woo hoo bought a light meter

[Eero Makela]

THE LCD on the back of the Camera is usually way off at least in those cases when the photo is in actual fact totally exposed incorrectly. I totally messed up one session due to not having a light meter. Not that the second one was much better but at least I was able to fix them in post.

NOTE: if you over expose the detail is lost and can never be fixed in PP. Under Exposure can at least be fixed to some degree even though there will be data loss at least you have a photo that you show.

When you fix a photo in RAW edit and look at the Histogram and have vertical lines these are where data was lost.

[Danlphot]

Originally Posted by Take12

If you're talking about plug-in editing filters you're right: they degrade IQ, because most of them subtract image data. But if you refer to RAW processing – which may involve blending a number of different exposures, a.k.a. 'HDRI' – you're dead wrong, Dan! Because with HDR/blending you add image data! A well processed HDR image is the result of X exposures, so it is the aggregate of X times the image data of just one exposure (which apparently is your m.o.).
But then you would need to have first hand experience to know the difference IRL, of course.

The proof of the pudding is in the eating, you see...

Have fun!

Combining multiple exposures to increase dynamic range is a horse of a different color. For "normal" photography the only way a reflective (in camera) light reading can be accurate is if the scene happens to reflect 18% of the light that falls on it.

You can't count on "chimping" the screen to get an accurate exposure since your eyes can be fooled by the ambient light falling on the screen. In this way modern digital cameras are like the large format cameras of old where you have to shield the screen/ground glass to even see the image in bright sunlight.

In-camera meters read the light bouncing off the subject whether it be dark, light or somewhere in between. Can you accurately guess what this percentage is? Incident meters read the light falling on the subject. Once your meter is calibrated you know what exposure will make black look black, white look white, and 18% gray will be reproduced as 18% gray. This gives you an accurate starting point if you want to adjust exposure to record more detail on either end of the spectrum.

[Loa]

Hello,

I can't even understand how the meter and LCD can be way-off. In my years with the D70 and months with D300, it's never happened that an entire "session" was off.

Sure a photo comes up over or underexposed once in a while if you're not careful. Or while you're learning to use a new body. But way-off? An entire session? I can't even understand how that could be possible.

The LCD is not, by a long shot, a 100% faithful rendition of the captured image. I'll grant you that. But even on the old D70 it was more than adequate enough to gauge your exposure. With the D300 you can zoom to 100% and check the histograms if you're unsure. Again, the histograms represent the jpeg data and so they're not 100% accurate. Yet they're more than enough to see if you "totaly messed up" your shot or not!

Can you really have this situation: the image on the LCD looks good but on your computer it looks awful? Is this even possible? If you shoot jpeg it shouldn't happen as the image on the LCD is the jpeg. And if you shoot RAW, set your jpeg prefs to something conservative so that the jpeg shown on the LCD won't be too far from the RAW.

I certainly hope something like this never happens to me. But while I'm not a pro, I've still taken upwards of 30 thousand images with 2 Nikon DSLRs and never has exposition been a problem.

Loa

[Loa]

Originally Posted by Danlphot

You can't count on "chimping" the screen to get an accurate exposure since your eyes can be fooled by the ambient light falling on the screen. In this way modern digital cameras are like the large format cameras of old where you have to shield the screen/ground glass to even see the image in bright sunlight.

I don't fully agree with that: yes we're not going to see the correct brightness as ambiant light will mess up our eyes. But we *will* get a pretty good idea of the contrasts within the image. It may turn out brighter or darker than we thought, but we can usually make out contrast. And that is, again, usually enough to determine if the exposition is good enough.

Loa

[Danlphot]

Originally Posted by Loa

I don't fully agree with that: yes we're not going to see the correct brightness as ambiant light will mess up our eyes. But we *will* get a pretty good idea of the contrasts within the image. It may turn out brighter or darker than we thought, but we can usually make out contrast. And that is, again, usually enough to determine if the exposition is good enough.

Loa

One definition of contrast is: "The difference in brightness between the light and dark areas of a picture, such as a photograph or video image." An image can have plenty of contrast and still not be accurately exposed. The viewfinder provides subjective data while the meter provides objective data. Which is why I'll stick to my personal caveat: "Trust the meter, not the viewfinder."

