Details about Metering Principles

Reflected meters (the necessary type in cameras) are aimed at the subject from the camera, and read the light reflected from the subject. For example, as demonstrated on the previous page,

• A white color (a dress or shirt) will reflect a lot of light (bright), which the meter sees as too bright, and will darken the scene to be middle tone.
• A black color (a dress or shirt) will not reflect much light (dark), which the meter sees as too dark, and will brighten the scene to be middle tone.

The Reflected meter averages the various colors and tones in the scene to be one average value, and this average tone will be placed to be at about middle tone. So if occupying much predominant area, white is often underexposed, or black is often overexposed. The meter is just a dumb chip, it just reads the average with no human intelligence to be able to recognize anything, or to know how anything ought to be. The middle is its only reasonable solution, not too bright, not too dark. Fortunately, many average scenes do average out to be a middle tone (a mix of many shades of tone, of trees, sky, mountains, faces, etc) and so often do come out near right, but there are many exceptions (for example, a white wall or a bright window seen behind the subject). We just learn these things, and must realize what we are metering, and must make necessary correction (Exposure Compensation).

We expect this, so when we walk up to a scene with major areas of untypical light or dark color, the alarms should immediately sound. We need to realize that we will need to take corrective action (because the reflective meter is going to be fooled). This is no big deal, it's just photography, and it's easy to learn how to handle it.

Spot meters (in some handheld and some camera meters). These are just reflective meters, but measuring only a small spot instead of averaging the overall scene area. Instead of the average of the larger scene, only that spot is made to come out as a middle tone. Beginners often don't understand that colors still matter, so hopefully we selected a spot color that should be middle tone. But as usual, we can compensate the exposure to correct it.

Incident meters (are necessarily handheld at the subjects position) instead read the actual light source (meter is aimed at camera to see the light, from the subjects position.) The meter is Not aimed at the subject. The middle of that range will be placed at the middle tone.

So this mid-tone middle leaves room for white dresses to appear white (brighter), and black dresses to appear black (darker). Incident metering is usually correct, because it does not see the subject, it instead meters the actual light incident on the subject, which makes it independent of the variations of colors reflected by the subject. Incident works for whatever is there in that light. So then any subject's tone, be its colors light, dark, or middle, is shown as it is. Kind of a big deal. Incident meters have the accuracy that newbies imagine their reflected meters ought to have (but can't). This is not possibly done at the camera, incident meters meter the light incident on the subject (actually from the subjects position, which is all important due to the Inverse Square Law). However, it can be less convenient to meter at the subjects position instead of just pointing the camera at it. Incident metering is sort of point and shoot metering, and probably correct and is extremely useful in studio situations.

Meters like Sekonic L-308X-U often offer both metering methods, incident or reflective.

Incident meters tell you settings for how bright the light is, and reads either continuous light or flash. It reads the incident light directly. Reflected meters tell you setting about how much of the continuous light is reflecting from the subject's colors. Reflected meters are extremely popular, and are used from the camera location, but we need to learn a bit of skill about using them. Incident meters are metered at the subject, which is extremely desirable for manual studio flash. The article on next page compares a reflected meter in a camera, with a handheld Sekonic L-308S incident meter.

Three Ways to Meter Light

• Metering the light with a handheld incident meter (reading light incident on the subject, at the subject's position, because inverse square law applies). This is independent of the subject and the reflectivity of its colors. The meter is aimed away from the subject, toward the light source (specifically, actually aimed at the camera lens, and the hemispherical dome worries about the incident angle of the light). The point is that we are actually metering the incident light, instead of that portion of it reflected from the colors of the subject. If we measure the direct light itself, then in the subject, black things should come out black, and white things should come out white (we still might have to compensate slightly, if we want them "more white" or "more black" than the general case). Generally, since the reading is not influenced by the subject colors, there is less question about if the incident reading is accurate or not (but our metering technique can introduce variables — we learn to be consistent). Again, the advantage of incident metering is that it is independent of the subject's reflectivity, it measures the incident light directly. The disadvantage is that we must walk to the subject's location (metering under their chin, so to speak), to measure the effect of the inverse square law at their location. Meters built into cameras cannot do that, they are not used at the subjects position.
• With a reflective meter (like in the camera), pointing the meter at the subject, directly metering the light that is reflected from the subject colors. This does Not measure the incident light level, but only how much the colors reflect. Reflected meters are the usual case, but as was shown on previous page, in the case of any of the individual gray, white, or black cards, everything is going to come out being the same middle gray intensity average. This is true of brides in white dresses, or grooms in black tuxedos too. The reflected meter reading is dependent not on just the light intensity, but also on how much of it the subject's colors can reflect. This is just what reflective light meters do (you did see the previous page?).

