Incident light meters question

Discussion in 'Exposure Discussion' started by jmal, Dec 20, 2009.

  1. jmal

    jmal Member

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    So, I know that incident meters measure the light falling on a subject, but I would like to know how they arrive at an exposure recommendation. I have always used center weighted reflected light meters in my cameras and know that I can measure an area of the subject and adjust upward or downward depending on whether I'm exposing for the highlights or the shadows. I am in a position where I need a meter to use with an unmetered camera and it seems that most affordable hand held meters are incident meters. So, what does the reading tell you? Does it simply tell you what exposure is needed for a middle gray based on the falling light? Also, any recommendations for something under $200, new or used, and not too large? Thanks.
     
  2. Chris Nielsen

    Chris Nielsen Member

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    I just got a Gossen Lunasix F incident/flash meter for $50. Nice size dome, works very well.

    Just put the white dome across the sensor, hold in in the same light, optionally pointing towards the camera from the subject, and take a reading. Put that in your camera and shoot!
     
  3. rthomas

    rthomas Member

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    My understanding is that an incident light meter gives you a reading approximately equal to a gray card reflectance of the light falling on the subject (and thus the range between the highlights and shadows is ignored). Works great in most situations, but it still helps to know the contrast range.

    My favorite meter is the Sekonic L-308s (or any of the previous versions). It's a digital meter; a new one is within your price range. It takes 1 AA battery, will do incident or reflected for ambient or flash and is about the size of a cell phone. The ISO and aperture range of this meter is outside anything most of us are likely to use.
     
  4. eddym

    eddym Member

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    An incident meter has nothing to do with the subject. It has no idea what the subject is, because it doesn't look at it. It tells you how much light is FALLING ON the subject, not how much is reflected by it. But WE know that dark subjects will reflect less light than white subjects. And we know that the subject contrast range is rarely less than 7 stops. So for the vast majority of scenes, all you have to do is meter the ambient light, which is what an incident meter does. Dark subjects will be dark and light subjects will be light. You only need to worry if you know that the brightness range is going to exceed the range that your film is capable of capturing. In that case, you will have to choose whether to lose highlight or shadow detail, and that depends upon the film you are shooting. These situations are more accurately metered with a spot meter rather than incident. But with experience, you will usually know whether and how much to adjust your exposure. All others should bracket.
     
  5. 2F/2F

    2F/2F Member

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    An incident meter measures existing light that is falling from the light source itself, regardless of what light levels are being reflected off of the things within your composition. If you know this, and know your film speed, then you can suggest an exposure that will make a grey card grey. That is all that an incident meter does. Where other tones fall on your negative in relation to the grey card will depend on how many times more or less light than middle grey they reflect, combined with the contrast of your film. If you know through experience that your film with normal exposure and development will not render the range of luminances within the composition in the way you would like, you can tweak exposure and development to manipulate the way your film behaves.

    If I had to use only one meter, it would be an incident meter. They are almost 100% idiot proof, and give far more practically useful information than a reflected meter in most circumstances, IMO. If I have time, however, I use an incident meter and a spot meter (which measures reflected light) together. When I do this, I only really use the spot meter to measure luminance range, or luminances of certain objects in relation to middle grey, not to actually decide an exposure.
     
    Last edited by a moderator: Dec 21, 2009
  6. Jim Edmond

    Jim Edmond Member

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    I suggest reading the incident meter technique outlined by Phil Davis in his Beyond the Zone System book. It describes an advanced method to set exposure and determine subject brightness range (SBR) for subsequent development time.
     
  7. MattKing

    MattKing Subscriber

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    When you are using an incident meter, don't forget that most subjects receive light from more than one direction. In many cases, subjects receive light from more than one source.

    It can be very useful to take more than one incident reading. As an example, for a subject that receives most of it's illumination from a window, as well as additional light reflecting off an adjacent wall, a reading that measures the general highlight illumination (window plus wall reflected light, plus a reading of the light that is hitting the parts of the subject in shadow (wall reflected light only), will give you lots of useful information about contrast and character of your resulting photograph.

    Matt
     
  8. eddym

    eddym Member

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    You must live on a planet of a binary star system...

    (joking! joking! Your explanation was relevant.)
     
  9. bowzart

    bowzart Member

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    Gosh, I don't see where anyone mentioned that the incident meter works from the subject pointed toward the camera. You are actually measuring the light that illuminates the subject from the direction from which the camera sees it. Of course, if you are in the same light as the subject lit by a distant light source, like the sun or sky, you can be at the camera position and point the meter away from the subject, preferably along the axis passing through the subject and the camera.

    If you are at the camera pointing the incident light toward the subject, you may be doing a good job of measuring the illumination on the backside of the subject, away from and invisible to the camera. Most of us wouldn't generally want to do that.

