Details about Metering Principles

If thinking of skipping this page, there is a Summary of Flash Metering Principles below.

Two Types of Light Meters

There are two types of light meters, reflected meters (at left) aimed at the subject from the camera or from the camera direction, which reads light reflected from the subject. And incident meters (at right) aimed at the camera from the subject position, which reads the actual direct light incident upon the subject - at the subject, but totally independent of the subject. Since cameras are not located at the subject, they can only use reflected meters.

Three ways to meter

• Metering the light with an incident meter (incident on the subject's position, because inverse square law applies). This is independent of subject reflectivity- the meter is aimed away from the subject, toward the light source. 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.

• With a camera's reflective meter, pointing the meter at the subject, directly metering the same subject that is photographed. This is the usual case, but as was shown in the case of any of the individual gray, white, or black cards, all are going to come out being the same middle gray. 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, but also on how much of it the subject's colors reflect. This is just what reflective light meters do (shown on previous page). So we might tend to question the meter's accuracy here, until we understand what the meter is telling 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.. So... even if we might imagine 18% ought to be at histogram midpoint (it is not ), you should know it won't matter which card you photograph, you will get a middle 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.

  Spot Metering is just a special case of Reflective Metering. Spot Metering isolates the small metered area from the background (not influenced by including the background), so that the small spot will be made to come out middle gray, regardless of any other area. It does not mean the spot is "correct", it only means that spot will be made middle gray. This is in contrast to averaging a larger area of the picture to come out averaging middle gray (which larger mixture generally has better odds of being "correct" as a middle gray average).

• 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 (also implying scene and card are at same distance from the light - inverse square law always applies). Then the camera will expose the subject in the same way. This is more like 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. Specifically, this means that any tones in the subject which match the cards 18% reflectance will also come out middle gray.

  Note that the term middle gray card (analog) and midpoint of the histogram (digital) are not the same thing - very different concepts - not related in any way. Generally, the card idea is that if we think this subject's average overall tone matches an 18% card, the result will come out about right. And it often about does, at least for many typical wide range scenes, but Kodak tells us if we meter the reflection off of their 18% gray card, and then use that exposure for a scene in the same light, we should increase that exposure by 1/2 stop. If we meter on an 18% card, and then open Kodak's 1/2 stop, that is the same as metering on a 12.7% card, all else equal (our light meters probably use 12.5%). This method provides a known reflectivity to be metered, metering an actual middle gray subject, which the meter will make it come out middle gray, therefore striving for a more accurate result - specifically independent of the subject. Be sure to angle the card slightly to prevent any shadows or overly bright glare/flare.

  The idea is that this gray card method is independent of the subject's own reflectivity values (like incident metering is independent). Any error this way depends on the difference in the scenes actual average, and the 18% card's average. It can also be done several other ways. If in bright sun, metering from the clear deep blue sky (low, and away from sun) works about the same as an 18% card. A green grass lawn is close too. In the old days, Kodak told us metering on the yellow box the film came in (included black ink) was about the same. Don't expect great precision, things will vary every time you move your camera - we are speaking ballpark. And this logic will always still depend on your actual subject also being average.

  Or we can use the open palm of our hand as a gray card. Metering from our outstreched 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 of course 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, or 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 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 (for shutter half press to lock exposure, Nikons may need one of the AE-L Exposure Lock options to do this, menu C1 on some). Result will be greatly better than ignoring it, normally it is great. But 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% notion in photography. I cannot imagine that Ansel could have ever seen a digital image or a histogram (in the late 1930s), so don't confuse the two systems, analog film and digital. However, our meters are set closer to 12.5%, (thought to be more realistic, on average), and Kodak says we will need to open 1/2 stop if using their 18% card (this 1/2 stop more is equivalent of 12.7%). So any and all scenes are exposed to come out about 12.5% middle tone average - regardless if they are typical 12.5% scenes or not. 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, but the results are always near the same middle tone (as here). BTW, 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).

It should be obvious that any plan to calibrate a light meter by metering an 18% gray card is not a well thought out plan. This was popular in analog film days, 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). Photographing the 18% card has no significance (any scene will come out middle tone, the 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. 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 - from any subject.

