Film Testing (WBM) Curves 320TXP in XTol 1:1 Too Contrasty—How Did I Mess Up?

Discussion in 'B&W: Film, Paper, Chemistry' started by Rafal Lukawiecki, Aug 24, 2012.

  1. Rafal Lukawiecki

    Rafal Lukawiecki Subscriber

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    I have just completed my first, Way Beyond Monochrome 2, film test, this morning. Since I have not used 320TXP (4x5) for a while (normally HP5+) I decided to test it, in my usual developer, XTol 1:1 20˚C. I use CombiPlan, with fairly intensive agitation: constant during first 30s (~15 full inversions), then 5 rapid full inversions taking a total of 6 seconds, every 30s, with a triple-rap-tap to dislodge bubbles. Incidentally, my sheets stay put, they never slip out with 320TXP, HP5+, or FP4 (I would get a rare slip with TMax 100). I did 5 sheets at a time.

    Looking at the resulting curves (see the attached Excel spreadsheet), it seems I am getting too much contrast right from the beginning, even with short development times, eg. average gradient 0.59 at 4 min, and 0.92 at 16 min! It seems I cannot get N, not to mention N-1 this way... Clearly, I have done something wrong while testing.

    I have a few suspects for the cause, and I wonder if those of you who have done this before, or who have other film testing experience, would be kind to suggest a clue and a fix, as I will re-run the test again in a while:
    1. I think I have underexposed the whole thing by 1.5+ stops. WBM suggests metering at box speed, so I used ISO 320. After calculating the bellows factor (1.5 stops in this case), I was running against long exposure reciprocity (Irish summertime), and I went ahead with an uncorrected 1 s exposure at f/9, while I should have used a longer time. Further, my Nikkor runs 1 s as ~0.9 s. Can I blame my underexposing?
    2. As I asked on another thread I was not sure how to photograph my Stouffer 31-step 4x5 transmission tablet. It was recommended to me that I should stick it to a window, as the test needed daylight (I photograph landscapes). That is what I did, but using 300mm Nikkor, with even a 52cm extension, all I managed to get is about a 70% reproduction, so the tablet on my negs is smaller than the real thing. I wonder if its overall density could get "squished" because of the smaller reproduction. Does the test require repro at 100% scale? If so, I am not sure how to do that with my field camera (Ebony SV45Te).
    3. Through the window, I could clearly see distant objects (10-50m away). I placed a sheet of milky perspex about 8m away, angled towards the cloudy sky, outside in the garden, so I had a more even illumination behind the tablet. Even with the background well out of focus, I suspect there was a different illumination between the upper (1-16) and lower (16-32) tablet bars, as the tops of the bars 1-16 have less density than the bottoms of those bars on my 25 developed sheets (bars 16-31 are quite even). I collected the data consistently in the same spot, as close to the centre as possible, using a Heiland TRD-2. If this is the reason, then the through-the-window technique not going to work for me.
    4. I worked fast, but this is Ireland, and the weather, cloudy with our normal drizzle, could have been slightly changing the lighting. I tried to compensate by shooting 5 sheets for each development time, and I have averaged readings within each development time series of 5 sheets, but I could not compensate for a gradual change in lighting across all the series. With hindsight, I should have grouped the sheets differently.
    5. This box, like most of my film, has been through at least 2 airport hand-luggage x-rays, mandatory in Ireland and UK (no hand inspection allowed), but I doubt this would have other than the same overall effect.
    6. I am agitating too much for those development times.
    I am off to photograph in Wyoming for two weeks, tomorrow. I will use my 320TXP, and I plan to use the rule-of-thumb-rating of EI 200 for N, 250 for N+1 and 160 for N-1—suggestions? When I am back, I will run another test, hopefully helping me figure out the best dev times.

    Please help me make the best choice, and thank you, for sharing your experience, for which I am always grateful.

    Rafal
     

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  2. ic-racer

    ic-racer Member

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    I don't use your same testing method, so I cannot comment on your times. I get good prints with my equipment using a gradient around 0.75 and printing on multigrade paper.

