A Primer on Incident Metering.

A Primer on Incident Metering.

  1. markbarendt

    markbarendt Subscriber

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    markbarendt submitted a new resource:

    A Primer on Incident Metering. - A Primer on Incident Metering.

    Read more about this resource...
     
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  2. cliveh

    cliveh Subscriber

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    You have outlined the multiplicity and complication of exposure to record a scene in camera. Which is precisely why fine tuning a given exposure against lighting ratio, with negative development and printing with diffuser or condenser in a given printing developer, temperature/concentration is of prime importance? Only consistency of practice can help perfect this.
     
  3. Bill Burk

    Bill Burk Subscriber

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    This is a great article Mark Barendt! Great Job.

    I agree with your statement that ...most of us could do just fine using this metering technique alone for the rest of our lives...

    And recommend using this technique, as a sanity check, when using any other technique.
     
  4. markbarendt

    markbarendt Subscriber

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    Thanks gents.

    I did get a suggestion in a PM that EV could be defined better, that is true. The EV needs to have an E.I. or ISO number tied to it to actually define a value.
     
  5. jp498

    jp498 Member

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    Nice article. I happily incident meter as well and you've mostly covered it.

    With flash, I also use the incident meter to estimate the light in other parts of the scene in addition to the face. Such as the background or hands, to make sure I've got things lit the way my eyes see it. We all too often replace the incident flash meter with a DSLR these days.
     
  6. markbarendt

    markbarendt Subscriber

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    Thanks.

    Oh Yeah, I agree, it is a perfect tool for setting up flash scenes.

    I also really believe that flash and other forms of artificial lighting controls are ignored by way too many people.
     
  7. Mahler_one

    Mahler_one Member

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    Hello Mark.

    Thanks for initiating a discussion of incident metering. Your discussion is interesting, and added some basic information for those not familiar with incident metering. However, forgive me for staing that in my opinion, significant parts of "the story" have been omitted.

    The dial on the incident meter will attempt to make everything middle gray, and hence as you have hinted, a single shadow reading will be rendered as middle gray as will a single highlight reading. To be unaware of the need to double the film speed when metering the shadows ( or raise the film speed as much as you desire to render the shadows other than middle gray ) and to make similar adjustments when metering the highlights, is to invite error.

    Incidentally, where exactly should one place the EI? You have chosen to follow the recommendations of the film manufacturer, but correctly infer that each individual must define one's own EI. Many analog photographers have found that the manufacturer's EI values are not optimal when used with the film developer, printing paper, and print developer that one uses. As you might agree, the optimal EI value to use can be defined by testing of one's materials....or through making a large number of exposures as defined below which is, of course, one way of "testing".

    The need for testing is mentioned, but hardly emphasized. The exposure of a negative is simply one part of the equation, with film developing adding another very key variable that must be controlled. Certainly "develop for the highlights" has become an accepted paradigm for many analog photographers. One can apply a considerable degree of artistic control by metering the highlights so as to raise or lower the subject brightness range ( as you know, the SBR will help define the developing time by allowing one to deduce the correct time to develop one's film ) and in so doing, control the length of development and the density ( highlights of course in the print ) in the negative. However, how much should one develop a scene for so called "normal" development? If one is indeed using fixed graded paper then the need to be precise in both exposure and development is paramount. Yes, one of the more alluring features of VC paper is the ability that one has to "overcome" a wide variety of exposure and development errors. However, as you state, even those who use VC paper ( and VC paper does have some problems, but such is grist for another mill ) should aim to produce negatives of optimal quality.

