Incident vs Reflected light in sun

spl · Sep 27, 2021

I am wondering about metering in sun. I understand these things: Incident light falls on the subject, reflected light is the light that bounces off the subject and enters the lens. If your subject is assumed to be 18% grey then incident light is about 5 times reflected light when measure in lux, or about 2.5 stops because the relationship is logarithmic.

Now I get how that works with diffuse light. I see that many light meters have a sliding or detachable window to switch between incident and reflected mode, which presumably makes this 2 stop / 18% lux adjustment. And that's all good.

Now, if I have a subject under sun or a landscape under sun, without clouds, so the light is not diffuse but is a point source (sun) and I put the window on my light meter to convert to incident mode it doesn't get me anywhere because the meter reads all different depending on whether I aim it near the sun or at clear blue sky elsewhere.

Does this mean that incident readings can't be taken under sun? Are there any books that deal with information like this to recommend.

Alan Edward Klein · Sep 27, 2021

In incident mode, the dome on the meter does diffuse the light.

BrianShaw · Sep 27, 2021

The dome both diffuses and integrates. Any basic photography book published in the last century or so will explain incident light metering. Most light meter manufacturers sites will also. I especially like to tutorial material at the Sekonic site.

MattKing · Sep 27, 2021

If you are using the dome, you don't point the meter at the sun. You stand where the subject is, and point the meter at the camera. The dome integrates the light from the sun (which is a moderately small source, but not a point source), the sky, and any light reflected off of other surfaces, like the ground.
If you want to measure things like lighting ratios, you can also take the same reading from the shadowed areas of your subject, and then compute the difference.
Some incident meters are set up to permit readings without an integrating and diffusing dome - those are the ones used to measure only the light from the main source, excluding secondary sources. Normally those are used in controlled, studio or laboratory situations.

Sirius Glass · Sep 27, 2021

Incident meters work well for general photography regardless of the subject. Reflectance meters work well for general photography except when the subject is white on white or black on black, the the incident meters rule.

Zathras · Sep 27, 2021

Incident meters work very well in sunlight. I prefer them for my shooting, especially with 35mm cameras
When I used to use the built in meter in my 35mm SLR's, my exposures were all over the place, since
my camera's meter was recommending different exposures based on what it was seeing, even if the
light falling on the scenes didn't change. When I got my first incident meter and learned how to use it
correctly, my exposures became much more uniform and gave me better negs as a result. Since then,
none of my 35mm cameras have batteries inside them, except for my Minolta XE7. I have to use a
battery with that camera because it has an electronic shutter.

Alan Edward Klein · Sep 27, 2021

MattKing said:
If you are using the dome, you don't point the meter at the sun. You stand where the subject is, and point the meter at the camera. The dome integrates the light from the sun (which is a moderately small source, but not a point source), the sky, and any light reflected off of other surfaces, like the ground.
If you want to measure things like lighting ratios, you can also take the same reading from the shadowed areas of your subject, and then compute the difference.
Some incident meters are set up to permit readings without an integrating and diffusing dome - those are the ones used to measure only the light from the main source, excluding secondary sources. Normally those are used in controlled, studio or laboratory situations.

I think you meant that you point the dome at the camera. Since the dome can be in the so-called front of the meter or on the top or on another side of the meter, there is no front of the meter.

MattKing · Sep 27, 2021

It is funny - I always equate "pointing the meter" and "pointing the light receptor on the meter (in this case the dome)" as being the same. But if Alan's clarification assists ....

Sirius Glass · Sep 27, 2021

Alan Edward Klein said:
I think you meant that you point the dome at the camera. Since the dome can be in the so-called front of the meter or on the top or on another side of the meter, there is no front of the meter.

Point the dome at the subject from where the camera is located.

