b+f of TMAX 400 and my so-called 'densimoter'

Discussion in 'Darkroom Developing and Printing' started by Phil Glaser, Apr 1, 2004.

  1. Phil Glaser

    Phil Glaser Guest

    In a previous thread
    (http://groups.google.com/groups?hl=...03171641.474a2dd3%40posting.google.com&rnum=1)
    we discussed the possibility of using the Ilford EM10 exposure monitor
    with a step-wedge as a densitomter. At $23 at B&H, this unit seemed
    like a worthwhile investment and I've gone ahead and tried using it.

    In general this methodology seems to be registering meaningful
    results, and when I have more leisure I shall elaborate. For now, I am
    stuck on base-plus-fog.

    With my enlarger at 16.5 inches and aperture at F16, I used the EM10
    to take the following readings from my step-wedge. Step 1 (.05) reads
    43 and Step 2 (.20) reads 53. For interpolation purposes, this gives
    us .015 desnsity units per EM10 calibration unit within this step (you
    have to use a different interpolation scale for different steps due to
    the non-linearty of the EM10's gain control). Now I left a frame on my
    test role unexposed for measuring base-plus-fog. The unexposed frame
    made the EM10 go green at calibration number 51. Doing the math, and
    adding the result to .05, gives a density of .17. I'm sure that the
    EM10 is not _that_ accurate, but even making an impressionistic
    guestimate, you can see that the unexposed frame comes out a lot
    closer to the .20 step than to the .05 step.

    The film in question is TMAX 400 developed in HC-110 dilution "H"
    (1/63). One roll was developed for 10 minutes, another for 12 minutes,
    both giving equivalent base-plus-fog readings (as I suppose you would
    expect.)

    Does a desnity of .17 for TMAX 4000 sound plausible? I've always heard
    that b+f should be around .10. On the other hand, I've also read that
    fog is affected by different developers. Is it possible that this
    development regime could result in b+f of .17? If it seems that .17
    (or thereabouts) is just utterly impossible, I would be inclined to
    discard the approach of interpolating the EM10's readings.

    Thanks.

    --Phil
     
    Phil Glaser, Apr 1, 2004
    #1
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  2. Phil Glaser

    Jorge Omar Guest

    Phil

    From my EM-10 reference curve (not measured, found on the NET), the
    region from 40 to 50 in the dial is acceptably linear, so maybe there's
    some other reason - stray light?

    Jorge

    (Phil Glaser) wrote in
     
    Jorge Omar, Apr 1, 2004
    #2
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  3. Phil Glaser

    Dan Quinn Guest

    RE: (Phil Glaser) wrote
    I'm pleased the method is working for you. I would'nt want to give
    anybody a bum steer.
    That sounds very good. The lowest I've read on my well calibrated
    Tobias TB+ with Pan F is .11 .
    Readings in the upper teens and lower 20s are quite in line. Upper
    20s readings are commen. Although I've read of fb+f in the 40s I think
    that is generally considered quite high and associated with pushed
    high speed film. Dan
     
    Dan Quinn, Apr 1, 2004
    #3
  4. Phil Glaser

    Phil Glaser Guest

    Hi Jorge,

    You know what, I neglected to search the archives before posting my
    question (mea culpa!!!) and discovered some earlier postings that are
    relevant to this question, and discovered that I left out the very
    important point that I currently working in 35mm!!!

    http://groups.google.com/groups?hl=...$
    http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&selm=99qj38$tgq$03$-online.com
    http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&selm=35trj6$

    While I suspect there would be disagreement about various numbers, all
    seem to agree that the "anti-halation" layer of 35mm makes its b+f
    greater than what you find in 120 and in sheet films. One of the posts
    suggests that it can be as high as .29!!!

    The observation that Tri-x has a denser base than TMAX is borne out by
    some additional tests I did on film that I had developed a while back
    in a different darkroom, using different tanks, different developer,
    different everything. The b+f fog of Tri-x was indeed .29 and that for
    TMAX-400 was .21.

    I dont' know how to account for the difference in density of the TMAX
    b+f then (.21) versus now (.17) except to say that it was a different
    developer (Tmax developer) and fixer (don't remember) combination.
    I'm also wondering if fixing can affect b+f. Since I'm a little
    trouble with color distinctions, I'm leary of depending on my own
    judgement about the pinkness of TMAX as a measure of its having
    completely cleared, so I fix for 7 minutes (in Kodafix), two minutes
    longer than the manufacturer's recommendation. Perhaps that might
    account for the difference?

    Any additional comments would be welcome.

    Thanks!!!
     
    Phil Glaser, Apr 2, 2004
    #4
  5. Phil Glaser

    Jorge Omar Guest

    Hi, Phil

    Developers may change base fog due to chemical fog. I've never used TMAX
    dev, so I cannot comment in it, but Diafine WILL give more base fog
    (compared to others).
    Fixing/washing may give slightly different densities also, depending on the
    removal or not of the anti-halation layer ('pinkish look').

    So, from the links you posted and the above, I would not worry unless
    someone post some disagreement data.

    Jorge



    (Phil Glaser) wrote in
     
    Jorge Omar, Apr 2, 2004
    #5
  6. For 35mm with its grey base, my understanding is that FB+F is about
    0.40. For 120 film, which has non-tinted base, it is quite a lot less.
    There must be some figures somewhere on the web.

