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When Is Your Camera Meter Wrong? (And What To Do About It)

By fotosiamo on August 23rd 2012

It’s true. The metering in the modern DSLR is highly advanced. Just take a look at the specs from the highly-regarded Canon 5D mkIII, which features an “iFCL Metering with 63 zone dual-layer metering sensor that utilizes AF and color information for optimizing exposure and image quality.” Sounds great right? Well, we wanted to test out just how accurate a modern DSLR metering system can be compared to a lightmeter like the Sekonic L-358 Lightmeter.

Before we get to the test, though, let’s take a look at how camera metering works.

Behind the 18% Gray or Middle Gray

Practically all DSLRs have some sort of complex algorithm that determines what is considered a “proper exposure.” To photographers, the term “proper exposure” can be very subjective, of course. Some of us tend to like our photos to be on the lighter side, while others prefer their photos to be darker. When it comes to a camera, though, its goal is to get the exposure to be at “18% gray.” This means that the scene is reflecting 18% of the light into the camera sensor.

This gray is also called middle gray because it is about 3 stops brighter than pure black and about 3 stops darker than pure white. In Ansel Adam’s Zone System, middle gray is the center patch of the system at Zone V.

What About 12% Gray?

Some photographers like Thom Hogan, however, say that 12% gray is a more accurate exposure for digital sensors. It is what the ANSI (American National Standards Institute) prescribe as the truer middle gray. Lightmeters like the Sekonic L-358 Lightmeter are calibrated to this standard, and since I do use my lightmeter when I can, I tend to fall into this camp. The 12% gray exposure is 1/2 stop lighter than 18% gray, so if you are using an 18% gray card to meter your exposure, you just open up the exposure by 1/2 stop as well. Otherwise, you can always buy a 12% gray card.

For a more technical explanation on 12% gray, you can read Richard L Hess’s article.

Knowing Your Camera Metering Mode

Today’s DSLRs typically have these 3 common metering settings:

  • Evaluative or Matrix – The camera meters a wide area of the image in the viewfinder and sets the exposure according to the average exposure of the scene. Higher-end DSLRs have a sophisticated way of biasing certain tones like skin and object distance from camera.
  • Center-Weighted – The camera meters a good portion of the image in the frame, but puts more bias around the center area.
  • Spot – You can specify a metering point and have the camera base its exposure calculation on only that point. This is useful for backlit situations like shooting a subject with the sun behind him or her. You would place the metering point on the subject so the exposure reading would not be affected by the backlight.

Canon also has a Partial metering mode that meters an area that is less than Center-Weighted but is more than Spot metering. We will also be testing the Partial metering along with the other 3 standard modes.

Reflected vs. Incident Metering

All cameras from the simple point-and-shoots to DSLRs and medium format cameras use reflected metering. This means that the metering sensor inside the camera reads whatever light is being reflected from the subject and the scene into the camera.

Canon 5D mkIII

Incident metering directly measures the light that falls on the subject. This is how a lightmeter measures the light. You accomplish this by holding the lightmeter under the light where the subject is positioned.

Holding-a-Sekonic

Your Camera Meter Can Be Fooled

The main problem with your camera’s metering system is that it always wants to find middle gray. So if you have a scene that has a lot of white, like a bride’s dress or a snowy landscape, your camera wants to make it all gray. Therefore, your camera will underexpose the scene until the dress or the snow appears gray.

Conversely, when there is a lot of black, the camera meter wants to change that black to gray, so it would overexpose the scene until the black color looks gray.

The Metering Test Methodology

For our metering test, we are using the following equipment:

Lighting Diagram for Metering Test
Lighting diagrams courtesy of Sylights


We shot three different subjects with both the white background and the dark background:
Test Subjects

There are four variables that stayed consistent throughout the entire test:

  • ISO 200 on the 5D mkIII and the Sekonic lightmeter
  • f/2.8 aperture on the 5D mkIII and the Sekonic lightmeter
  • The key light from the Lowell continuous light
  • The 5D mkIII’s position

For each subject-background variation, I metered with the lightmeter and the four Canon 5D metering modes, Evaluative, Center-Weighted, Partial, and Spot. For each camera mode, I adjusted the shutter speed until the camera’s exposure meter settled at 0 EV. I tested each mode 3 times just to make sure that the reading was consistent. Each subject was placed in or near the center of the shooting frame in order for it to be picked up by all the metering modes correctly.

