Dealing with luminance ranges

Discussion in 'Exposure Discussion' started by dancqu, Apr 14, 2005.

  1. dancqu

    dancqu Member

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    I can not find the word luminance in my dictionary. Luminescence
    I can find; an emission of light. Do I need a bigger dictionary? Dan
     
  2. Stephen Benskin

    Stephen Benskin Member

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    From The Focal Encyclopedia of Photography:

    Brightness
    The visual experience that is approximately correlated with the luminance of objects seen as light sources. Since brightness is a psychological concept, there are no units of measurement as there are for luminance, a psychophysical concept.
    L. Stroebel and R Zakia

    Luminance
    The quotient of luminous intensity of an extended surface in a specified direction by the projected area in that direction (i.e., candelas per square meter). The luminance of an extended source or surface is invariant with viewing distance. Luminance is also invariant within a lossless optical system because changes in image size are balanced by inverse changes in solid angle. The luminance of a Lambertian (ideal) diffuser is invariant with viewing angle because the reduced power reflected off-axis is balanced by a reduction in projected area.

    Luminance is the property of a source of surface that most closely correlates with the subjective perception of brightness, which, because of adaptation and contrast effects of the visual system, cannot be used as a reliable measure.
    Syn: photometric brightness (obsolete)
    J. Pelz
     
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  3. jimgalli

    jimgalli Subscriber

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    Luminance is that quality of a finished print that makes it seem to light up the room it's in. Yes, good topic and a lifetime to learn. I was thinking along these lines today. I bought a set of filters that are no longer made. Colored polarizers (g-y-r-bl) and I was looking at each one trying to decide what the different effects would be on B&W film. It's something that's not as easy for me as some other aspects are.
     
  4. noseoil

    noseoil Member

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    Reading last night in Adams book 5 on artificial light and his take on luminance was refreshing. He compared brightness and luminance in very simple terms.

    His explanation of brightness deals with the inherent property of reflected light from an object, without necessarily dealing with the amount of light directed at it. A side in shadow reflects x amount of light and a side in full light reflects y amount of light, simple zone system parlance and metering.

    His take on luminance deals not with the reflected light from surfaces, but with the light falling upon it. He then explains how light intensity can be manipulated (additive or subtractive) to allow for creative interpretation of a given subject in a finished print. It really is a shame he died so soon, as his understanding of light and the ability to explain it was wonderful.

    I would have liked to have seen him in a discussion of techniques with Phil Davis. We owe both of them a huge debt.
     
  5. Stephen Benskin

    Stephen Benskin Member

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    Thanks Jay for starting this thread. I believe this is an important topic. We all have a tool box of techniques that we carry with us when shooting, so why only use the same one or two tools? It is just part of visualization after all. The problem is to find a good example to start.

    For very short luminance ranges.

    I have this image of a detail of a gravestone. It was late in the day. The weather was dark, windy, and with light rain. It was a typical day in Ireland. The stone had almost no separation. The light was so soft, there was virtually no "shadows" cast.

    I wanted the final image to be very dark where it looked almost totally black until you walk up to it. I decided to place the exposure of the stone just under the midpoint, or about Zone IV. Even though I wanted the image dark, I didn't think it would work without a lot of local tonal separation. Extended processing has more of an affect on the upper part of the curve than the lower, so in order to maximized the amount of tonal separation with processing, I placed the exposure higher on the curve than I needed knowing I could print it down. I gave the film +2 development knowing it wouldn't be sufficient, but also knowing I could print it on a grade four paper and use a number of additional techniques if needed.

    It did print on a grade 4, and I did just a touch of bleaching to emphasis a few places. Why not just push the film 4 stops? Three reasons: One, extended processing of film increases the higher densities to a greater proportion than the mid tones and shadows, whereas increasing the paper grade expands the mid tones to a greater extent. Two, the undesirable factors that come with pushing film such as grain. Three, it's also extremely difficult to visualize how all the elements will look at such an extreme contrast increase. Not over processing gives you more options.

    One of the problems of extremely expanding short luminance ranges it that areas that you don't want to expand, also expand. Sometimes this creates looks of small annoying white spots, and sometimes it makes the overall image look harsh.

    Some times it's easy enough to spot out the annoying stuff. I have an image of a burnt wall which I handled in a similar manor as the gravestone. It takes two hours to spot out the new created highlight speculars that now look like dust.

