What exactly does "evaluative" metering mean?

[Dazz1]

Just reading my camera's manual and some posts here. It seems to be a fairly common metering mode, but the explanation my camera gives is unclear (to me).

"For typical shooting conditions, including backlit shots.
Automatically adjusts exposure to match the shooting conditions."

How does it manage to do this? Does it measuring different parts of the frame, depending on what type of photo it guesses you might be trying to take? How reliable is it likely to be - or should I switch to something else, like centre weighted, for safety?

[ricktas]

evaluative metering is the term used to a manner of assessing the scene and determining a 'correct exposure'. Basically the camera's metering system assesses the scene, looking at the bright parts, the dark parts, backlighting, subject etc and then the camera will set the exposure settings (ISO, Shutter Speed, Aperture) based on an evaluative or average of the metering it does across the scene, to try and get an exposure that covers all the elements of the whole scene. So evaluative metering basically looks at a range of values and averages them.

This differs from say spot metering, where a particular 'spot' in the scene is used, and everything outside that spot is ignored. The camera then uses the details from just that 'spot' to determine ISO, Aperture and Shutter Speed.

[Dazz1]

Basically the camera's metering system assesses the scene, looking at the bright parts, the dark parts, backlighting, subject etc and then the camera will set the exposure settings (ISO, Shutter Speed, Aperture) based on an evaluative or average of the metering it does across the scene.

So, given that the camera has 2 other possible settings, spot metering, and an average (but centre weighted) meter, I am wondering how this average is different. Does this mean that "evaluative" is just a fancy name for non-centre weighted - i.e. true average across the scene, or is it also implying some fancier image recognition going on that tells it when to ignore parts of the screen depending on what it thinks you are trying to photograph.

[ameerat42]

Who exactly knows? Or even approximately?
Have a look at this article in Wikipedia, where a bunch of names is bandied about for possible evaluative meaning.
Am.

[ricktas]

it could be called a 'true' average, but depending on your camera, it is limited. It does not look at the light levels etc at every pixel and do the calculation, rather it takes a sample at various points across the scene and uses those. How many points and where those points are depends on your camera body and what the manufacturer decided to setup as the evaluative metering points.

So whilst it uses more points than spot and centre weighted, it doesnt use the entire scene as a whole, rather a wide spread selection. So calling it True is probably not 100% correct, but maybe multi point metering would be better. Nikon call it Matrix metering cause it use a matrix of points to work out the average, not the whole scene as such. In most new Nikon DSLR it uses 1005 points in the scene.

So looking through your viewfinder consider how 1005 points (that are evaluated to determine the correct settings) would cover what you see. So it is fairly damn comprehensive, but it is not perfect, then nothing is.

[Dazz1]

Who exactly knows? Or even approximately?
Have a look at this article in Wikipedia, where a bunch of names is bandied about for possible evaluative meaning.
Am.

Very informative. I found the bit about pattern matching with an inbuilt database to determine what is being photographed, particularly interesting.

- - - Updated - - -

it could be called a 'true' average, but depending on your camera, it is limited. It does not look at the light levels etc at every pixel and do the calculation, rather it takes a sample at various points across the scene and uses those. How many points and where those points are depends on your camera body and what the manufacturer decided to setup as the evaluative metering points.

So whilst it uses more points than spot and centre weighted, it doesnt use the entire scene as a whole, rather a wide spread selection. So calling it True is probably not 100% correct, but maybe multi point metering would be better. Nikon call it Matrix metering cause it use a matrix of points to work out the average, not the whole scene as such. In most new Nikon DSLR it uses 1005 points in the scene.

So looking through your viewfinder consider how 1005 points (that are evaluated to determine the correct settings) would cover what you see. So it is fairly damn comprehensive, but it is not perfect, then nothing is.

Thanks, I am becoming a lot more comfortable with the concept now. If the implementation in my camera continues to work well, I will feel better about using it now I know more of the way it works.

[Hayaku]

My question for the more advanced users, do you have a usual metering method set, or do you just set it on a case by case basis?

[ricktas]

My question for the more advanced users, do you have a usual metering method set, or do you just set it on a case by case basis?

To be honest I rarely look at the metering. It is designed to tell you when you have a correct exposure, and be effective in the auto and semi auto modes on your camera, where you are letting the camera decide some/all of the settings (ISO, Shutter Speed, Aperture). As your photography progresses and you learn more about how it all works, you will find you start to know what settings to use in what situations. You will want to control the result yourself, by choosing the ISO, or the aperture to determine exactly how your photo(s) will turn out. So I tend to shoot in full manual and from experience, in most situations, have a fairly good idea of what settings I need, without looking at the metering of the scene.

