Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,832   Posts: 1,582,311   Online: 1027
      
Page 1 of 7 1234567 LastLast
Results 1 to 10 of 65
  1. #1
    markbarendt's Avatar
    Join Date
    May 2008
    Location
    Beaverton, OR, USA
    Shooter
    Multi Format
    Posts
    5,796
    Blog Entries
    3
    Images
    19

    A Primer on Incident Metering.

    Why do we meter?

    Simply put, film that is accurately exposed makes makes printing easier and humans are not really that good at assigning accurate EV numbers to all the scenes we see. So the primary goal of metering is to "reliably" find a camera setting that will allow us to easily get our desired print. (It is not about making pretty negatives, it's about making pretty positives.)

    Sure in a front lit sunny 16 situation we can do okay, but when the subject is backlit, when the sun is setting, when we move indoors, when the light source is a camp fire, or when the clouds roll in; we can normally benefit from a little help.

    A second, and optional goal, is to get a contrast measurement so that we can make well considered film development choices that will make our printing even easier.

    That's basically the whole enchilada.

    A few definitions.

    Incident light is "the light that is falling on the scene". This can be from the sun, house lights, open sky, reflections off the snow, or anything else that is throwing light at our subject.

    Reflected light is simply "the light reflecting off our subjects that our eyes and cameras see".

    E.I. is exposure index, it is a personal setting. This is often improperly referred to as film speed, it is not. It is just a number we use to tell our meter how we want things done given all the variables involved.

    The ISO film speed rating, aka box speed, is found through standardized testing. Film manufacturers do this for us. If we get good at following the manufacturer's instructions for normal, we can come very close to getting the same results they do. I normally use this number as my E.I.

    EV is exposure value. In common terms, it's how bright the scene is. More properly this is a measure of luminance.

    Luminance is a photometric measure of luminous intensity, how much light.

    Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light.

    Three concepts to help understand metering and meters and help dispel some myths:

    1-"A given amount of incident light, falling on a subject of a given reflectance, produces a given amount of reflected light."

    For any given E.I. incident light meters know how much incident light it takes to make a middle tone subject fall as a middle tone on the film.

    For any given E.I. reflective light meters know how much reflected light it takes to make a middle tone subject fall as a middle tone on the film.

    That is a fancy way of saying that both types of metering are fully capable of getting us to the exact same camera setting in any situation.

    2-"Our meters have absolutely no clue about what they are being pointed at."

    Here is where incident metering and reflective metering differ most in practical use.

    Reflective metering is truly handy because many times the meter is built into the camera so there is nothing extra to carry and with spot meters we can pick specific subjects/targets to meter from quite a distance.

    For incident and reflective meters to get us the same camera setting reliably though, the reflective meter needs a target in the scene with a known offset to the proper camera setting. We don't always have or put a known target in our scenes, more typically we just pick a random target and make judgements/guesses about the characteristics of what the meter is seeing. That introduces the distinct possibility of human error. With experience this issue is minimized, but still reflective metering is normally subjective.

    Incident meters are stand alone tools, so it is an extra piece of kit that adds weight, costs money, needs a free hand, and an extra pocket or a strap to keep them handy. Their big advantage though is that they don't need a target in the scene and they provide an objective reading. They don't get fooled by the reflectivity of any given subject. Snow, lots of bright clouds in the sky, dark clothing, water, reflections, blah, blah, blah... none of these will fool an incident meter because incident meters don't see the scene, they see/measure the light falling on the scene.

    3-"When we know the placement of one point in the scene, we essentially know where the rest will fall."

    If we know from testing that there is a specific offset that is common in our shots, like a 2 stop difference between the proper camera setting and the shadows with good texture, or 1 stop difference between say Caucasian skin and the proper camera setting, then by measuring either of these, we can know the placement of the other. Technically it makes no difference which point we measure.

    This is why if we are familiar with our tools, even when we use different techniques and methods, we can regularly end up with equivalent camera settings.

    A few words about E.I.

    Your own E.I. is simply a reference point. You can change that reference to any value you please for any reason you please. If it works for you, its fine for you; that doesn't mean other people's numbers will help you though, or that your numbers will help them.

    If you think you need or want to use an E.I. different from the box rating, do some testing, make sure it solves your problems. Encourage others who want to mimic you to test too.

    I say this because every E.I. is a subjective choice. Your preferences of subject matter, camera equipment, metering methods, lighting situations, lens filters, printing process, paper choices, and your artistic biases all effect the E.I. you choose.