    One way to fix that problem and when the image looks overly harsh is to deal more with only the tones you want to change. A good example is rock art. Petroglyphs are drawings created by etching through the desert patina to expose the lighter rock underneath. The contrast range is very limited, but often the sun is hitting the rock creating a normal luminance range or at least expanding the luminance range some. The question is how much can you push the film before the image just looks too contrasty and unrealistic? Using the above technique might work in certain conditions, and look harsh in others. A good way to approach such a scene is to give it normal or +1 processing, and then print it so that the rocks look natural. At this point, the petroglyphs will still look flat.

    Off the top of my head, two techniques can help here. One is to use a contrast mask while printing the image. The mask will add density only to the areas you want. This will lighten up the drawings without adding contrast to the rocks. Another way is to bleach. Take a paint brush and paint over the drawings using potassium ferricyanide until they reach the point you want.

    The concept that I like with this thread is that this is where theory (such as tone reproduction theory) meets creativity. It is the very essence of photography. Nice idea Jay.

    Here's an interesting question. Except for special cirumstances, all scenes look best in a print when there is a full range of tones. Why can't we let a flat scene remain flat in the print (apart from artistic considerations)? It's flat in nature, why not the print? Maybe a question for another thread.
     
  6. Claire Senft

    Claire Senft Member

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    One further thought. Mr. Robert Pace, a very experienced printer has these thoughts about making a more interesting print.

    Use color transparency film.

    Contrast mask the film with one color light

    Make your negative with the mask in place using a second color of light.

    His contention is that this method allows for far greater manipulation of tone reproduction than just the use of a B&W film in conjunction with a filter.

    These thoughts are stated in his self-published book "Masking" which is the best reference that I know about on the subject of masking.

    I apologize for being somewhat off topic but it seemed to fit the discussion at hand.
     
  7. Stephen Benskin

    Stephen Benskin Member

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    You're not at all off topic. Do you have information where the book can be purchased? My concern about Pace's method is that you lose a generation with the negative. Sounds like a good read though.

    Thanks
     
  8. NikoSperi

    NikoSperi Member

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    That's a great description of Applied Adams, Stephen. After that, I've become very curious to see what the result looked like! Any chance of posting it?
     
  9. Stephen Benskin

    Stephen Benskin Member

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    It is exactly applied Adams, as Adams was applied tone reproduction, as tone reproduction is, well, tone reproduction. My thoughts are this is the culmination of all the technical knowledge we struggle to learn.

    The image might not translate well here because it isn't about a full range of tones. One point I forgot to mention in the previous post is that the original, very flat, subject was primarily light gray.
     
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  10. NikoSperi

    NikoSperi Member

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    Cool, thanks for that. As they say about the thousand words and an image... I'm just starting to explore the extent of "interpretation" one can give to an exposure and development. The Adams book The Print has a fern on the cover. I have tried to replicate that fern with the same film under the same conditions. You really need to stretch the envelope to take a one-stop scene and turn it into a multi-toned print. Good job and thanks for sharing the how-to and the result.
     
  11. Stephen Benskin

    Stephen Benskin Member

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    Another example is one that I frequently use. If the scene is about a step under normal, I usually will process it normal and print it on a grade three. One of the rules I keep in my head is that processing extends the highlights and printing brings out the mid tones. Most of the time, I'm more interested in having good local separation of the mid tones than a negative that will print on a grade two paper. Both pushing the film +1 and processing it normal and printing it on a higher grade paper will produce the full tonal range, but they produce very different local contrast. This can be graphically depicted in the upper right quadrant of the tone reproduction diagram.

    Along the same lines as the above technique is taking a scene with a normal luminance range and expanding the mid tones with an unsharp mask. I have a good example of this. It was late in the day just after a storm. The sun was moving in and out of the clouds and was coming from a slightly back lite condition. The scene was an iron age broch on the Isle of Lewis, Scotland. The luminance range of the main subject was normal with the assumption that the upper clouds would have to be burned in (I usually don't factor the sky into the exposure calculation). The broch is made of stones of very similar values. Processed normal and printed on a grade two, the "main" subject of the broch would look weak.

    I shot the scene using an orange filter and processed it normal with the intent of using an unsharp mask. The unsharp mask also acts as a contrast mask, so I was able to print the negative on a higher grade and pull out the mid tones. I also did some bleaching in a couple of spots to "pop" them up.
     
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  12. Kirk Keyes

    Kirk Keyes Member

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    And would you add to that "exposure brings out the shadows"?

    Kirk
     
  13. Claire Senft

    Claire Senft Member

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    The shadows in my asked opinion are primarily set by exposure with out much influence from development. The use of the unsharp mask can have a very visible impact on the shadows...depending on mask exposure and mask development.
    If the exposure/development for the unsharp mask is such that it does not allow for any density of the high lights then the mask will have its effect primarily in the shadows and midtones.
     
