N+1,N-1,...

Discussion in 'B&W: Film, Paper, Chemistry' started by henk@apug, Jun 14, 2012.

  1. henk@apug

    henk@apug Member

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    Say you determined EI and N development, is there a rule of thumb
    that says for example 10% extra dev gives N+1,...

    Thanks
     
  2. polyglot

    polyglot Member

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    Depends on the film and developer combination, but it's typically on the order of 15-25% difference in development time for each +1 or -1. Tabular (TMAX, Delta, Acros) films typically are more sensitive to development changes, so they're closer to 10% in the required change.
     
  3. David Allen

    David Allen Member

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    To identify N+1 and N-1 development you need to do your own tests because it is dependent on film, developer, agitation, personal EI, metering technique, what you identify as a Zone III and Zone VIII, etc.

    However, as a starting point for testing the rule of thumb is minus 20% for N-1 and plus 20% for N+1. This will get you 'in the ball park' BUT will not be the final adjustment that you will need.

    A simple way of testing without using a densitometer is to:

    1. Photograph a scene with a full range of tones multiple times on one or more rolls of film so that you can cut the film(s) into at least 6 sections.
    2. Process one section for your N development time
    3. Process one section for N time minus 20%
    4. Process one section for N time plus 20%
    5. Print the piece of film that had N development time to achieve a print that you are happy with.
    6. Print the N-1 negative using one grade harder than the grade you used for the N developed film and try and match as near as possible to the print that you made using your N developed film
    7. Print the N+1 negative using one grade softer than the grade you used for the N developed film and try and match as near as possible to the print that you made using your N developed film
    8. If you normally selenium tone your prints, then tone all of the test prints, wash and then leave to dry before assessing the results
    9. If the prints are pretty much similar (with probably subtle variations in the mid-tones) then your N, N+1 & N-1 development times are basically correct
    10. If your N-1 test prints have blown out highlights then you need to reduce the time more (use one of the remaining test films and process for 25% less than your N development time).
    11. If your N-1 test prints have grey highlights then you need to increase the time more (use one of the remaining test films and process for 15% less than your N development time).
    12. If your N+1 test prints have blown out highlights then you need to reduce the time (use one of the remaining test films and process for 15% more than your N development time).
    13. If your N+1 test prints have grey highlights then you need to increase the time more (use one of the remaining test films and process for 25% more than your N development time).
    14. Repeat your print test and then, if necessary, make further minor adjustments from there.

    Please note, this is more long-winded to write than to actually do!

    Best of luck,

    David
    www.dsallen.de
     
  4. Steve Smith

    Steve Smith Member

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    Another vote for about 20% per stop here.


    Steve.
     
  5. henk@apug

    henk@apug Member

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    Thanks for the good info !
     
  6. smieglitz

    smieglitz Member

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    The shadow areas gain or lose a little density as you develop differently from N. So, if you have found a film to have an EI of 200 when developed normally (N), if you go N+1 development you probably want to slightly underexpose by 1/3-stop. IOW use an EI of 250 when pushing/expanding 200 speed film. If you are to do N- development, go 1/3-stop the other way to compensate for the reduced development. So, then you would use EI 160 to achieve a 1/3-stop overexposure. For two stop development changes, use EI adjustments of 2/3 stop to compensate. For the above example N+2 would be exposed at EI 320 and N-2 would be exposed at EI 125.

    If you are doing roll film testing and don't have a transmission densitometer, you might want to invest a few dollars (~$16) in a Stouffer 31-step density tablet #T3110. It has 31 different densities in .10 increments out to a maximum of about 3.05 density. Since .30 equals a 1-stop change in density, each .10 step will equal 1/3-stop change. You can use this information to figure out the correct speed point for your film (usually .15 above fbf for roll film and .10 for sheets) by laying the wedge on the clear film adjacent to your test frames on a lightbox. (Leaving a blank frame between speed point test frames facilitates this visual comparison.) The wedge has an initial density step of about .05 so the second step should be about .15 with each adjacent step .10 more (i.e., .25, .35, .45, ... 3.05).

    The stepwedge can also be used to get a handle on the exposure range of your printing paper. For example, you may find your printing paper produces the 18% Zone V tone at a density of .70 when contact-printed. YMMV. Another paper, development, or enlarger combo might print this tone at .60 or .80 density. But, the contact print of the stepwedge will show you the total range of densities your paper is capable of printing given a certain treatment. You will be able to discern where the steps block up when printed giving max white of the paper base (Zone IX, X, or XI depending on who you read).

    The important thing to realize is that the step wedge shows you what the abstract mathematical densities visually translate to on the actual materials you use. Not only can you find speed points for film, but also maximum black Zone 0, Zone I, Zone V, and maximum white exposures for your printing materials. Want to nail down N+1 development? Compare the effect of development change on the printed steps from the N and N+1 tests. The Zone VII exposure frame given N+1 development should equal the tone of the Zone VIII exposure frame with N development. I would estimate that target density (~1.20 above fbf net density) would occur on the 13th step (~1.25 gross density of the wedge). (The respective test frames should both read about 1.20 above fbf if you used a transmission densitometer.) Hope that makes sense. It's actually very easy to use the stepwedge. You don't need a transmission densitometer. You can simply see the effects using a stepwedge.

    I've always thought it odd that most Zone System instructions don't start out by recommending using a density stepwedge test to find the exposure range and target densities of the printing materials. How else would you know that a Zone V exposure should have a density of .70 above fbf on your film if you don't know what .70 prints like on the paper? IMO, a paper test should be done before any film testing is begun.
     
