Reflective vs. incidence meter reading??

[markbarendt]

I'm an amateur, but...

The subject is three-dimensional. So some choice has to be made about not just "the light falling on the subject", but the light falling on certain parts of the subject. Sometimes the subject will be lit evenly but that's rare unless you specifically set out to do so (and do it well). If there's a streetlamp reflecting off a newspaper box and illuminating my subject's rear while I'm taking a picture of their face from the bust up, my "incident" reading will be a lot more useful if it takes into account the light falling on the subject that will actually be in the frame.

Is that wrong? I realize that semantically this makes it maybe more a consideration of "reflection", in a sense, but... at a fundamental level reflected light is the only thing that matters, since it's the only thing we see. Or not?

It is not wrong to consider all the tones.

In the end though you have to pick one setting for the camera.

Using your example with an incident meter and a reading taken at your subjects nose the meter would automatically place:

Caucasian skin a stop or so brighter than middle gray, which is normal.

Dark hair will be darker than middle gray.

A white shirt in the same light should be white, black shirt, black, blah, blah, blah.

Incident meters are great for finding the normal exposure.

Context is important though.

If you are shooting in a situation where you want the subject's face to be darker than normal, say under a street lamp at night for mood, you would just stop down some. This would be an artistic adjustment to a technically perfect reading.

 

[2F/2F]

Not quite true.

We usually want to have the bit the camera sees, the bit that will be captured on film, to be exposed the way we want it. Who cares about the parts of the subject we don't see?

So where the camera lens is relative to the subject does indeed matter. It determines what parts of the subject will be on film, which will not.

They don't say those things for nothing, you know.

That the metered areas falls within the frame is a given. That you meter for the light falling on a part of the subject that is seen by the lens is also a given.

Nonetheless, I almost disclaimed anyhow, just because I knew someone would say something. I just got lazy, I guess.

Also, I simply said "where the camera lens is", not "where the camera lens is relative to the subject". What I meant was that when metering, seeking out the location of the lens for something at which to point your meter is a method that does not make sense at all, technically.

It is really as simple as: Point the meter at the light you want to measure.

 

[Chuck_P]

This is why I say that the contrastier the light on the subject, the more important it becomes to meter the main light source instead of the "down the middle" average, which is what you get by pointing the thing at the camera all the time.

All good points you made.

Averaging could be done without just pointing it at the camera-----it could also be done by taking the reading on the main light source side and then the shadowed side, either way, in natural light when sun and shadow is the case, an averaged reading would seem to afford the best negative, IMO, coupled with wise development.

 

[2F/2F]

Why would an averaged reading make the best negative? A shot metered for the main light would be correctly exposed, and a shot metered for the average would be overexposed. Which of the two is best?

Now, if you are talking about purposeful overexposure on negative film (for one or more of the many reasons one might have to do this), that is a special circumstance, and should not be used to guide standard working procedures. Overexposure and altered development is something you'd do to change the contrast of your film, not something you would do in all occasions.

 

[Q.G.]

What I meant was that when metering, seeking out the location of the lens for something at which to point your meter is a method that does not make sense at all, technically.

Well, no. That's the point. It does indeed make a lot of sense.

It is really as simple as: Point the meter at the light you want to measure.

I wholeheartedly agree.
The light you want to measure is the light that is illuminating the bits that will be captured on film. The bits your camera lens is seeing.

See how it makes sense?

But it is a general rule, and needs to be adapted - fine tuned - for specific situations. Still makes sense even then though.

 

[2F/2F]

But wouldn't a corollary be that the light falling on the subject from the direction the camera is viewing is very likely to be the light we want to meter for? Since, after all, that's the light that we'll be viewing the subject in for the photograph.

As I said, this is true in low-contrast light, and the more contrasty the light, the less it is true. However, when it is true, it is not true because the meter is pointed at the camera lens. It is true only because in that particular lighting situation, pointing the meter at the camera lens will give the same reading as pointing the meter any other direction. This is why I say the location of the lens doesn't matter, but where the light is coming from matters. Your meter doesn't know what a camera lens is. It only knows what light is.

The "at the camera" method is a rule of thumb that will get printable exposures on negative film. It is exactly the kind of method that instruction books are full of, but that anyone who is teaching more detailed and technically correct methods would not recommend.

 

[Q.G.]

As I said, this is true in low-contrast light, and the more contrasty the light, the less it is true.

Yes and no.