    So, how does one go about defining one's material? One can attempt to implement the methods of Adams, Minor White, and others in order to define the characteristics of their printing paper and to relate such to the film and developer combination that they use. Such testing methods are most often used by those who use the zone system and reflected metering. One can attempt to learn to develop by inspection as has been done for years, and which method is very well explained by Michael Smith. Incident or reflected metering can be used if one desires to DBI. Incident metering is part and parcel of the Beyond the Zone System approach as formulated and popularized by the late Phil Davis and now carried out through Fred Newman at the View Camera Store. In my opinion, those who are seriously interested in using incident metering would be well advised to read some basic material concerning the BTZS approach. One can of course, go into the field and take lots of negatives in various lighting situations at various EI values, develop for various times, and print the negatives at various filter settings on the enlarger. I would posit that such testing is immensely tedious and can be wasteful of time and materials. Bruce Barnbaum supplies his paradigm for testing in his estimable text...one might go on and on, but the need for testing should not be ignored.

    Yes, by all means consider incident metering....however, such metering needs a framework with which to apply the readings obtained. Without an understanding of exactly how incident metering and EI are related to one's film, film developer, printing paper, and printing developer such metering will be subject to educated guesses.

    Elliot
     
  8. Poisson Du Jour

    Poisson Du Jour Member

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    An interesting article indeed, Mark,addressing one form of metering, but I have a question:

    How and why is incident metering a precedent over more precise methods such as spot metering (including, but not limited to, duplex/averaged spot metering)?


    Yes, it's the cut and thrust of the discussion, but incident should not be seen as the be-all and end-all of precision in metering. Because it is not. Many beginners are likely to be easily befuddled by contrasty scenes incident metered; I was one of them many years ago. For portraiture, incident is quick and fuss free, but in landscape, a much more critical and deliberated approach must be taken.

    Incident metering, like reflective, assumes the scene (and its many luminance values) are average — which in a myriad cases it is not. True, it has a proven role in controlled studio-flash/strobe use where the precision of spot metering would add complexity and deliberation (something studios don't have now with digital, nor need nor can afford).

    This is potentially haphazard with slide film where latitude does not allow grace for error and metering should be more critically employed. In high contrast scenes all critical luminance values from dark to light must be analysed individually because the scene is not average. This is the crux of the limitation. Even Uncle Adams would point this out.

    Visualisation of the tones of the overall scene is essential before relying on what a meter suggests. This is particulary critical using transparency film where detail is required in highlights and shadows, with the requisite midtone providing the balancing point. If you cannot get detail in highlight and shadow areas on transparency film, then you are working outside the parameters of the film, not the meter. Not all films are suitable for all conditions, and transparency film is a solid example.

    I would strongly recommend people actively diversify with metering besides incident.
     
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  9. AndreasT

    AndreasT Member

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    If we do what Mahler_one / Elliot wrote I we would arrive at the same conclusion as Mark Barendt. Go through the hard stuff then it becomes easier.
     
  10. markbarendt

    markbarendt Subscriber

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    Yes Elliot there are significant chunks of info missing, you are starting to help fill the holes by participating, that is exactly what I was hoping for, thanks.

    You are also right in highlighting the need for some testing. Part of the practical info that I'm trying to get across is two fold, 1- we humans are the weak link in the system, problems are typically caused by our mistakes or lack of understanding and 2- the makers of our tools and materials have fully tested them.

    What is untested is "us".

    I disagree about your assertion that E.I. needs to be adjusted on the meter to deal with shadows though. Meters, all types of meters, simply provide reference points. This is what I was getting at with the notion that the meter has no clue about what it's seeing, we have to fill in the blanks and adjust accordingly.
     
  11. markbarendt

    markbarendt Subscriber

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    Garyh I completely agree that reflective metering can be a great tool but not that it can be more accurate, equal sure but not more.

    What I will say is that each method requires a different mindset.

    Reflective spot metering allows us to tie a very specific point in the scene, typically the shadow point for a landscaper, to a very specific point on the the film curve. Measuring that specific point that one wants to tie to the film is mentally a strong connection, it feels emotionally tangible. The reality is though that picking the point in the scene to measure is purely subjective and arbitrary.

    Incident metering requires that we ask ourselves, when we look at a scene, do we want more or less shadow detail than normal?

    Both approaches can get us to the same camera setting.
     
  12. Mahler_one

    Mahler_one Member

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    Good point regarding slide film Gary. I use only black and white film and hence I defer to those like you with the experience to comment on metering when using color film.

