B&W contrast filters and zone-system

Discussion in 'Exposure Discussion' started by henpe, Aug 1, 2018.

  1. henpe

    henpe Subscriber

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    I would like learn how you efficiently combine the use of b&w contrast filters with a zone-system way of thinking!

    I believe I understand the basic stuff about contrast filters, i.e. that yellow filters in general have filter factors of approx K=2 and hence calls for exposure compensations of +1 stop for *average* scenes, red filters calls for 2-3 stops in general etc.

    But, how to efficiently understand and apply the effect of contrast filters in zone-system work where you often use spot metering to read the EV of small regions that, more often than not, are homogeneous in color? Can I use the filter factor approach and expect that the factor only applies to areas in the scene that are in the complementary color of the filter? Should I meter the scene through the filter? One often reads that the latter approach is not recommended due to the spectral response of the meter not matching that of the film.

    An example: I recently shot a landscape scene in which there was a gray stone wall, some grass, some foliage and a blue sky. The deep shadows in the stone wall read 10EV using my hand held spot meter and I decided to place those shadows into zone III. The grass and the foliage read about 9.5EV and hence fell into zone V.5, which is fine I believe. The blue sky read about 14 EV, a would fall into zone X, which is a bit too high up in the tone scale I would say.

    In the example above, one could either compensate for the high subject brightness range (SBR) by applying N- development, use a contrast filter to darken the sky (e.g yellow, orange, or red), or both techniques in combination. In my case, I did not want to apply N-2 development to bring the sky into zone VIII, since I thought that would compress the tone scale of the foliage etc. I decided to use a yellow filter (K=2) to darken the sky somewhat. Due to the filter, and since the stone wall was grayish (neutral in color), I decided to apply a +1 stop exposure compensation to avoid the stone wall to drop into zone II (right or wrong?). However, I have no solid experience in how effective the filter is on darkening the blue sky, and hence do not know what to expect in terms of where the sky will fall on the tone scale, will I still need to apply N-2 or maybe N-1 development? How would you approach the problem? Suggestions are most welcome!
     
    Last edited: Aug 1, 2018
  2. howardpan

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    I typically use a gradual density filter to reduce the brightness of the sky.

    Otherwise, I would burn the sky a little more when I print in the darkroom. Film can capture a very wide subject brightness range and a little dodge and burn can help to bring the print to a new level beyond a straight print.

    I have only used color filters to change the relative brightness of one color versus another in order to highlight the subject (eg a red or pink flower from its green leaves). I have not used it for the sole purpose of adjusting subject brightness range.

    Your method is quite interesting albeit less straightforward and perhaps have unintended consequences.
     
  3. OP
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    henpe

    henpe Subscriber

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    Thanks for you input howardpan!

    Your suggestions are fine and I sometimes use these techniques myself.

    I forgot to mention that in this particular example, the sky is in the background and behind the foliage of some threes; a graduated filter will also darken the trees and even though burning in the darkroom is possible, it may be tricky due to the lack of a "clean" horizon.

    I realize the complexity of my "problem", just curious to know if there are solid approaches to tackle this complexity.

    Regards
     
  4. Pentode

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    The rationale behind your exposure decisions in that instance seems about right to me.

    I’ll admit I don’t adhere very strictly to zone system practices and that, when shooting B&W, I almost always use a yellow filter but your reasoning made perfect sense to me and I would expect your outcome to be what you imagined.
    Sorry.... I meant to say “visualized” :wink:
     
  5. jeffreyg

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    You may be able to find graduated color filters but if not you can make your own. Some time ago I did just that. I made graduated yellow and orange orange filters using Rit dye and clear (UV) Lee filters. It takes a bit of time but its not difficult. Warm a pot of dye on the stove and dipping up and down you can create the desires result with whatever amount you want to remain clear. I already had the filter holder but if the camera is on a tripod you can hand-hold the filter in front of the lens.

    http://www.jeffreyglasser.com/
     
  6. Alan9940

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    Sorry, I'm confused... Placing a deep shadow area in Zone III (at EV 10) and having a sky that reads EV 14 would place that sky into Zone VII, not Zone X. I don't see the problem.
     
  7. Sirius Glass

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    Depending on the camera I either meter through the filter or take a meter reading, adjust for the Zone, and the adjust for the filter.
     
  8. Doremus Scudder

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    Henpe,
    Your EV numbers seem to be off. If EV 9.5 falls in Zone V.5, then the initial Zone III placement has to be EV 7, not EV 10. I imagine that is the case and you simply mistyped...

    At any rate, what you are trying to do with applying the Zone System to using filters is not as simple as it might seem at first. The main reason is that using filters, either by applying filter factors or reading through the filter with your spotmeter is simply not as accurate as we would like. Factors are averages and the optimum factor actually varies for each scene, dependent upon color temperature of the lighting and the distribution of colors in the scene. There's a fair amount of guesswork and reliance on experience whenever a color-contrast filter gets used.