    I can say that if exposure is having an effect on the gradient there is a major problem in your method; like the values of your stepwedge are not evenly spaced or not evenly illuminated.

    If you are not interested in calibrating your system for 'speed' then a contact print of the step wedge may be less problematic for you.
     
  3. Bill Burk

    Bill Burk Subscriber

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    Holy cow! Last time I got gradients like that the answer was obvious... I'd reached for the Dektol instead of the D-76
     
  4. pentaxuser

    pentaxuser Subscriber

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    I know nothing of the WBM method so can't comment over points 1-5 but it seems to me that there may be substance in your concern over point 6. I have always understood that about 8-10 inversion in the first 30 secs( I prefer 8 inversions) were about right and about 2-3 inversions( I prefer 2 only) in 5 secs every thirty secs

    5 inversions in 6 secs is better than a cocktail waiter can do :D

    I'd certainly slow down and reduce both sets of inversions. I have no idea by how much the contrast will be reduced but it should help. I'd imagine that at 6 in 5 secs every thirty secs the Xtol must get quite bubbly. Mine did even at 3 inversions over 5 sec so I took it more gently.

    pentaxuser
     
  5. Rafal Lukawiecki

    Rafal Lukawiecki Subscriber

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    Bill, you seem to have taken a liking to film testing curves, judging by your earlier comments on CPorter's, and others' threads. I'd love to hear any suggestions you may have...

    Thanks. I get very even development, and no bubble-related issues, but I suppose this has to influence the gradient. I just wonder if that is the key reason for my numbers.
     
  6. Rafal Lukawiecki

    Rafal Lukawiecki Subscriber

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    I measured the original step-wedge—those numbers are also in the spreadsheet—and it seems quite even. I don't know if the 70% reproduction scale has any effect, though I would not think so.

    How would I contact print a transmission step-wedge to a negative using natural light, with accurate timing? And also, how important is it that I do this test using natural light? Ralph, in his book, seems to suggest that it is important.
     
  7. pentaxuser

    pentaxuser Subscriber

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    No I didn't get any bubble related issues either it was just the fact that there were bubbles at the top of the Jobo tank when I removed the red cap to chek after each 30 secs that suggested to me that even 3 inversions was over vigorous if it made it froth as much as it did.

    pentaxuser
     
  8. ic-racer

    ic-racer Member

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    This is how I do it, I put an 80A in there for daylight correction:
    [​IMG]
    [​IMG]
    Other knowledgeable people (like PE) use an enlarger to make the contact exposure of the stepwedge on the film.

    Unless you are testing for film speed, you don't need a precise exposure. You just need to get enough bands exposed to make a reasonable graph.
     
  9. Bill Burk

    Bill Burk Subscriber

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    Hi Rafal,

    I just saw the part where you are taking off tomorrow... I think your rule of thumb for EI will work fine.

    You can finish film testing when you get back. The meter readings and interpretation that leads you to Zone System processing notations (e.g., N-1, N and N+1) will not change if you change developer or times in developer later.

    The only time this strategy (test later) failed me was when I rated some expired TRI-X at EI 320 when it later developed and proved to only be capable of approximately EI 64. So I had insufficient camera exposure to overcome fog. You will not have that problem.
     
  10. Bill Burk

    Bill Burk Subscriber

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    Hi Rafal,

    I drew the graphs on paper and estimated the Contrast Index for each curve. Yes you could expose more next time (one stop), but that doesn't affect the information in the curves. CI by graph is somewhat subjective (the way I do it anyway) so a careful analysis could prove my numbers here are off by 0.10 on the steepest curve.

    4 minutes = 0.4 CI, 5.5 minutes = 0.55 CI, 8 minutes = 0.65 CI, 11 minutes = 0.75 CI, 16 minutes = 0.87 CI

    You have good tests here. You just have to decide what CI is considered Normal and work from there. I use 0.62 (but with a non-flare contacted test).

    p.s. I work for Kodak but the opinions and positions I take are my own and not necessarily those of EKC.
     