They use a dome for incident light metering. Not a flat surfaced diffusor.
That integrating dome, admitting light from a 180 degree angle, will 'see' the contrast.
So you get an averaged result automatically, when pointing the dome at the camera lens.

The "at the camera" method is a rule of thumb that will get printable exposures on negative film. It is exactly the kind of method that instruction books are full of, but that anyone who is teaching more detailed and technically correct methods would not recommend.

They certainly would. Because it is a sound, valid method.

They would also talk about fine tuning the method.
That fine tuning involves deciding what you want to have exposed in what way. Decisions that also determine what you meter.
Which, by the way, is the same for any metering method.

 

[Lee L]

I'm not inclined to answer point-by-point, but here are some factors to consider.

Very few reflecting surfaces in the real world have either perfectly specular or lambertian reflective qualities. I.e. they don't reflect like a mirror nor do they perfectly diffuse the light striking them over 2 pi steradians. Most surfaces reflect more strongly back toward the light source and more weakly at angles off that axis. So measuring the light striking an object from 90 relative to the camera position is not measuring the amount of light reflected from that object toward the camera. Therefore a measurement taken with an incident dome pointed at a light source 90 degrees from the camera will underexpose to varying degrees, depending on the reflective qualities of the object being photographed.

With the light meter dome at the subject pointed toward the camera, light from a source at 90 degrees from the camera axis will light half the translucent dome directly, and any light reflected by nearby objects will fill in on the rest of the incident dome. Once the direct light and reflected light enter the incident dome, it will scatter and reflect off the interior surface of the meter dome and back to the sensor cell, so the dome is self-compensating mixing box that sees both the direct and reflected light falling on it. It's designed to be a self-compensating system with the dome pointed at the camera.

The dome on an incident meter used for 3-D subjects is three dimensional, and by design acts to account for the action of light reflecting off a 3-D object when the dome is pointed toward the camera. For shooting flat art copy work, incident meter manufacturers often supply a flat incident diffuser to simulate a flat surface. For the same reasons of specular/lambertian properties in the object being photographed as mentioned earlier, the flat incident meter diffuser does a better job of simulating the way light reflects from a flat object. Flat diffusers are also very handy for determining lighting ratios in the studio with more than one effective light source (two or more lights, or light + reflectors).

The reason that you keep seeing the instructions to point the incident meter dome at the camera repeated everywhere is because it is designed to work that way. The meter dome should be placed to account for all of the light that a three dimensional object can possibly reflect toward the camera. If you point the incident meter dome directly at a light source that is 90 degrees from the camera, a large percentage of the light you're measuring can't possibly be reflected toward the camera by a 3D object that's entirely within the field of view of the camera, and you're not metering the reflected light from opposite the main light source that can be reflected back toward the camera.

Lee

 

[2F/2F]

Well, no. That's the point. It does indeed make a lot of sense.



I wholeheartedly agree.
The light you want to measure is the light that is illuminating the bits that will be captured on film. The bits your camera lens is seeing.

See how it makes sense?

But it is a general rule, and needs to be adapted - fine tuned - for specific situations. Still makes sense even then though.

I see what you are saying, of course...but I would say it this way: In general, the direction you point the incident meter will be well within 90 degrees of being pointed right at your camera lens.

However, there are a few situations in which the light you want to measure is not always the light that is illuminating what is captured on film.

In all situations, however, the light you should measure for deciding exposure is the light for which you want to expose.

Sometimes that will be the light that is falling on a part of your subject that does not appear on the film (is not "seen" by the lens).

The most obvious example is when you have a primarily backlit person and want to expose for the background instead of the person; a classic silhouette.

Another time I would meter with the dome more than 90 degrees from the camera lens would be simply to get a background reading to see how many stops away from the foreground reading it was. I do this all the time.

...and yes, the flat disc is the better tool for this...but the dome works this way just fine.

...and no, no instructor whose technical expertise I respect has ever taught me to point the dome at the camera. They have taught me specifically not to do so (obviously).

 

[ricksplace]

It's not common, especially now, but my Kodak Retina Reflex cameras are fitted with Gossen meters. They came with plastic diffusers to clip on the front to take incident readings.


Steve.

That reminds me. My Retina 3c has a built-in meter attachment for incident readings, as does my Rolleiflex T. Both meters are made by gossen and both attachments are a plastic diffuser that snaps over the meter cell.

