Densitometer + Dektol 1:9 + ERA 100 + Step Tablet

Discussion in 'B&W: Film, Paper, Chemistry' started by Pastiche, Mar 14, 2009.

  1. Pastiche

    Pastiche Member

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    What could these things possibly have in common? Me.

    I'm working through my first ... er.. attempt at using my densitometer (xrite 810) to get "perfect" development times.

    Here is where things take a left hand turn:

    I'm using Dektol. 1:9

    I'm also using an unknown film (ERA 100) - which, despite any fears I may have about their QC, I'm quite certain that there is less variation in THEIR process than in my own.. so if there ever were to be something wrong, I'd suspect myself first. (even though I'm a fairly meticulous lab tech)

    So... using a film + developer combo that is essentially "unknown" pushed me to pick up a densitometer.

    NOW. . . I had some issues copying the densitometer in camera (the light behind the tablet, even though being bounced from a diffuse white surface {card}, was not even. So, the steps are meaningless b/c the light seen through them is not constant)

    I've decided to try exposing the film to the Stouffer 21 step tablet in a contact print frame.

    I'll be putting a lens with a copal 1 shutter in the enlarger head, and metering the exposure via .. .

    Yeah.. via....

    That is where my questions are.

    how the hell do I meter this situation?

    Do I spot meter the step 10 (let's say, I put the tablet on a white card, spot meter step 10?)

    Do I take an ambient reading just above the contact frame? (I'd raise the enlarger head all the way up to give me the best chance of getting a reading where the thickness of the meter itself does not significantly change the distance of the film/light source when compared to the point metered/light source)

    Do I put the spot meter lens under step 10 and point it at the lens??

    er..

    yeah. What?

    Thanks for your thoughts on this.
    I'm not afraid of burning up some film - but I AM considering that what I might really need to do is to go back to the studio and set up the step tablet again and shoot it in camera (compensating for bellows extension... yes)
     
  2. dancqu

    dancqu Member

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    For film I use an uniformly lighted large gray board. With
    camera in position I expose a number of frames at one
    stop increments. My Tobias TB+ does the reading.

    For paper, the step tablet as though a negative to be printed,
    is placed in the negative carrier. Dan
     
  3. Pastiche

    Pastiche Member

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    [​IMG]

    OK... so here are my first two curves.

    Film: ERA 100
    ISO used: 50
    Developer: Dektol, 1:9
    Jobo processed, CPP2, 20 degrees Centigrade (68F), 5min.

    One sheet of film was exposed for .3", the other for .1" under a condenser enlarger, in a contact frame.

    To determine exposure I did the following:

    Set the meter to 50ISO, f/1.
    opened up the enlarging lens all the way.
    focused the lens on the neg. carrier (which had no neg in it, used the edges of the carrier for focus)
    adjusted the height of the head until the meter told me to use 1/2" exposure time.
    The meter was held under the contact frame's sheet of glass while metering.
    Ambient metering mode.


    I actually did three sheets, one at .5", one at .3", and one at .1"
    Of the three, I only measured the last two, as they "looked best" . . . and they both had two or more "clear" steps after step 21 on the Stouffer tablet.

    It appears to me, from looking at these curves, that I need to dilute my chem out a little bit more (shouldn't that lower the slope of my curve? i.e. change my contrast index?)

    I'm still fuzzy on how to determine film speed from the curve, particularly as I'm fuzzy on how exactly to meter the *blipping* exposure to begin with.
    AND - I'm not sure that using the enlarger's timer at such short times is effective. In the future I think I'll try to stop down till I get the exposure time close to one second.

    Later on I'll measure and generate a curve for the third sheet of film, that one exposed to .5", which I have not included here.

    Ideas? Suggestions? What am I missing here?
     
  4. Pastiche

    Pastiche Member

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    Oh.. I forgot the mention a few things:

    a) my "film base plus fog" seems to be ... .20 NOT .10 as I've seen suggested as the "right" measure. Might this be because of the characteristics of Dektol? Would diluting the solution help lower FB + F ?

    b) the max values on my step wedges were : 1.94 for the one exposed to .3", and 1.75 for the one exposed to .1" ..... the FB+F numbers for both sheets were .01 apart, which I assume to mean they are virtually identical.

    Again, the meter told me to use .5" exposure, but that sheet looked WAY dense to my eye.... I'll grab the numbers from it latter on.

    Questions -

    The total range of densities seems to a) start high and b) end even higher.
    I've read that the "goal" is to push the tones around till they are separated by 1.30 units.
    I'm thinking that what I need to monkey with is the dilution & times... not the ISO.
    Does it seem like that to you as well?
     
  5. ic-racer

    ic-racer Member

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    Nice curves. It is perhaps futile to determine EI from H&D curves unless you have a calibrated sensitometer. The best exposure for the step wedge, in that case, is one that produces an acceptable range of values to plot. (Best way to get EI is just expose a frame to a uniform source at zone I and see that it is 0.1 log d).

