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.
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/forum48/1...-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/Sensito...20Part%205.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.
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 fašade 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.
Mark could you clarify a bit more on this what you mean.
Originally Posted by markbarendt
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.
A meter reading is only as good as the negative/slide density it produces, coupled with the developer/development and time temperature used.
Well we are talking about incident metering, not just exposure. Measuring contrast is a distinct part of that.
Originally Posted by AndreasT
What I'm talking about is that systems: BTZS, ZS, mine, yours; are all based on assumptions.
BTZS assumes lots of shadow detail is important, similarly it wants to keep good highlight detail; that describes a longer than normal SBR. To fit the extra detail that the system expects into a straight print on given grade of paper the negative needs to be developed to a lower contrast than normal.
Phil's bias brings with it a generic reduction in film contrast to make room for more shadow detail without losing highlight detail, but that bias has a side effect, the local contrast across the mid tones gets flatter, loses some snap if you will.
This loss of snap is I'm guessing is part of the problem you fixed with a bit more development. Yes?
You applied a patch to the system by making a decision "outside the rules". You eliminated Phil's bias and applied your own
In Davis's BTZS he writes about a normal contrast of 0,5 which I used in the beginning and got flat negatives. He talks about an average flare of 0,02 which I based my exposure on.
I quickly moved back to a "normal contrast of .57 and got better results like the time before I tried out BTZS. This confused me for a long time.
Then I read a few things from Stephen Beskins (a lot I still do not understand), explaining a bit more about flare.
As I understand it the flare mostly showed by BTZS is just too small. At least the way I understood it.
Although flare is discussed, the dominant usage of such a small amount of flare made me use too small a amount.
Been following the thread-----I would have to disagree on this, I think Davis is merely stating a fact about incident metering in general, IMO. An incident reading in full sunlight can't account for the shadow area in that same full sunlight. Since an incident reading is based only on the intensity of the light falling on the subject, it stands to reason that all the various reflective surfaces would be properly exposed, only if they are all receiving the same illumination. This can't possibly be the case in a high contrast lighting such as full sun with distinct shadows. As it's been stated, I think, averaging the sun and shadow reading is a step in the right direction, but by itself, the full sun reading can leave the shadows hugely unprotected.
Originally Posted by markbarendt
In the attachment with Ross---in A, the meter is placed in a full sun area, the shadows are under exposed; in B, it's placed in a full shade area, the high values are over exposed; in C, the meter is placed in an area that is not full sun nor is it full shade, the exposure is about right; and in D, the exposure is based off an in-camera reflective reading, the exposure pretty much matches that in C.
Nice illustrations Mr. Porter...thanks. I agree that averaging the highlight values might well be the best way to proceed. As noted below, it is wonderful that you are obtaining great results using your metering methods. Nicely done.
I think one must recall that incident metering via Phil Davis/BTZS does NOT involve only one meter reading. I respectfully state that those who are commenting about the BTZS system as being based on a single highlight incident meter reading are not accurately reporting on the BTZS system/ method. Please consider avaiing yourselves to the material available on the BTZS system and incident metering.
If those who are using only a single incident shadow or highlight reading are obtaining the results that they desire...well done! I have nothing further to add or suggest. Add a stop, subtract a stop...heck, who cares if your results are as you desire.
Mark: In his text Phil David clearly states that if absolutely necessary, basing an exposure on a single highlight reading will be incorrect unless one INCREASES the exposure. Without such action, the meter will render the single highlight reading as middle grey. If one MUST base one's exposure on a single shadow reading then one must decrease the exposure so that the tones are moved down from middle gray. Increasing the exposure will raise the highlights to a more "correct value"....and will of course increase the shadow exposure. As to the 18% illumination and 5 stop range that Mr. Davis alludes to: Everything is very well explained starting on page 131 of the 4th edition of his book. The 5 stop range is based upon studies that are well detailed. Of course, feel free to differ from Mr. Davis's conclusions. You are entitled to your opinions and surely such are based upon sound experimental or empiric data as reflected in your negatives and prints. I am very pleased that your "system" works for you, and that most of your film exposures and prints meet all of your expectations. Well done. As to your comments about teachers: All teachers synthesize material and interpret such. Students can decide to reject or modify the material presented. However, if they do so then such changes should be accompanied with illustrations and information as to the methods that they have used to deconstruct the information presented, and the data illustrating the validity of the reinterpretation that they have applied to the chemical and physical realities of the photographic process. Of course, if you are at the stage that teachers cannot offer you any useful information and advice then you have progressed far beyond what must of us here have attained. Again, well done!
For emphasis: The BTZS system depends upon two readings, highlights and shadows. The zone system depends upon two readings-highlights and shadows- with appropriate placement so as to determine the time of development. In both systems one can manipulate exposure so as to render the negative with the tones that one desires. In both "systems" a single reading will not suffice.
If one wants to use a single shadow reading then another approach might be developing by inspection in which one will expose for the shadows and then determine development by the appearance of the highlights under a green safe light in the darkroom. DBI is fun, and many will eventually acquire the necessary visual skills. Moreover, one can learn to develop 4-6 sheets of film at one time.
Exposing for the highlights was a method that at one time the late Fred Picker advocated. Perhaps those who have studied with Fred can comment.
Andreas-I am sorry that you are having some problems with the BTZS system. As I offered, we can discuss any issues via PM. I and others are ready to help.
Some are successful using reflected metering and the ZS, others using BTZS and incident metering, and still others use whatever "system" they have devised based upon their material and metering methods that work for them.
Now it's time to once more go into the field and take some photos. Use whatever "exposure system" works for you; if you are getting the results that you desire, who cares.
Thanks for chiming in.
Originally Posted by CPorter
The first question I have for you regarding the scene in your example is "what is the subject(s) and where do you want them to fall?" Tough to make a metering plan without knowing what the expectation for the print is.
I will quote myself though:
The examples you provided are a good example of where I'd use that principle and some imagination.
Originally Posted by markbarendt
My second question for you is "what are you willing to compromise in this situation; highlight detail, shadow detail, print contrast?" And "what other tools are you willing to bring to bear, reflectors, strobes, scrims, pre-flashing, dodge, burn?"
I ask because the scene in your examples probably won't straight print acceptably, seriously if you want detail in the door and the shaded bark which are how many stops apart?