  NOTE: A cute habit is that I usually say middle gray just meaning middle intensity as seen by our human eye. It seems the right word to me, but maybe it's a habit from the old B&W film days? I don't mean gray unless it started at white or black, either metered value being reproduced at middle gray intensity. But Red or Yellow or whatever won't be gray, but will be a middle intensity.

  So we might tend to question the meter's accuracy here, until we understand what the meter is able to tell us. The reflected meter reading is dependent on the subjects reflectivity, and regardless of however bright or dark that might be, the camera will try to place the average of that result at a middle gray intensity. So even if we might imagine 18% ought to be at histogram midpoint (it is 18% actually, but gamma can fool us thinking it is higher). But you should know it won't matter which card on previous page that you photograph, you will get a middle intensity average. But the photographer can see this subject, and ought to learn how the meter will respond, and then we stand ready to help correct it. We simply just know that white or light colored things will be underexposed, and black or dark colored things will be overexposed, and we plan ahead for it. This is the purpose of the Compensation buttons on the camera. Camera metering usually can be selected from Matrix, Center Weighted, or Spot metering (more below).

• Spot Metering is just a special case of Reflective Metering. It is mentioned up here first because there are dedicated external spot meters, but the cameras can do that too now. TTL flash does not do Spot metering (nor Matrix metering either, even if the camera selects it. Flash has its own fixed center metering system), but for the ambient light, Spot Metering isolates a small metered area from the background (not influenced by the background), so that the small spot will be made to come out middle gray intensity, regardless of any other area, or regardless of the intensity the spot color ought to be. Spot metering absolutely does NOT mean the spot will be "correctly metered". Far from it, it only means that spot will be made middle gray brightness (which is what light meters do). So choosing a spot that ought to be middle gray has the best chance. There are not so many of those, but the way Spot metering is often used for example, is to meter on a Caucasian face, which is known that it ought be compensated about +1 EV to be a normal appearance. Do be prepared to adjust your compensation though. This is in contrast to Center Metering averaging a larger area of several tonal values of the picture to often come out averaging middle gray intensity (which the larger mixture of colors generally has better odds of being "correct", averaged brightness actually being middle gray intensity).
• This seems a good place to again mention the oldie but goodie Kodak Tech article, Accurate Exposure With Your Meter, that is linked on the previous page. It is about how to use your light meter in ambient light. All this about metering has been known for many years, and it's definitely about the first fundamental thing beginners need to learn. There is more to photography than just point&shoot.
• And it needs to be said somewhere that TTL flash metering is something different. It is reflective metering from the reflected colors, and it is much like Center metering, but not the same as the camera's Center metering menu. TTL meters the very brief preflash pulse instead for the longer shutter duration. I am only familiar with the detail of the Nikon TTL flash system (including old film TTL and todays digital iTTL flash), but it is handled different (and I doubt the other brands are much different). This is true of the cameras internal flash and also the hot shoe flashes. Speaking specifically Nikon, flash metering in the camera is much like Center metering, but is quite separate, and it does not respond to any of the camera's Center Metering controls. But flash is metered in a central area, of slightly different size and which is moved to follow the focus spot in the viewfinder.

  Nikon flash has two modes named TTL or TTL BL, which are metering differences. I will try to say TTL mode when it has that meaning, and just TTL when it means either mode. TTL mode can only be selected on the flashes own menu, and not in the camera (with the exception that if the camera selects Spot Metering, then TTL BL mode is forced to be TTL mode (Spot has no background to balance). The camera settings are set first from the metered ambient, and the TTL flash adjusts flash power level to work with those settings (exception is that some camera models closer to top end have the menu E2 Flash Shutter Speed which sets a Maximum shutter speed with flash (30 seconds to 1/60 second), and that typical default is not slower than 1/60 second unless this option is set off. Because normally we would NOT want a shutter speed slower than 1/60 second. This is NOT a metered exposure then, but merely a limit keeping shutter from going very slow, which then results in the background being underexposed. But we are using flash instead (and the shutter speed can go faster to the actual metered value if the light is stronger than this limit). But then TTL mode flash mode ignores ambient and first sets flash power level for whatever is needed for the flash to work alone (as the Main light, basically same as a Guide Number calculation). If ambient is usefully strong, then this results in overexposure unless Flash Compensation corrects the flash exposure, like maybe -2 EV Flash Compensation.