Chan Tran · Sep 27, 2021

spl said:
I am wondering about metering in sun. I understand these things: Incident light falls on the subject, reflected light is the light that bounces off the subject and enters the lens. If your subject is assumed to be 18% grey then incident light is about 5 times reflected light when measure in lux, or about 2.5 stops because the relationship is logarithmic.

Now I get how that works with diffuse light. I see that many light meters have a sliding or detachable window to switch between incident and reflected mode, which presumably makes this 2 stop / 18% lux adjustment. And that's all good.

Now, if I have a subject under sun or a landscape under sun, without clouds, so the light is not diffuse but is a point source (sun) and I put the window on my light meter to convert to incident mode it doesn't get me anywhere because the meter reads all different depending on whether I aim it near the sun or at clear blue sky elsewhere.

Does this mean that incident readings can't be taken under sun? Are there any books that deal with information like this to recommend.

The incident meter measure in lux but the reflected light meter doesn't measure in lux but rather candela/m².
When you measure incident light you aim the meter at the camera and the reading is correct.

Alan Edward Klein · Sep 27, 2021

MattKing said:
It is funny - I always equate "pointing the meter" and "pointing the light receptor on the meter (in this case the dome)" as being the same. But if Alan's clarification assists ....

I guess it depends on what meter you have. With my Minolta, the dome is on the top side where the LED display of settings is where on my Sekonic it's in the "front" of the meter. I hardly use that meter so I guess one would have to reverse the meter making the reading upside down to face the dome to the camera. When I put on the reflected viewfinder on my Minolta, the "front" of the meter is on the bottom. It's all very confusing.

MattKing · Sep 27, 2021

Alan Edward Klein said:
I guess it depends on what meter you have. With my Minolta, the dome is on the top side where the LED display of settings is where on my Sekonic it's in the "front" of the meter. I hardly use that meter so I guess one would have to reverse the meter making the reading upside down to face the dome to the camera. When I put on the reflected viewfinder on my Minolta, the "front" of the meter is on the bottom. It's all very confusing.

When you take the reading, you are standing either where the subject is or, if that is not possible, between the camera and the subject, in the same light as the subject.
So when you point the meter at the camera, you are holding and reading from the meter exactly the same way you would be holding and reading from the meter with a reflected light meter - except you (the photographer) are turned around and looking back to where you have positioned/will be positioning the camera.

wiltw · Sep 27, 2021

Sirius Glass said:
Point the dome at the subject from where the camera is located.

This comment is NOT how you use an incident meter!!!

With incident meter, point the dome toward the lens ideally with meter at subject position, take the reading. If impossible to be where the subject is, you can stand in the direction of the subject and aim at the lens but the assumption is the light is identical there as it is at the subject (which sometimes is not a valid assumption!)

If using a reflected light meter, you aim it from camera position toward the subject.

foc · Sep 27, 2021

spl said:
Does this mean that incident readings can't be taken under sun? Are there any books that deal with information like this to recommend.

An incident light reading can be taken in any lighting situation.
It is very simple to do. You place the incident meter where the subject is and you point the white dome towards the camera. Then take the reading. This will give you the correct exposure for your subject.
This is how it would look from the camera's point of view.

You could have a look here for some more explanations
https://www.sekonic.com/benefits-using-light-metering#

Alex Benjamin · Sep 27, 2021

spl said:
if I have a subject under sun or a landscape under sun, without clouds, so the light is not diffuse but is a point source (sun)

Few things here. Sun light is not "a point source". It is diffused light. You have the general light coming from the sun directly on the subject, but this does not function like a spot light on a stage. Sun light goes through the atmosphere, through clouds (and is reflected by them), then bounces all over the place, and all this light falls on your subject. In other words, you never have just one light source, and this is what is meant by diffused light.

That diffused light is also what lights your shades.

Other thing. If your subject is under sun without clouds, don't complicate your life, go with sunny 16.