    I completely agree that incident metering when taking landscapes can be difficult. Such difficulties arise, IMO, mainly when one tries to interpret the highlights. Small changes in meter placement can affect the SBR range significantly and result in a negative that can be either too low or too high in contrast. However, those who use VC paper have some means to rectify metering errors that are not off the charts. Of course, as we all know, shadow details must be on the negative for such to appear in the print. See below.

    Mark-good comments. IMO, incident reading of shadow values are easily defined by simply placing the meter in the shadows where you want detail to be recorded. Subjects deeper in the shadows will of course show no detail. To obtain more detail further in the shadows? Simply move the meter deeper into the darker areas. The entire incident metering procedure has been well detailed by Phil Davis in his book.

    I also agree that one should feel comfortable using both reflected and incident meter readings. As you both you and Mark infer, there are situation where one method might be "better" than the other.

    Yes Andreas...testing materials is the "hard stuff", but the results make the rest of the process easier. However, testing for BTZS methods is rather easily and inexpensively done. This is not the forum to comment on film testing services. Feel free to PM me if you need more details.
     
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  13. markbarendt

    markbarendt Subscriber

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    Actually Elliot, two things, pegging to and understanding the highlights is quite easy with an incident meter and exposure placement changes do not change the SBR.

    When we use an incident meter pointed directly at the light source, we get a reading that protects the highlights nicely. This is a direct objective measurement of the real luminance involved, it can be expressed as a real number that our industrial photographic process equation understands.

    To put this into to practical terms, think front lit subject matter mid afternoon on a beautiful sunny day, the perfect "Sunny 16" situation. The utility of this measurement is well proven. Given a tested E.I. is being used, there is no question about whether or not the incident meter pointed at the light source in that situation will provide good technical placement, it will be right period. The only wild card here is if the photographer has calibrated him or herself to the system and any artistic bias.

    Life is rarely that simple though. If our subject is in that situation but their face is turned away from the sun say 120 degrees we are faced with a problem. Most of their face is not not lit by the sun directly but some is. Most of the face is now lit by open sky and the reflections off the landscape. In this situation we get a second reading with the meter pointed along that 120 degree line back toward the camera. That reading alone will get us a perfect exposure for the subject as lit by the open sky and reflections.

    At this point we have the info we need to decide on how to deal with both light sources. A simple averaging of these two readings is simple duplexing. It is a compromise. It does its best to protect detail from both lighting situations. It allows a little shadow and a little highlight detail to fall outside the straight print range. This is exceptionally useful for slide shooting. It also provides the info needed to make decisions about contrast, maybe we choose Astia or Provia here instead of Velvia to adjust to the SBR we decide we want. With negatives we can decide on development choices because we have the info needed to know if contrast is "normal" for us or not.

    Onward, SBR is a chosen range that we pick out of the scene. It isn't effected by anything else.

    With negatives as long as we get our whole chosen SBR somewhere between toe and shoulder on film, the exact placement doesn't matter to the contrast calculation. Sure an underexposure where we let things fall off the toe or overexposure where highlights fall off the shoulder are a problem but if we get in the middle there is no loss nor gain of SBR. Anything on film but outside our chosen SBR has to be accessed by using burn or dodge or changes in paper grade.

    Our challenge, when our SBR is in the middle, is matching our chosen SBR to our paper.
     
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  15. AndreasT

    AndreasT Member

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    Thanks Elliot for your offer I may get back on that. I have been using BTZS for a few years and had some issues with it.
    I have not used slide film or colour film for over ten years now (unless I take photos of my cat). Isn’t it more important to orientate ones exposure a little more to the lighting using slide film? Letting more fall off in the shadows.
    With negative film pointing the dome directly to the light source will give us a high SBR and if we develop accordingly we do get rather soft negatives.
    I think it is important to keep the contrast up a bit and do the rest in the darkroom. At least in a high contrast scene.
    Personally I prefer the incident light meter since I believe (for me) it is easier to get good usable negatives where I get the information on the film.
    Still there should be a easy and simple rule how to use a light meter. There are enough people who take wonderful photographs and do not care about testing. Often I get asked how to measure a scene and I never find a simple way to explain it.
    The above article does help.
     