I exposed the lightmeter every time I cycled through each subject-background variation to ensure that I am still getting the same reading as before, and as expected, the Sekonic’s measurements remained consistent at f/2.8, 1/320 sec, and ISO200.

The Metering Test Result

Monkey-White by SLR Lounge

The Evaluative metering picked up a lot of the white background and proceeded to turn it gray, thus lowering the correct exposure by -1 full stop. Surprisingly, the Center-Weighted metering lowered the exposure by another -1/3 stop even though it should be more biased to the monkey’s exposure. The Partial and Spot metering were not any better than Evaluative despite both of them reading mostly off the monkey and not the background.


Monkey-Black by SLR Lounge

The black background did a better job in balancing out with the monkey, with Partial metering registering the correct exposure and the other 3 modes being off by only +/- 2/3 of a stop. The Spot meter once again underexposed the monkey even though it was measuring the area between the monkey’s eyes.


Lens-White by SLR Lounge

Although the lens was black, the 5D mkIII was reading more of the whites from the background and the floor when it was in Evaluative and Center-Weighted mode. Partial metering measured just enough of the white background to balance out the black lens and was only off by +1/3 stop. When I used Spot metering however, the camera only metered the lens, and as a result, it overexposed the scene by +1 2/3 EV.


Lens-Black by SLR Lounge

The black lens coupled with the black background really threw off the metering of the Canon 5D mkIII. Here, the camera just wanted to turn everything gray and overexposed the frames from +1 2/3 stops to +3 stops over the correct exposure! It’s interesting that Spot metering the lens with the black background resulted in +1 1/3 higher stops than Spot metering the lens with the white background.


Paper Towel-White by SLR Lounge

Just like the black lens on black background, the white paper towel on white background really confused the metering system. All of the white was turned to gray across the board. If this was a ski resort or a bride’s dress, you may be in trouble unless you compensate the exposure by +2 stops.


Paper Towel-Black by SLR Lounge

The white and black balance in this set helped the camera obtain a more correct exposure, with Evaluative and Center-Weighted being off by -2/3 and -1/3 stops, respectively. The Partial and Spot mode were only metering off the white paper towel, which is why it underexposed the paper towel more significantly than the other two modes.

So How Do You Get a Better Exposure?

If you can carry an 18% or 12% gray card with you, you can use it to get a more accurate exposure in difficult scenarios similar to the tests. The way you meter using a gray card is to take a photo of just the card under the main light and see where the spike of the histogram is located. Then, you would adjust your exposure settings so that if you take another photo of the card, the histogram spike will be in the middle.

You want to make sure to zoom in with your lens or move in with your camera so that you fill the entire gray card in your frame when you shoot it. This way, the exposure reading is coming from just the gray card.

If you don’t have a gray card, you can use the palm of your hands as a makeshift gray card. Now, of course, we all have different skin tones, so be sure to test how far off your skin tone’s exposure is from a correct exposure.

You can also manually compensate your exposure reading when you have a lot of white or black in your scene. Every camera model is going to be off by different degrees, so it’s best to test your camera out beforehand. So for the Canon 5D MkIII that I used, I would increase the EV by +2 stops whenever I am shooting a scene with a lot of whites.

Why Chimping is Not Always Accurate

Chimping is the colloquial photographic term where you use your camera’s LCD to review the image that you just captured. While this is one way to check for your exposure, it is also not the most accurate. Believe it or not, when you are looking at an image on the back of the camera, you are not actually seeing the true RAW representation. Instead, you are seeing a Jpeg image preview that has been processed with your chosen picture profile, color space, contrast, and brightness preference. That’s why a lot of times when you import the images into Lightroom or Capture One, they may not look the same as they would on the back of your camera.