  7. henk@apug

    henk@apug Member

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    I have read about a such a density
    tablet in the book 'Advanced B & W Photography' from Kodak, but I did not think they
    would still be available !

    I am going to try to define my EI and
    dev times by "eyeballing" testprints and
    see where I get.

    If results should not be consistent,
    then I'll try a more 'technical approach'

    I am afraid that it will be hard for me
    to judged a density tablet, but this is only a thought since I never used (seen)
    one.

    Thanks again for another good procedure !
     
  8. smieglitz

    smieglitz Member

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    A stepwedge is not hard to use at all. It is basically a transparent gray scale. If you look at the density of your test frame (assuming you have photographed a single toned surface as your test target) with the stepwedge on a blank portion of the film adjacent to it on a light table, you can easily match the two densities. One of the steps will look identical (or very close) to the appearance of your test frame and that will tell you the density you have achieved on the target frame.

    Henry Horenstein describes a similar procedure in his book on introductory B&W photography using gelatin neutral density filters instead of a stepwedge, but it is the same idea.

    John Schaeffer in his Ansel Adams Guide (book 2 ???) also uses a stepwedge to zone test sheet film with one in-camera exposure instead of shooting each zone on a separate sheet. His technique is pretty cool and is quick and easy, and it saves an awful lot of time and film to get to the data needed. I would recommend both of those books to someone starting out with Zone System testing.

    A third book to check out would be White, Zakia & Lorenz' The New Zone System Manual. Harder to read due to Minor White's semi-mystical contribution but certainly a different way to think about what is going on with the Zone System.

    You can probably find all aforementioned three books at a local library.

    If you want further detail. read on.


    Your comment about "eyeballing" vs. a more "technical approach" is understandable, especially if you've only read Ansel Adams or Phil Davis, etc., on the subject of the Zone System. If you are reading a bloated text confounded with page after page of technical info, numbers, and charts, the technique may seem daunting at first. The stepwedge simplifies everything because you don't need to refer to all those abstract things. You can simply compare results visually:

    [​IMG]

    Let's say your fbf density of the film is .07 and the first step on the wedge is .05 density (which is the fbf of the stepwedge). Since the first film frame matches the density of the overlain stepwedge's step 1, it has a gross density of .12 (=.07 for the film fbf and .05 for the stepwedge fbf). However, you are not really interested in the gross density but rather the net density caused by the exposure and processing. The net density of that exposure on the film is .05 over fbf since it visually matches the overlain stepwedge step #1. That is not enough exposure for the speed point and is an underexposure for Zone I.

    The second and fifth frames above are blank to facilitate comparing frames to the stepwedge.

    The third frame matches at step 2 of the stepwedge. The net density there is .15 (= .05 step 1 fbf for the stepwedge + .10 step incremental increase). There's the speed point frame and the proper exposure density for Zone I.

    The fourth frame has a net density of .25 [= .05 fbf for the stepwedge + 2(.10) for two additional steps @ .10 each)]. That's too high for the speed point and is an overexposure for Zone I.

    One final note: a transmission density stepwedge is invaluable when determining exposure times for any alternative process like Platinum/Palladium, Van Dyke Brown, Albumen, Salted Paper, Cyanotype, etc. It will pay for itself the first time you use it.


    [​IMG]
    Here it is showing the different tonal response in a comparison of emulsion ratio between part A and B in cyanotype chemistry and 2 different papers, ecruwhite and bright white Crane's Kid Finish. Note that the contrast changes as well as the overall tonal range given identical exposure and processing to each test strip. Interesting that the use of 2% citric acid solution instead of water as a rinse deepens the maximum tone but also causes bleeding in the highlights. It tells me I want to avoid the use of that chemical with these papers and emulsions.


    [​IMG] [​IMG]
    Here I've isolated the same middle gray tone against the various test strips and duplicated the matching area to show differences between treatments. Matches are made at steps 9, 6, and about 10.5 in the different treatments. (Probably easier to see in the desaturated copy.) This tells me that I need more or less print exposure to get a middle gray tone depending on the emulsion composition, processing and paper. (Note I've used a 21-step tablet here instead of a 31-step tablet. Each step on this tablet increases .15 or 1/2-stop with the first step about .05.) I'd need a density of about 1.25 (step 9) to reproduce the midgray tone on the first strip, only .80 (step 6) in the weaker second strip condition, and about 1.50 (between steps 10 & 11) for the last strip condition.

    You would see similar effects using different silver gelatine papers or contrast filters, paper developer formulas or dilutions, toners, etc. Once you test, you can determine exactly how you should print a negative based on its negative density range (DR). For example, you might find a certain DR matches the 3# multicontrast printing filter while a different DR fits a #2 filter. The step wedges are very useful things.

    Well, sorry to be so long winded. I hope this clarifies rather than confuses things.
     
    Last edited by a moderator: Jun 15, 2012
  9. henk@apug

    henk@apug Member

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    My old graflex 135mm f4.7 optar is sharp but soft. So before starting my
    tests I was wondering if it should not
    be better to test directly for grade 3
    instead of grade 2 ?

    Any thoughts on that regarding soft lenses ?

    Thank you.
     
  10. RalphLambrecht

    RalphLambrecht Subscriber

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    all development times are determined by the film test.
     
  11. henk@apug

    henk@apug Member

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    Oh, I surely did not understand something, I'll give things a re-read :smile:

    What I mean is if I do my filmdev tests of -10%, -20%,... should I evaluate on grade 2 or grade 3 paper