    Last edited by a moderator: Aug 25, 2012
  11. Rafal Lukawiecki

    Rafal Lukawiecki Subscriber

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    Hi Bill,

    Many thanks for manually slaving over my numbers with graph paper in hand. I owe you, let me know if you ever come to Ireland.

    I wonder if you used 0.1 as the speedpoint, or WBM recommended 0.17 in arriving at the CIs. I am trying to understand the difference in the calculations, I suppose I should check with Ralph, too.

    When I plugged your, much nicer I must admit, numbers back to the same WBM spreadsheet, I figured that my N is 6 min, N+1 8.5, N-1 5. Also, if I use the shortcut of EI 200 for N, I get an easy to remember sequence of EI 150 for N-1, 200 N, 300 N+1. However, I am not sure if I can use the spreadsheet for calculating those times if I use your kindly provided CIs, perhaps I need to arrive at them differently.

    I am also not sure what CI to consider normal, as this is the first time I applied a densitometer to the job. I was planning to follow WBM 0.57 or nearby, or to do a paper test.

    Thanks ic-racer for the contact exposure suggestions.

    Many thanks for helping me. I've just arrived in Denver, setting off to WY in two days, armed with a new table of EIs. Feels like fun.
     
  12. Bill Burk

    Bill Burk Subscriber

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    Hi Rafal,

    Thanks, it's nothing...

    Here is the graph.

    [​IMG]

    Shows how difficult curve fitting can be, where the goal is to find one number to represent the curve.

    The "c" marks I drew on the curves are the points I used to give Contrast Index (CI) estimates.

    Small diamonds are the 0.10 "speed" point (small diamonds to the right and above are the corresponding ASA triangle aim points). The larger double diamonds (kind of looks like a dream catcher) emphasize that you exactly hit the ASA triangle at 11 minutes.

    Drawing a straight line, ASA triangle is 0.62 CI. But ASA aims for different points on the curve than CI. The 11 minutes curve is 0.75 CI by my estimation. Crazy. Shows how badly a single number fits the curves.

    Also shows how much tolerance there is. A good argument can be made to choose anywhere from 7 to 11 minutes as Normal. I think 6 is a bit short side but have to agree it's close.
     
  13. pgomena

    pgomena Member

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    My reciprocity chart for Tri-X 320 4x5 says that a 1 second exposure should be corrected to 1.5 seconds, a 50% or half-stop difference. If your shutter gives you 0.9 seconds actual exposure at the 1 second setting, you're even more underexposed.

    The underexposure aside, your contrast is greater than you would expect. I'd agree you're agitating too much.

    Film speed is highly dependent on a number of variables. Meter, metering, exposure, flare, scene contrast, developer, agitation, temperature, color temperature of the light, etc. Starting to test at box speed is reasonable, but don't expect your results to match. My personal exposure for 320 Tri-X is 160. Yours likely will be different, but it will be yours, and once you've pinned down the variables and start to get consistent results, you'll be on your way. Film testing is just that - testing. One test does not indicate a trend. It gives you a starting point from which to compare more data.

    Peter Gomena
     
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  15. Bill Burk

    Bill Burk Subscriber

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    Peter Gomena,

    You have a valid point about the time.

    But because the image is a step wedge, in terms of "underexposure", it doesn't matter because you can see the curves rise up out of the toe and and reach practical exposure levels.

    Rafal,

    You have basically created a reciprocity failure study at 0.9 or 1 seconds. You should shorten the time a bit, unless you decide that the reciprocity failure at this time is reasonably close to what you normally shoot.
     
  16. Stephen Benskin

    Stephen Benskin Member

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    Let’s be careful not to confuse exposure with film speed. Metering or the scene luminance range has nothing to do with the speed of film, although the meter can play an important part with certain methodologies toward determining “film speed.”

    This brings me to another thought about film speed and that concerns expressing a film speed result without referencing the testing methodology used. We all know that different approaches yield different results. This is the strongest argument for standardization. When the ISO prefix is placed in front of a film speed, it is stating the procedures of the standard have been adhered to.