 

[2F/2F]

If you point the incident meter dome directly at a light source that is 90 degrees from the camera, a large percentage of the light you're measuring can't possibly be reflected toward the camera by a 3D object that's entirely within the field of view of the camera, and you're not metering the reflected light from opposite the main light source that can be reflected back toward the camera.

Lee

First of all, this is a fairly uncommon lighting situation, so should not be used to argue overall methods.

Even then, however, pointing the meter at the light in this situation gives you the right exposure, and pointing it at the camera gives you an overexposure (and a rather extreme one at that, assuming the main light is the only light). If you meter with the dome at the camera in this situation, you get an overexposed shot, and when you meter with the dome pointed at the light, you get a correctly exposed shot. Tests will prove this...and have informed what I am saying.

If you call this an underexposure, it seems you are using shadow values to judge exposure. If your shadows are too dark for your taste when metering a main light placed at 90 degrees to your subject, you simply don't have enough fill for what you want. It is not because you are underexposing the shot by metering that light.

 

[2F/2F]

So you get an averaged result automatically, when pointing the dome at the camera lens.

They certainly would. Because it is a sound, valid method.

An averaged result for the composition or for the subject is exactly what I don't want, in any situation, with any meter. It is exactly why I am recommending what I am recommending.

No one, in over a score of instructors in my life, has ever taught me to point the thing at the camera. They have always taught never to do so, unless, of course, the light is coming from the camera. Not one in-person instructor has ever recommended the at-the-camera method to me.

Your dome covers 180 degrees, but you get to decide which 180 degrees they are. They do not need to be the 180 degrees that are 90 degrees each direction from your camera lens. This is yet another way to make my point.

So, my method is an averaging method (as all incident methods are, as a given) that covers 180 degrees...but it is 90 degrees each way from the light source, not 90 degrees each way from the camera lens.

 

[Q.G.]

The most obvious example is when you have a primarily backlit person and want to expose for the background instead of the person; a classic silhouette.

In that case you shouldn't meter the light falling on the back of the person, but the light falling on the background. More specifically, the light falling on the bit of the background that is facing the camera lens...

...and no, no instructor whose technical expertise I respect has ever taught me to point the dome at the camera.

They must have assumed that you already knew that basic thingy...

They have taught me specifically not to do so (obviously).

Bad. Very bad.
They never should have. Because it doesn't make sense.


Anyway.
I think it is the astounding simplicity of incident light metering, or rather: people's believe that things can't be that simple and work, that produces such convoluted discussions time and time again.
We can avoid spreading so much unnecessary confusion if we would begin to accept that things really can be that extremely simple, and not just work, but work perfectly too.

I blame the spot metering, Zone crowd for that.
Although... No, i don't. We see the very same thing there too. Zone too is a (again) very simple, methodical way to get nice pictures, that in turn more often than not is obfuscated by people who think it is so complex that you can only hope to begin to understand how it works when you peel away its's simple (true) face to uncover/discover layer after layer of a highly complex dark art.

So i guess i appeal to all and everyone alike: don't make things more complicated than they are!

 

[zumbido]

If you call this an underexposure, it seems you are using shadow values to judge exposure. If your shadows are too dark for your taste when metering a main light placed at 90 degrees to your subject, you simply don't have enough fill for what you want. It is not because you are underexposing the shot by metering that light.

You seem to be basing your methods on the assumption that is always possible (much less desired) to adequately stage lighting. This strikes me as a much less universal and valid assumption than some others here...

 

[2F/2F]

You seem to be basing your methods on the assumption that is always possible (much less desired) to adequately stage lighting. This strikes me as a much less universal and valid assumption than some others here...

Not at all. It just makes examples more clear. Very little of my shooting involves staged lighting. Light is light, however. All artificial light is just a copy of natural light.

Natural lighting does tend to make incident metering much easier, and the at the camera method works better outdoors.

 

[2F/2F]

"In that case you shouldn't meter the light falling on the back of the person, but the light falling on the background. More specifically, the light falling on the bit of the background that is facing the camera lens... "

I meter the light that is illuminating the back of the person if I want to expose for the light that is illuminating the back of the person.

I meter for the light that is illuminating the background if I want to expose for the background.

I meter toward the camera if I want to meter for a light source that is coming from the same direction as the camera.

That is how simple it is. Meter the light that is illuminating that for which you want to expose; not the camera lens.