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  15. sanking

    sanking Member

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    Should we let a flat scene remain flat in the print? Purely a question of photographic aesthetics that has many answers. Just look at Peter Henry Emerson's platinum prints of the Norfolk Broads for an idea of a photographic aesthetic that is very different from that of today. Emerson, who based much of his theory on the work of Von Helmoltz's Physiological Optics, concluded that it was impossible to reproduce in a photograph the extremes of light and dark found in nature. To compensate for this he recommended a compression of tonal values, which explains why his platinum photographs, and those of several generations of pictorialists, have a very flat look.

    Anyone with a little time on their hands and interested in why we print the way we do might find his Naturalistic Photography for Students of the Arts an interesting read.

    Sandy
     
  16. sanking

    sanking Member

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    To repeat something I wrote in another thread, the issue of SBRs of less than 5 is for all practical purposes a mute question for photographers contact printing with in-camera ULF negatives on AZO #2 and many alternative processes, including albumen, carbon, kallitype, platinum and palladium and Vandyke. These processes have log exposure scales on the order of 1.5 to 2.2 and even normal SBR of 7 require negatives with a CI of .75 and higher.

    In reality very few films available in ULF have enough expansion capability to reach even SBR 5 when the CI even for normal SBR is so high. Ilford FP4+ and Efke PL 100 just make the grade but nothing else comes close.

    What to do if you print with alternative processes with in-cameras ULF negatives? Well, no point to obsess about exposure technique for potential SBR values below 5 since the available films won’t allow it anyway. The only option is to expose the film at the lowest SBR value your film/developer combination is capable of, which you would have determined from previous tests, and then use process controls to give the contrast desired on the print.

    As for the broader issue of Zone System versus BTZS, this is pretty much a non-issue for me. I use them both, depending on conditions. In fact, before I discovered BTZS I had been using Zone System for the better part of two decades. At this point, however, I will say that I prefer BTZS for about 90% of my work. But there are a few conditions where Zone is easier to use. If you have actually used both in the field you will, or should, understand this.

    Sandy
     
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  17. Stephen Benskin

    Stephen Benskin Member

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    King touches on another potentially interesting question that might be a good topic for a whole new thread, and that is about the conditions of the aesthetic criteria of alternative processes. Is there another set of aesthetic criteria inherent in different processes. There are for transparency film depending on the viewing conditions, i.e. viewing a projection or viewing the image on a lightbox. And transparencies have a very different set of criteria than print, so it should be fair to say that different processes within "black and white" will have different aesthetic criteria associated with it too.

    Keeping on topic, take Michael Kenna's work. He currently likes to make dark somber prints that aren't too contrasty and with a nice brownish tone. It's beautiful work no doubt about it. But would the prints be as acceptable if the tone was neutral? I believe he is able to print darker because color adds an additional element to the print, one that adds an additional dimension of mood, while a neutral print only has tones to work with. The additional "mood" makes up for lost shadow detail. In a way, his black and white images can be thought of a color images and there is a definitely a different set of criteria with color than black and white. My point is the use of color or alternative processes can also be a way of dealing with the presentation of luminance ranges.
     
  18. Claire Senft

    Claire Senft Member

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    I do get a bit confused with the way that you use the SBR terminology Sandy. Coirrect my thinking: SBR is BTZS Incident system terminology. An SBR of 5 is a flatly lit plane without any lighting variation. I get that impression that when you say SBR 5 that you are referring to 5 stops of difference in lighting ratios between lit and shadowed areas instead of no difference. I am no stickler for terminology but if each of us means something different when using the same term the communications of concepts and ideas can get quite muddled.

    I also believe that SBR is a term that applies only to a scene.
     
  19. Stephen Benskin

    Stephen Benskin Member

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    Jay, I'm not going to touch BTZS use of terminology, but Subject Luminance Range does only refer to the scene. The luminance from the scene is then illuminant upon the film after it enters the camera. At which point it is referred to as the exposure E, the amount of light falling on the film in one second, or the photographic exposure H with represents the exact amount of light striking the film in a given exposure. Remember the old I x t = E? It's now E x t = H. Exposure times time equals photographic exposure. This equation is good for either sensitometric exposure or camera exposure. Of course, finding E is a whole other story.