    In your example, there's really no way to know exactly how much the yellow filter will darken the blue sky (and the shadows lit by it). The closest you'll get here is metering through the filter, but, as you pointed out, the difference in spectral response between filter and film introduces error into the reading. Using a factor gets you even less quantification; you just hope that the sky will be darkened the right amount.

    Given all the imprecision in using filters, many just meter, apply the factor and hope for the best. Having a lot of experience using particular filters in particular situations helps a lot here. E.g., one gets a feeling for how saturated the blue sky is in the high country vs. the seashore and compensates (or even on a particular day, "wow, the sky's really blue today! better give extra exposure for those skylit shadows if I don't want 'em to go black.")

    Bracketing is a good way to deal with the uncertainty of using filters in many cases. Sometimes I'll shoot two shots with the same filter and different exposures, or I'll shoot the same shot with different filtration, etc.

    FWIW, here's my approach: Despite the inherent discrepancies between the response of meter and film, I meter through my filters. AFAIC, it's the only way to halfway get an idea of how the values of adjacent colors might appear in the final print. A green copper roof against a blue sky might read exactly the same when spot-metered without a filter. Just tossing on a filter and applying the factor gives you very little idea of how much these two things may be separated (if at all). So I'll read through several filters till I get a difference in the readings that at least gives me a chance of getting what I want.

    That said, I've done tests with my films and the filters I use to arrive at some "fudge factors" to tweak exposure for readings taken directly through the filters. Stronger filters (e.g., red, dark green) seem to need adjustments while the weaker filters (yellow, light green) don't need much, if any. For example, with 320Tri-X I'll add 2/3-1 stop when reading through the #25 red filter. Note that this depends on the particular film/meter combination used, so you'd have to do your own tests.

    Still, none of this is perfect and things often don't work as intended. I think we simply have to accept the absence of precision that happens when we decide to use filters and use our experience and whatever techniques we've developed to do the best we can.

    Hope this helps,

    Doremus
     
  9. OP
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    henpe

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    Sorry, I did misstype. The shadows were 7EV.
     
  10. Alan9940

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    Ah, that makes more sense. Going back to your original post, I don't think filtration would help anything, in this case, unless you wanted the tonality of the sky darker. Don't forget, using, say, a Yellow filter to darken the sky could also darken the shadows due to blue light therein. If I were shooting the scene as you described, I'd bump the shadows up the scale as far as possible, then do an N-2 development.

    Also, metering through a filter is generally not a good idea, unless you have a modified meter that accounts for the spectral response characteristics of the metering cell.
     
  11. btaylor

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    Complex questions, EV numbers all over the place, right, wrong, etc.

    Test. That's how you're going to find out how these combos work in the field.
     
  12. pentaxuser

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    It is time I tested what a 25 red does to the exposure through my camera's meter. I have always accepted whatever the camera's meter give through the 25. Can I ask by how much more in factor terms your 25 red plus your personal compensation adds to this alleged 3 stops often quoted in articles, forum post etc . Does the red add much more than the conventional 3 stops that is associated with a 25 red?

    Thanks

    pentaxuser
     
  13. Maris

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    Use film to determine filter factors. Shooting a series of stepped exposures of a neutral subject through the filter in question will reveal the negative you prefer and your careful notes will reveal the exposure compensation, alias filter factor, required.

    Then also take a meter reading through the filter of the test subject. The difference between the filter factor suggested by the meter and the real filter factor discovered by the film is the meter's "fudge factor". For example my Sekonic L-758D meter suggests 2 stops for a #25 red filter but typical panchromatic film requires 3 stops. Hence the red filter fudge factor for this meter is "add one stop".

    This "fudge factor" is very accurate (to a fraction of a stop) and zone system decisions can be reliably made BUT the factor is exactly true for only that filter, that film, that meter, and that light quality. If you calibrate in daylight and then switch to fluorescent or led lighting the numbers may be off. More....testing.
     
  14. DREW WILEY

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    Is this your mom's fudge recipe, or your Grandma's? It can make a big difference. But even otherwise similar pan films can
    differ. For example I recently tested TMax100 against Delta 100. Both are relatively high-contrast med speed T-grain films.
    And both need 3EV compensation for a 25 Red. But when in comes to a medium green Hoya filter, Delta needs 2-1/2 EV compensation, while TMX need only 2 stops. So their spectral sensitivity is different, and different enough to get you in
    trouble with deep shade if your filter factor is insufficient, esp since Delta can't resolve shadow detail as far down the curve
    as TMX. I could cite other problems. Substitute a 29 red and a another film, ACROS, which can't even see that far into the red, so at a certain point, you can't even compensate for it with any factor. There is simply no substitute for specific testing.
     