    Using a reflected light meter, such as the one in the camera, you can replicate the incident meter's function by holding your hand in front of the camera, palm facing the lens and parallel to the film plane. Be careful not to cast a shadow on it and entirely fill the frame with the palm. Doesn't have to be in focus; better to leave the focus where the subject requires to avoid extension errors. Take the reading the camera gives you and add one stop. That is, if it's f/11, give f/8, etc.

    It doesn't matter whether you are racially puce, blue, pink, or green. Palms are remarkably consistent regardless.

    For all the zone system stuff he promoted, Minor White could often be seen taking readings like this.

    Edit: Looking again, I see that Chris, above, mentioned taking the reading from the position of the subject.
     
  10. grahamp

    grahamp Subscriber

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    I used to meter the palm of my hand with a Weston before I found a dome for it. Worked fine as long as I remembered to take my glove off... It is also useful to have a white card around for low light conditions. The correction is more than one stop, and a quick test will tell you how much. It does help with meter sensitivity, especially if, like most selenium cells, the low end tends to be optimistic.
     
  11. CPorter

    CPorter Member

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    This has been answered. But you need to remember that an incident reading will not compensate for shadow values within the scene/subject. That is why all reflective surfaces should be as evenly lit as possible, such as on a sunny day but in evenly illuminated shade or on an overcast day.
     
  12. eddym

    eddym Member

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    Good grief! I can't believe I said that! I should have said, the subject contrast range is rarely more than 7 stops.
    Mea culpa...
     
  13. dfoo

    dfoo Member

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    Where i find things tricky is when the subject is partially in shade, partially in the light. With an incident meter only what do you in this case?
     
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  15. Q.G.

    Q.G. Inactive

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    You decide.
    Just as you would when using any other type of metering.

    You decide what you want to expose for.
     
  16. Q.G.

    Q.G. Inactive

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    Not sure that i understand, but...
    The incident meter doesn't need to 'compensate' for shadow values, because it 'automatically' allows shadows within the subject to be and remain shadows.

    All reflective surfaces only should be as evenly lit as possible if you want them to appear shadow- and featureless in the image you will be creating.
    I rarely want such a thing, am very happy instead with the way light 'sculpts' things. :wink:
     
  17. 2F/2F

    2F/2F Member

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    I disagree. The way I was trained, it works from the subject pointed toward the light. You point the meter at the main light source that is illuminating the part of the composition for which you would like to expose. This is not always at the camera. Where the camera is has no effect on what light is falling on the subject. In the studio, you point the meter at the main light from where the subject is. You then measure the other lights and other areas of the composition in relation to the main light to find the lighting ratios/relationships, and hence figure out what your picture will look like. Outside on a clear day, when the sun is directly illuminating the entire composition, you point your meter at the sun. In a scene in which indirect (reflected or diffused) light is providing the illumination (backlit, overcast/hazy, shade, etc.), then you just hold the meter where the subject is, perpendicular to the ground. (This is the "at the camera" method.) The whole point of incident meters is to measure the light coming from the light source and hitting the subject, not the light coming from the camera, so point it at the light source. While the "at the camera" method will work fine in many situations (specifically, those in which the main light source is effectively coming from the same direction as the camera), it is really just a rule of thumb, and does not make one understand what they are doing by measuring incident light, and in the studio, does not give one control over lighting ratios.
     
    Last edited by a moderator: Dec 22, 2009
  18. dfoo

    dfoo Member

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    Its not all that helpful :smile: Of course you decide. The question is what you decide. If you incident meter the shadow is it a direct meter, or a meter value -1 stop. If you meter the highlight and use that value (as you would if the subject is in direct light) then the shadows will likely be very dark (assuming here negative films not a slide).
     
  19. dfoo

    dfoo Member

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    I don't think what you say is correct. If the subject is, for example, back lit you certainly don't want to meter the backlit portion. You meter on the front of the subject towards the lens.
     
  20. 2F/2F

    2F/2F Member

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    It is correct. First of all, how can you argue that a general theoretical technical statement is not correct, and then use a very specific example to make your point? If you are going to dispute what I said, do it using technical theory, not a special-purpose example. Second of all, what I said does not conflict with your example in any way whatsoever. Your statement means that in a backlit situation, you think that the backlight is directly illuminating the front of the subject (which is what I said to meter for: the light that is directly illuminating the subject). It is not, by simple definition of the term backlit. Reflected light from a field, street, buildings, other lights, etc. is illuminating the subject in these cases, so you measure this reflected light. That is exactly what I said to do above. In this situation, if you want to meter for the back of the subject, meter the backlight. If you want to meter for the front of the subject, point the meter at the things that are sending the light onto the part of the subject for which you want to expose. You meter the main light. A backlight is NOT a main light, even if it is brighter than the main light (and is almost always is in a backlit situation).

