Collins is most correct, and it is a damned shame that so many will unbudgingly argue otherwise without even thinking about it, because it is what they have always been told and what they have always done.
Originally Posted by ghostcount
It is simple to theorize, and easy to prove; in uneven lighting (i.e. not 1:1), if you point the dome at the camera, you overexpose. Plain and simple. This is because the dome is not measuring the actual light falling on the brightest side of the subject (which is what you should expose for to get a "proper" exposure), but is measuring less light, due to "dilution" with the reading from from the dark side.
To get the textbook "correct" exposure, you should point the dome at the light that is illuminating the part of the subject that you want to be most properly exposed. This light could be a studio lamp; it could be the sun. It could be surrounding plant life – a field of grass, for instance; it could be a bounce card or a wall. All that matters is that you point the meter toward the thing – or toward the "general area," in many natural lighting situations, which tend to be much larger than studio sources – that is providing the most light to the part of the subject that you want to properly expose. The shape of the dome accounts for all other light that is illuminating that part of the subject, e.g. spillover/flare from other light sources, light skimming in from the sides, etc. This is the beauty of the dome, not that it is shaped like a human head for the purposes of averaging two lights in uneven ratio.
If it is hard to visualize why this happens in theory, try it out on some transparency film or instant prints to see it in practice. Set up a 1:1 ratio, a 2:1, 4:1 ratio, and so on and so forth. For each different lighting ratio that you set up, make two exposures: 1) dome facing the main light, and 2) dome facing toward the camera.
In totally even lighting, the 1:1 shot, you'll see that it doesn't matter where you point the dome; you're going to get the same reading.
In the 2:1 shots, you will see that the shot metered for the brighter light has a correct exposure on the bright side of the subject, and the darker side is where it is expected to be with that lighting ratio. In the shot metered down the middle, you'll see that the brighter side looks about 1/2 stop too bright, and the darker side appears about 1/2 stop lighter than you would expect it to appear in that lighting ratio.
In the 4:1 shots, you will see that the shot metered for the brighter light has a correct exposure on the bright side of the subject, and the darker side is where it is expected to be with that lighting ratio. In the shot metered down the middle, you'll see that the brighter side looks about 1 stop too bright, and the darker side appears about 1 stop lighter than you would expect it to appear in that lighting ratio.
In other words, if you meter down the middle in uneven ratio lighting, you will overexpose by half the difference in stops between the two sides. This is easily overlooked with negative film, as the actual lighting ratio is not severely changed; you just have "global" overexposure of the image, which is naturally compensated for when test stripping. But do it with a Fujiroid, a transparency, or digital, and you've got a problem.
If you want the most accurate representation of the lighting ratio that exists at the subject, you should meter the strongest light that is illuminating the part of the subject for which you want to expose. If you specifically want to average the main and the fill (i.e. deliberately overexpose), which you may want to do in order to prevent futzing about when working with negative film, then you can place the head of the meter on a line between the main and fill lights. In cases in which the two lights are on a plane parallel to the film plane of the camera, then yes, would be pointing the dome at the camera.
And there is no difference in theory between outdoor and studio light. What differs are the specifics of isolation and control, and the fact that sources outside are generally far more broad. But light is light; it all behaves the same. It is either even or uneven, and you should meter accordingly in any situation. Outside there is always a main source of light (e.g. the sun on a sunny day, the grey haze on an overcast day, or the sky and surrounding objects when shooting someone in open shade); there is also a less intense light coming from other directions (e.g. reflected light from the ground, sky, and/or buildings). In the event that both of these have an equal effect on the subject, you can point the dome at the camera and get a textbook exposure.
And, of course, you point the dome at the camera if the light is coming from the direction of the camera. That goes without saying.