    Comparing the WBM method and the ISO method clearly illustrates my point. Without getting into the merits of either method, there is around a 0.15 to 0.23 log-H difference between the two speed points. The same test wedge with the same data will yield speeds differing between ½ to 2/3 stops. So, if communicating speeds results is to have any validity, I thing the testing methodology needs to be included.
     
  17. pgomena

    pgomena Member

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    Bill -

    Yes, you are correct about the step wedge readings and exposure, it's kind of a relative thing because you can see the information in the graphed data. Metering and exposure in the field is more critical and demands consistent methods if you're going to get consistent results, and it's a whole lot more challenging out there than it is in the darkroom! Whether a person's exposure index for a film matches box speed, or is half or twice box speed is irrelevant. The amount of light hitting the film needs to be correct and consistent regardless, and consistent testing will support good results.

    Peter Gomena
     
  18. Stephen Benskin

    Stephen Benskin Member

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    Bill, the problem with having the CI 0.75 curve fit the ISO triangle is that it is way too high. Long toed curves do require a slightly higher CI to fit the ISO triangle, but not this much. So, what is happening here? The testing under the ISO standard and the determination of the ISO triangle is done under no flare conditions. Rafal's test consisted of sticking the step tablet up against the window and shooting it with his camera (optical system). He emphasized the need for testing under daylight conditions but missed that such a set-up will produce flare. As we know flare compresses the shadow area. ISO speed is determined using the gradient of the shadow. CI is determined more from a fuller range of the film. In order to raise the gradient of the compressed shadows sufficient enough to fit into the ISO triangle, the CI will be excessive like we see with Rafal's examples.

    What is happening here is that a non-flare interpretation is being used with a test that incorporated flare. Any results are questionable at best.
     
    Last edited by a moderator: Aug 28, 2012
  19. Bill Burk

    Bill Burk Subscriber

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    You are right, Stephen.

    The ASA triangle is undefined in this set and must be discarded. And a good thing too, it feels wrong.

    Just guessing, I think the development time that would fit ASA triangle (suppose Rafal makes a contact step wedge) might be a lot closer to 8 minutes.

    The toes on all these curves show what you would draw as dotted lines (to show flare) on a contacted step wedge test set.

    Since this test includes flare, it's good to visualize placement of scene values and predicting densities on negative. And it is certainly good enough for process control.

    The CI values are not truly what I quoted (they might be "close), and the ASA triangle needs to go.
     
  20. Stephen Benskin

    Stephen Benskin Member

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    And not just the triangle either. All of the various gradient measurements are based on no flare curves - the gradient for contrast index or the base point for average gradient. Then there's the subject of speed determination with a flare curve vs a non flare curve. This is an excellent example of the importance of contacting step tablets.

    I've superimposed a contacted curve of TXT in Xtol 1:1 over the curves you generated. The CI is 0.64 using a modified version of CI.

    ISO Triangle example.jpg
     
    Last edited by a moderator: Aug 29, 2012
  21. Bill Burk

    Bill Burk Subscriber

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    I think we need to "back out" the flare, perhaps with 0.4 assumption...
     
  22. Rafal Lukawiecki

    Rafal Lukawiecki Subscriber

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    Thanks for pointing this out. On this thread I asked about the correct way to photograph the transmission tablet. It was suggested that I should tape it to a window. In post 7 I was concerned about any reflections from the surface of it, when it is taped to a window.

    Are those reflections the main source of the flare that you are referring to, or could they be an additional reason for the steep curves which resulted in my test?
     
  23. Michael R 1974

    Michael R 1974 Subscriber

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    Reflections could definitely distort results but I would expect those errors to be more obvious.

    Flare could be coming from several sources in this test setup. First there's the bright area around the transmission tablet. There are several ways of reducing this effect, such as surrounding the tablet with black paper, or masking the lens or masking the camera or combinations of these.

    Then there's the fact using a backlit transmission tablet (or a front-lit reflection tablet) will put some degree of flare into the test anyway. As long as you are using a wedge/tablet (ie a wide range of adjacent "luminance values" in a single frame), there is no way to eliminate that kind of veiling flare other than contacting the wedge, which is the no-flare method Stephen refers to.