    Last edited: Aug 1, 2018
  15. Sirius Glass

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    If you are in Washington state, Colorado or California, can pot be added to the fudge? Or heck, if you gottem, smokem.
     
  16. DREW WILEY

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    ... get Sirius ... or are you speaking from "experience"?
     
  17. Sirius Glass

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    When I first moved to California I was at a party and this woman was sad because no one was eating her brownies. She warned me that they were Alice B Toklas cookies, but I did not know what that was and did not want to admit it. Between the two of us we ate a double brownie batch with four lids of pot in it. I later floated home and my roommates had to keep reaching up in the air to grab my wrist and pull me back down to the sidewalk. True Story.
     
  18. DREW WILEY

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    Now we gotta worry about more and more people "floating" down the highway, as if cell phones didn't make their driving distracted enough already! Glad I don't have to commute rush hour anymore.
     
  19. OP
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    henpe

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    Getting back to the subject .... :wink:

    .... Thank you all for your inputs! As 'btaylor' points out I asked a complex question indeed; I appreciate this community respond to such posts also. The comprehensive responses from Doremus, Alan and others confirms what I expected - there is no simple method to approach this matter and you kind of have to accept that you cannot be in complete control perusing the perfect negative.

    Testing is fine, but in my book you first need a solid idea / principle to either reject or confirm by the testing. My original post was an attempt to learn from your experiences and narrow down to something that can be tested and evaluated by myself. I have received some valuable feedback I think that I will use in future; I will start taking meter reading both with and without the filter in front of the reader and make careful notes and comparisons. I hope I will get some experience from that!

    Regards
    Henrik (alias henpe)
     
    Last edited: Aug 2, 2018
  20. cowanw

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    The solid idea or principle is that a yellow filter will allow yellow to pass as normally metered and non yellow or specifically blue to not pass. How much yellow is in the various colours of the scene and how good the filter is at not allowing non yellow to pass, are the variables. The reason yellow is lightened is that one exposes more on purpose or one prints lighter on purpose. If your stone wall is Caen stone it will react as if yellowish. if it is composed of blue stone then darker. The fact that a red filter makes the sky even darker than a yellow 12 filter demonstrates the mutability of reality. Generally speaking only you are seeing what you want to photograph and only you can hypothesize how that scene will respond.
     
  21. Doremus Scudder

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    Maris did a superb job of answering your question. I can only emphasize that you really need to use your meter and film choice to make the test since meters vary in their spectral sensitivity. The "fudge factors" I generate for my 320TXP and my aging Pentax spot meter aren't even good for my newer spot meter and the same film.

    To complicate matters further, strong filters like #25 red and #58 green will change the contrast on some films. For example, with 320TXP and a #25 filter I usually give +2/3 stop extra exposure from what the meter reads and then reduce development (N-1). For TMY on the other hand, I should increase development a bit (but usually don't; just print at a higher contrast).

    As for the real answer to your question: I don't know how much my metered and "fudge-factored" exposure differs from just applying a filter factor anymore. I haven't compared the two in years. I just meter through the filters now. It could be that the adjusted exposure is exactly the same as using the filter factor. The advantage I have with metering through the filters is that I can compare small areas of a scene with filtration applied to see if the filtration is doing what I want it to do.

    Best,

    Doremus
     
  22. For example, here's a screenshot of the page in my Pentax Digital Spotmeter manual that addresses its spectral sensitivities):

    2018-08-02 (1).png
     
    Last edited: Aug 2, 2018
  23. OP
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    henpe

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    Hmm...The table addresses the reflectivity of different colors, which is something different from the spectral sensitivity of the meter. I think you should interpret the table like if you shine white light on a perfect mirror, 100% is reflected. White light on a glossy white surface will reflect almost 100%. A standard reference gray card will reflect 18% (if i recall), which is within the range of the "standard index", equally so for a green surface. Other colors reflect less or more compared to a reference gray card. The 18% reference reflectivity is a standard that enable one to approximate the incident light level from a reflective measurement. Someone correct me if I am wrong!
     
  24. I stand corrected, henpe ...my bad!. Your understanding is the proper one.
     
  25. To add a little more info to this, you can see in this screenshot that the “standard index” number is close to 3. So if metering a yellow subject and wishing to place it on Zone V, the Pentax recommendation would be to use Index Number 8 to arrive at the desired camera settings. Per the screenshot, the example shows the Standard Index adjacent to EV10 and Index Number 8 adjacent to EV12, so changing to Index Number 8 amounts to two stops less exposure. Similarly, an orange subject, using 6-7 index, might need 1-1/3 stops less, and so on. To summarize:

    Yellow > Index # 8 > 2 stops less

    Orange > Index # 6-7 > 1-1/3 stop less

    Red & Blue > Index # 5 > 1 stop less

    Indigo & Purple > Index # 2-3 > 2/3 stop more

    But the bottom line, of course, is to test the film with specific filters.

    Pentax Spotmeter Dials.png
     
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