    The gold standard for both exposure and development is a good looking print. So, I work back from that. I determine a development time that produces a good print by trial and error. Then I determine the contrast index of that setup (by making the curves, as you are doing). I use this contrast index as a starting point for my next 'unknown' film developer combination.

    So, again, you have what looks like appropriately constructed curves, but they don't mean anything until they are matched with good prints.
     
  6. Pastiche

    Pastiche Member

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    Thanks IC, for the input.

    Yeah.. part of my plotting these curves is that I want to know in which direction to take my process.... I'm using two unknowns, a paper developer as film developer, and a film that has virtually no process info available for it (besides some VERY broad guidelines).

    My prints have been a bit too contrasty, and much to my surprise, sort of lacking in the deepest shadow details (like... a black belt as it rounds off to the shadow side of the figure, even while shot outdoors in open shade) .. . .

    Plus, every time I make changes to my process I feel like I'm sort of driving around in the dark not knowing what to expect (or to what degree to expect it).

    And.. finally, I guess I'm one of those nerds who just needs to KNOW . .. does that make sense? I'm not a cabinet maker, but if I were to build cabinets, I'd want to really UNDERSTAND the construction process. I expect that in the long run I'll be able to pick up strange films & developers and get to the kinds of results I'm hoping for via a minimum of trial and error. Also - I'm hoping that once I know how to do these tests efficiently, I'll be able to minimize lost materials and time when "trying to find" a sweet spot in the film/developer/paper/developer processes.

    Idunno... maybe I'm just a control freak. :smile:
    I do follow you though - the finished product IS the gold standard.
    If I'm at point A with my process, and wish to get to point B (let's say, changing the contrast index, or reaching a particular contrast index), I'd like to learn how to do it in as few steps as possible (vs. trial & error).

    I've found a .pdf by Kodak that is over the top on sensitometry (at least for me, at this time).
    Here's the link to the publication titled Basic Photographic Sensitometry Workbook

    I've also found a page that describes development testing in this way, and includes a link to a spread sheet app. that takes in your density readings and spits out the curves I've been posting here. Also giving projected times for development at N +/- 1,2 & 3 Here

    Here is a screen grab of the curves I got from developing last night.
    [​IMG][/IMG]

    I'm STILL a little lost on why my lowest readings are so high. .20 as the lowest density? I guess I'm not sure if I'm getting light going through even the darkest step on the Stouffer tablet, or if this is just an artifact of my developer's properties.... Next time I develop I'll include an unexposed sheet straight from the box and see what that gives me.

    In that Kodak pdf on sensitometry is states how to determine if the film has been "properly developed" . . .
    Now, caution about "technically correct" vs. artistically apropos aside, I'd like to know that I'm "technically" getting it right before I start wandering off into the wilderness of expressiveness. I'm not short on the latter, but I do need a known starting point from which to depart.
     
  7. Pastiche

    Pastiche Member

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    IC - I forgot to say: my densitometer is calibrated (from a step wedge, notated by Xrite)
     
  8. nworth

    nworth Subscriber

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    The film base + fog density can be anything. The confusion here is that the speed point for film is measured at a density of 0.1 above the film base + fog level. High fog is usually an indication that something is wrong, however. Sometimes it shows up with old film, and sometimes it indicates a mismatch between the film and developer. Sometimes it is OK.
     
  9. Pastiche

    Pastiche Member

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    Thanks nworth.

    I'll keep that in mind as I go on down the road of testing this combo that I have on hand. :smile:
     
  10. Stephen Benskin

    Stephen Benskin Member

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    It looks to me like the gradient is around 1.00. You might want to adjust the processing some before settling on an exposure time.
     
  11. nworth

    nworth Subscriber

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    It looks like you are getting a gamma of about 0.67 with this development (time, temperature, and developer). That is reasonable (maybe a bit higher than some would like), and the fog level does not sound unreasonable, so you seem to have a good starting point for developing the film. Now you want to determine the speed. You can do that from the curves with an incident light meter reading, but it gets pretty fussy. You also run into inaccuracies due to the warm up and cool down time of the enlarger bulb and possibly from the reciprocity characteristics of the film. It is better to take pictures with a camera. The lazy way would be simply to take some bracketed exposures of a high contrast scene and determine which exposure gave you the best (zone placements reasonably correct) result. Another way is to take bracketed pictures of a paper gray scale (the Macbeth color chart has one, and so do many of the Kodak Photoguides).
     
  12. Pastiche

    Pastiche Member

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    Stephen,

    My uneducated guess is that I want to lower the values of my VI & up....
    I'm (again, uneducated guess) thinking that I need to dilute my developer out a BIT more.. not half again..I'm at 1+9 now.. I'm thinking of going to 1+12...
    Then fussing with the development times to get the proper separation in tones.

    Does that jive with your statement re: gradients? (this is sort of the same trouble I'm having with the Kodak sensitometry workbook... it tells me what I SHOULD have, but does not tell me which variables have the most direct effect on the outcomes I wish to alter)...

    A gradient of 1.00 what gradient might be considered "normal". . . ?
     