    P.S. In my post with which you took issue, I said just as much (emphasis added):

    "In a scene in which indirect (reflected or diffused) light is providing the illumination (backlit, overcast/hazy, shade, etc.), then you just hold the meter where the subject is, perpendicular to the ground."
     
    Last edited by a moderator: Dec 22, 2009
  21. Q.G.

    Q.G. Inactive

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    That's right. (You (!) could also use a middle value).

    You (!) decide. You (!) have to decide.

    I understand that it would be nice if you could leave the decision to something else, but there are things you really have to do yourself. Making a decision like this is one of them. Only you can decide, because only you can know what you (!) want.
    :wink:


    Important to keep in mind as well (and why it came up) is that this has nothing to do with what type of metering you are using.
     
  22. 2F/2F

    2F/2F Member

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    See my first post in the thread. Incident meters tell you one thing: How to make middle tone at the location of exposure into middle gray on a print. It is up to you to know how to take this information and use to to get what you want. You do this by knowing how to judge the light within your composition, and knowing your materials and methods. If you use a film that is contrasty in contrasty lighting, and follow what the meters says directly, then of course you will have dark areas in the composition. That goes without saying. Take steps to change this if you don't like it. It also goes without saying that how dark the dark areas will be will change from situation to situation and film to film, so general statements such as "the shadows will likely be very dark" should be avoided.
     
    Last edited by a moderator: Dec 22, 2009
  23. 2F/2F

    2F/2F Member

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    errmmm....You suggest tailoring your light to your meter? I don't get it. You should be able to use your meter in any light in order to get what you want. Otherwise, it is worthless. Telling someone that their lighting needs to change because of the meter they are using is defeating of...well, just about everything! The light comes first. You get it how you want it, or see it how it is naturally. Then you use the meter, in conjunction with your head, to guide your exposure. There is no way that your stated conditions need to be met to use an incident meter.

    What I think you are talking about is addressed by the following (emphasis added):

    "An incident meter measures existing light that is falling from the light source itself, regardless of what light levels are being reflected off of the things within your composition. If you know this, and know your film speed, then you can suggest an exposure that will make a grey card grey. That is all that an incident meter does. Where other tones fall on your negative in relation to the grey card will depend on how many times more or less light than middle grey they reflect, combined with the contrast of your film. If you know through experience that your film with normal exposure and development will not render the range of luminances within the composition in the way you would like, you can tweak exposure and development to manipulate the way your film behaves."

    No; you "should" not tweak your light to match your meter. You "should" choose the right materials and methods to capture what you want from the lighting that you want. Lighting is everything. It has to take priority. Everything else serves that and is controlled by it. It should not be tweaked just because you feel like reading your meter directly and using any old film with any old exposure and development. If we are not putting lighting first, and making everything else revolve around it, why are we taking pictures at all?
     
    Last edited by a moderator: Dec 22, 2009
  24. dfoo

    dfoo Member

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    The manual for my light meter says very simply

    "This is used to measure people, buildings, and other three dimensional objects. Measurements are basically made by the method of measuring with the lumisphere aimed in the camera direction (more precisely, in the direction of the lens axis) at the position of the subject."

    Seems to contradict what you say.
     
  25. 2F/2F

    2F/2F Member

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    "While the 'at the camera' method will work fine in many situations (specifically, those in which the main light source is effectively coming from the same direction as the camera), it is really just a rule of thumb, and does not make one understand what they are doing by measuring incident light, and in the studio, does not give one control over lighting ratios."

    Posted by me, a few posts ago.

    "Seems to contradict what you say."

    It "seems" to do so if you take it as absolute fact, and don't bother to read it carefully.

    It is a rule of thumb...the kind of thing you might find in a brief explanation in an instruction manual. The writing makes this obvious. Hell, they even use the word "basically", so you know that there is more to it than what they wrote. Rules of thumb are things that give acceptable results a good deal of the time to people who don't bother to learn specifics of things. They are not technical explanations or thorough, detailed instructions. They are designed to give average photographers average results an average amount of the time.

    Reading comprehension is a very important skill. Everything you have questioned me on could have been answered by simple high-quality reading of things already written in this thread and in your manual.

    If you want an average direct reading, point the thing at the camera. If you want to measure light, and then use your head to decide what to do to get what you want, you will point it at what you actually want to measure. This may or may not be the same direction as the camera, depending on the situation. At no time did I ever say that you would never be pointing the thing at the camera.
     
    Last edited by a moderator: Dec 22, 2009
  26. dfoo

    dfoo Member

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    Ok, I understand what you are suggesting. Thanks, helpful!