Nothing is truly idiot proof if you really are an idiot, however. Thus, the complications with incident meters; the most simple, reliable, and across-the-board correct light metering method there is. IMO, I am with you. The over complication of technical matters is the idiotic part of photography. The basics are quite simple, but they are not treated as such.

I blame the in-camera metering "crowd" for the fact that very few people know how to properly use light meters.

The Zonies I blame for nothing. At least they are trying to get it right by themselves...

 

[Mike1234]

An incident meter can only tell you how much light is falling on a given area. It cannot tell you the reflectivity of that area. If you can get a standard (wide-view) reflective meter close enough to read a relatively even area then you can adjust your exposure to compensate for the Zone V reading the meter gives you... less exposure for charcoal and more for snow (loose rules of thumb). Nothing is more accurate than taking multiple spot meter readings and the knowledge of where you want to place those values on the final print. Essentially, meter for the darkest shadow area and place the exposure where you want that shadow area to fall on the final print then develop and/or tone or intensify the film to place the brightest values where they'll render the desired brightness and texture on the final print.

Sorry... but incident light reading can't do this with the same accuracy as spot metering because spot meters read the direct luminance of the object itself which is what the film sees. I have nothing against incident meters. I just choose the accuracy of spot meters.

 

[Chuck_P]

Zone too is a (again) very simple, methodical way to get nice pictures, that in turn more often than not is obfuscated by people who think it is so complex...................

Oh, so very true!

 

[2F/2F]

Sorry... but incident light reading can't do this with the same accuracy as spot metering because spot meters read the direct luminance of the object itself which is what the film sees. I have nothing against incident meters. I just choose the accuracy of spot meters.

Why are you sorry? It's not a question of one being better than the other. It is a question of knowing how to use either to get what you want.

I use both together when I have the time. Incident to get the "base" exposure, and spot to read the luminance range and tonal falls at the base exposure to inform me as to which alterations to exposure and development I might want to make. Usually, unless the scene looks high in contrast, I don't even bother to measure the luminance range. Sans spot meter, I guess the luminance range. Not hard at all.

I have not used a spot meter alone for quite some time. Sometimes I will do this for products or still lifes or portraits, but I usually use the incident as well in these situations. I will sometimes use a spot meter alone in a graphic, compositionally simple, tonally simple, high-contrast portrait, to place a skin tone or a backdrop precisely, while the rest of the shot is in shadow.

 

[2F/2F]

Oh, so very true!

Indeed. The only real thing I have against it.

Kind of like that bumper sticker that reads: "Lord, protect me from your followers."

 

[markbarendt]

The only thing any meter does is provide a reference point. It's just a tool.

2F/2F isn't doing or suggesting anything that is wrong, nor were his teachers.

Off angles are simply a creative/artistic use of that tool to get a specific result. I will admit that I rotate the head too.

The only reason I stayed away from talking about or suggesting off angles so far is simply that the thread started with a very basic question and off angles seriously complicate that discussion and can confuse anyone who hasn't really figured out what meters really do.

If we all do it the same way we can all see the same result, that is important.

Once you "get it" and can do it well the plain old boring way, all bets are off and it's time to experiment and play.

My photographic goals are artistic, not technical.

 

[Chuck_P]

Why would an averaged reading make the best negative? A shot metered for the main light would be correctly exposed, and a shot metered for the average would be overexposed. Which of the two is best?

Was going back through the thread, somehow I never saw this post from you.

Referring back to my post #29 with the photo examples----- as simplistic an example that it is, for the 3rd shot, if I had averaged the exposures from the shadowed reading and the sunlight reading, I would have used 1/250 at f13 on my camera, a +1/2 stop difference from the in-camera reading of 1/250 at f16. In this instance an averaged reading would have provided enough exposure to adequately render the shadowed area and a reduced enough exposure to keep the sunlit wall within a printable density, certainly not overexposed.

I can't necessarily agree that averaging is going to lead to overexosure---I believe any overexposure solely depends on the reflective values that are present. Some may indeed reflect too much light, thus leading to that surface(s) being overexposed.

This is why I don't use an incident meter with my LF stuff. The feeling of absolute control with the spot meter allows me to know exactly what important reflective surfaces will need their final negative densities moderated during development. But this is just my way, others can certainly get that feeling of control with intelligent use of an incident meter.

I use an incident meter with my 35mm negatives. I simply will move through the area where I'm shooting and while holding the button in on my Luna Pro F with the dome toward the direction from which I'm shooting, I will observe the fluctuations of the needle in both sunlight and various shadow areas and then make a determination on the best averaged reading. If I'm concerned about some reflective surfaces being too strong for the averaged reading, I will plan reduced development to the roll.