Sekonic specifications (L-358 for example) specifically says 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 (Canon, Nikon, and Sekonic) and 14 (Kenko and Pentax); the difference between the two values is approximately 1/6 EV."

Camera Reflective Metering Modes

TTL flash - Is largely undocumented by Nikon, but my notions are this: We can forget about Nikon Matrix and Center and Spot metering for indoor flash (unless using high ISO to create significant ambient). Those modes are about metering Ambient continuous light. But the Nikon iTTL flash system is a separate system with its own methods. It seems apparent that flash instead meters in its own spot always in the center of the frame (does not follow the focus point). In significant ambient, Matrix metering mode might affect the ambient metering, and therefore how TTL BL flash might be set to mix with it, but for flash indoors with insignificant ambient, it really won't much matter which camera metering mode you use, because flash doesn't use any of them, so there isn't much difference.

A few things do matter, regarding differences you will see between Nikon TTL BL and TTL mode.

• In brighter ambient, TTL BL level is reduced significantly to not overexpose the ambient, and to provide fill level instead of full light. This is a major difference. TTL BL exposure seems a little more influenced by the ambient background indoors.
• Spot metering mode does switch TTL BL off, to become TTL. The effect we see is TTL, which is something like Spot.
• FV Lock - The camera manuals say that FV Lock also uses a smaller center area for hot shoe iTTL flash (both modes), more like the Spot we imagine - but says Commander/Remote AWL flashes (which is TTL BL, unless Spot metering) still meters the full area of the frame. FV Lock can change (often improve) TTL BL flash exposure, but probably does not much change TTL mode flash exposure.

That first one is a major biggie (in brighter ambient), but in general for indoors, it seems not very productive to worry about camera mode for ambient. It may help in choosing a mode or a procedure, but as for the details, as always, simply just watch, and do what you see you need to do (flash compensation). That need never changes, and it isn't hard, but we do have to get involved. You will quickly know what to expect for your way of working.

The mode topics below are about ambient light.

Spot metering - Beginners beware. This is a techie tool that requires greater experience, definitely NOT point&shoot. 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. Spot has no concept of a background to match, so Nikon TTL BL flash mode will change to become TTL mode if Spot Metering. Only that small spot matters, that small area will become middle tone.

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, 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. Yes, spot metering can isolate a face from the influence of a black or a white background, but should that face come out middle gray? The skill we need to know is how to compensate it, either way. That face will likely need about one stop additional exposure to make it as bright as it should be, so this is two tricks to learn. The original idea of spot metering was to meter the highlights, and to meter the shadows, to be able to determine the range between them, as a way to determine a middle compromise. Center and Matrix metering try to automate that averaging for us. Accuracy is normally better when a larger overall area is averaged to be middle gray.

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 adjustable). There is no sharp dividing line at the circle, the boundary slowly tapers, typically 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. All the tones in this circle are 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, Center metering remains in the center.

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).

For those new to these terms, the on-line Nikon Glossary says this (italics added by me):

These rose and card test pictures (on previous page) used Matrix metering (because many people do), but I normally use Center metering, to emphasize the central subject more than the edges. Center metering is very useful for portraits, or even 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.

My human brain can almost visualize and understand Center metering, to help predict the result, and my own opinion is to shun the automation of Matrix metering and TTL BL flash, simply because I know it never has a clue about what the subject is, and I'm never sure what the computer is 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. 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.

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.

Direct Flash and Bounce Flash are Different

The general case of TTL metering is that bounce and direct flash are rather different situations for TTL metering. The TTL system does automatically compensate for the longer path of bounce (it simply measures the preflash that arrived via that same route), and you will see the same reflected meter's averaged middle gray result for both, but there are scene differences in bounce and direct flash.

The Inverse Square Law describes how light falls off with distance, therefore direct flash backgrounds are often dark (the room behind the subject). For example, a background that is as far behind the subject as the camera is in front (background is 2x farther than subject) will therefore be two stops darker than the subject (influencing metering, since dark scenes do overexpose). The TTL reflective meter and preflash meters the scene that way too, sometimes lots of dark is seen, which then frequently overexposes a foreground subject as a result of the reflective meter helping in its way. So to direct flash, a distant background is seen like the black paper background before, influencing exposure to be brighter. Also direct flash can cause also dark shadows, generally hidden behind the subject, but in some cases are seen below, and metered by preflash too.

