Understanding Incident Metering

[IanBarber]

I would like to get a better understanding on how to properly use incident metering for subjects other than portraits.

Scenario: Street scene where subject maybe in both sunlight and shade.
I would normally walk into the sunlit area, point the meter back at the camera and take a reading and dial those numbers into the camera.

What I am trying to learn, is what this is doing and how can I visualise what the negative is going to look like. On the gray scale, where will the bright and dark areas be for example.

Scenario: Indoor still life with even North light, no shadows visible.
How can I visualise what the negative is going to look like. On the gray scale, where will the bright and dark areas be for example.

Thanks, Ian

[Pere Casals]

Scenario: Street scene where subject maybe in both sunlight and shade.
I would normally walk into the sunlit area, point the meter back at the camera and take a reading and dial those numbers into the camera.

The incident metering is based on the light that arrives to the subject, so if the meter is illuminated by direct sunlight you know the exposure for all subjects than are sunbathed.

If the meter is in the shadow then you know the exposure for all subjects that are in the shadow.

We can add that the angle of the subject surface and of the canmera to the light (if it is directional) will have an impact.

...so if you have subjects both in the shadow and also sunbathed in the same scene then you have to take 2 readings, and then decide.

In general shadows are 4 stops under the sunlit area, so if you place the sunny area at +2 you should have shadows at -2, if shadows are open, this is not in a hole, but illuminated well by the blue sky.

Anyway sun always delivers the similar light power, it can vary a bit depending on time, latitude, etc but as Sunny 16 rule states a sunbathed subject needs at ISO 100 some 1/100s at f16

Scenario: Indoor still life with even North light, no shadows visible.
How can I visualise what the negative is going to look like. On the gray scale, where will the bright and dark areas be for example.

It depends on the situation, what window size, distance to the window, white or dark wall ?

Again you have to take 2 readings, for the bright area and for the dark one, then decide exposure.

[IanBarber]

In general shadows are 4 stops under the sunlit area, so if you place the sunny area at +2 you should have shadows at -2, if shadows are open, this is not in a hole, but illuminated well by the blue sky.

So thinking in terms of Zones, anything in the sunny area is effectively on Zone VII and anything in the shadows will fall on Zone V ?

[Luis-F-S]

Use a spot meter. An incident meter gives you no information about the scene, only the light striking it! It will reference this light to middle gray, or zone V.

[Pere Casals]

So thinking in terms of Zones, anything in the sunny area is effectively on Zone VII and anything in the shadows will fall on Zone V ?

No... it will fall around 4 zones, if something is 2 stops overexposed in the sunny area (Z VII) it will be at around Z III if placed in the shadow and if conserving the same exposure.

Also remember that the Zone in what a subject will be (if exposing what incident metering says) depends o the subject's reflectiveness, as subject can be white, grey or black...

So imagine your subject is a 18% grey card, you read the incident light to expose... the card will be at Z V. If instead the card you have a subject that reflects 36% of light towards the camera then (with same exposure) the subject will be in Z VI.

[IanBarber]

No... it will fall around 4 zones, if something is 2 stops overexposed in the sunny area (Z VII) it will be at around Z III if placed in the shadow and if conserving the same exposure.

Also remember that the Zone in what a subject will be (if exposing what incident metering says) depends o the subject's reflectiveness, as subject can be white, grey or black...

So imagine your subject is a 18% grey card, you read the incident light to expose... the card will be at Z V. If instead the card you have a subject that reflects 36% of light towards the camera then (with same exposure) the subject will be in Z VI.

Thanks Peter. So just to confirm I have this correct...

incident meter reading from in-front of a textured tree would roughly put it on ZV, I would simply close down 2 stops to effectively put it n the region of Zone III and anything in the scene which is reflecting the same light would also be in the same zone

[Pere Casals]

Use a spot meter. An incident meter gives you no information about the scene, only the light striking it! It will reference this light to middle gray, or zone V.

I also prefer spot metering, but incident metering is also nice.

IMHO incident metering is not for all situations, but when we have homogeneous illumination it delivers very consistent results: what is recorded is subject's refectiveness, because metered exposure does not depend on if we take the reading in a darker or lighter surface.

If one is used to incident metering then it's easier to use flash meters in the studio, because regular flash meters are a kind of incident meters...

[Bill Burk]

So thinking in terms of Zones, anything in the sunny area is effectively on Zone VII and anything in the shadows will fall on Zone V ?

A flat 2-dimensional picture has only 5 stops of Subject Luminance Range (SLR). (Zones IV to VIII).

Even when it's in the shade, a part of a 3-dimensional picture has only 5 stops of SLR (but it's down in the shade in the range of Zone II to Zone VI).

Taken together (both sunny and shady parts of the picture), the camera might see a scene with 7 stops of SLR.

The incident meter will try to position the exposure over the whole 7 stops of range (Zone II to Zone VIII).

[IanBarber]

A flat 2-dimensional picture has only 5 stops of Subject Luminance Range (SLR). (Zones IV to VIII).

Even when it's in the shade, a part of a 3-dimensional picture has only 5 stops of SLR (but it's down in the shade in the range of Zone II to Zone VI).

Taken together (both sunny and shady parts of the picture), the camera might see a scene with 7 stops of SLR.

The incident meter will try to position the exposure over the whole 7 stops of range (Zone II to Zone VIII).

Is this why with the BTZS system, you take a shadow and highlight reading and add the different to 5 ?

[Pere Casals]

Thanks Peter. So just to confirm I have this correct...

incident meter reading from in-front of a textured tree would roughly put it on ZV, I would simply close down 2 stops to effectively put it n the region of Zone III and anything in the scene which is reflecting the same light would also be in the same zone

Ian, it depends on the texturized tree. If it reflects 18% of the light, then it will end in Z-V. If the bark of the tree is very dark then it would end perhaps be in Z-III or IV.

So if you use the incident reading to set exposure then all that's illuminated by that light will be in Z-V if it is has same bright than an standard grey card, if it is darker or lighter, of course, it will be recorded in another zone.

To get practice with the incident light meter I'd suggest you an exercise with different scenes. Take the incident metering of the light that's illuminating your sujects, place also an standard grey card in the scene. Then take an SLR or DSLR (an F65 for example) and with its spot meter measure different spots of the scene. You will see that the grey card will be at Zero of the SLR meter, and some dark spots will read -1 or -2, this is Z-IV or III, while white spots will be perhaps at +2.5.

After the incident meter recommends an exposure you just set same ISO and exposure in the SLR and then you can check in what zones will end any spot of the scene. In this way you will get necessary practice to predict the result.

Note that we can meter incident light without having an incident meter, we just need to place the standard grey card in the scene and taking an spot metering of the card. Note that incident metering depends on the direction we meter, in the same way it also depedends on the grey card orientation. Kodak grey card instructions sheet explains how to use the grey card.