[Songman45]

Well kids, make it sound like a design fault all you want. 18% reflectance (grey) is the standard. Its been the standard since the fathers of film, Eastman and Kodak developed (no pun intended) a standard for exposure for processing and for printing. I"ll save you the history lesson but all meters and all exposure cards are set to 18% grey. It is not the perfect color, density, or reflectance but it is the anchor point. Naturally a photographer would realize this and adjust his camera according to his specific subject matter as it relates to the constant of the grey card.

Lets talk about the perception of grossly innacurate meters in current cameras. YES, the calculation is derived by the cameras meter system assuming that 18% grey. If you are in spot metering your spot might be as small as 6mm, as large as 12mm or might be averaging the spot against the totality of the scene. So, what you going to do? Sample a 6mm size dot of an overall image that does not represent the whole of the image?

Take into account there are not only different skill level people using the same make and model of camera but photogrpahers with different uses and needs. I enjoy shooting portraits and the majority of my formal education is in that genre. I have been making a living photographing show horses for more than the past year. Here's a common challange: A cute little girl about 9 yrs old is in the irons. She's wearing traditional English style riding appearal, tan breeches and a black or navy riding jacket with a light colored blouse. She's wearing a traditional black riding helmet and has on black riding boots. Her mount is a dapple grey, not far from white. The arena fence is white, the footing (ground) in the arena is reflective light colored. Do you think there is a single spot in this whole scene thats going to expose all the elemets properly? Expose for the shadows and let the highlights fall out? Only if you want a snow white horse and a pasty complected girl with a lovely dark jacket on. Other way around? All the things that looked good before now look bad except maybe the horse. Nothing in this entire scene is 18%.

Add to this equation that the ideal image will be the horse with bent knees in mid air just breaking the plane of the jump and the little girl's attention set on the next jump. They are not going to freeze in mid air and let the photogrpaher run up and meter this, then get back to his vantage point and line up the shot. I do not know how fast a horse crosses a jump but I know its less than a 9th of a second. You know the next little girl is going to be on a jet black horse and the one after that on a bay.

Guess what? The meter in the camera is the only option. Knowing how to set the metering options so the camera returns the values as they are required is a huge plus. Yes, sometimes I miss the exposure and yes sometimes i miss the focus spot. But if I take the resulting image and examine it closely it is very easy to see that the camera did just what it was supposed to do, the user was in error.

Steve

[MyPerspective]

First of all, when calibrating a light meter, we're not calibrating it because the meter is wrong. Nor are we calibrating it because the camera is wrong. But only that in calibrating, we are correcting-for the losses in the lens and any filters that we (might) be using.

There are no two lenses that are the same. For example, a 50mm f/1.4 is going to have less light-loss than a zoom (the prime has a third as many elements as the zoom. Therefore, as the zoom has 3 times more elements, there is more light loss. i.e., slightly more opaque). How would a light meter know what lens you are using without you telling it? That's what you are doing when you calibrate. You are telling the meter what lens you are using .... or actually, the losses in the lens and filters.

When you use a light-meter, you don't take a new light reading for each picture you take! Outdoor lighting doesn't change that fast! Sure light does change fast as you're right-at sunset, but that's the only time I've ever seen the lighting change within minutes. Most of the time you can go for 30 minutes or more before needing to take another light reading as the light just doesn't change that rapidly. And indoors, artificial light doesn't change at all! Only when you change scenes do you need to take a new light reading. We're talking still scenes, not sports! And for the outdoor lighting, such as the example of a youngster on a horse, if it's sunlight, sunlight is evenly lit across the entire arena! But with shadows, I agree, at times when the horse and rider are changing from sunlight to shadows, there's no way to freeze the moment and quickly take a meter reading! But if you could, it'd be by far the most accurate reading!

We're not fixing for metering errors in our cameras! The only reason why you would use a light meter is that different colored objects reflect light differently. An incident meter doesn't read the light that is reflecting off of the subject. It gives us a reading of the amount-of light that is falling-on the subject! Therefore, the color of the clothing, or the reflectivity of the object doesn't give a false and incorrect reading! That is why it gives us a more accurate reading than our cameras.

Please re-read the example on Sekonic's website!
Sekonic Classroom: Metering Techniques

[Songman45]

Thank you for the advice and your opinion. I would like for you to do two things. First take one of your best photographs and put it safely away. Secondly, print out what you just explained to me and place it with the photograph. In 10 years I'd like you to review both; you will be astonished.