On top of that, each picture profile has its own exposure bias. Some may lean towards a brighter image, while others may favor a darker exposure. So even if the metering is correct, the photo you see on the LCD may look brighter or darker than the actual RAW image.

What about the Histogram?

The histogram doesn’t tell you if you have the correct exposure on your subject. Instead, it only shows you the tonal distribution of the colors and exposure in your shot. The histogram of a photo taken with a very light background will look very different from the histogram of a photo with a very dark background.

In these two images, all the settings and variables are exactly the same, and the monkey is properly lit. The only thing that is different between the two scenes is the black foam core I placed behind the monkey.

Monkey-Lightmeter by SLR Lounge

Why I use a Lightmeter

Sekonic L-358

The ideal way to get a proper exposure consistently, however, is to get a lightmeter like the Sekonic L-358 Lightmeter. A lightmeter’s exposure measurement is subject-neutral because you measure by pointing the lightmeter at the light, not at the subject or background. It doesn’t get confused if the background is too bright or too dark or if the person is wearing a white shirt or a black shirt. The only thing that matters is how bright the light is when it hits the subject.

Although the Canon lens is very black and the paper towel is very white, they are both properly exposed at where the light is hitting both objects. You can see the details in both objects, and in this lighting, there was no clipping in the shadows or highlights.

Lens-Lightmeter by SLR Lounge
Paper-Towel-Lightmeter by SLR Lounge

Using a lightmeter is very easy and quick, as well. You first set the lightmeter to measure the ambient lighting, flash lighting, or both. After that, you can set the aperture value in ambient mode, or shutter speed value in ambient or flash mode. Make sure that the white dome is raised when measuring incident light, since it allows the lightmeter to read light in a 3-D space.

Sekonic L-358 Dome

Finally, you just position the lightmeter in front of the subject (usually under the chin or the nose), point the white dome to the camera, and hold the trigger button to take a reading. If you are using flash, you can trigger the flash manually or use the optional Pocket Wizard transmitter to trigger the flash that is connected to a Pocket Wizard. That’s it!

Holding-a-Sekonic

Once you understand how this works, you can literally measure the light, set your camera control, and shoot away within a few seconds. This is much faster and easier than taking a photo and looking at your camera LCD, analyzing the histogram, and making an educated guess.

Conclusion

Today’s DSLRs are sophisticated machines. But they are not perfect. Because your camera still uses reflected metering, it’s important to know when it can be fooled. This is especially true in a scene with a lot of white or black color.

To obtain a proper exposure in difficult lighting scenario, you can compensate your EV manually if you know your camera’s metering bias, use a gray card, or use a lightmeter. The most accurate and consistent way to meter properly is with a lightmeter.

Creative exposure is subjective, of course, but it is still important to have the foundation in dialing in the proper exposure in any lighting scenario. After you can do that, the creative choices are up to you.

Stay creative and keep on shooting!

You can buy the gears used for this test with these links below:

About

Joe is a rising fashion and commercial photographer based in Los Angeles, CA. He blends creativity and edge with a strong style of lighting and emotion in his photographs. Be sure to check out his work at www.fotosiamo.com and connect with him on Google Plus and on Facebook

26 Comments

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  1. Michael Clark

    Overall this is a very well written and informative article.

    I do have a couple of nits, though:

    “This means that the scene is reflecting 18% of the light into the camera sensor.”

    That’s not what ‘18% grey’ means. That’s not at all what it means.

    “Although the lens was black, the 5D mkIII was reading more of the whites from the background and the floor when it was in Evaluative and Center-Weighted mode. Partial metering measured just enough of the white background to balance out the black lens and was only off by +1/3 stop. When I used Spot metering however, the camera only metered the lens, and as a result, it overexposed the scene by +1 2/3 EV.”

