard and it used to
    calculate the speed.
     
    Richard Knoppow, Oct 31, 2007
    #59
  20. Well, I have used both films but haven't actually
    exposed a roll of each to the same targets in the same
    camera. I also have some favorite test subjects including a
    row of houses across the street. I probably have a hundred
    pictures of these from my front yard. I will have to get a
    fresh roll of the two films and try this. My usual developer
    is D-76 diluted 1:1. This is included in the charts for both
    films and should work well with them. I don't know when I
    will be able to get to this, I guess I will just have to
    make the time. The problem is that unless one is shooting
    sheet film one is required to sacrifice most of two rolls of
    fairly expensive film in order to shoot the subject at
    nearly the same time in the same camera. I guess I could
    bracket and use up more film plus compare the tone rendition
    for several exposures.
     
    Richard Knoppow, Oct 31, 2007
    #60
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