Advanced Metering

Advanced Metering

In the blog post “How to Shoot in Manual” I gave some very basic information about where you meter is in your camera and how to use it. In this post we’ll talk really In-Depth about your Camera’s meter

and how to get the most out of it and when to know when it is lying to you and how to correct for that.

What type of Meter do we have in our camera?

The Meter we have in our cameras are known as “Reflective” meters. What they actually meter is the light reflected off of our subject, what we are shooting. This is different than Hand Held Meters. While those meters can be used also to measure reflected light, they normally measure the light source itself also known as “Ambient” or Incident” light and are mostly used to measure the light from Strobes/Flashes that a reflected meter can not.

Metering Modes

All DSLRs have a few different metering modes for different situations and are very helpful to get a correct exposure. Much improved over earlier meters and superior to reading settings off of a film box (In the olden days) or knowing the sunny 16 rule (Highly debatable but go with me here)

Matrix or Evaluative Metering


(Example showing right focus point selected)

This is the standard metering mode metering mode on DSLRs. Nikon calls it Matrix, Canon calls it Evaluative. Other brands use similar names. This mode uses the area under your focus point on your subject and then also samples the rest of the image area and makes a determination of what would be the best exposure to satisfy both needs. This is very often used in portrait photography to get a good balance between the person and the background.

We have to keep something in mind to use this mode correctly. Since it uses the chosen focus point for a large part of the calculation, you must; if you focus and recompose (say using the center focus point), lock the exposure also at the time you lock focus. Or, use a focus points other than center, use one that covers your subject and keep it there on the subject.

Moving the focus point to another area than intended can change the metering significantly. Think of it, if that focus point ends up on a bright sky instead of a person, how it would read that differently? (You would end up with a dark subject)

This is the most often used Metering Mode, but actually the one I use the least. But make this decision for yourself. Do NOT do as I do, you may not shoot like I do or what I do.

Spot and Partial Modes

(Spot)

(Partial)

These modes both work the same way, they just cover different amounts of area. Spot and partial cover a small area just in the center of the viewfinder and essentially disregard the rest of the screen. Spot metering covers an area of about 2-5% of the screen, Partial covers an area of about 9 – 11% of the viewfinder, choosing which one depends on the scale of your subject in the framing of the image.

A lot of people assume that spot metering is the best mode because they believe it to be the most accurate. However that may not really be true in practice

The important part about using these two modes is that you meter on something that is mid-toned, but more about that in detail later in this piece.

This mode is best used if there is a wide difference between the subject and the background in brightness, such as, shooting a person backlit by a bright sky. Or, the opposite, in say a concert situation where the person is brightly lit against a dark background. In other words, if the mid-toned area is small in comparison to the rest of the image area.

Because these modes are so small and precise you will need to make an artistic decision

On what is actually metered for and what you want to accomplish in your shot. If you are looking for a silhouette, you need to meter the background not your subject. If you want your subject well exposed you need to meter on them. You have to make a conscious decision and compromise on what needs to be exposed the most correctly (silhouette, expose the background correctly, vastly underexpose your subject, Backlight, expose your subject correctly and blow out the background)

And once again, if you are metering and then recomposing make use you lock the exposure where you want it before you recompose. You can lock the exposure either by using manual camera or if you are using Aperture or Shutter Priority modes, using the Exposure lock button on your camera (see your camera’s manual)

Center Weighted Average

This mode takes an overall meter of the entire scene but puts more emphasis on the center of the viewfinder. This is probably the least used mode by most people but the mode I end up using 50% of the time for my landscape work. It just works for me and the way I shoot. It works for me because most times I have equal light between my foreground subject and the background but since I want my foreground subject to be the most prominent/perfect exposure it takes that into consideration.

Let this button be your friend.

I mentioned before about “Locking your exposure” before recomposing. (I can’t stress this enough that why I have repeated it 3 times) A little used button by most DSLR users is the Exposure Lock button. Now it may be a stand alone button or it may be nested under another button. In truth it can also be set to be locked when you lock focus by choosing that in the Custom Function menu of your camera. But find this button and use it.
(As shown on a Canon Camera, Consult your camera manual for the location and options on your camera)

Now if you shoot manual, well you won’t need to use it since you essentially lock your exposure all the time anyway. Just remember to set your exposure BEFORE you recompose.

But, if you shoot one of the Program Auto Modes or a Semi Auto Modes, like Aperture or Shutter priority, this button should become your best buddy. Find the area you want to expose for and press this button to lock exposure and then lock focus so that it does not change as you shift your composition giving you a less than desirable exposure.