Best Regards
Steve

Originally Posted by MyPerspective

First of all, when calibrating a light meter, we're not calibrating it because the meter is wrong. Nor are we calibrating it because the camera is wrong. But only that in calibrating, we are correcting-for the losses in the lens and any filters that we (might) be using.

There are no two lenses that are the same. For example, a 50mm f/1.4 is going to have less light-loss than a zoom (the prime has a third as many elements as the zoom. Therefore, as the zoom has 3 times more elements, there is more light loss. i.e., slightly more opaque). How would a light meter know what lens you are using without you telling it? That's what you are doing when you calibrate. You are telling the meter what lens you are using .... or actually, the losses in the lens and filters.

When you use a light-meter, you don't take a new light reading for each picture you take! Outdoor lighting doesn't change that fast! Sure light does change fast as you're right-at sunset, but that's the only time I've ever seen the lighting change within minutes. Most of the time you can go for 30 minutes or more before needing to take another light reading as the light just doesn't change that rapidly. And indoors, artificial light doesn't change at all! Only when you change scenes do you need to take a new light reading. We're talking still scenes, not sports! And for the outdoor lighting, such as the example of a youngster on a horse, if it's sunlight, sunlight is evenly lit across the entire arena! But with shadows, I agree, at times when the horse and rider are changing from sunlight to shadows, there's no way to freeze the moment and quickly take a meter reading! But if you could, it'd be by far the most accurate reading!

We're not fixing for metering errors in our cameras! The only reason why you would use a light meter is that different colored objects reflect light differently. An incident meter doesn't read the light that is reflecting off of the subject. It gives us a reading of the amount-of light that is falling-on the subject! Therefore, the color of the clothing, or the reflectivity of the object doesn't give a false and incorrect reading! That is why it gives us a more accurate reading than our cameras.

Please re-read the example on Sekonic's website!
Sekonic Classroom: Metering Techniques

[Eero Makela]

Originally Posted by Songman45

Thank you for the advice and your opinion. I would like for you to do two things. First take one of your best photographs and put it safely away. Secondly, print out what you just explained to me and place it with the photograph. In 10 years I'd like you to review both; you will be astonished.

Best Regards
Steve

Your memory of the photo changes. When you take the picture you look at it and remember all the ideas and thoughts that went into creating it. If something occurred during the shoot you remember that as well. With time these memories fade.

Today you take a picture and it is Perfect in every way and you love it. In 10 years time you are now shooting totally differently and the whole world has changed around you to have different style and different norm.

You look at that 10 year old photo and say what the heck is this, who took this photo not me, and then you realize that it was your photo.

The above I learned during a recent photo shoot course.

[Eero Makela]

Originally Posted by Songman45

They are not going to freeze in mid air and let the photogrpaher run up and meter this, then get back to his vantage point and line up the shot. I do not know how fast a horse crosses a jump but I know its less than a 9th of a second. You know the next little girl is going to be on a jet black horse and the one after that on a bay.

Guess what? The meter in the camera is the only option. Knowing how to set the metering options so the camera returns the values as they are required is a huge plus. Yes, sometimes I miss the exposure and yes sometimes i miss the focus spot. But if I take the resulting image and examine it closely it is very easy to see that the camera did just what it was supposed to do, the user was in error.

Steve

I agree 110% in this case you need to use the camera meter there is no way to meter with a light meter. But then we always knew that, if the subject is too far away or in a place where we can not put the light meter then you need to use either Reflected meter or the one in the camera. Since the subject is moving and will only be there for what 1 second or less then you need to use the fastest way the cameras meter.

(the rest of this applies to the main subject of this thread and not at horse photos, of which I have no clue about. I have only taken pictures of racing cars doing 200 mph and this translates to the length of a football field in the time your eyes stay closed during a sneeze, so drivers don't like to sneeze at 200mph and drive blind for that distance. At 60mph you travel 66 feet/sec ; 200+ = 293 feet/sec) So I don't have time to use a meter here either.

However you also need to understand your cameras meter and how it does this. I have 2 cameras D50 and D300 They both have Matrix metering and NIKON has raved about this for who knows how long that it has been created using 1,000s of different lighting setups to create the best picture in 99% of the situations (Not recall the % they say).

For me this came to a grinding halt. 4 years ago my D50 created images using Nikon Matrix and I used it 100% of the time. I learned to trust it as it was good every time.

