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I have my FM2 with me and I want to make a portraiture. For that I use Sekonic L-308X-U as my light meter and I use incident metering.

Is the distance of light meter to camera important? If so what is the maximum or minimum distance should I place my camera from the light meter?

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It makes absolutely no difference where an incident reading is taken. The only thing that matters is that the meter sees the same light as the subject does, and with the same orientation relative to the source and camera (angle of incidence).

I.e. if the light source is the sun behind you and you want to take a picture of a mountain 3 miles away; then just point the meter towards the sun (as if it were the mountain looking back towards the camera). If the light where you are is different than it is at the subject (i.e. you're standing in shade) then the meter needs to be relocated to where it is the same.

Edited to add oversimplified drawing to help explain situations mentioned in the comments.enter image description here

The closer a directional light source is to the subject, the closer to the subject the light meter must be placed in order to have the same angle of incidence and to account for light falloff.

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  • \$\begingroup\$ What do you mean by "with the same orientation relative to the source and camera"? For example, if you are taking an outdoors sunlit portrait of someone, using an external incident meter, what then does it mean for the meter to have the same orientation relative to the source and camera? Do you point the meter's dome at the camera lens? At the sun? Does it matter? \$\endgroup\$
    – osullic
    Aug 5, 2019 at 14:45
  • \$\begingroup\$ You want to meter the light that is incident at the subject (same source) with the same angle of incidence (angle of reflection). If the sun was behind the mountain you would still point the meter behind you (i.e. metering shadow side). And if the sun was overhead between you and the mountain, then you would point it towards the mountain. \$\endgroup\$
    – Steven Kersting
    Aug 5, 2019 at 14:52
  • \$\begingroup\$ This works if, for instance, there are no clouds or there is perfecly even cloud cover. In my experience there often are clouds and they often are not perfectly even, which is why I like to meter where the light is actually falling. \$\endgroup\$
    – user82065
    Aug 5, 2019 at 14:55
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    \$\begingroup\$ @StevenKersting well, of course you dispatch one of your myriad underpaid assistants with a walkie-talkie for this :-). Seriously, nothing is: that's why I'd use a spotmeter. \$\endgroup\$
    – user82065
    Aug 5, 2019 at 15:52
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    \$\begingroup\$ Light fall-off obeys the inverse-square law. If the Sun is the light source, then the measured light at the subject vs. closer to the camera wont be different because the Sun is about 93 million away; a few feet more or less wont make a difference. But if the source is closer (e.g. a strobe) then a few feet can make a difference and the incident meter needs to match (or just be very similar to) the subject distance. \$\endgroup\$
    – Tim Campbell
    Aug 5, 2019 at 16:13
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Incident is Old French for "about to happen". In other words, light is about to hit the subject. You place the meter near the subject. Point the meter back towards the camera and take a reading. An incident reading should read about the same as a reflective light meter reading taken off an 18% gray card. The accuracy of the incident reading gives rise to its high popularity.

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  • \$\begingroup\$ Two niggling details: I would substitute 'ease' for 'accurate.' Also, the readings will probably be different but the indicated exposure should be about the same as… . \$\endgroup\$
    – Stan
    Aug 5, 2019 at 14:18
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    \$\begingroup\$ 'incidence' and 'incident' come from the Latin word incidere, which is composed of in- meaning ‘upon’ and cadere meaning ‘to fall’. \$\endgroup\$
    – osullic
    Aug 5, 2019 at 14:41
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If you are measuring incident light, you want to measure it at the place where whatever it is incident on is. So, for instance, if you want to measure the light falling one someone's face, you measure it as close to their face as you can. If you wanted to meter incident light on the Moon, you need to go to the Moon to do it, even if you plan on taking the picture from Earth.

Obviously if there is very even light, then you can meter anywhere. That's almost never the case for the kind of photography I do, at least.

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  • \$\begingroup\$ I mean how far should I place the camera from the incident meter (I edited my OP) \$\endgroup\$
    – neversaint
    Aug 5, 2019 at 13:07
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    \$\begingroup\$ @neversaint: that makes no sense. You meter incident light at the object you care about: how far the camera is away from that depends on what lens you have and how you want to compose the picture: it's nothing to do with the metering. \$\endgroup\$
    – user82065
    Aug 5, 2019 at 13:17
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    \$\begingroup\$ I wasn't planning a trip to the moon but I have a good excuse now \$\endgroup\$
    – timvrhn
    Aug 5, 2019 at 13:35
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    \$\begingroup\$ The only reason to take an incident reading as close to their face as you can is if the light on the face is different than it is everywhere else... i.e. using a gridded/snooted light. You would have to go to the moon at night though, because it is seeing the sun and where you are on earth is in shadow \$\endgroup\$
    – Steven Kersting
    Aug 5, 2019 at 14:40

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