For bounce flash, most of the room is more nearly about the same distance from the ceiling (via flash path), so (within reason) the rest of the (normal size) room simply lights up. Preflash meters the scene that way too, not so dark back there. Less contrast, no dark shadows, no dark distant walls, which is generally easier to expose satisfactorily. However, then maybe white walls are well seen, which the reflective meter tends to underexpose due to the lighter objects seen.

These are the kind of things that give errant meter readings. It may seem that flash needs compensation more often, but not necessarily so. Flash is more intensely local, so the contrast varies more, but it is still about these same metering concepts, about the scene in front of the lens. Compensation is about the scene, and is NOT about calibrating the camera gear.

Bottom line is, (camera reflective) metering, and also compensation, are entirely about the scene in front of the lens. We always need to watch the TTL results, and stand ready with Flash Compensation, to get the picture that we want. You being the photographer, this is your job to do. Simply realizing this is your job is the first full step ahead.

Flash Modes

The Nikon system uses two automatic TTL flash metering methods, called TTL and TTL BL modes. There is more about these in Fundamentals Part 4, but will add some here.

The TTL menu choices in the Nikon Commander, and also for the Nikon internal flash itself, are always in fact TTL BL mode (unless Spot Metering is selected, which is TTL). It is after all a TTL BL system. The speedlights (except SB-700 and SB-400) have a TTL/TTL BL menu mode able to select and override the camera TTL BL metering system to be actual TTL mode.

Off-camera TTL with the Nikon Commander seems to routinely need about +1EV Flash Compensation as the starting point. I don't know why, except it is always TTL BL mode (except for Spot Metering mode), which also needs a little more compensation in otherwise dim indoor scenes.

If using fill in bright sun, and you don't want to bother with compensation, then this is what TTL BL mode is for. It tries to do the necessary compensation for fill flash, as point&shoot flash. But if you also plan to control it too, then too many cooks ruin the soup. All of the Nikon camera manuals recommend TTL mode if using Compensation (no surprises). I do not imply it is a "big deal", certainly we can compensate TTL BL Mode too, but we really do not know what TTL BL is doing, and plain TTL mode offers less interference with our own control.

If you do similar tests (the rose tests on previous page) on TTL BL Direct Flash, you may see some differences, due to D lens distance information (speaking only of TTL BL and direct flash, specifically, with the flash head level, not tilted). Nikon TTL BL Direct Flash sometimes uses the D lens distance information (the lens reports the focused distance). Nikon doesn't explain this well, but similar experiments clearly show that the D lens can sometimes be a safety check to prevent overexposure for overexposed meter readings (TTL BL and direct flash). See a TTL BL and D lens Test showing that. Only overexposure, it does not prevent underexposure. And the flash has a head tilt switch which prevents using this lens distance information when the flash head is tilted up (bounce for example), because then the lens distance does not match the bounce distance (up to ceiling and back down is farther than the direct lens distance). And TTL mode does not use the lens distance information at any time. Only TTL BL direct flash does.

The effect actually seen on this rose with TTL BL here (Direct Flash) was that there was very little difference on the white background - Direct TTL BL still comes out underexposed about the same amount as the TTL. Nothing different - it is how the meter works. But the black background was quite different, in fact, it was a little underexposed instead of the overexposure expected. It seemed that the lens distance information prevented overexposure by the TTL BL direct flash - if the speedlight head was not tilted up.

A Summary of Flash Metering Principles

Flash usually involves a few different factors of metering. Flash Compensation can help all of them.

• There are two exposure settings when using flash (Part 4).

  Flash pictures typically are affected by a double exposure of two factors, the ambient light exposure controlled with camera settings, and the flash exposure controlled with flash power level settings. These add together (within the range of the flash). We do read about 3D matrix metering of backgrounds and subject, and our imaginations run wild thinking of all those parts of the scene, but we need to remember:

  1. Camera settings provide ONE exposure of the ambient light (sometimes referred to as "background", back where the flash isn't).
  2. The flash provides ONE exposure by the flash level. Flash exposure certainly does vary with distance from the flash, but any one flash unit only uses one power level, correct at only one distance (sometimes referred to as "subject").
  3. All else is a compromise, within this one situation, of ambient and flash settings. However, flash pictures in less bright light (indoors) can use low ISO and maximum shutter sync speed to eliminate the ambient effect. Or not, as a control of the ambient.