  Or TTL BL is the Balanced Flash mode) and is the camera flash default unless specifically set otherwise to TTL mode in the flashes menu. Balanced Flash means the Ambient (if strong enough) is the default main light, and flash is adjusted down to be at Fill flash level for the ambient light. Indoors, this is likely mixing White Balance values. So in bright sunlight, TTL BL would likely reduce the flash exposure that -2 EV just mentioned, in that case. But if ambient is insufficient level to be a Main light (true of most indoor situations), then the flash becomes the main light. But the flash will not do Spot Metering or Matrix Metering, nor even the same Center Metering. Flash simply has its own methods, very similar to Center Metering, but in its own system regardless of what the camera selection for ambient is. Flash exposure is of course only meaningful at the one distance of the main subject, since flash illumination falls off with distance.

Middle gray is a term with special usage in photography. It just means our eye sees it as mid-tone. It does not necessarily mean gray, but might be mid-tone green or blue in such a color image, but it would be middle gray in a black and white image. It's an old term from B&W times, which conceptually means mid-tone in the human eye which sees 18% where we would call it 50% (but middle does NOT mean 50%, and does NOT mean middle in our gamma histograms). I still tend to habitually say middle gray when thinking mid-tone. More below about "18%".

The simplest trivial test is shown next, anyone can easily check this. Spot Metering DOES NOT mean correct exposure of the scene, or even of the spot, or of anything. It only means the spot will come out middle gray (mid-tone), regardless if it should or not. So if you selected a spot that should be middle gray, it could come out correct, but the results depend on which spot you choose, and how you will compensate it. A typical usage example of Spot metering might be that a Caucasian face ought to be about 1 EV brighter than middle gray, so Spot metering on the face also with + 1 EV compensation might come out OK.

No compensation was done below, and each Spot case here varies exposure of the background substantially. Reflective meters only seek a middle gray result, including Spot metering. Spot metering simply produces a middle gray spot, on whatever Spot you choose, but you can compensate it as you please. It is up to you to know how to compensate it correctly. My concern is that beginners don't seem to realize this, seeming to think of it as something that can produce magical results, but instead Spot metering is an advanced subject, the furthest thing from point and shoot, and it's important that you should know something about what Spot Metering does before trying it.

Example of Spot Metering: D800 camera A mode, f/5.6, ISO 100, hazy bright sun, near noon. Black and gray and white cards.

My point was to show that Spot metering reproduced the black card as middle gray at 1/60 second, or the gray card as middle gray at 1/400 second, or the white card as middle gray at 1/1250 second. Yes, the 1/60 second certainly helps the background shadows, but it blows out the cards — the card results were overexposed, and simply not the black or gray they should be (the black card comes out middle gray). Or spot metering on the white card makes it come out middle gray. Spot metering merely makes the selected spot be middle gray. That could be correct or not, which is your choice and your call and your responsibility. Note Spot metering only sees the spot, and totally ignores all the rest of the scene.

So the point is, if using Spot metering, you also better know how to compensate so the spot comes out its correct brightness. There is much thinking involved in spot metering. If spot metering on a Caucasian face, it is common knowledge that a proper starting point is to open up one more stop. You need to know too. The human brain is the most important light meter accessory. 😊

As said on previous page, black reflects little light, and is seen as dark, and then the camera meter overexposes it to get middle gray. White reflects a lot of light, and is seen as bright, so the meter underexposes it to get middle gray. That is simply how reflected meters work. It is all they can do. They cannot recognize the scene to know how it ought to be. It is very helpful to realize this. The Center Weighted metering saw a large center area of mixed colors, and averaged that result to middle gray, which is generally about correct in typical cases. Matrix metering saw that too, but also saw the sky area at the edge, which was pretty bright, so in this case, it reduced the exposure (1/3 stop). But IMO, my subject was in the center, and I'm a fan of Center Weighted metering.

We spot meter to ensure that spot comes out middle gray intensity (specifically, for the purpose to be independent of all other areas). We might Spot meter on a face to isolate it from the background, but hopefully then we know we must compensate about +1 EV to make the face come out right. Odds are that Center metering (which includes more spots, more area) normally has a better chance. I'm just trying to say, Spot metering is no magic plan, it is very special, and instead it requires considerably more thinking and knowledge about what we are trying to do. We should know how we plan to compensate it. The concept of Spot Metering has no meaning for Incident metering (which the camera cannot do anyway). If we meter the incident light itself, all spots will be reproduced with reasonable accuracy.

Spot metering has unique meaning for TTL flash. The flash system does NOT do Spot metering (flash has its own central system). But selecting Spot does switch TTL BL mode to be TTL mode — meaning no balancing with background. This is because ambient Spot is about the spot, and has no knowledge or concern about the background. And again, only ambient light does spot metering, the flash system does not, but TTL mode does switch off reducing the flash for the ambient. Spot metering is often used for flash indoors to force TTL (more below).