Last year I was at a car show took pictures with my Cheap 18-55 Kit lens (I forget but I think I only had the built-in flash at that time). The picture was very well light and the model in the photo was very well light.

One year later I have the D300. Same car show and same location and Same Cheap 18-55 Kit Lens. Using matrix metering and I am too dark by about 1.5 to 2 stops.

So yes we need to know our camera. I don't recall but I did look at the pictures in the LCD on back and they looked ok. Later on the computer I see them as dark. I may not have had my monitor Calibrated then, but it was set at as bright as it can be.

In this case a light meter reading using the same meter (assuming it does not change over time and I don't think it does, I have only had mine for a few months) would have helped. My subject does not move around and she all is a good friend so using a light meter would have been fine. Next Time I will for sure take my meter along.

Also at this years show I also had my D50 with me and had my other cheap 55-200 lens on it and using matrix and took shots of the same model at almost the same time (as per EXIF it is like within 1 min or less of those taken with D300 and being an indoor event with artificial lights I can guarantee the light could not have changed by 2 stops in less then 1 min) Granted the two lenses are different but they are very close in F value 3.5-5.6 and 4-5.6

Also 95% of my current photography is dark night club shooting. I use Matrix or now CW and iTTL flash set to Balance most of the time. So I have learned to trust my cameras meter in this setting.

[Loa]

Originally Posted by Danlphot

One definition of contrast is: "The difference in brightness between the light and dark areas of a picture, such as a photograph or video image." An image can have plenty of contrast and still not be accurately exposed. The viewfinder provides subjective data while the meter provides objective data. Which is why I'll stick to my personal caveat: "Trust the meter, not the viewfinder."

Hello,

Maybe I went too fast on that one. Let me rephrase: if, on the LCD (not the viewfinder) you can see detail on the face of your subject (or whatever else is the most important part of the picture), then you have a pretty good idea if you're correctly exposed or not. If on the other hand, that detail is washed out or all dark, you instantly know that something is wrong.

Sure in some circumstances our eyes will mess our subjective reading. But again: this is something you can learn and adapt to. Our eyes will be messed up, but if you *know* that you're in very bright ambient light, you can use your brain to correct your perception. Just like when you see a window with blue glass you don't say: "Oh my God! The people behind that window all have blue skin!" Of course not! You "know" that something is affecting your perception.

I still stand by what I said earlier: most DSLRs that are about 5 years old or younger will have a good enough meter and LCD (which you will have to *learn* and understand) so that external light meters are obsolete for nearly all situations.

In theory, measuring incident light can have its advantages in some rare situations. But in practice, a photographer can learn to compensate for this and make the shot. Aided, of course, by his trusty LCD display.

As Songman said: if you need to shoot quickly or in diverse situations (in his case: on the parade ground, in the shade while the contestants wait for their turn, in the stands where incident light will vary according to where you are (radially) relative to the sun...), the meter will usually do a very good job.

Now imagine if you take that same camera meter and take your time (first to learn it, then to use it properly)! Suddenly that very good job turns into an excellent job.

Using the in-camera meter doesn't mean putting your camera to automatic and matrix metering all the time... This debate is not between such a configuration and a 300$ light meter: it's between a judicious use of the in-camera meter and that same 300$ light meter. That word, "judicious", is really the key here...

I haven't seen or read anything here that made me think: "Well, maybe I ought to try one." Maybe someone will come up with a sufficient reason?

Loa

[Loa]

Originally Posted by Eero Makela

I don't recall but I did look at the pictures in the LCD on back and they looked ok. Later on the computer I see them as dark. I may not have had my monitor Calibrated then, but it was set at as bright as it can be.

This is exactly what I mean by learning to use your LCD. My monitor has only been calibrated by the software in the control panel, so nothing fancy here. But one of the first things I did when I got my D300 was to take a variety of pictures in a variety of situations (flash no flash, sun no sun, sunsets, mid-day, nighttime photography, etc...). I then uploaded those images to my computer without deleting them form the camera.

Then I started to compare what I was seeing on my monitor and on the tiny LCD. Same principle: I did that at night using artificial light in the room, then in daylight with the drapes opened, etc... Soon enough, I was able to understand some of the limitations on the LCD display, and where I should be careful.