    One might argue that the external light meter underexposed the black lens and that the spot meter got it more correct. If the goal of the photograph was to show details of the surface of the black lens it certainly did.

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  2. Lee Bushen

    Very useful. I’ve always wondered why manufacturers don’t offer a small wireless incident light meter that slots into the camera’s body. You could walk over to your subject, press the button and it would transfer the correct settings to your body!

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  3. Joseph Prusa

    Nice article.

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  4. Paul Wójtowicz

    I’m having a lot of trouble following the reasoning behind the methodology of the spot meter tests found in this article. Why would one ever want to zero out the exposure while using spot metering unless the subject is neutral? The exposure will only be correct at 0 if you are shooting a subject in neutral tonality. This is not a reflected meter flaw this is by design. So in reality this is not a problem of reflected vs incident readings. You are supposed to compensate the exposure for the subject tonality. Otherwise the camera will assume its gray and make it so. Therefore, all this exercise shows is that spot metering was used incorrectly. If the subject tonality was placed in the correct zone the exposure when compared to the incident light meter should be more or less identical.

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  5. Lelia

    You’ve made some good points there. I checked on the internet for additional information about the issue and found
    most individuals will go along with your views on this web site.

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  6. Pedro

    What is “bias”?

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    […] camera metering has a tendency to want to turn that much whiteness into 18% gray or middle gray. As I mentioned in my other article on metering, middle gray equates to roughly the middle of the gray scale and is called 18% gray because middle […]

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    […] Off-setting a light meter Here's another couple of takes. When Is Your Camera Meter Wrong? (And What To Do About It) tutorial __________________ Members don't see ads in threads. Register your free account today […]

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  10. Jay Medeiros

    Interesting article here but I would say the lens with the dark background is at least 1/2 stop underexposed using the light meter. The table surface appears to be quite a bit darker than any of the other light metered shots.

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  11. Patricio

    This article was great, I wonder if you could post something related to how to use the sekonic L-758dr in spot meter mode. I just bought it and I am trying to achieve the right exposures but im a bit confused to where should I point my spot meter in the scene. I like taking pics with lots of clouds and ground with different colors at the same time so the exposure is quite hard to manage. in those cases, should I meter the brightest and then the darkest to make an average? or should I point the middle grey part of it and that’s it? Thanks !!

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  12. Jenvdw2

    This is a great read with sooo much info thanks so much xx

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  13. Bob DeLellis Photography

    Excellent, excellent, excellent article.  I attended the Brooks Institute of Photography Wedding Program last year.  One of our instructors was a big advocate of incident light metering and I really fell in love with the results.  There are certain times during a wedding where incident metering is not practical but, for example, during the formals, it works great to have an assistant meter for you.  If you don’t have an assistant, you can take a reading in each location when you start the formals, and then it only take a couple seconds to re-check your settings after posing your next group of subjects.  

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  14. Chris Martin

    Did you calibrate the Sekonic first?

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  15. Anthony Riordan

    What about an expodisc?

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    • Joe Gunawan

      That is actually more for white balance, not proper exposure calibration.

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  16. Anonymous

    Great article! Lightmeters are fantastic tools, but I feel like they limit me. In a controlled, studio setting, it would be fantastic… but in a “run and gun” environment, I want to be well versed in using my experience and intuition to capture proper exposure. That’s just me tough… I’d always rather not rely on a tool if possible.

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  17. Mail

    Hey! Dont tell everyone! That is what makes me a pro’ and Uncle Bob a “weekend low quality warrior”! ;-)

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  18. Patrick C N Wong

    I know I need it but can’t affort

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  19. Marat Nigametzianov

    Mate, you like a monkey with a hammer.

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  20. m43

    Now throw a mirror-less into the mix ;)

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  21. Stevelig

    Nice article!! Anyone carry around one of these at a wedding? I’d love to but I don’t see a practical way to do it.

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    • Melanie

      Mine has a neck strap.  Works like a charm.

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    • Sbrenray

      Yes I do, an assistant is useful, once you use a light meter you’ll never trust a camera again.

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