 

[Q.G.]

I meter the light that is illuminating the back of the person if I want to expose for the light that is illuminating the back of the person.

Where does that back of the person then end up on the curve?

That is how simple it is. Meter the light that is illuminating that for which you want to expose; not the camera lens.

To avoid prolonging the confusion, the lens is aimed such that it projects on film what you want to have exposed on film.

The dome of an incident meter is made such that all light that could hit what the camera lens sees is measured. If pointed from the subject at the lens (or in similar light, when held parallel to the direction subject-lens).

You can bias, fine tune, that by allowing light from one direction to weigh in more than that from other directions, by pointing the dome more toward where that light is coming from.

Just like you can select a part of your subject to meter, instead of metering the entire scene, when using reflected light metering.

But the basic method, the average metering one, the one in which you point the dome from the subject towards the camera still is correct. Still works.

You may not always want an average reading.
But that doesn't mean it is wrong. It isn't.
So if the aim is to learn how to use a meter, you do have to know that. You do have to know and understand that it indeed is the basis, the point of departure for any 'fine-tuning'.

 

[Q.G.]

An incident meter can only tell you how much light is falling on a given area. It cannot tell you the reflectivity of that area. If you can get a standard (wide-view) reflective meter close enough to read a relatively even area then you can adjust your exposure to compensate for the Zone V reading the meter gives you... less exposure for charcoal and more for snow (loose rules of thumb). Nothing is more accurate than taking multiple spot meter readings and the knowledge of where you want to place those values on the final print. Essentially, meter for the darkest shadow area and place the exposure where you want that shadow area to fall on the final print then develop and/or tone or intensify the film to place the brightest values where they'll render the desired brightness and texture on the final print.

Sorry... but incident light reading can't do this with the same accuracy as spot metering because spot meters read the direct luminance of the object itself which is what the film sees. I have nothing against incident meters. I just choose the accuracy of spot meters.

That's often said, but never quite true.

The thing is that you do not learn anything about the reflectivity of any part in a scene when you point a spot meter at it. You just get a reading.

You, noone else, will have to work out how much of the incident light that particular part of the scene reflected. Your meter will not tell you, unless it is either aimed at a reference surface, or it is able to perform an incident light reading too.

The "accuracy" you get using a spot meter is in how it is able to tell you how the relative reflective properties of different parts of the scene compare.
But point a spot meter at anything, and it will always say the same thing: grey, grey, grey, ... What will be white, what black, what middle gray is up to you (and noone or nothing else) to decide.

And that's the hidden bit in those ubiquitous 'spot metering is more accurate' thingies. You can use that same accurate 'computer' - your judgement - to decide about those thingies in incident light metering as well.

 

[jeroldharter]

These are not real good negative scans but the point is conveyed---some examples of this point about incident metering.

There is obviously more light than dark in this subject. But when composing the third shot, I made sure the center-weighted meter of the camera was influenced more by the dark shaded area. The meter's outer, less sensitive regions were also a factor in determining the exposure, just not as much, but ultimately gave a more satisfying result.

Taking an incident reading in the sun and then the shade could have been done and then expose for the average reading. That would probably be the better use of an incident meter IMO, since it does take into account acutal reflective values at both the dark and the light end of the range. It actually attempts an average exposure rather than letting the reflective meter alone try and average the scene, which can lead to some pretty poor exposures if the scene is nowhere near average.

I skimmed this thread and I don't think anyone has mentioned the BTZS method for using an incident meter which is what I use now. I used to use a spot meter for zone system work.

Basically, you take an EV incident reading in the shadow (or simulated shadow) of the scene; then take an EV incident reading in the bright area of a scene; add 5 to the difference and that equals the scene brightness range. An SBR of 7 is normal. Other values require the usual expansion or contraction process. I find this to be much faster, easier, and intuitive than using a spot meter. It took me awhile to believe it though but my results proved the point. The only potential problem is when you cannot get a highlight reading - for example what is the highlight reading of the distant mountain scene when you are standing in the shade? I have found ways around it most of the time. With a spot meter, there is a lot of room for error with the actual "spot" as well.

I have a big Sekonic spot meter which I thought was great but I leave it at home and instead use a miniscule Gossen Digisix meter that is about the size of a stop watch and much less expensive than a spot meter.