That's nowhere near as good as I could have done using a proper monitor calibration tool and a room that's constantly lit the same way.

But even using those very simple pragmatic tricks, I've quickly learned to read the LCD. Took me 2 hours in total, tops. But I can only guess at the amount of time it saved me in the long run.

---

Also, matrix metering on the D300 is, as it's been widely discussed on the net, *very* different from the Dx0 (and probably from the D200 as well but I don't know). It gave you underexposed images; it gives me nearly always overexposed ones. Go figure!

I still haven't figured it out, but it's now a lot more sensitive (reactive) to small changes of light. Since getting my D300 I've stopped using it, forcing me to think more about proper exposure: one problem eliminated and some experience gained.

Loa

[Danlphot]

Originally Posted by Loa

Hello,

Maybe I went too fast on that one. Let me rephrase: if, on the LCD (not the viewfinder) you can see detail on the face of your subject (or whatever else is the most important part of the picture)

You are still assuming that the LCD screen (sorry, I incorrectly referred to it as a viewfinder) is showing the scene the same way that the camera's sensor is "seeing" it.

In-camera and hand-held meters are calibrated to a luminance of 12-13% ( Meters Don't See 18% Gray by Thom Hogan ). If you want to accurately control which details in a given subject will fall within your preferred medium's (be it film or sensor) limited range of a few f-stops you need to start with an absolute known value (gray card, target, etc.).

If the range of your subject is greater than the sensor's and you are not basing your exposures on a known value, then the camera's meter, not you, is determining which information is being recorded or lost.

If being close most of the time is good enough, then you don't need a gray card or incident meter. Critical control of the final image however does require starting with an absolute known value and an incident meter is the fastest and most accurate way to do this.

[Loa]

Originally Posted by Danlphot

You are still assuming that the LCD screen (sorry, I incorrectly referred to it as a viewfinder) is showing the scene the same way that the camera's sensor is "seeing" it.

Well you must have skipped a few posts while reading:

Originally Posted by Loa

The LCD is not, by a long shot, a 100% faithful rendition of the captured image.

And in any case: the problem with a bad exposure is either loosing detail in the highlights or shadows. In the end, if you see the detail you need on the LCD, you can be sure that it will be there on the monitor.

Originally Posted by Danlphot

If the range of your subject is greater than the sensor's and you are not basing your exposures on a known value, then the camera's meter, not you, is determining which information is being recorded or lost.

That is true *only* in the case of someone not looking at the LCD. If you take a photo of a scene you know has a higher DR than your camera can capture, just look at the LCD after the shot! If it did not capture the correct portion of the DR, adjust and shoot again. Really in a hurry? Bracket!

It seems like the proponents of the external light meters all think that the LCDs are next to useless. That's not the case at all. As I've said they not as good as having a 30in monitor in a dark room. But that's not the point: their function is to let us check correct exposure (among other things). Histograms will also help with that (with the caveats I mentioned).

Is it 100% fool-proof? No, of course not. Nothing is, even a hand-held light meter. But a hand-held meter use correctly, like a in-camera meter used correctly (that means knowing which metering method to use for the scene, and where to target your metering in that scene) will give you great results. Letting the camera on Matrix metering and "forgetting" about it on full automatic mode is akin to using a hand-held meter pointed randomly in your scene. It's worthless, because that's not the way it was designed to work.

Originally Posted by Danlphot

If being close most of the time is good enough, then you don't need a gray card or incident meter. Critical control of the final image however does require starting with an absolute known value and an incident meter is the fastest and most accurate way to do this.

My guess is that this *was* a fact years ago, and that it's slowly becoming less of a concern. The key problem is in this word "critical". Just how critical *is* critical? With a RAW file you can easily adjust for +/- 1/3 stop with no problem whatsoever. And unless your scene is maxing your sensor, +/- 1/2 stops is also quite easy to achieve.

If 1/10 of a stop is what you mean by critical, then RAW adjustments will be more than enough to compensate a discrepancy between LCD and actual sensor data.

If 1 stop is what you mean by critical (which I doubt), then you will indeed need a light meter for those 1% of photos that in-camera meter will have estimated *that* badly. But the thing is: when the error is really that bad, the LCD will show you, regardless of any ambient light messing with your eyes.

In the early days of digital photography, even minor exposure adjustment in post-processing was very risky. But that's long gone, especially if you're using RAW.