General Metering Variations

General camera reflective metering is greatly affected by the reflectivity of the subject's reflected colors.

Exposure methods that are independent of variable subject color reflection:

• Incident metering (next page) directly measures the actual light at the subject, independent of subject colors reflections.
• Reflective metering on a 18% gray card in same light (next below) - Ballpark for many average/typical scenes.
• Sunny 16 Rule - Judged by approximation of outdoor shadows, Not metered, Not precise. Popular before 1960, but your meter today is better.
• Flash Guide Numbers - Handles Inverse Square Law for direct flash, if Guide Number is accurately known.

Gray cards: We can directly meter the reflection off of a 18% gray card (from close, including nothing else in that meter's view), and then use the same exposure settings for a scene in the same light (assuming scene and card are in the same light, and at the subjects position — same distance from the light — inverse square law always applies). Then the camera will expose the subject in the same way. This simulates using Incident metering, in that the light incident on the gray card will be independent of the reflectivity of the actual subject, and will instead depend on the reflectivity of the card (chosen for the purpose). Specifically, this means that any tones in the subject which average to match the cards 18% reflectance will also come out middle gray intensity.

Or we can use the open palm of our hand as a gray card. Metering from our outstretched palm is not "average", and will be nearly one stop brighter than 18% (is more like spot metering from the face). Then we know that we will want to set the camera for about one stop more exposure. No matter what we meter, a reflected meter will place the result at middle gray — regardless of where it "ought" to be placed. Then we compensate for how THAT middle gray differs from the actual scene's actual gray average. The metered object must be in the same light (and same distance from light source) as the intended subject.

And there are other metering tricks possible (called technique). Say the subject is sitting in the shade under a tree with very bright background, or is indoors with their back to a bright window. In those cases, our camera meter mostly sees the bright sunshine background behind the subject. It does not understand that the background is not our subject. It exposes for the bright sunlight, and the picture of the subject comes out very dark. Spot metering can help then, or faster, we can just aim the camera down lower, maybe as far down as to focus on their feet, specifically down enough to exclude the bright background, and then meter there. The light level is often about the same lower there, and the subject distance is essentially the same there (our brain is a great tool to evaluate situations), but this view specifically omits the bright problem outside. Half press the shutter, and hold to lock this reading (locks metering and focus), then raise camera to reframe, and the final shutter click will use that locked meter setting for this subject (Nikon AE-L Exposure Lock options can interfere or modify this method which is menu C1 on some). But this new result will be greatly better than ignoring it, normally it is very satisfactory. If you instead also want to maintain the exposure of the bright outside, then you meter on that, and will need to use fill flash, to equalize things.

Old timers all understand this. Novices imagine their fancy modern camera ought to understand it too, but this blind faith will be disappointed. Instead, it all works as mentioned above. The meter is a helpful guide indeed, but just watch, and always do what you see you need to do. Sometimes it can be too big a job for a dumb computer, but the human brain can always help.

Ansel Adams thought his Zone System's middle zone 5 ought to be 18% reflectivity, and he promoted the 18% card notion in photography (in the 1930s). I cannot imagine that Ansel could have ever seen a digital image or a histogram back then, so don't confuse the two systems, analog film and digital. However, our meters today are set to 12.5%, (thought to be more realistic, on average), and Kodak says we will need to open 1/2 stop if metering on their 18% card (this 1/2 stop more is equivalent of 12%). So any and all scenes are metered to come out about 12.5% middle tone average — regardless if they are typical 12.5% scenes or not (the reflectance of the scenes colors can vary away from "typical"). If photographing that card itself (as previous page), then no matter which card you meter, black, white, or gray, these cases do cause very different exposure settings, with results always near the same middle tone. None are necessarily at 128 on the histogram, which is simply the wrong idea (the histogram data is gamma encoded anyway — and the 18% card was an analog film concept). There is also a Gray Card page here.

It should be obvious that any plan to calibrate a light meter by metering an 18% gray card is not the best plan. This was popular in analog film days, and it is not far wrong (perhaps a bit practical, but it is NOT theory). Kodak always told us if metering on their 18% gray card, we should open 1/2 stop more exposure. And the Sekonic calibration method does not mention an 18% card, but the specifications do specify the 12.5 constant (reflected). But a digital histogram is something else (a related link, explaining why 18% gray is Not the midpoint of the histogram we see, is at Histograms are Gamma Encoded). Metering the 18% card has no calibration significance (any scene will come out middle tone, a white card and the black card too... what significance is the 18%?) The correct way the 18% card is used is that we can meter from it, and then use that reading for the exposure of some other general scene in the same light. Kodak always said to open 1/2 stop more. Most wide range scenes (beach scene, mountain scene, sky and water and trees and human faces) do often average about middle tone, which is what lets reflective meters be useful, since that is what they do too.