Like I said, modern exposure meters most times work great, but they need to be used correctly for them to get the most out of them.

Hi, I’m your Meter, I just lied to you. Sorry!

In camera meters are designed to get a correct exposure on a Mid-tone, think of Green Grass or Blue Skies, But more precisely an 18% reflective Gray area. Which in most cases works out great since there are so many mid-tones in most scenes we shoot. Even people’s skin tones can be a mid-tone. But what if the predominate subject in our viewfinder is not a mid-tone? What if we have almost all black or almost all white in an image? (The proverbial black lab in a coal mine, polar bear in snowstorm) The meter will still make them gray because that is all it knows to do.

In the example below I shot pieces of white, black and gray paper. In each case I shot the paper at a center meter for “correct” exposure and then also exposed each at -2EV (exposure value) and +2EV or in other words under and over exposed each by two stops.

In every case, 0 Meter made each piece of paper gray, (The gray paper correctly) -2 made everything black, + 2 made everything white. Now we probably would have had to go to +-3 to get pure black and pure white but I didn’t want to go past my meter and use a calculation. I wanted what the meter does.

So like I said before the meter is set to expose a mid-toned subject and this proves it.

Just as a little aside here, remember back a few paragraphs when I talk about the olden days and the Sunny 16 Rule? Well this image was shot of all three papers at once. No meter. Just using the Sunny 16 rule (Sunny16 Rule, on a sunny day set your aperture to f16 and your shutter speed a reciprocal of your ISO i.e. 1/ISO or in right brained terms. Set your Shutter speed the same as your ISO such as ISO 200 use 1/200 Shutter speed)

Hmmm funny, it got all three exactly right….so much for OLD technology huh? But what it also shows is that if I were to meter and I metered on the Gray Mid-tone area or object, it would get the exposure correct everywhere from black to white (Shadow to highlight). So remember that, IF you can meter on something mid-tone do it. If not…well see the next paragraph

But getting back to our 3 papers shot at 0 meter. So what does that tell us in real life use? Well, if we are shooting a scene with a predominately Black or White, we need to compensate for that or our images will be either underexposed in the case of predominate white or over-exposed in the case of predominate black. You can either do that easily in manual mode or if shooting in P, TV(S) or AV(A) modes, by using exposure compensation.

Exposure compensation (see your camera’s manual on how to set this) allows you to preset a given amount of negative or positive exposure into the camera. So say you know you will need -1 stop exposure, you can dial in -1 into exposure compensation and it will keep it there until your scene changes and you no longer need to compensate

In real life

What may be some of these situations? Shooting snow is an obvious one, try shooting +1 to +2 on it just making sure you don’t overexpose so that you loose detail. Shooting a sky with large puffy white clouds. If there are some blue breaks in the clouds switch to spot metering and try to meter off that area. Or once again try +1 or more to make your white, white and not gray.

Another common occurrence is shooting a white wedding dress. If it is just the dress, well you can try just shooting +2 again. But suppose there is a person in the dress, as there usually is. In this situation the most important thing to have in correct exposure is the bride’s face. You can image if you metered on the dress how dark her face would be. Image even more if she were dark complected or Afro-American.

So in this case it may once again be a good time to switch to spot metering and meter the brides face. Trying to strike a balance between good exposure for her skin but keeping some detail in the dress. If you have to make a choice, go for the face.

Situations for overexposing Black. Of course a black dog on a dark background is the easy one. But how about this; Concert shots. Most concerts are poorly lit with the exception of a large arena show which may have as much light as daylight. But think of most concert shots or small clubs and even the big arena shows where you have a solo spot light on a single performer. You have a performer in the middle of a sea of black.

While most people think because of the low light they will get an underexposed shot, in most cases people over-expose the performers. You can see this by the glowing performer and the background…yes turning gray. So once again you can correct this by knowing and understanding it and choosing to under-expose by 1 to 2 stops. Or, once again, you can choose spot metering and try to correctly expose the performer and not let the abundance of black influence your exposure.

How can I tell if I am getting it right? Well without relying on your LCD which can lie to you, try using your histogram.

If you are shooting white or black and you get a big spike in the middle of the histogram that tells you there is a good chance you are under or over-exposed.

If the Spike is to the left on a black image, it is probably correct


If the image is predominately white the spike should be to the right

And then to help you on a white image if you start to see “Blinkies” in your histogram display, you know you have most likely overexposed the whites

Metering Modes in Practice

Let’s see in a real world example what everything we just learned looks like. This is a typical “Tough” example; a large white surface dominates the image. We’ll step though all the metering modes and metering areas to see what works and what doesn’t. Remember the mode that works best in this example may not work in a different situation. That’s why we have more than one mode and metering subject in our image.