    I quote below some lines from an article by Geoffrey Crawley in which
    he compares the new Delta 400 to the older 400 Delta, and also to
    HP5+, and their suitability for pushing. This indicates FB+F figures
    around 0.40.

    <begin quote>
    ...... The new film has a noticeably lower base/fog level than its
    ancestor. Processed to 400, 800, and 1600 gave Dmins of 0.38, 0.4 and
    0.42, compared to 0.45, 0.48, and 0.54. HP5 gave 0.4, 0.42, and 0.44 –
    again proving the quality of the popular traditional material.
    <end quote>
     
    John Stockdale, Apr 2, 2004
    #6
  7. Soak a piece of film leader in Clorox or equivalent chlorine bleach to
    remove the emulsion. Measure the density of this piece to find the
    minimum you could possibly get with that film. I think 400TMax, 400TX,
    and HP5+ are all different, HP5+ having the most dense base.

    Next, measure an undeveloped, fixed piece of film to find the component
    of B+F due to gelatin without silver. A higher density than base +
    gelatin is to be expected after development of an unexposed piece due to
    chemical fog. It is the chemical fog that can cause increased grain.
     
    Patrick Gainer, Apr 2, 2004
    #7
  8. Phil Glaser

    Frank Pittel Guest

    : Hi, Phil

    : Developers may change base fog due to chemical fog. I've never used TMAX
    : dev, so I cannot comment in it, but Diafine WILL give more base fog
    : (compared to others).
    : Fixing/washing may give slightly different densities also, depending on the
    : removal or not of the anti-halation layer ('pinkish look').

    : So, from the links you posted and the above, I would not worry unless
    : someone post some disagreement data.

    I always thought that the reason for the higher base density of 35mm compared
    to sheet film and 120/220 was the addition of something to prevent "light piping"
    into the canister through the exposed leader. The theory being that if the
    base was clear the light would be transmitted through the base not unlike light
    through a strand of fiber and fog the emulsion. This cannot be removed during
    processing.

    There is also as you and others have mentioned the issue of chemical fog and
    incomplete removal of the pink anti halation coating.




    : (Phil Glaser) wrote in
    :
    : >
    : > I dont' know how to account for the difference in density of the TMAX
    : > b+f then (.21) versus now (.17) except to say that it was a different
    : > developer (Tmax developer) and fixer (don't remember) combination.
    : > I'm also wondering if fixing can affect b+f. Since I'm a little
    : > trouble with color distinctions, I'm leary of depending on my own
    : > judgement about the pinkness of TMAX as a measure of its having
    : > completely cleared, so I fix for 7 minutes (in Kodafix), two minutes
    : > longer than the manufacturer's recommendation. Perhaps that might
    : > account for the difference?
    : >
    : > Any additional comments would be welcome.
    : >
    : > Thanks!!!
    : >


    --




    Keep working millions on welfare depend on you
     
    Frank Pittel, Apr 2, 2004
    #8
  9. Phil Glaser

    Phil Glaser Guest

    In general this methodology seems to be registering meaningful
    Yeah, I'm quite happy with this approach. There were two things that I
    came across that helped with the consistency of ther results. My first
    few trials were done with a home-made cardboard "negative" carrier for
    the test tablet so that I would not have extraneous light -- i.e., it
    was cut to size for the step tablet. The mistake here was that the
    position of the strip was inconsistent, so that at times it was being
    projected from the edge of the enlarger's light beam. This resulted in
    fall-off, so that readings were noticably different from one area of
    the same step to another. I therefore created another mask that fits
    into my normal negative carrier and readings are now consistent across
    the frame.

    The second bit was to understand that its best to get the range of
    readings up into the 40s and 50s because, as Jorge points out, that's
    where the readings are more linear. So for the Zone VIII reading I
    lower the enlarger to 6 inches and stop up to 5.6. For the Zone I
    reading I raise the enlarger to 16.5 and down to F16.

    I still find that from one session to another there are variations and
    I need to recalibrate each time. I suspect that this is due to the
    battery in the EM10 draining or perhaps to power-fluctuations in the
    enlarger. When I get around to some kind of votage regulation for the
    enlarger I'll see how that changes things. I might also try one of
    those power supplies that has a 9v connector for replacing a battery.

    In any case, this system works quite well enough for me at this stage
    of my learning process. I am grateful for the suggestion, and for all
    the additional information in this thread about b+f.

    Many thanks!

    --Phil
     
    Phil Glaser, Apr 4, 2004
    #9
  10. Phil Glaser

    Dan Quinn Guest

    RE: (Phil Glaser) wrote
    IIRC, your reason for using the "sub.-dens." EM10 is to evaluate
    film/developer combinations. You might consider Zone III - VII. Those
    are the five Zones which show in a print. Also you will be able to
    see the density vs exposure curve.
    When I do that I need not reset my lens f stop when exposing the
    film. Resetting the stop introduces a variable which I feel is best
    handled with resets of the ETRSi electronic shutter. I have done ten
    exposures for nine zones doubleing up at Zone five with no f stop
    variation. I don't think that can be said of all lenses. I avoid
    exposures greater than 1/4 or less than 1/125.
    There may be some play involved when changeing stops. Other than the
    old fashioned way of slipping in stops the only way we've been left
    with is turning the ring. Dan
     
    Dan Quinn, Apr 4, 2004
    #10
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