The camera meter is a "reflected" light meter. A reflected meter is aimed at the subject, and reads the light reflected from the subject (which is very variable, depending on what it is) The reflected meter tries to make all scenes it sees to average out to be near middle tone. That is all it can do. This is more easily seen with a blank paper subject, but all scenes come out averaging a middle tone. The meter is calibrated to make that result tone be about 12.5%. Post processing can change it. This value is NOT related to the center of the histogram. This value is not related to an 18% gray card — 18% is not a factor. The meter's "calibration" value and result causes this one same resulting middle gray tone intensity — from any subject.

Techie details: Sekonic specifications are in all of their manuals (L-358 for example) specifically shows their reflected K=12.5. Wikipedia explains more and says "ISO 2720:1974 recommends a range for K of 10.6 to 13.4 with luminance in cd/m². Two values for K are in common use: 12.5 (Sekonic, Canon, Nikon) and 14 (Kenko and Pentax). The difference between the two values is approximately 1/6 EV." (Minolta meters are Kenko now)

A quick summary: There are normally many colors in our subjects scene, but we can only set one camera exposure for any one picture. So correct exposure generally means something like this:

• Hypothetically, our goal is that we hopefully meter a middle average value for the scene. Brighter colors will then come out brighter, up near 255. Darker colors will then come out darker, down towards zero. Middle colors will come out more middle. Every color finds its level. The purpose of a histogram is to show the distribution of those bright and dark tones (our normal purpose of looking is only to check exposure, to ensure no clipping, etc).
• If we directly meter the subject with a reflected meter, we aim the meter at the subject. Its reading is influenced by how the subjects color reflects the light to the camera. Bright colors reflect well and read high, dark colors reflect less and read low. The meter will place either scene in the middle (but a bright or dark scene probably is not correct at middle). So a brightly colored scene (like white) will come out underexposed, and a dark colored scene (like black) will come out overexposed. Bright and dark is speaking of the colors and their reflectivity, and is NOT about the light level on the scene. Meters can handle light level, but are ignorant about how it ought to be, about color and reflectivity. Bright can be about any color, it refers to tone and reflectivity. Many "typical" scenes of mixed colors are an average mix of reflectivity, and do reflect an "average" amount of light, which exposure often works out well. But some scenes are not very typical, and don't (a kid playing in the snow for example, the white snow will underexpose it). Bottom line, we must learn to pay attention to the colors in our scene, and react accordingly (with exposure compensation). Novices expecting the camera to always get it right are due for big surprises. 😊 The camera is just a dumb computer, but the only brain present is in the photographer. The reflected meter is only a guide, but a good one which we can learn to use well (involves thinking now and then).
• If we instead meter with an incident meter, then from the subjects position, we aim the meter at the camera (aimed away from the subject), and directly meter the actual light incident on the subject. Then the bright and dark colors will find their own correct level in that properly metered light. As good as this is, it is necessary to be in the same light AT THE SUBJECTS POSITION, which is rather less handy than point and shoot. However regarding exposure, this is the point and shoot, it works. It doesn't get better than this. Incident meter accuracy generally even lives up to novices expectations (if they can tolerate the use), but reflected meters... well they don't, it depends.
• Or metering on an 18% gray card with a reflected meter (and opening 1/3 stop more) sort of simulates an incident meter, so long as in the same light at the subjects position. The point is that it is also independent of the subject and its colors. Metering the reflectance of known middle gray in the incident light at the subject is sort of an inexpensive incident meter, but slightly less handy yet.

Camera Reflective Metering Modes

The mode topics below are about metering ambient light. Nikon TTL flash metering will be a different concept.

Spot metering - Speaking of metering ambient: Beginners beware. Spot Metering (ambient) is a techie tool that requires greater experience, definitely NOT point and shoot method (is about the furthest thing from it). You are advised to really know what you are doing with Spot metering. Only a small spot in the frame is considered, at the current focus point. Spot metering isolates this small area from the rest of the frame. The idea is NOT about "correct" exposure, the only idea is that this small spot area will be made to come out middle gray (correct or not), and all the rest of the frame is ignored — the rest comes out however it does, when this spot is made middle gray intensity (not color, but brightness). Only that small spot matters, that small area will become middle tone.