In our first example we are using evaluative (matrix) metering and using the center focus point. Remember in evaluative metering, the focus point is used as the point of metering.

The image is under exposed by about 1 stop, it would be worse if evaluative did not take the rest of the scene into consideration

This image was again using evaluative but the focus point was moved to the point over the flowers

It’s a much better exposure and I would say judging by the histogram just about perfect

This next image uses Partial Metering and is metered on the fence (all other metering modes do not use the focus point but instead use an area of the screen.)

This image is severely under-exposed by about 2 full stops. You can see the white fence is gray so we can see the meter is doing what it wants, looking for gray or making gray

In this image, partial metering was used but I metered on the grass and then I recomposed the image

This image is slightly over exposed by about 2/3rds of a stop. I’ll explain why in a moment.

The next two images were shot with spot metering just like I did with partial metering but the meter covers a much smaller area.

We get the same results

But look what happens when I spot meter on the flowers but I catch the white flowers in the Spot area of the meter

This didn’t occur with the Partial metering because it covers a larger area and the white was not as large a part of the metering area.

The last set was shot with Center weighted average. This metering uses the whole scene in our viewfinder but puts more emphasis on a large center area. The first metered with the fence centered.

Since this mode takes in the whole scene, it’s under exposed but not as bad as modes that only consider a small area

This is Center weighted but with a meter reading taken on the flowers

Once again the image is over-exposed by about 2/3rds of a stop

So as we have seen in 3 examples that were metered on the green grass area they were slightly over-exposed. Why is that? Well as it turns out grass is not a perfect mid-tone it’s a little dark in fact it’s about 2/3rd of a stop t darer than middle gray. That’s why the over-exposure.

In this next example I used spot metering and metered on the blue sky

As you can see that’s a pretty perfect exposure. So why didn’t I just recommend to meter on the blue sky? Well, if you have one, do just that. But we don’t always have a nice clear blue sky like I have in this example. There may be clouds or haze or overcast that don’t give us the mid-tone we are looking for and green is actually the most common color in nature. So if we need to use green just remember to under-expose by about 2/3 of a stop.

If we don’t have either we can place an 18 %( or 12% depending on your opinion) gray card in our scene and meter using that.

And just for reference, this image was shot using a hand held incident light meter

And this image was shot using the “Sunny 16” rule. I’m actually surprised it’s just slightly under exposed

And finally just a word about Gray Cards. It seems they are not perfect either. (Sigh… is nothing?!) They actually depend on their orientation to the light source. They should be at a 45° angle to the light source or an easier way is just to shoot them on the plane of your subject to the camera.

As you can seem, the gray cards exposure doesn’t change much but look at the exposure of the flowers

Conclusions

So what mode is best? Well honestly as we can see, all the modes can work if we totally understand them and use them correctly and most of all meter the right subject.

And it will depend on the situation and how you feel best working. If you aren’t fond of changing focus points, evaluative (Matrix) metering will not be the best for you. If you are not very precise with what you meter, spot metering can be a nightmare but it can save your butt in a tough situation.

For me I’m not that keen on carrying around a gray card so I fully understand how Center Weighted Average works and us that to my advantage when shooting landscapes. But I will change to other mode as the conditions call for. I also like having a Hand Held Meter, but not everyone wants to have that extra expense. They aren’t cheap. My midline Gossen Digipro F runs about $270

Find what works best for you but as you can see not understanding metering can cause a Huge swing in your exposure and a bad exposure can either cause loss of detail in highlights or extra noise in the shadows. So get it right in camera as best you can.

Hope that helps,

PT

2 Comments

  1. Russ August 16, 2013 at 12:41 am #

    Hi, Nice read but for me there is only one way to meter and get a correct exposure, Hand Held Meter. IMO to many variants when using an in camera meter, most have a 5% spot or in that region, dependency on the lens selection at meter time.Grey cards now seem to be in debate as 12 % or 18% for digital.
    Hand held meters can be bought used nowadays quite cheap and even the older type can give a more accurate reading than in camera. JMO
    Russ

    • Peter August 16, 2013 at 8:47 am #

      Thanks for the Comment Russ

      Yes, I enjoy My Handheld Meter too

3 Trackbacks

  1. By Hand Held Meters and HDR on August 5, 2012 at 1:37 pm

    […] inaccuracies if your subject is not a midtoned object (see our sister site See N Learn article on advanced metering for more on this) But for the most part they work just […]

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  3. […] be correct because the light had not changed, only the subject’s reflectance See the article on advanced metering for more on […]

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