    My concern about Davis' use of the different terms is that while it works within the limited number of people using BTZS, it creates confusion when attempting to communicate the ideas to the outside community. My personal opinion why Davis uses such outdated terms such as SBR and ES is because they were used in the seminal papers Davis must have read when learning theory. He used them in the first edition and then was stuck, so in the later editions he was forced to use a disclaimer. Personally, I think he should have corrected the terminology before it became too engrained. Note: The BTZS part is just conjecture and opinion, so please do not consider it a call to arms.
     
  20. Stephen Benskin

    Stephen Benskin Member

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    Of course subject luminance range can be measured with a spotmeter. In fact, you can only assume the range with an incident meter. There's an interesting paper by Jack Dunn entitled Expose for the Middle where he talks about how an incident meter is perfect for the criteria of the transparency.

    When you are talking about the curve you are talking about the range of exposure (H) usually referred to as log-H range or sometimes LHR. LSLR basically becomes the log-H range in the camera. Your right in thinking that the two are associated with each other.
     
  21. Claire Senft

    Claire Senft Member

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    Jay i would interpet it this way. The stepwedge useage tells you what your materials are capable of with different exposure and development for both film and paper. When dealing with the stepwedges you are not at that time dealing with either zones or SBR. That basic data is used in either application to zone system work or incident system work. The SBR is only referenced to the incident system and does not deal whatsoever with the zone system. Go to your BTZS manual and see if you can find with the zone system the usage of the term SBR. Go to the incident system and I am certain that you will find it being used with regularity.

    Of course Claire may have egg colored face if you find such a case.
     
  22. Claire Senft

    Claire Senft Member

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    I believe that a spot meter could be used to determine an SBR if one was trying to make it function as an incident meter by reading of, for instance a gray card in the shadow and in the lit area of the scene and determining the difference in f stops between the two. It would, in my opinion, be sort of cludgy because one would have to be very careful in reading the card...the angle between the meter and the card etc and one would also be introducing some fare in the reading by using the spotmeter. I believe the single largest problem in the incident approach is the freedom from flare in using the meter while there is bound to be some in reality. I believe the spotmeter suffers from having flare that is very likely to be different the the camera/lens combination, not to mention color sensitivity different from the film, and the need to bias your reading through experience that you have gained, when reading dark areas at various distances.
     
  23. sanking

    sanking Member

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    Jay,

    HP5+ has had a reputation for low contrast among platinum and palladium printers for many years. People often compared results with TRI-X and found that by comparison HP5+ gave much less contrast. This is in part due to the fact that when these films are developed to the contrast necessary for pt./pd. the curve of HP5+ tends to shoulder slightly while that of TRI-X rises.

    About 2.5 years ago there was a change in HP5+ that made it much more suitable for alternative printers. Ilford made no mention of the change but several experienced pt./pd. printers soon noticed and commented on it, and I confirmed it for myself in both film tests and field work. Simply put, the new Ilford HP5+ is capable of a much higher CI than the old one.

    You are correct in the assumption about the effect of stain. An HP5+ negative developed in a staining developer has a much higher effective printing contrast for UV sensitive processes than for blue and blue/green sensitive processes.

    BTW, you should understand a couple of things about my plotting procedure. It is based on the assumption that the process has a log exposure scale of 1.75, which is about right for AZO #2 and for processes such as carbon, kallitype and palladium, and I always incorporate a small factor for flare into the data. If you use my assumptions for ES and flare in your plotting I think you will find the same thing I have found, i.e. there is no film/developer combination available for ULF workers that will give the CI that is needed for a SBR value of very much below 5. Dick Arentz gives data in his new book for film/ developer combinations useful for SBR values down to 4.2, but his assumption is for a process ES with a maximum of log 1.6.

    In any event the TRI-X versus HP5+ comparison is pretty much a moot issue at this point because the former is only available by special order and Ilford just announced that it would no longer supply HP5+ in ULF size.


    Sandy
     
  24. wm blunt

    wm blunt Member

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    Claire,
    I use both incident and spot meter with the Zone Dial by Davis. One side is for incident readings and the other for zone system. After taking a reading with either you just turn the thing over and it tells the SBR and that is how I determine dev. I seem to have better luck with the incident side but at times the spot meter come in handy.
    Wm Blunt
     
  25. Jorge

    Jorge Inactive

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    SBRs from a curve can be obtained by a geometry formula. G=ES/SBR which is nothing more than the Tangent. This is in the book, at least in the 2nd edition.

    Spot meter readings can be converted to SBRs by the following formula:

    SBR=(7*(D-N))/D

    where:
    D= spread
    N= N number (development)

    This I got from Phil when I first started using the BTZS.
     
  26. Ole

    Ole Moderator Staff Member Moderator

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