Speaking of metering flash: Spot metering is NOT Spot Metering for TTL flash — it is still regular old flash metering. The ambient light might be set to Spot metering then, but its level indoors might be well below the flash except Spot mode does silently switch TTL BL flash metering to be TTL mode metering (i.e., Spot is never concerned about ambient background). For ambient, yes, it can be Spot metering, not concerned about any of the rest of the frame — it only sees this tiny spot. But the flash metering will see a much larger area. Spot metering of ambient has no concept of a background to match, so Nikon TTL BL flash metering will change to become TTL mode if Spot Metering. Note that's about the only change for indoor flash, since the indoor ambient level is typically far below the flash level (ambient metering ignored, Spot or not), so then all Spot really does for indoor flash pictures is to force actual TTL mode (vs default TTL BL mode). Which might be a good plan sometimes.

Spot metering is NOT a general purpose metering mode for beginners — Except it does become more general with metered flash in dim ambient areas. Because Spot metering does switch TTL BL to be TTL mode (independent of background). Novices mistakenly confuse Spot metering with a general purpose metering mode, and assume it means that this spot will come out correctly exposed. But reflected meters don't "come out correctly exposed", and Spot metering is a very special case (only about that one spot), and it just means that spot will come out middle gray intensity, which is NOT about being "correct" — unless hopefully, we choose a spot which ought to come out middle gray (which puts the full responsibility back on the photographer). Frankly, for beginners not understanding the details yet, bracketing multiple exposures seems more helpful than spot metering — helpful both to produce immediate results, and to aid learning about the compensation that various scene types require. Pretty soon, you will just already know.

Center Weighted metering - The entire frame is metered in some degree, but significantly greater importance (weighting) is given to a large center area (default diameter is roughly half frame height, but is adjustable). There is no sharp dividing line at the circle, the boundary slowly tapers, typically like a Gaussian Bell Curve. Usually the center area is weighted about 75%, i.e., tones in the center count as 3x more important (toward the picture's average) than at the outside edges. So the outside edges are only weighted about 25% (not as important as the center), but the frame edges are not ignored (i.e., white edges will meter higher than black edges.) All of this area is averaged to one average tone, and exposed so that this average tone is made to come out about middle tone. It is very suitable for many typical or average scenes, especially portraits, because subjects are often in the center of the scene. Note that while we might move the focus sensor towards one edge of the frame, but Center metering remains in the center. Matrix metering will move with the focus point.

Matrix metering - The focus point area has substantial weighting, but a wide area of the frame is also watched for exceptions, with the camera firmware making other judgments to factor in areas with exceptions. These rules are unknown to us, it does what it does, a mystery to us, but often pretty close. Don't assume too much magic however (and Nikon TTL flash meters in the center of the frame).

As your skills grow, and they will, then by thinking about it, you will acquire a better understanding of when it might be beneficial to use other metering options.

Maybe Matrix can help beginners, but no one knows what Matrix does, or will do, other than we know it watches the full frame. It surprises me when there is some bright spot somewhere at the edge, when it will cut back on the exposure of the full frame (like next below, and like in the first pictures above).

So as an oldtimer, I'm a big fan of Center Weighted metering myself (usually where my subject is). The Nikon default is the center area diameter metered is half of the frame height, but there are menu options to resize it. The term 75% center weighted means that while the outer frame edges are seen in some degree, this center area counts for 3/4 of the importance of the exposure. Not at all a sharp dividing line, it is a Gaussian function (Wikipedia) gradually feathered out to the edges, but the effect from the edges is minor. The center subject is the important thing.

Flash does NOT do Spot or Matrix metering.
Ambient can, but TTL flash does Center metering.

The camera metering modes of Center, Matrix, and Spot refer only to the ambient light. The TTL flash system has its own metering method and area (which is always a center area, similar but not exactly same area as Center Weighted). However, there can be a big effect on flash. Spot metering mode does switch the flash metering mode from TTL BL (balanced) metering to be TTL metering. Here is a quick example. It has a bright North window at left (intended to be hard for Matrix), and a black card at the center focus spot. Nothing easy about it. Nikon D800, camera A mode, SB-800 hot shoe direct flash, no compensation. All pictures are f/5.6 ISO 400.

Showing that Matrix can affect the ambient differently than Center (depending on what the metering area sees), but Matrix or Spot does not affect the metering zone of the flash. Spot metering certainly affects the ambient (the Spot tries to become middle gray intensity, which is NOT ALL the same as becoming "correct"), and Spot Metering selection does switch TTL BL flash metering to be TTL flash metering, and TTL mode is NOT balanced with ambient, but Spot does not affect the metering zone of the flash.