CMoore · Sep 27, 2021

For those of you that meter the palm of your hand, do you typically put that at Z-6.?
Thank You

wiltw · Sep 27, 2021

CMoore said:
For those of you that meter the palm of your hand, do you typically put that at Z-6.?
Thank You

Measured with a spotmeter vs. an 18% grey card, the human palm (regardless of the race of the person) is about +1EV brighter than the grey card

gone · Sep 28, 2021

I tend to look for a nearby area of grass to get a middle zone of metering rather than metering off the palm of my hand, if only because if I have the camera in one hand and the meter in the other hand, I then need a third hand to meter off of.

A camera's reflective meter is all I use. My Nikon has 3 types of metering including spot, and the only time I ever sorta wanted an incident meter was when shooting 4x5.

guangong · Sep 28, 2021

As I recall, incident meters and readings were developed for directors of photography for movies in order to maintain consistency from shot to shot, with uniform film processing. It is a reliable method of determining exposure for most situations, but there are times when photographer is unable to place meter in same light as subject. Then a reflective or spot meter is useful.
No matter which method...incident, reflective, or cardboard calculator...a human brain must be engaged.
My meter collection contains an model of an early Hollywood meter, but having a Biden right now and name skips my mind. The Sekonic selenium incident meters were based on these meters.

Helge · Sep 28, 2021

The dome or disc is an idealised platonic (goes double for model shoots) subject.
It's a stand-in for the face, rock or any object you photograph.
Except it's neutral.
A very dark or light subject measured directly, would throw the reading off, and make the subject and background over or underexposed.
Therefore it's paramount to put the meter dome in as much the same light as the subject as possible.
Most of the time that goes without thinking by just putting the dome near the subject and pointing it at the camera. But there are possibilities for error.
Very contrasty light, strongly patterned directional light (through blinds, leaves etc.) and sudden introduced shade (your own body or someone else's for example (this can happen without you noticing easily).

Sirius Glass · Sep 28, 2021

wiltw said:
This comment is NOT how you use an incident meter!!!

With incident meter, point the dome toward the lens ideally with meter at subject position, take the reading. If impossible to be where the subject is, you can stand in the direction of the subject and aim at the lens but the assumption is the light is identical there as it is at the subject (which sometimes is not a valid assumption!)

If using a reflected light meter, you aim it from camera position toward the subject.

No, never. PERIOD! The dome is aimed toward the subject from the position of the camera; that is the dome points the same way the lens does, not towards the lens. The concept is to get the same light as the subject. Take a look at the manuals, they are all consistent.

Alex Benjamin · Sep 28, 2021

Sirius Glass said:
No, never. PERIOD! The dome is aimed toward the subject from the position of the camera; that is the dome points the same way the lens does, not towards the lens. The concept is to get the same light as the subject. Take a look at the manuals, they are all consistent.

It's the opposite.

Incident light metering: You are measuring the light falling on your subject. Meter, with dome on, is at the same place as the subject (under the same lighting conditions) pointing towards the camera.
Reflected light metering: You are measuring the light reflected by your subject. Meter (in camera, independent meter with dome off or spot meter) is pointed at subject. Meter does not have to be at the same place as camera (unless it is the camera's meter, of course).

Sirius Glass · Sep 28, 2021

Alex Benjamin said:
It's the opposite.

Incident light metering: You are measuring the light falling on your subject. Meter, with dome on, is at the same place as the subject (under the same lighting conditions) pointing towards the camera.
Reflected light metering: You are measuring the light reflected by your subject. Meter (in camera, independent meter with dome off or spot meter) is pointed at subject. Meter does not have to be at the same place as camera (unless it is the camera's meter, of course).

Alex Benjamin · Sep 28, 2021

Sirius Glass said:

Drawing from the Photopills website.

faberryman · Sep 28, 2021

Sirius Glass said:

Fortunately you are shooting with Hasselblads so you can get perfectly exposed negatives even if you are metering incorrectly.

Incident vs Reflected light in sun

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Incident vs Reflected light in sun

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