---

As I said: in theory you're perfectly right. Measuring incident light with a good grey card will give you the absolute best results. But in practice, does it make all that much of a difference?

Just as clean ISO 1600 images are now possible with the D3, minor adjustments in exposure are now possible with RAW files and good converters. And we have such good converters now. I said minor, but you said critical: critical means fractions of a stop. Well, those fractions of a stop compensations are easily achievable with 12bit losslessly compressed RAW files. More so with today's 14 bit RAW files.

Loa

[MyPerspective]

OK, so one figures that they'll just "fix it" later with software.

Now isn't that a FRIGHTENING THOUGHT when you realize that very few people have calibration tools and properly calibrated their monitors and video cards?

To me, I'd rather leave a picture alone and accept it as is, than think that you're "fixing it" with an uncalibrated monitor! That's as FOOLISH as one can be! It'd only be "right" on your uncalibrated system! Know what I mean?

[Ellbee99]

Congratulations! I finally started using the light meter my husband tried to get me to use. I love it! It makes a big difference!

[D.Rodgers]

Originally Posted by Ellbee99

Congratulations! I finally started using the light meter my husband tried to get me to use. I love it! It makes a big difference!

Thanks Lori..I'm glad to hear that you can see the difference,it takes a lot of guess work out of high contrast scenes and of course flash work..

[tekdiver500ft]

Originally Posted by Take12

95% nostalgia.

0% nostalgia. 100% desire to get the image right. Anyone who thinks they can get images just as good without a meter is not particularly bright.

[Loa]

"just gets the perfect exposure..."

"makes a big difference..."

"Anyone who thinks they can get images just as good without a meter is not particularly bright."


Still nobody can tell me why my view on the subject is wrong. And if you think you can't make 1/3 of a stop corrections on a RAW file, you're living in the past. I don't go around correcting exposure on all my files: the D300 (and most other recent DSLRs) have very capable meters built-in. But I know that if I have to, I can.

In any case, "correct exposure" is, most of the time, a subjective decision. Most photographers don't simply want to "record" the world they see around them. We're not copy machines.

Regardless, I've been convinced by good arguments to try out RAW a couple years ago. Never went back actually. But so far, I haven't seen any argument that truly held up to examination by today's standards. I know the point of this thread was not to convince anyone, and I'm glad you like your light meter David. But I know for a fact that your D300 can meter a LOT better than what you showed on the original post.

And if you others don't *want* to fix or retouch or correct your images in post, that's just fine. On the other hand, don't tell me that it's impossible or "so darn destructive". It's not. Regardless of monitor calibration, RAW Vs jpeg, light meter vs in camera meter, etc... the ultimate judge is how you (and your client if that's the case) like what you get on screen or in print. If you need a hand-held light meter to get there, that's also quite fine. But saying that the only way (or else you're not *bright*) to have a correct exposure is using one is just ridiculous. It's one way, among many.

Without good arguments, this is nothing more than preaching. Not exactly what this forum is known for. I would love the chance to learn something new about (digital) photography (in 2008 ). So to all of you guys that can't live without hand held light meters, please tell me why.

Loa

[D.Rodgers]

Originally Posted by Loa

"

Without good arguments, this is nothing more than preaching. Not exactly what this forum is known for. I would love the chance to learn something new about (digital) photography (in 2008 ). So to all of you guys that can't live without hand held light meters, please tell me why.

Loa

Ok this is getting old.I feel like an old man watching the kids quibble.
Bottom line is most photographers who make a living shooting use incident meters and i mean the ones who shoot with the big guns not only the compact cameras we carry around yes i mean The D300 and other Dslrs...
I'm not going to explain why a meter works so well, thats for you to learn,when you're ready.
I will post why reflective meters are inferior .

1. Your light meter only measures the light reflected back from a scene, not the light on it.

2. Your light meter assume all scenes have an even distribution oh highlights, midtones and shadows.

Therefore the reflectivity of your subject strongly influences the accuracy of the final reading. In the same lighting conditions, white or shiny surfaces will reflect more light than dark surfaces.

Second, when your meter assumes even distribution of highlights, midtones and shadows, the overall value of these tones blended together reflects the same amount of light as a spectrally mid-tone grey with 18% reflectance. What this means is that your meter is at risk of under or over exposing a scene that is predominantly very light or very dark because it ASSUMES they all adds up to grey.