• Reflected metering

  The previous black or white scene situation (speaking of scene extremes with predominate metering areas of unusually low or high reflectivity from the subject colors - as shown with the rose on previous page) is merely the expected situation regarding fooling the reflected light meters (not unique to flash). The expected over and under exposure dependent on subject colors is simply how reflected meters work. There are no exceptions for reflected meters (only exceptions are the incident meters, or the flash Guide Number method, or with help from the human brain). The human photographer knows to expect this, and he must always watch and check, to compensate all situations properly, by doing what he sees he must do, to get the results that he wants.

• Direct Flash vs. Bounce Flash (on camera, as affected by reflected metering)

  The general case of TTL metering is that bounce and direct flash are rather different situations, not unexpected.

  The Inverse Square Law describes how light falls off with distance, therefore direct flash backgrounds are often dark (in the room behind the subject). For example, a background that is as far behind the subject as the camera is in front (background is 2x farther than subject) will therefore be two stops darker than the subject (influencing the metering). TTL preflash meters the scene that way, so if a relatively more-distant background, often lots of dark is seen and metered, which then frequently overexposes a near subject as a result of the reflective meter helping in its way.

  For TTL BL direct flash, the D lens distance info feature can specifically help prevent this, using a Guide Number check to override obvious bad cases of overexposure (only for TTL BL, and only for direct flash - assuming the subject is actually where the lens focus imagines it is, with respect to the flash). The D lens focused distance feature is apparently not used to help underexposure, but overexposure is the worst thing, unrecoverable in digital. TTL mode does not use this feature, even for direct flash, since its rule is "do what the metering says" (Nikon words it "regardless"). Frankly, I like that (when less automation is helping), as I more nearly know what the system will do then, and I only have to worry about what the metering will do. We simply know that we compensate TTL mode flash fill ourselves, and we know -1.7EV is often the right amount. Whereas, we need to know that TTL BL tries to do that for us. But photographers using reflective meters do know every case of everything must be monitored for the need of compensation.

  For bounce flash, most of the room is more nearly about the same distance from the ceiling (via flash path), so the rest of the (normal size) room simply lights up. Preflash meters the scene that way too, not so dark back there. Fewer extremes, less contrast, generally easier to expose satisfactorily. However, then maybe white walls are well seen, which the reflective meter tends to underexpose. Bounce cannot use the D lens distance feature, because the distance up to ceiling and back is unknown (and there are additional unknown losses at the reflection surface). There is more about bounce.

  Exceptions: Cases involving incident meter metering, or guide number flash, or metering from a gray card at subject, or even eyeballing Manual flash mode (anything not directly measuring light reflected from the subject) are something else, more directly related to the actual light, independent of subject's own colors.

• TTL BL mode, and TTL Mode

  Nikon describes TTL BL and TTL modes this way:

  TTL BL - Automatic Balanced Fill-Flash: The flash output level is automatically adjusted for a well-balanced exposure of the main subject and background.

  TTL - Standard TTL flash: The main subject is correctly exposed regardless of the background brightness. This is useful when you want to highlight the main subject.

  Meaning, if the ambient light is strong to be significant (meterable and usable), TTL BL will automatically reduce the TTL BL flash to be an appropriate fill flash level (balanced). TTL mode doesn't do that, it comes ahead on strong anyway (but we can always manually compensate it for same lower fill flash effect). However, when the flash is the sole light source (in insignificant ambient), TTL BL becomes more like TTL mode.

  The Nikon iTTL system is TTL BL by default. Some flashes (SB-600, SB-800, but only the SB-910 in current production) provide a TTL mode override. Also, Spot Metering mode changes all cases to TTL mode (there is no concept of background metering in Spot Metering mode).

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, 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.

Did I mention that Flash Compensation is how we control TTL flash? Watch, and just do what you see you need to do, to get the result you want.

Continued - A Histogram is Not a Light Meter