The flash pictures were all were 1/60 second (minimum shutter speed with flash in camera A mode), which is less ambient exposure than even the 1/40 second metered above, which underexposes indoor ambient, a couple of stops here without the flash. A better try would be to use camera Manual mode, to be able to set any shutter speed desired to obtain any desired ambient effect. But here, we let automation run, this is camera A mode, which does 1/60 second in indoor flash situations. Basically indoor levels have reversed things — the reduced ambient is now the lesser fill level for the TTL flash (outdoors in fully metered bright sun would be the opposite). Larger differences certainly are possible sometimes, but this is an (easy) middle gray subject, and these flash pictures are mostly alike, the point being: TTL flash metering is not affected by Matrix or Spot metering of the ambient. Two complications are that TTL BL flash level is reduced to accommodate bright levels of ambient, in Center or Matrix metering modes. In Spot mode, TTL BL is changed to be TTL mode.

In the middle row with TTL BL flash, Matrix metering of brighter window ambient reduced the (balanced) flash level slightly. However, notice that the window dark shadow at right behind chair is still visible (there are two exposures here, ambient and flash). If this had been a full proper metered ambient exposure, we would see a large difference in TTL BL and TTL flash mode.

Spot metering would have still affected the ambient if faster shutter speed had not forced underexposure. What Spot metering does for flash is to change TTL BL metering mode to be TTL mode (no influence to reduce TTL flash by the ambient). Said again, Spot metering only affects the ambient metering, except it changes TTL BL flash metering to instead be TTL metering, but which is Not Spot. There are only slight hints in this try, hard to see here with the other influences, so claims are based more on experience. TTL BL indoors does often tend to need more +EV Flash Compensation than TTL (maybe +1 EV), but both are dependent on reflective metering. Balancing flash with ambient is not much factor indoors, normally ambient is well down at minimum shutter speed with flash (unless ISO is high). This picture is an exception, aimed into a bright window light, more in between indoor and outdoor (regarding bright ambient). Otherwise, my routine starting point for indoor TTL BL is +1 EV Flash Compensation. But for TTL mode indoors, then 0 EV (starting point). In bright sun outdoors, it is TTL that needs about -2 EV compensation, when TTL BL does not.

The last row with TTL flash are all rather equal flash exposure (not affected by Matrix or Spot metering). When comparing TTL BL and TTL, larger differences are possible, but Spot is more alike because both are TTL (which does not Spot Meter).

This one test situation should not be considered typical of all comparison situations. We can easily contrive other TTL vs TTL BL situations to show different results, either way between those two. TTL is a computer program looking at light from reflected subject colors and trying to decide what it is, and what TTL exposure should be. TTL BL is also that, but with more program trying to decide how much to reduce the flash due to how the ambient reflected colors look. I hope to not be discouraging, it is not difficult at all. Just pick one system (either one you have), and learn what it does and how to use it, and all will be good.

You can also do simple tests like this. You should, so you can see it, and will know what to believe. At least in photography, we ought to be able to see what we claim to believe. But do try a different thing or two to see if notions still hold up.

Note that Spot metering with flash indoors can normally be said to have Only the effect of selecting TTL flash mode, because:

• Flash mode never does Spot metering, only ambient metering can. Spot does prevent balanced metering of the flash (since only the spot was metered), which does then force (unbalanced) TTL flash mode. TTL flash mode (unbalanced) can be a plus for flash indoors (less underexposure).
• Ambient is normally dim when we need flash. Since the ambient indoors is so far underexposed anyway (relative to the strong flash), it normally doesn't matter how the ambient meters, since it does not register very well anyway. Camera A or P modes enforce (typically) a 1/60 second minimum shutter speed with flash anyway, which ensures dim ambient is true (Slow Sync or Rear Curtain Sync are exceptions, allowing very slow shutter speeds with flash).
• We can easily use camera M mode (indoors with flash) since the indoor ambient level is typically too low to matter at any reasonable shutter speed anyway (and the TTL flash is still automatic flash in any camera mode). We could use a slow shutter speed to pick up the ambient better, but it's our choice, since camera M mode settings are Manual, the manual settings are not affected by the camera metering, Spot or otherwise. Spot metering can affect what the meter reads, but Manual mode ignores the meter reading (Auto ISO may be an exception, in some TTL flash cases (some camera models) Auto ISO can be affected by meter reading).
• So normally, flash indoors usually only means that Spot Metering selects TTL flash mode, nothing else (Slow Sync and Auto ISO can be exceptions). However then going outdoors into daylight with Spot is a very different story.