Dean Collins worked that way in a specific system of his own that used multiple lights in a controlled studio setting and he taught that in workshops. He also shot Polaroid tests to make final adjustments. His incident metering method was a personal style and the methods he demonstrates should be taken as teaching his methodology, not as instructive of how an incident meter should always be used. He used either fill light or reflectors in a studio setting. He really doesn't take into account the intentional design of the meter dome that Bruce mentions. Collins was a nice guy, but he teaches a very specific way of shooting. None of the pros I worked for in studios went to his seminars when he was in town. They already knew how to light in a great variety of ways and how to use a meter. Collins drew mostly wedding and portrait studio folks, and he helped them a lot.
The Weston Invercone and standard incident domes were designed and calibrated specifically to be used pointed at the camera from the subject (or in that same orientation in identical light levels). Other methods may work if you know how to account for any necessary adjustments (or take other readings or adjust lights and reflectors to determine fill ratios like Collins does), but they are not using the incident meter dome as intended by the designers.
Case in point is Phil Davis' method of using an incident meter to find subject brightness range for an incident meter Zone System method. His method shows an excellent understanding of the characteristics of film and of incident reading methods. You'll notice, if you read his method, that the dome is pointed at the camera for metering light levels in both the fully lit and shadow portions of the subject. With Davis' method, incident readings are perfectly functional in a Zone System setting.
Incident and spot metering methods are both extremely flexible, and someone who doesn't understand them can get lousy results with either. Someone who does understand both can get great results with either. Special circumstances can make one method or the other preferable, but either can cover a great majority of circumstances.
Not real sure what you are getting at here.
Originally Posted by ghostcount
The reason I say that is that artificial light used well with a specific standard development regime can make printing very easy. It may not even be necessary to adjust enlarger exposure to print negatives from different sessions. Heck the vignette and everything can be designed into the shot with the lighting. Camera settings can even be standardized.
I find what 2F/2F says very convincing. Just to visualize it, imagine a portrait where the main light is a very lateral one (going by heart, Churchill's portrait by Karsh). Pointing the dome at the camera would bring overexposure. One does not want to "average" light and shadow, but to expose for light and then devise and use shadows to give more or less volume, "drama" etc. to the subject, so it is the main light that should drive the exposure.
I always use reflected metering but I'm going to get out with my incident light meter next time and do some practice. Maybe the dome of certain light meters is made in a way that it reads the same value both if the light source is at 0° (front) or at 45°. Maybe the dome of other incident light meters is more "directional" and that would lead to the problems pointed out by 2F/2F.
Besides, in a test in my balcony, my Gossen Sixtino II gave, in incident light, results that are way off what I get with the Gossen Multisix and what one gathers from experience. The Sixtino II in incident light, pointed toward the camera, would lead to gross overexposition. For many years my Sixtino II was all I had for incident light and I considered incident light measuring for years as a devilish trick or a mystery.
The Multisix has an hemispheric dome. The Sixtino II has a curious rolling shutter that must be moved in front of the cell. That I suppose is quite directional, and now I infer that the Sixtino II must be used the way 2F/2F points out, toward the light source, to give reliable results. I'll do some text when I have a proper sunny day.
I always thought it was to be pointed towards the light. Then reading posts here and in other places I was convinced that it should point towards the camera.
Originally Posted by 2F/2F
Towards the light makes more sense to me.
Yes, let's visualize it.
Originally Posted by Diapositivo
Rule number one with light meters is to always remember that regardless of what is measured the meter always displays a reading that should place that measured brightness as middle grey.
By pointing the incident meter at the source light you are choosing to measure something closer to highlight placement, as you might with a spot meter.
Pointing an incident meter at the source rather than the camera will provide a reading that creates an underexposure.
The only real exception to this rule is for sources like ring lights that are directly in line with the camera lens axis.
An incident meter will always take an average of what its sensor sees. Ideally that should be the same as what the camera lens sees. It's the intended use of that type of meter.
Now, what you do with that reading is something else entirely. You can intentionally over-expose or under-expose your film, and you can intentionally under-develop and over-develop it too.