  13. Pastiche

    Pastiche Member

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    Nworth

    right... so the gamma would "normally" be closer to the low 60's, mid 50's... to reproduce an average scene with out introducing a whole lot of snark... yes?

    And determining the speed.. yeah, I'll start out by shooting some sheets bracketed around zone 1, and see that I'm getting something that my densitometer says is .1 or so higher than film base plus fog. The plus side of this is that I will just meter the gray card, stop down 4 stops, bracket, which means I'll be working from the shutter I really want to be clicked into. If I can land my grubby hands on a paper gray scale I'll shoot that! I know someone who's got a MacBeth color chart.
     
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  15. dancqu

    dancqu Member

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    I use a gray Sturdy Board about 22x28 inches then wait for
    about 15 minutes of clear blue sky. Doubling of zone five with
    a change in f stops will keep shutter speeds reasonable
    and serve as a check of f stop accuracy.

    Sometimes I shoot only zones 3 through 7. Below 3 and
    above 7 lies very little print image detail.

    Sturdy Board is a crafts shop item. Dan
     
  16. Pastiche

    Pastiche Member

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    thanks for describing your process Dan.

    Even lighting IS so critical... I think I'd use a north facing wall and stay in the shade. Metering for every exposure & then making the adjustments necessary.

    Today I'm doing some tests on getting my development dilutions straightened out... I want a curve with a little less slope (gradient).

    I'll post some curves this afternoon/evening.
     
  17. dancqu

    dancqu Member

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    I'd think a 5 to 10 minutes shoot would do for all
    zones. Avoid near twilight for the series as the
    level of light drops rapidly. Dan
     
  18. Pastiche

    Pastiche Member

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    Point noted Dan. :wink:

    Here are the curves for my last test of this film/developer

    All curves are:

    ERA 100 shot at 50 ISO
    Developed in Dektol at three different dilutions: 1+9, 1+11, 1+14
    68deg.
    5 min.


    [​IMG]

    According to the Kodak guide to sensitometry, the total span of densities between the lowest and the highest densities "should" be about 1.30
    It looks as though the process that most closely resembles that is this film/ISO combo in Dektol 1+11 (1:12), 5 min. Rotary process, 68 deg. F.

    The question that lingers in my mind is - these curves seem to be telling me that my effective ISO is actually not 50, but something close to ... 12.
    (iso 50 minus two stops... = 12, right...)

    I'm arriving at that conclusion because the toe on the curve seems to hover at .2, and only rises to .1 above that around step #3... or be it, two stops more exposure. Yes??
     
  19. ic-racer

    ic-racer Member

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    I usually just null the densitometer on the base + fog. If you include it in your curve, you have to go and subtract it back for anything you do with your curve. Also, if the density is high what are you going to do about it? Send the film back and say it's old? Who is going to take it back :smile::smile:.
     
    Last edited by a moderator: Mar 18, 2009
  20. Pastiche

    Pastiche Member

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    Err.. I think I've made a mistake..
    The speed point for this process seems to be at about step "II" on the step wedge.. which amounts to one stop more exposure.
    WHEN I get off to trying film speed testing I'll use ISO 25 as my "center point", and bracket around it two stops in either direction.
     
  21. Pastiche

    Pastiche Member

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    Ha.. yeah.
    I realized that I was noting the wrong numbers on the spread sheet that is generating the curves...

    I THINK that I've now gotten fb+f numbers that seem reasonable.
    Now that I've pretty much settled on the 1:12 dilution for dektol I'll run a blank sheet through it to see what I get (I'm just not quite trusting the 21st step on the tablet as being perfectly opaque.

    Next up -
    Run a blank sheet through the process.
    Then think about ISO testing...
    Then, then I'll start wondering about moving the image further into the straight line portion and away from the toe... or I might just give up at that point and keep on keepin on :wink:

    Thanks IC
     
  22. Pastiche

    Pastiche Member

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    The problem I think I'm having is that my info is not in "log E" units... I am working off of the steps on the step wedge.

    I think I could measure the density of the steps on the step wedge, and then run inverse logs on them to yield equivalent units to the Lux I'm looking for???
    But that seems awful ... er.. contrived.

    When I look at my graphs, assume that the steps are one half stop off of each other, consider that one full stop in exposure is equal to .30 change in density.. .. then it seems that my graphs tell me that my development in not "correct" .. . i.e. to get a .8 change in density above D-min I must go up almost five stops on the step wedge. When it should be something closer to two and a half steps.. ??? (but that then would seem to give me ridiculously steep curves, which are too contrasty.. no?) . . .

    ugh... I can imagine why people don't do any of this jazz... it's either ALL nitty gritty, or it all unravels into ever more fine tuned questions.

    :smile:
     
  23. Pastiche

    Pastiche Member

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  24. Anon Ymous

    Anon Ymous Member

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  25. Pastiche

    Pastiche Member

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    I'd be delighted to talk about the reading if you get into it...
    I think the article is rich with things that (for the relative newb like me) merit discussion.
     
  26. Anon Ymous

    Anon Ymous Member

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    Go ahead. Even if I don't understand something, chances are that someone else will have an answer.