Incident Light Meter Use

Discussion in 'Beyond the Basics' started by Commonman, Apr 23, 2007.

  1. Commonman

    Commonman TPF Noob!

    Jan 4, 2007
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    St. Paul, Minnesota
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    I just purchased a Sekonic L-398M light meter. It appears to be a very high quality instrument.

    Although I have a manual and have read the manual, I'm still a little confused about how to use the meter. I may be a little slow and some of the meanings in the manual may have been "lost in translation."

    The instructions seem to indicate that one should uses the Lumisphere (a dome like semi transparent white plastic light diffuser) over the sensor and point the light meter back at the camera to obtain a reading. But, what if you're taking a landscape? How do you go to a mountain that is 1000 or more yards away and get a reading?

    For "distant scenes," the manual indicates one should take a reading of the sun and the subject and take the mean of the two obtained values. Then it gives an example using 320-foot candles and 80-foot candles. They say the mean of these two values is 160 but the mean of 320 +80 is 200 (unless I am going nuts). Now, I can see that 160 is mid-way between 329 and 80 on the scale of the meter but it's confusing to use the term "mean" which to me means "average."

    The meter has a thing called a Lumigrid (diffuser with holes in it) which I think is to measure reflected light, but the instructions do not appear to indicate this should be used for distant subjects.

    Another thing that I'm wondering about is an accessory called a "Direct Reading Slide." I have such a slide that is a little place on the back of the meter that says, "carry slide here." I figured out that this slide is inserted in a slot on the light sensor. I have the slide that says "High." Unless I am missing something, I don't see where it explains the
    application of the High Slide. Do I use it when there is exceptionally high light? And, what applications do the lumidisk (which semi transparent white plastic is a light diffuser that is flat).

    So, in summary, I just want to make sure I understand the applications of the various accessories. When would I want to use a Lumidisc as opposed to a Lumisphere or Lumigrid? And, when do I use the "High" slide.

    I'm also wondering under what circumstances it would be best to use the "point back to the camera" technique and the "point to the subject" technique.

  2. Don Simon

    Don Simon TPF Noob!

    Jul 4, 2005
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    You don't. :) You simply wouldn't use the incident meter for that purpose.

    Point back to the camera with incident meter (i.e. with white dome over sensor), and point at subject (or something of neutral tone in same light as subject) when taking normal (reflected light) readings.

    Sorry I'm too tired to look at anything with numbers; hopefully someone else can answer the rest of your questions.
  3. Torus34

    Torus34 No longer a newbie, moving up!

    Jan 26, 2006
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    Tottenville, Staten Island, NYC USA
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    With the Lumisphere in place, your meter is an incidence meter and measures the average light falling on the subject. One way to take an incident light reading is to position the meter at the subject with the Lumisphere aimed at the camera.

    With the Luimigrid in place, your meter becomes a reflectance meter and measures the light coming from the subject. If you wish to photograph a scene, you would stand beside the camera and point the Lumigrid at the scene. Additionally, you can use the reflectance mode to determine the exposure for highlights or shadows within a scene.

    For a basic 'how-to' on reflectance metering, you can check the 'film exposure' section of:

    While the discussion is centered on b&w film, it is applicable to color as well.

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