There is more about TTL and TTL BL flash metering in Fundamentals Part 4.

I used Matrix metering for those rose and card test pictures on previous page (only because many people do), but I normally always use Center metering, to emphasize the central subject more than the edges. Center metering is very useful for portraits, or even for this rose (Center more nearly matches what TTL flash metering will do). Center metering still works for scenes like landscapes that may not have any central subject (they do still have an average tone). We ought not to imagine any great understanding is present in any metering system. It is just a computer chip, which sees some light, and can measure it, but with absolutely no idea what it represents, or how bright it ought to look. The meter's only goal is to make whatever it is come out middle tone — all it knows, all it can do, which happens to often be an acceptable result.

My human brain can almost visualize and understand Center metering, to help predict the result, and my own notion is to skip the automation of Matrix metering and TTL BL flash mode, simply because I know it never really has a clue about what the subject is, and I'm never sure what it's going to do. Possibly the automation can help sometimes, but as a personal philosophy, I simply try to avoid those unknown complications. 😊 But regardless of your method, you will always need to watch and stand ready to help. YOU are the photographer. No one else is going to do it. Your human brain is the only intelligent tool present that can judge "correct" or not. Your human brain is the only intelligence present that can recognize a black cat in a coal mine from the polar bear on the snow. Any reflected meter is going to make both come out to be middle gray intensity. Realizing this makes all the difference.

This is NOTHING new, reflective light meters have always worked this way, for many decades. Don't skip that previous Kodak link: Accurate Exposure With Your Meter. Kodak is gone now, but their classic tech article is available.

In contrast to Reflected meters, Incident meters measure the incident light directly, independent of, and without reference to the subject — so then it is not about how the subject's colors reflect light. Incident is about the light itself, and typically more accurate (without that influence) — But incident meters must meter the light actually incident at the subject's exact position (Inverse Square Law). Direct sunshine may not matter where you measure it (it is typically the same everywhere), but any incident light more local than that cannot be metered from the camera position.

So there are often more factors than merely aiming the camera (thinking about what we see does always help). It was shown how reflective light meters work (meters in cameras are reflective meters). Reflected meters only have this one way they can work. They are a dumb silicon chip, without any human brain. The meter has absolutely zero recognition about what the subject is, and has zero knowledge how it ought to look. The meter does not know if the subject is black and ought to be dark, or if it is white and ought to be bright. The human brain probably recognizes it instantly (in its surroundings), but the meter has absolutely no clue — no brain. The meter simply sees a blob of light. It can measure that light accurately, but it has absolutely no clue what it means. Its best try is going to make that light come out middle tone, which is a good compromise, considering — not too dark and not too bright, perhaps usable. The reflective light meter's every answer is "middle gray". However, every subject may not be. It is good that we realize this, to work with it, instead of against it.

The reflective meter can only attempt to reproduce whatever it may be, to come out as a middle tone average. And this middle tone will be halfway ballpark (not too dark, not too bright, but close enough that we can recognize the subject), but if that result is correct or not depends entirely on the subject that it sees. Most typical scenes do have wide range (portraits, beaches, mountains, jungles), and do average out about middle tone, which is how the system works. But not every scene is a typical scene.

The photographer does need to keep a close watch on things. Bottom line, we can moan and complain about what the meter does, or we can simply just watch and learn to easily fix it. This latter way works much better. It is called experience.

We certainly need to be aware of this, so a similar experiment is one of those things which you should try at home. To become a believer, you should do similar tests as these, yourself (previous page), to see it, to believe it, to be able to use it. Just do it, so you understand it. If you are metering a light scene (meaning, colors which reflect much of the light efficiently), it is going to come out underexposed. If you are metering a dark scene (meaning, colors which do not reflect so much), it is going to come out overexposed. Because, both will come out averaging middle gray intensity, which may or may not be a "correct" result for that scene. Our human brain can recognize this and plan ahead. The least we can do is to look at the result and compensate. What we ought not do is to act surprised. 😊

The meter is a big help, and it is still pretty easy. The idea is, you have eyes, you have a brain, and if you use them, then with just a little experience, you quickly come to know that a light scene with enhanced reflection (a white dress, a beige wall, the snow covered ground, etc) will need additional exposure, more than TTL thinks. You quickly come to know that a dark scene with relatively little reflection (black tuxedo, dark colors, dark open background, etc) will need less exposure than TTL thinks. Pretty soon, you will just already know about how much more. A little experience goes a long way, just think a little about what you see in front of your camera. Digital is easy, it allows us to see the first exposure result, and to react.

Continued - A Histogram is Not a Light Meter

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