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# Thread: Metering using an incident meter from the camera position

1. Think carefully about what an incident meter measures, as opposed to what a reflected meter does.

It measures the light that falls on its dome, not the light coming from the subject.

Therefore, if the same sunlight that is hitting your subject is hitting you, you are OK to meter from where you are.

Closer light sources than the Sun are a different story. Remember the inverse square law, which applies to all light: The amount of light falling on an object is inversely proportional with the square of the distance of the object from the light source. Therefore, you lose or gain light exponentially with distance. Thus, the closer your subject and light source, the greater an effect a given change in distance will have.

On a clear day, what is the distance of the Sun to your subject? About 90 million miles. On an overcast day, what is the distance of the blanket of haze to your subject? Likely several thousand feet. Considering the inverse square law, at these distances, what difference does 5, 10, 20, 30, etc. feet have?

Now, in the studio, with a 1K hot light, what is the distance of the light from your subject? What about with a 1000Ws studio flash piped through a main and a fill light? Very close. Under 10 feet 99% of the time, in my experience. Apply the inverse square law to those distances, and you get huge differences in illumination with small differences in distance. Take a main light that is four feet from your subject, move it back one foot, and you already need to change your exposure setting by 1/2 stop.

Besides this theoretical explanation, there is simply the practical fact that in the studio, I cannot think of a situation I have shot in which the same light that is falling on my subject was the same light that was falling on me and the camera.

Therefore, I would make the general statement that outside, in natural light, if the light you are in is no different than the light your subject is in, take the reading from where you are, and if you are using artificial light, take the reading from where the subject is. I hate making general statements, but this is a pretty decent one.

With incident metering, you are measuring the light source itself, from the subject (or from the same effective distance from the subject). So, always point your meter AT the light source, not at the camera lens.

2. You are one sharp guy 2F/2F! Many of your posts in this area of the forums have really been helping me understand. Thank you!

3. Originally Posted by 2F/2F
With incident metering, you are measuring the light source itself, from the subject (or from the same effective distance from the subject). So, always point your meter AT the light source, not at the camera lens.
That's what i'd say, with one small, but important difference:
point the light meter AT the light source that is illuminating the part of the subject you want to expose 'properly'.

In backlit situations, if you do not want a black silhouette against a well exposed background, meter the light that is falling on the side of the subject facing the camera. Not the light that is falling on the (mostly invisible from the camera bright side of the subject.
If you want a silhouette, measure the light falling on the bright bits.

So sometimes, you might indeed want to point the meter at the camera lens.

4. Yes, a good story. Almost as good as the ones concerning those who used a flash to illuminate the moon when there was a partial eclipse. Possible? Those who witnessed the flashes going off swear it's true.

Ed

5. Originally Posted by Q.G.
That's what i'd say, with one small, but important difference:
point the light meter AT the light source that is illuminating the part of the subject you want to expose 'properly'.

In backlit situations, if you do not want a black silhouette against a well exposed background, meter the light that is falling on the side of the subject facing the camera. Not the light that is falling on the (mostly invisible from the camera bright side of the subject.
If you want a silhouette, measure the light falling on the bright bits.

So sometimes, you might indeed want to point the meter at the camera lens.
True indeed. To make it more clear, I should have said what Q.G. said: point the dome at whatever is illuminating the part of your subject that want to expose for in the pic.

I did not, because for a backlit or shaded situation, I was not considering the Sun to be the light source for the composition (though as he sez, in a backlit situation, it is the direct source for the BACK of the subject). I consider sky light and reflected light from the ground, walls, etc. to be the light source in these cases, so would measure them, not the Sun. I should have explained that, however.

6. You also want to make sure that you get your own body out of the hemisphere covered by the integrating bulb of the light meter. This is especially true if you're wearing light colored clothing which can add extra light that will not be in the picture at the time the shutter is triggered. This is often why you will see photographers stick their arm way out when taking an incident light meter reeding as this cuts down on their body light.

7. Originally Posted by Mahler_one
Yes, a good story. Almost as good as the ones concerning those who used a flash to illuminate the moon when there was a partial eclipse. Possible? Those who witnessed the flashes going off swear it's true.

Ed
HAHA!!! It would have to be a rather long exposure as it takes 1.3 seconds for the light just to reach the moon, then another 1.3 for it to get back.

Then there is the whole inverse square law thing to deal with; twice actually.

8. Originally Posted by PeteZ8
HAHA!!! It would have to be a rather long exposure as it takes 1.3 seconds for the light just to reach the moon, then another 1.3 for it to get back.
Isn't that what the "M" flash sync setting is for?

Lee

9. Originally Posted by Lee L
Isn't that what the "M" flash sync setting is for?

Lee
And here I was, the whole time, thinking the "M" was for "Modest" and the "X" was for nudes...

10. Originally Posted by PeteZ8
HAHA!!! It would have to be a rather long exposure as it takes 1.3 seconds for the light just to reach the moon, then another 1.3 for it to get back.

Then there is the whole inverse square law thing to deal with; twice actually.
Actually use the 1/r^^4 [1/r**4] rather than 2 * 1/r^^2 [2 * 1/r**2].

Steve

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