  16. Mahler_one

    Mahler_one Member

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    HI Mark:

    Thoughtful reply, and thanks.

    We will simply have to differ a bit in our ideas about the SBR being unaffected by the metering of the highlights. Perhaps I am not completely understanding your position (pun not entirely intended!).

    Note that I most often follow the BTZS methods in which the SBR value is obtained by high EV minus low EV plus five. Once again, this forum is certainly not the best place for a complete discussion of the pros and cons of the BTZS methodology which knowledge can be best obtained by reading some articles at BTZS.org and reading Mr. Davis's interesting book. Now might be a good time to remind folks that "BTZS" does NOT stand for "Better than the Zone System" as some have mistakenly believed. Indeed," Beyond the Zone System" is the correct translation!

    To extend your comments about metering: If you've a moment, simply walk into the light and meter a shadow point in our scene. Then point the dome of the meter at the make believe camera position and slowly rotate the dome upwards directly towards the sun. The EV reading will increase as the dome is pointed upwards; the SBR will increase ( high EV minus low EV etc), the developing time based upon testing meant to keep the film exposure on the "straight line" of the curve will decrease and the highlights are-as you pointed out-protected. Now point the dome directly at the make believe camera position so that the sun light strikes only the top or part of the dome rather than the "complete" circumference of the dome. The highlight EV value will decrease, the SBR will decrease, the developing time will increase, etc.. Note for emphasis that I am alluding to BTZS methodology. We entirely agree that one can manipulate the SBR for creative purposes-roughly analogous as zone shooters do when they "place and values fall". Of course, as we also agree, matching the SBR both to our creative vision and to the combination of paper and paper developer that we use, provides the creative control that analog black and white photographers seek.

    Incident metering is another tool, and one that some find extremely useful and even easy to use. However, like every tool, such metering will have to be applied correctly and modified by experience, results, and creative wishes. So, we agree in what is important: Making images that reflect one's intent and vision.

    Stay well Mark.

    Thanks again for stimulating the discussion.

    Elliot
     
  17. Mahler_one

    Mahler_one Member

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    No argument at all Andreas. BTZS adherents certainly do control the contrast of the negative by the placement of the highlights. Experience with such placement-when used with one's particular materials-allows one to affect the contrast of the resultant print.

    My last visit to Berlin was about 6-7 years ago. The cranes were all over the skyline, and Museum Island was being resurrected. The Parthenon....

    Chuss,

    Elliot
     
  18. AndreasT

    AndreasT Member

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    Yeah at least what you saw back then is finished although they are still building something new next to the Parthenon, with have to check how far they are there. Haven’t been down there for a few months.
    But have you heard about the Airport. About two years behind schedule and it proberly going to take another two years. Embarrassing!!
     
  19. Mahler_one

    Mahler_one Member

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    Yes, I had heard recently about the construction at the Berlinairport. Then again, in my adopted home town of Hamburg construction at the new Harbor City is also encountering delays and massive cost over runs.

    Elliot
     
  20. baachitraka

    baachitraka Subscriber

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    Incident metering the shadows(placement is critical) and decreasing the exposure by a stop, works for me for roll film. But then testing is required to establish E.I and development times for seven stop development(personal choice).

    Thanks Mark Barendt and BTZS.
     
  21. markbarendt

    markbarendt Subscriber

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    Elliot I fully agree that where and how the head is oriented for each reading does make a distinct difference to the SBR calculation.

    Your reference to BTZS does bring up a good point, when we talk about and try to mentor others our frame of reference is very important.

    In my frame of reference and practice, when duplexing or measuring contrast I always point the incident meter directly at the light source for the highlight measurement then I measure parallel to the camera axis. I use these two because the highlights and the mid-tones are of most importance to me personally. Typically I only feather the meters head to bias my exposure when using a single dome out reading.