[ameerat42]

My question for the more advanced users, do you have a usual metering method set, or do you just set it on a case by case basis?

Hayaku. Mind if I answer your Q?

My metering method is: "Oh, what's it on? Yeah, about 1/320sec f/11, ISO200." For most daylit shots.
Am.

[Mark L]

My question for the more advanced users, do you have a usual metering method set, or do you just set it on a case by case basis?

Will depend on the photo you're taking.
When taking photos of birds I'll use partial or spot metering. Want the bird exposed correctly, not anything else.
mmm, ..... Using RAW does give more latitude if you get the exposure a little wrong.

[Steve Axford]

Everyone uses the camera metering unless they use a separate light meter (I have heard of some, very rare, people who do this). Even if you use manual mode, you are still looking at the metering to adjust the shutter speed, etc of your shots.

Whoops, sorry, there is another way. You could guess, then take a picture, look at the histogram of that picture, adjust up or down accordingly, then take another, etc. I would suggest that using the metering is a very good way to get that first guess. For any picture you should check that it was correctly exposed and for difficult exposures you should adjust and retake until it is correct.

Like Mark said, the type of metering you use will depend on the type of scene. Landscapes - evaluative. Birds, macros etc, - spot. But this is only a best guess. Sometimes you will find that it is a very good guess and no further adjustment needs to be made. Sometimes you will need to add a compensation up or down. And sometimes you will need to go manual as you don't want the exposure to change just because you moved the frame slightly. Play with it. Use the histogram.

[William]

From Rick, AM and Steve, Yep, Yep , Yep I agree and do the same , I'm like Rick and shoot manual all the time , Evaluative metering for everything , Spot metering for my surfing shots , Mainly cause I shoot surfing always in unfavourable light , Early dark winter mornings , Or around here mornings shooting directly into the sun

[Steve Axford]

Yep, surf needs manual - and maybe average for the best guess.

[*~Min~*]

I think I've been led a bit astray with understanding metering. I was told that, even in manual settings, the camera adjusts the ISO, Shutter Speed, and Aperture automatically depending on the metering mode. But this is incorrect isn't it? The different metering modes only adjust the 'correct' exposure on the light meter? Sorry if these are obvious questions, just want my understanding of it all to be set straight

[ricktas]

I think I've been led a bit astray with understanding metering. I was told that, even in manual settings, the camera adjusts the ISO, Shutter Speed, and Aperture automatically depending on the metering mode. But this is incorrect isn't it? The different metering modes only adjust the 'correct' exposure on the light meter? Sorry if these are obvious questions, just want my understanding of it all to be set straight

In manual mode (full manual) it is up to you entirely. You control the camera. Though in the semi-manual modes the camera will make some choices. Say you have it in Av mode, you choose the aperture and the camera chooses the shutterspeed and ISO (by using the metering to let the computer software work out what it thinks is best)

[Mark L]

Say you have it in Av mode, you choose the aperture and the camera chooses the shutterspeed and ISO (by using the metering to let the computer software work out what it thinks is best)

That's if you use auto ISO.
If you have ISO 400 set, then chose your aperture, the camera will decide the shutter speed only.

[arthurking83]

..... I was told that, even in manual settings, the camera adjusts the ISO, Shutter Speed, and Aperture automatically depending on the metering mode. But this is incorrect isn't it? The different metering modes only adjust the 'correct' exposure on the light meter? ....

Err... not necessarily.
As already said, the camera can adjust some settings according to how you want the meter too, but in manual mode it adjusts nothing(except maybe ISO, if you set the camera to AutoISO).

It may also depend on the brand/model of camera you choose to use.

The different workings of each metering mode type only affect the way the scene is metered, not the way the exposure variables work.

That is, each variable type(shutter/aperture/ may be set differently, but this is not always the case.

What each metering mode does is to see the scene differently and adjust those variables accordingly.

In manual mode tho, unless the camera is set to AutoISO, no variable will change it's value unless physically changed by the camera operator.

[*~Min~*]

Okay, that clarifies a lot. I've been pushing myself to take photos only in manual so I can better understand the different settings. I like throwing myself in the deep end I suppose. Now I'm going to experiment with the metering modes, so thank you all for your explanations!