I use the incident meter always with the dome pointed to the camera. Like Mark says, if I point it to the light source, you will not average what the camera sees, and it will not be consistent. Brightness range varies from scene to scene to scene, the light source could be of varying strength. The only consistent way of using the incident meter is to point it towards the camera to get an AVERAGE of what the camera lens sees.
I'm sure that there are other ways than my way to use the meter, and I'm not saying it's wrong to do so. But, I wouldn't want to try to keep track of brightness range of varying lighting scenarios with an incident meter. I was sure that that was what spot meters are for...
Sources I have at hand that say point the incident meter at the camera from the subject position (or along a parallel axis in the same light):
Gossen, Sekonic, and Minolta incident meter instructions, i.e. the people who design and manufacture the meters. (They also say to use a flat disc for metering lighting ratios while pointed at the light, but the dome pointed at the camera for the full exposure reading for 3D objects. And use the flat disc for photographing flat art.)
Six well-known and well-respected photography manuals: Vestal, Adams, Davis, London & Upton, Horenstein, and the Leica Manual.
So that's about nine for 'point at the camera'. As I said earlier, all the dozen or so studios I worked in pointed at the camera when metering for the exposure. (At the light source for measuring lighting ratios.)
Sources (besides Collins and acolytes on the internet) that I have seen that say always point the meter at the light:
The dome of an incident meter is a 'model' of a 3D subject. The reason it's pointed at the camera is so that it simulates the 180 degree portion of the subject that the camera can see, thereby reading the light incident on what the camera can see. If you point the meter off the axis toward the camera, you're metering stuff the camera can't see. Going off axis a little bit doesn't often change the reading enough for you to notice on film.
There are obviously times when metering with an incident meter won't work well this way. Say I had a backlit white scrim with no source of light on the camera side. I wouldn't get a proper exposure for the scrim if I incident metered from the camera side with the dome pointed at the camera. Both incident and reflected meters need an operative brain to get consistently proper exposures.
As always, you're free to use your equipment in any way you want. But it does pay in the long run to understand its design. As the unix guys say, RTFM.
P.S. It's apparent that a member of my very short ignore list is now in this thread, so this is my last post here since I'm not reading everything.
Don't completely agree if I get right what you mean (maybe I don't get it right though).
Originally Posted by markbarendt
With an incident meter you get an exposure value that is supposed to be right both if the subject is dark or is bright. (This is probably not perfectly true at the "extremes" of pure white and pure black which made the OP raise the question, but that's irrelevant now).
The incident meter give you a value that will have the bright (more reflective) appear bright and the dark (less reflective) appear dark with that light condition. The bright details will appear bright because they actually reflect more.
With an incident light meter, if there is a middle-grey subject you should have it as middle-grey, but if the subject is darker (portrait of a black man for instance) or brighter (portrait of a pale white man, for instance) you will have the same reading and you don't need to "place" zones.
The incident meter will not give you a reading that renders a certain subject as middle grey but a reading such as a middle-grey subject will be rendered as middle grey, and a bright subject will be rendered as bright, and a dark one as dark.
Only when using a reflected light meter you have to keep in mind that what is measured (not necessarily middle grey) will be rendered as middle grey.
Hope this is not a too pedantic post ;)
EDIT The point 2F/2F raises is that if the lighting ratio is low (similar lights) an average makes no damage, if the lighting ratio is high (quite different lights) an "average" will might lead to blown highlights. One controls the highlights with the exposure (pointing the lightmeter to the light source so as not to blow them) and the contrast with the management of secondary light. I find this to be perfectly reasonable and maybe this is also what Mark meant.
Incident meters are designed to measure the light that the camera will be able to see and give you a camera setting, to do that you have to point the dome at the lens. If there was a gray card in the scene it should expose as expected at zone 5. Skin tones, any, should fall appropriately also.
When you point the dome a different direction all bets are off.
Having the highlights blow is a different problem. You may want to measure that so that you can decide how to develop the film but in most cases with negatives, that's not a big concern.