    For others, shadows and mid-tones, or shadows and highlights, may be more important to peg, there's no rule against picking different lines and places to measure, or to feathering the meter head one way or another, those are very reasonable artistic or technical choices.
     
  22. Mahler_one

    Mahler_one Member

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    Excellent points Mark.

    Together with a good friend of mine Ben who is a skilled photographer and retired Chemist, an attempt to better define the "proper way" to meter the highlights has been the subject of some recent contemplation and discussions. I refer now to BTZS methods. Ben has wondered if metering by averaging the readings taken by pointing the dome at the light source AND at the camera along the lens axis would be a "reasonable" way of determining the highlight values. If one points the dome at the light source the mid tones are rendered well in the print. However, there can be-and we have easily demonstrated such by a few prints on Azo paper using Amidol-a decrease in print contrast ( higher SBR, shorter development, highlights held, mid tones separated well ). For emphasis, the separation of the mid tones is wonderful on Azo papers. On the other hand, pointing the meter at the camera which lowers the SBR, drives development and increases contrast, the midtones are somewhat compressed ( again on Azo/Lodima paper using Amidol ) and the highlights can be at zone 8 and sometimes detail is lost on the high end. So, Ben suggests averaging the two highlight values so as to, and I am mixing metaphors a bit, having one's cake and eating it-separation of the mid tones, AND slightly increased contrast.

    I am seeking to replicate the more "measured" contrast in my prints rather than the "West Coast approach" which is (seen for example in the wonderful work of Ansel Adams ) certainly more dramatic. Although once again I don't want to stray too far from the subject of incident metering it is worth repeating that we are attempting to take advantage of the properties of silver chloride papers developed in Amidol ( increased mid range tones and a very long tonal scale ). Those using VC papers might approach their metering paradigm differently as might those who use, for example, Gallerie graded enlarging papers. Also those who contact print might find that metering in a certain way yields negatives that print better vs. those who prefer to projection print. Of course, we haven't even touched on the efforts of those who are making negatives for alternate methods such as Platinum printing!

    And, that is exactly the point that we both are emphasizing: Incident metering is a tool that can be learned and applied when one understands one's materials and attempts to use such metering to render the scene as one envisions. The latter point should be understood and used as a reference to whatever metering method is chosen, i.e., the characteristics of one's materials, one's intent, and one's vision guides the exposure of the negatives.
     
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  23. markbarendt

    markbarendt Subscriber

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    A couple thoughts given your description.

    Systems like the ZS, BTZS, et al are built on pieces of information and cobbled together into a workable "system". These systems, of necessity, move us a step or two or three away from the "real" theory and principles they are built on.

    Here's a link to a discussion talking about one of the building blocks involved, ISO film speed. http://www.apug.org/forums/forum48/...tion-constants-question-stephen-bill-etc.html The builders of the various systems are trying to help us make good pictures even if our eyes glaze over when given this level of detail. To be blunt it has to be dumbed down a bit because a huge number of us don't really care about knowing the theory, so many details are left out.

    A one of the complicating factors here IMO is the classic teacher/student relationship where students ask questions and teachers are supposed to provide answers. Teachers do their darndest to answer well but they are human and we regularly get the teachers opinions interjected, not always the real story. Along the way the developers of the systems interject their own thoughts to explain how things work and relate to each other.

    Looking back over the last 50 years across almost any discipline that we might choose, we can see a huge variety of examples where our understanding has been updated.

    In this piece by Phil Davis http://www.btzs.org/Articles/Sensitometry Part 5.pdf I think there are examples of the above issues.

    In the middle coulomb of the second page (31) Phil makes the assertion that incident meters assume a 5-stop SBR because of an 18% transmittance. In the third coulomb he goes on to assert that a full sunlight measurement "almost inevitably results in of underexposure in the shadow areas of the subject".

    IMO in both of these assertions Phil is personally trying to "fill in the banks" and by doing so he was unintentionally creating myths/misinformation.

    To the best of my knowledge incident meters don't assume a given range, a single reading doesn't do anything except gather luminance info at a given point in space. There are meters that can spit out SBR but they need at least two readings. There has even been experimentation with "back leak" to allow this to be done with a single push of the button, I don't think this ever made it to the mainstream though.

    Also incident meter domes aren't necessarily allowing exactly 18% of the light they "see" onto the sensor. The percentage of light the dome transmits to the sensor is irrelevant except to the meter's builder, the real percentage is just a number in the equation. For example, a builder could easily use a more transparent dome to improve low light usability and simply adjust the equation to make the displayed readings come out right.

    Next, Phil's expectation with regard to shadow detail is to be frank, just his own. It's a purely subjective preference. Nothing wrong with that but that preference carries through into his system, into his equations, regardless of your preferences or mine.

    Which brings us to the contrast issue you and Ben are trying to address, that when you input certain numbers into the BTZS system, from readings I assume are taken in the normal BTZS manner, the BTZS spits out answers that aren't getting you the results you hoped for. This failing is a direct result of Phil's preferences and biases.

    Now I want to be clear here, this criticism doesn't mean I think the BTZS or the other systems are without value, for me it just means that they need to be taken with a grain of salt. Ben's patch is a good example of seasoning BTZS to taste.

    We need to understand that the idiosyncrasies of any system do not necessarily represent the real physics of photography.
     
  24. Diapositivo

    Diapositivo Subscriber

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    If I can give a simple rule for simple 35mm photographers that would be:

    If the subject is not in contrasted light (not a high SBR subject), put the dome in front of the subject pointed at the camera and you'll be fine;

    If the subject is a contrasted one - half in shade, half in full sun, imagine the façade of a building not entirely in the sunlight - then your choice is simple: with slide film place the dome in the sunlight, with negative film place it in the shade. Point to the camera and you'll be fine;

    Only exceptions to the rule above are the cases when one has important details in the top highlights or important details in the bottom shadows. In the former case close a bit (let's say half a stop) in the latter case open a bit (half a stop).

    The exceptions are due to the fact that incident metering will end up placing a very bright and strongly lit subject high in the film curve which, for slides, means a region with small detail, not much texture (when not burned). By the same token, incident metering will end up placing dark details in the shade in a region with small detail, not much texture (when not blocked).
    A studio picture of some flour or sugar (something perfectly white and very, very reflective) when using incident reading would correctly render the flour, or sugar, perfectly white but that means not much texture if using slide film. Basically no slide film has good texture for perfectly white subjects. By closing we lose "pure whiteness" but we get "texture". Our mind "adjusts" for pure white because it knows sugar is white.

    The normal case in real life is snow in the sun. With slides just use incident metering and close half a stop. The snow will bend toward "dirty snow" but the texture on the surface will clearly describe it as snow. Your "mind" will then bring it to pure white even when it isn't.

    Incident metering is good for us because there is no need to place anything, to figure how grey is the subject. When we use reflected metering any metering cannot abstract from the question "what is the reflectivity of the subject". When we use spot metering we cannot abstract from the question "how is exactly shaped the characteristic curve of this film".

    When we use incident metering in 99% of the case we have no thinking to do at all and it will yield good results regardless of subject reflectivity and film curve. Incident metering makes life much easier.

    That's my experience but, again, I only use small formats and never deal with more sophisticated approaches such as ZS and BTZS.
     
  25. AndreasT

    AndreasT Member

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    Mark could you clarify a bit more on this what you mean.
    I changed over to the BTZS a few years ago and got terrible results in the beggining. Forcing me to push up my development.
    Yes I know we are talking about exposure, but that was fine on my films.
    The clarifications about flare, (which I ignored a bit) I fell are badly discussed in his book.
    With the help of a few other here I could clear this problem. Those crazy guys who dream about this stuff.
    Using the Incident light meter gives more secure results.
     
  26. cliveh

    cliveh Subscriber

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    A meter reading is only as good as the negative/slide density it produces, coupled with the developer/development and time temperature used.