    Testing need not be formal. If in your normal shooting and printing you find that shadow detail is lacking adjust your E.I. to add a little more exposure. If you consistently have more shadow detail than you want you can adjust your E.I. to reduce exposure a bit. Just make sure you are solving real problems.

    Contrast rate.

    For clarity here I'm going to deal with and assume that contrast rate decisions are made before the camera settings are chosen. I also want you to understand why and when film contrast needs adjustment.

    First, you need to answer this question before adjusting the film contrast. "Will it matter?"

    If, unlike Ansel Adams, your plan is to use modern variable contrast papers to adjust print contrast or your lab will be printing for you digitally, then I strongly suggest that you stick to making normal contrast negatives and skip film contrast adjustments unless you find a real problem.

    But, if like Ansel Adams, you are specifically targeting a grade 2 fixed contrast paper and you are testing your work all the way to that paper, then film development changes are important.

    Be honest with yourself here, because if you don't test clear to the paper, you are just guessing. I played this guessing game before I had my enlarger, before I started printing. My negatives from my "guessing period" are very hard to print compared to the "normal" contrast negatives I make today.

    Okay, so if you decide that it matters and you need to adjust film contrast, what is important in taking an exposure contrast measurement is finding out how far and which way contrast is different from your normal.

    With an incident meter this is regularly found by getting one reading with the meter pointed at the light source and another pointed at the camera. Practice and testing are important here. You need to know what normal is and you need to see how changes effect your various subjects before these measurements become meaningful.

    The basic reason for adjusting film contrast is to make printing easier. As with adjusting E.I., adjusting contrast is subjective.

    It's also important to understand that changes in film development do not significantly change how much info the film captures nor the real speed of the film, your exposure choice is the biggest factor in how much and what range of detail the film captures, bar none. Plus or minus development, simply changes what "straight prints" onto a "specific grade of paper".

    Being able to burn and dodge to print more detail is the proof that negatives normally have "extra" info available outside the "straight print" range.

    Reliability and why normal matters.

    I have found that without exception the manufacturer's of my photographic kit, including meters, cameras, chemicals, films, papers, and everything else have really done a wonderful job. Their products typically work exactly as described and even though it may seem like magic seeing the film come out off the reel with images or when watching a print come up in the developer, it really is a well proven industrial process.

    If I want a given output, I simply need to apply the proper input.

    In any industrial process knowing what normal is and understanding how to get there, is important. Yes, I really believe that film exposure, development, and printing are mature industrial processes. Most of us are using off-the-shelf products and or well proven recipes. Within these constraints; given inputs, beget given outputs, with no surprises. The real wild cards in the system are you and I; our failings or successes in the application and understanding of the various inputs determine the quality of our results.

    For me choosing to use an incident meter and to follow the manufacturer's instructions for shooting and processing my film has proven incredibly reliable. Those two choices remove most of the human fallibility and unfounded mythos that surround exposure, film choice, development, and printing. Those choices have provided me a baseline that has allowed for huge improvements in my prints and my understanding of photography.

    So, why do I want to be normal? Because normal means getting reliable high quality repeatable results. I like that.

    So lets talk about what is your incident meter sees?

    Incident readings are typically suggested to be "taken at the subjects nose with the dome pointed at the camera". In certain situations, like for a studio or window light portrait, metering at the subject's nose is important because the subject's relationship to the light source makes a big difference. Outside though we just need to be in the same general light as the subject, not at the subject.

    Incident meters normally have two "modes", dome in and dome out. That choice controls it's angle of view.

    Dome out mimics 3-D subject matter, it sees and measures all the light coming from all the directions that may have an effect on the subject being recorded on our film.

    Dome in readings are meant to see the light that will effect flat subjects, like art, and or used isolate the effect of different light sources. For example with contrast readings and in duplexing which are meant to measure the effect of two different light sources. (More on duplexing in a moment.) The main light in the scene, which for a window portrait would be the window and the secondary light coming from behind the camera, which might be house lighting. Outside this could be the sun as main light and open sky or the reflection from a building behind the camera as the secondary light.

    Camera setting

    So, as I said above, the normal way to use an incident meter for 3D subjects is dome out, at the subjects nose, pointed at the camera. If the meter has been set with the proper E.I. taking a reading in this orientation for use with most negative films will provide an exposure setting that will give you a really nice general purpose negative that can make a very nice print where the subjects will look normal with a nice amount of shadow and highlight detail.

    I honestly believe that most of us could do just fine using this metering technique alone for the rest of our lives. It is that good, that simple, and that reliable.

    Adding artistic biases.