    The problem is to balance the factors and make sure the test is meaningful. For example, in order to generate the "purest" possible (let's call it "native") comparitive curves of different films in some sort of standardized way, contacting is useful because it removes flare from the tests. However, to then evaluate a film in the context of the actual photography you will be doing, it always seems to me contacting is too far removed from actual conditions to give you an accurate picture of what the film is doing - unless you typically photograph under low-flare conditions. Depending on flare, speed can change, as can contrast particularly in the low densities (ie shadow values). Of course speed and toe contrast are interrelated. Flare flattens local contrast in the low densities.

    I keep meaning to post the curve results of a comparison (flare/no flare) test to the other thread I started recently regarding flare, but I just haven't had the chance. Hopefully this weekend.
     
  24. Stephen Benskin

    Stephen Benskin Member

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  25. Michael R 1974

    Michael R 1974 Subscriber

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    Stephen, this is still confusing to me. Are you saying the tests are conducted under no-flare conditions (ie contacting) and that flare impacts are then manually overlayed on top of the raw no-flare curves to give a working curve for the determination of speed, development time etc? If so, how exactly is this done? How, for example, does one add a one stop flare factor to a given zero flare curve?
     
  26. Stephen Benskin

    Stephen Benskin Member

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    Michael, there are two different ways to explain how this is possible with the ISO standard. The standard's contrast parameters (ISO Triangle) is really part of an equation that creates a good correlation between the fixed density method and the fractional gradient method. If a correlation didn't exist, I doubt the fixed density method would have been adopted. What this means is while the speed point is at a density of 0.10 over Fb+f, when the parameters are met, the factional gradient speed point will always fall approximately one stop to the right. As we all know, the fractional gradient point is the minimum point of exposure where a print considered of excellent quality can be produced from the negative.

    This except from Safety Factors in Camera Exposure by C.N. Nelson explains the reasoning.

    "Proposed Change in Speed Criterion

    The reduction in the safety factor could be accomplished simply by changing the constant in the ASA formula for deriving the ASA exposure index from the ASA fractional-gradient speed of the film. The present formula, which gives a safety factor of about 2.4, is

    Exposure Index = Fractional-Gradient Speed / 4Es

    or Exposure Index = 1/ 4Es

    where Es is the exposure in meter-candle-seconds at the fractional-gradient speed point and 1/Es is the ASA fractional-gradient speed. If the constant of ¼ were replaced by a constant of ½, a new type of "exposure index" would be obtained which would provide the proposed lower safety factor of about 1.2.
    There are several reasons, however, for adopting not only a new constant but also a different speed criterion. The fractional-gradient criterion was originally chosen because it has the desirable feature of giving speeds that correlate closely with speeds obtained by practical picture tests. It has the objectionable feature, however, of being somewhat inconvenient and difficult to use. Consequently, a simpler and more convenient criterion, such as that based on a fixed density above fog density, is often desired. Fortunately, as shown by the recent data of Nelson and Simonds, "a good correlation exists between fractional-gradient speed and speeds based on a density of 0.1 above fog, provided the development condition's are controlled so that a fixed "average gradient" is obtained...Thus the adoption of the 0.1 fixed-density speed criterion in combination with a suitable development specification would offer the advantages of convenience and practical significance."

    The other way to explain it is easier to picture. The ratio between the 0.10 fixed speed point and the metered exposure point is 10x or a range of 1.0 log-H. That's 3 1/3 stops. The average shadow falls 4 1/3 stops below the metered exposure point. That's a difference of a stop. The no flare curve uses a point one stop above where the shadows fall as the speed point because in practice flare will bring those shadows up.

    The reason why Zone System tested EIs tend to be 1/2 to 1 stop lower than the ISO speeds comes from a misinterpretation of the above concept. As I've pointed out before, in camera testing of a single toned target will yield almost zero flare. Zone System speed point falls 4 stops down from the meter exposure point or 2/3 stops below the ISO speed point with the 10x ratio. The Zone System testing method assumes a flare test condition for a no flare test condition thus causing the speed discrepancy between ISO film speeds and Zone System EIs.
     
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