    Typically when we decide to take a photo it is because something in that scene got our attention. We saw something we thought was important to remember or share. This is where the concepts of pegging exposure and place-and-fall become important, we need to get what we saw on the film.

    Pegging comes in three basic types; shadow, mid-tone, and highlight. When we peg we are simply picking one of the three as the most important point for that shot.

    Place-and-fall is the concept that the camera can only place or peg one luminance point, the rest of the scene "falls" relative to that peg.

    For example, if there are faces in the scene I will peg my exposure to the mid-tones because for me faces are always the anchor subject for the print and they need to be placed where they look best, the rest of the subjects in the scene are allowed to fall where they may.

    For landscape photographers the shadow point is the typical peg and the rest of the scene is allowed to fall.

    It is easy to bias our meter readings to accommodate different pegging choices for each shot by simply changing the direction we point the head of the meter. The motivation can be technical or artistic, it makes no difference.

    If you want to give shadow detail more importance and you are willing to compromise highlight detail just turn the head away from the light source some, if highlights are more important turn the head more toward the light source. This is like using salt, adjust to your taste, with experience you can find out how much works best for you.

    Certain situations require very accurate exposure to fit a scene onto our film. This is very typical of slide film. It can also be a concern where we wish to minimize exposure or with very long scale scenes on negatives.

    One technique that can help here is called duplexing. The motivation here is normally that you have competing priorities and a limited amount of room on film. In this type of situation we set the meter "dome in", measure two peg points and average the readings.

    For slide film typically the readings would be taken, one pointed at the light source (to protect the highlights) and the other pointed at the camera (to protect the mid tones). This technique works in all situations but is most useful in high contrast situations where the subject is backlit significantly.

    There's more than one way to skin a cat..

    Meters of all types simply provide exposure suggestions. Just because incident meters are really good at giving you the camera setting as a direct reading doesn't mean that's the only way to use it.

    If your subject is in sun and you are in open shade, or vice versa, and you can't get into the same light, you can simply apply an offset as you would with a spot meter reading. Sure this is a bit subjective but the world isn't perfect and its much better than just guessing.

    Use your imagination and you can find simple ways to make any meter do what you need.

    I could go on but I might never finish that way.

    Please comment and provide your techniques and ideas. If there's something here that doesn't make sense, ask about it so we can figure it out.
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  2. #2
    cliveh's Avatar
    Join Date
    Oct 2010
    Shooter
    35mm RF
    Posts
    3,661
    Images
    344
    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.

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  3. #3
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,565
    Images
    46
    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. #4
    markbarendt's Avatar
    Join Date
    May 2008
    Location
    Beaverton, OR, USA
    Shooter
    Multi Format
    Posts
    5,796
    Blog Entries
    3
    Images
    19
    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.
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  5. #5
    jp498's Avatar
    Join Date
    Oct 2009
    Location
    Owls Head ME
    Shooter
    Multi Format
    Posts
    1,467
    Images
    74
    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. #6
    markbarendt's Avatar
    Join Date
    May 2008
    Location
    Beaverton, OR, USA
    Shooter
    Multi Format
    Posts
    5,796
    Blog Entries
    3
    Images
    19
    Quote Originally Posted by jp498 View Post
    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.
    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.
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  7. #7

    Join Date
    Oct 2002
    Posts
    1,160
    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. #8
    Poisson Du Jour's Avatar
    Join Date
    Jul 2008
    Location
    Vic., Australia.
    Shooter
    Multi Format
    Posts
    3,682
    Images
    15
    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).

    For slide film typically the readings would be taken, one pointed at the light source (to protect the highlights) and the other pointed at the camera (to protect the mid tones). This technique works in all situations but is most useful in high contrast situations where the subject is backlit significantly.
    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.
    Last edited by Poisson Du Jour; 02-27-2013 at 09:04 PM. Click to view previous post history.
    “The photographer must determine how he wants the finished print to look before he exposes the negative.
    Before releasing the shutter, he must seek 'the flame of recognition,' a sense that the picture would reveal
    the greater mystery of things...more clearly than the eyes see."
    ~Edward Weston, 1922.

  9. #9
    AndreasT's Avatar
    Join Date
    Sep 2006
    Location
    Berlin
    Shooter
    Multi Format
    Posts
    355
    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. #10
    markbarendt's Avatar
    Join Date
    May 2008
    Location
    Beaverton, OR, USA
    Shooter
    Multi Format
    Posts
    5,796
    Blog Entries
    3
    Images
    19
    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.
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

Page 1 of 7 1234567 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin