Understanding metering, part two: what to use, when

In part one we examined why metering is important, and how the basics of how meters work. In today’s article, I’ll take a closer look at the different types of  metering, how they differ, and under what situations they should be deployed.

metering-viewfinder

A sample viewfinder – in this case, a rough representation of the Nikon D2H/ D2X finder.

With that background out of the way, let’s look at how the various metering options work, and what typical situations they might best be deployed under. Cameras typically have three options, or some variation upon that. Within these options, it’s also usually possible to fine tune various aspects of the meter’s operation. I’m going to leave out handheld meter operation since this is something that’s almost never encountered today. An important point to note is that all meters can be fooled by situations of uniform luminance, so don’t trust the readout blindly. Remember, meters function by averaging the entire evaluated area out to middle gray; this means if your evaluated area is meant to be black or white, you’re going to need to add or subtract some exposure compensation. For predominantly light/ white scenes, you need to add; for dark scenes, subtract. This holds true for every one of the different metering methods detailed below.

Average
The simplest form of metering evaluates the frame as a whole, and tries to expose it to middle gray – under the assumption that there will be shadows and highlights, but these will average out. Seldom used today because you will almost always require exposure compensation (making it unsuitable for the point and shoot crowd which constitutes most of the global camera market), but has the one enormous advantage of behaving predictably under every situation.

Spot
The simplest form of meter is the spot meter. This evaluates luminosity at the desired point only, ignoring everything else in the frame. There are two important things to be aware of with a spot meter: the location and size of the spot. The metering spot’s location is either in the center of the frame, or tied to the selected or active autofocus point; the logic there is that you would typically want to ensure your subject is both in focus and properly exposed. Variations on the spot meter include types that are biased for highlights or shadows – i.e. you meter a shadow or highlight and it doesn’t turn out over or underexposed. Don’t forget to add appropriate exposure compensation.

The size of the spot is also very important – don’t be fooled into thinking that it’s a tiny, precise eyedropper the same size as your autofocus area box – it isn’t! Most consumer cameras have a spot size that’s about 2.5% of the frame area, which is actually quite large – imagine your frame divided into six vertically and horizontally, i.e. a grid of 36 boxes; a 2.5% spot meter is the size of one of these boxes. Professional cameras might have a 1% spot meter; imagine a 10×10 grid of 100 boxes, and this is pretty much what you’ve got. In our sample viewfinder above, the cyan box is a 1% spot meter, tied to the active (red) AF point. Keep this in mind as you’re moving it around. If your spot meter is tied to the center of the frame, then you’ll need to assign another button – perhaps the shutter half press – to lock exposure once you’ve metered for your subject (unless it is of course dead center, which is highly unlikely).

The obvious question would be why spot meters aren’t smaller – firstly, you don’t actually want them to be that acute, otherwise moving the camera by a fraction of a degree might yield a vastly different (and incorrect) exposure – they’d be too sensitive to use. Secondly, some averaging is still a good thing – you can move the camera around a bit until the spot falls onto the right mix of light/ dark to give the desired exposure. With practice, this can be much quicker than using exposure compensation.

Use the spot meter in situations where your subject is in very different light to the rest of the frame – either much brighter or much darker – in order to ensure that the focus of your shot is properly exposed. It’s great for high key or low key images – put your subject in the shadows or highlights respectively, and spot meter there – or even general situations under which the luminance of your composition doesn’t vary that much. I don’t generally use it for street photography or fast moving situations, because it requires precision and/ or a little meter-and-recompose dance that can cost you valuable time.

One tip: the way I use the spot meter is always either covering my subject, if the subject is darker than the rest of the frame; or, on the highlights plus a bit of dark area if your subject is lighter than the frame. This effectively tricks the meter into adding a bit of exposure compensation to average out the bright/ dark areas – you need to do this to prevent your highlights from falling into middle gray and consequently completely losing your shadow information. It also adds a bit of speed in operation since you don’t have to muck around with exposure compensation.

Spot meters only came about when the metering cells in cameras could be made small enough to evaluate only a portion of the frame; they’re common now because our metering sensors are made up of hundreds, if not thousands, of discrete individual elements.

Centerweight
In our sample viewfinder, the circle around the center AF point represents the centerweight meter area border. That sounds like a bit of complex mouthful, but in reality it’s not. A centerweighted meter divides the frame into two areas – the circle in the middle, and the border. The circle in the middle is presumably roughly where most subjects are going to be framed, which in turn you would like to expose properly etc – it is metered separately from the border area. The two metering values are combined in a predetermined ratio – usually 70-30 in favor of the central portion, sometimes 60-40 – to determine the final exposure value.

Centerweighted meters are the predecessor to matrix metering – they try to average things out over the entire scene, and make a sensible assumption or two about what you would like to expose for. Modern cameras allow you to change the size of the center area – the D800E, for instance, allows a spot anything between 8mm and 20mm in diameter. The default center area is usually etched onto the focusing screen for reference. Note that centerweighted metering was the successor to evaluative metering, and shares its advantage of predictability: if you put your subject in the circle, chances are the exposure will be right; the advantage it has over evaluative metering is the ability to bias the exposure towards your subject.

In situations where spot metering would not be suitable – action, for instance – I actually prefer using centerweighted metering to matrix in unfamilar cameras; at least I have some idea of how the meter will respond. There’s nothing more frustrating than missing a shot to over or underexposure because matrix metering has gotten things very, very wrong.

Matrix
Matrix metering is either a miracle or a curse, depending on where you stand. For those who don’t want to take control of their cameras, matrix metering provides a higher ‘hit rate’ than evaluative or centerweight; the problem is, you have absolutely no idea when it’s going to get it wrong, and how much by. This can be rectified with experience with a certain system; as you encounter more situations, you get a better idea of when the camera is going to miss. It’s for this reason that the only time I use matrix metering in a situation where delivery is critical is when I’m shooting cameras I’m familiar with – the Nikons, and the OM-D. Everything else is either spot or centerweight.

That doesn’t of course explain how it works. The frame is divided up into a number of areas – up to 100,000 of them in the Canon 1Dx – and a reading taken of each area, for both luminance and color. The camera then either compares this to a database of similar situations (i.e. photographs converted into 100,000 or however-many pixel maps, along with exposure values) and then determines the exposure. If the camera can’t find a matching situation, then it makes an intelligent guess about what the exposure should be based on a combination of overall scene luminance, color, and the current AF point. With this many variables, it’s actually surprising that the meters get it right such a high percentage of the time – perhaps there are only so many possible luminance maps?

In any case, matrix metering tends to be more reliable in situations that don’t have extreme contrasts, or bright point sources in the frame, or very small subjects. Under quickly-changing circumstances, it’s the method of choice – it might get things wrong, but most of the time it will save you from having to move around the spot or use exposure compensation. For most users, matrix metering is sufficient, and you can always add or subtract exposure compensation and take another shot. It’s also worth noting that matrix meters that use the imaging sensor are much more accurate and reliable than those that have separate metering sensors simply because the tonal response characteristics of both match, making overexposure almost impossible. Presumably, these should also run some form of ‘expose to the right’ algorithm for digital cameras, but then again perhaps not as it would only be useful for RAW shooters.

I think considering some examples would be useful at this point. Let’s take a few of the images from my recent Introduction to Wildlife workshop:

metering-1-master

This image could be taken care of by either spot or centerweight; I have no idea if matrix would have been accurate or not. For centerweight, you would need to ensure the central spot is over the subject area, like so:

metering-1-cw

This implies a lock-exposure-and-recompose is necessary – or, perhaps not seeing as I intended to crop the final image to a more square aspect ratio anyway. You might wonder whether the 70-30 distribution – specifically the metered portion falling on the black water – would throw things out; in this case, actually it helped. The center portion would have metered the white bird to middle gray, i.e. too dark; the outer portion metered the black water to middle gray, i.e. too light. They averaged out.

metering-1-spot

We could also have used the spot meter, in a few different ways. For location A, no compensation would be required so long as we took a bit of the dark portion and a bit of the highlight portion – i.e. enough to average out to middle gray. Location B would have required some positive exposure compensation as it is a highlight, in zone VII-VIII or so. Location C falls in zone V anyway, which is middle gray – so no exposure compensation would haven been required. In this case, I would have picked location C if using an AF lens (I wasn’t) as it’s of both the right luminance value and subject distance – alternatively, the head would have been a good choice, too.

metering-2-master

Here’s our second example. This is a much trickier situation because of the thin rim of backlight around the bird; you don’t want to overexpose that else you’ll lose all tonal detail in the feathers.

metering-2-cw

You can see here that centerweighted metering wouldn’t work; the highlight areas – in this case, the subject from the meter’s point of view – is just too small. It would expose for the dark area and result in blown highlights. Spot metering, on the other hand, is ideal:

metering-2-spot

Location A is obviously nonsensical because although it might be the same luminance value as most of the bird, that isn’t the part we’re exposing for; using location A would result in huge overexposure. Location B is fine, and the highlight area is small enough that it wouldn’t require any exposure compensation since some of the dark background is also included – this is actually what I used – C and D are also workable options, though C might require a little negative compensation.

How about a few more examples?

_5014972 copy
Clearly, spot metering on the eye is the only way to go – all other options would have resulted in overexposure and both detail loss and an imbalance in the composition caused by the eye of the viewer not going to the intended area.

_5014910 copy
Actually, any metering option would work fine here – the scene is divided into relatively large portions of different luminance. If you used spot on the feathers, you’d have to add a bit of exposure compensation to keep things white; if you used center, you’d have to lock exposure and then recompose.

_5014793 copy
Our frame is fairly consistent in luminance, so once again, any metering method would work. However, all would require a bit of positive exposure compensation as the overall tone of the subject is light, and should be kept high-key.

_5015451bw copy
Small white subject against a dark background, intense contrasts – spot meter.

_5014828 copy
Here’s one situation where matrix metering would actually work better than the other options: you have relatively even luminance across the frame, a strong colored background (making centerweight possibly inaccurate) and a fast moving subject (making spot metering impractical).

Of course, knowing which metering method to use in a given situation is quite useless unless you have things set up so that it’s easy to switch between them; otherwise, pick one and get used to the way it operates. If you can lock exposure separately from focus, then you don’t really need to use exposure compensation most of the time – the spot meter is all you need. If you can’t be bothered to do the finger dance, well, that’s why matrix was invented. Needless to say: as ever, practice is the key to mastery. MT

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Comments

  1. Jamal Rashdi says:

    Ming, thank you so very much, your blog is the first read for me in the morning. I have and still am learning. One day I will be in one your workshops somewhere. In the meantime I will check out which video to buy to start with. Thanks a million for you kindness and your work is amazing. God Bless

    • Thanks – start with The Fundamentals and Outstanding Images, then move on to How To See and the Photoshop videos.

      I have places left for Melbourne (March) and London (July) workshops.

      • Ming, Thanks, I will. My schedule is sort of screwed up. But I will take your advice, as I just see, your images, as so damn good. Only if I could, 1/10th of that. Thanks. Just as as a side bar, I have been to Kl, almost took the job running the Ritz or Pankor Laut (of course a different place there. Thanks so much.
        All the best.
        Regards,
        Jamal

  2. Carlos Esteban says:

    As always, thanks for all that precious information.
    What you think about spot meter with +2EV compensation and meter the brightest area of interest? On OM-D it would be wise to set Fn2 (or 1) to lock exposure so you get separate areas for exposure and focus (but that avoid using it to focus magnifier for manual focus third part lenses).

    Regards, Ming.

  3. David Berry says:

    Ming ~ How do you get the black background?

  4. G’Day Ming
    fantastic articles and comments. instructive, informative and well presented. My knowledge of photography increases every time i read your articles.
    Thanks a million
    Steved

  5. Ming,
    I just finished reading all of your articles in the technique, technicalities and post processing section. 41 in total. I can’t thank you enough for the time spent in preparing these. It is my education in the arts I never had.
    Much Appreciated – Eric

  6. One thing I loved of my old Olympus OM-4 was it´s average spot metering: you could pick different readings at your subject and got the desired exposure. I wonder why they don´t implement it with the “new age” digital cameras, such as the OM-D.

  7. A reblogué ceci sur DmartienJ Space and commented:
    Great article

  8. Steve Jones says:

    Another excellent article from the house of Ming. My problem is that by the time I’ve fussed with my focus point, composition, choice of aperture and multi spot metering, the bird has gone! I can still hear him ( her? ) laughing at me from the trees though.
    I don’t think I’ve ever seen this topic presented so well.The blue green circles that indicate the metering areas are truly effective.
    My next camera should have those in the finder! Now, after reading this I simply must get around to exploring the metering possibilities on my OMD.

    • Haha, thanks Steve. With the OM-D, you’ve got the advantage of being able to see exposure live in the finder, so using regular metering + highlight display warning overlay + exposure compensation works too – it’s faster as you can just fix focus point and compensate as necessary using one of the dials. I think you’d probably be doing serious birding work with a legacy (i.e. manual focus) lens anyway, so you may not even have to worry about AF…

  9. Andrew McMaster says:

    What excellent stuff this is. I suspected I would be fascinated by what more could appear in Part Two when I thought that Part One was pretty comprehensive, and I have not been disappointed. Many thanks for what you contribute to us all.

  10. Jorge Balarin says:

    Highly instructional. Thank you very much.
    Some questions. How much compensation do you use in a situation like the one of the bird that is covering it’s face ?. Is it possible to lock the exposure but not the focus ? What happens when you are using a narrow depth of field and you need to make focus in your subject eyes, regardless of the light distribution ? Greetings, Jorge.

    • Thanks Jorge. For that shot, -1.5EV. Depending on which camera, yes, it’s possible to lock exposure and focus separately – I have my Nikons set up so that AE-L is on one button and AE-AF-L is on another. With the OM-D I used for that shot, AE-L is on the shutter half press – I’ll focus first, then lock exposure with a separate button. Or compensate, focus, and lock exposure – either works.

  11. These two articles are awesome! Just finished the first and scanned through this one. Have to re-read a couple of times to let it sink, but this fills a gap in my knowledge and skills! I have the feeling this is going to make a difference. Thanks for writing and explaining!

  12. I got half way through your article why you’re so concerned with metering and then realized you’re shooting moving subjects. Shooting landscapes I don’t use metering at all. I use manual exposure in live view, look out for highlight alerts after the shot, and then adjust as necessary. I use 3-shot or 5-shot HDR bracketing for practically everything. The need for metering doesn’t really exist in my world except to get a feel for where to begin bracketing. Such a different paradigm.

  13. Reblogged this on Olympus E-M5 Resource Blog and commented:
    Part 2 on metering deals with how different meter patterns determine exposure, and how to take advantage of them.

  14. Thanks Ming. I’ve just started working with my Leica M-E and this is a definite help in how I will use the Leica’s exposure compensation function and the way this camera meters.

  15. Steve Waldren says:

    Great article Ming. Afraid that I’d almost always used matrix on my D200, but always with exposure compensation – after a while you get to know what to apply to a given situation and I guess this is Ming’s thoughts on getting to really know a given system. With the relatively recent D800 aquisition I’ve enjoyed a type of photography more akin to what I was using with medium format film (slower, more contemplative, use of large image with live view etc.). I’ve been mainly looking at the shutter speeds I need for image quality while also ensuring the depth of field I need (I am usually looking to maximise DOF) – but I’d not really thought about using spot metering yet, until your article. What I’d REALLY like is a camera with a small enough spot (and the D800 is OK) linked to a zone – as on my zone-calibrated handheld Pentax spotmeter. Your points about spot metering and placement are informative, I think Adam’s zone system still has much to offer: and I’m looking forward to working this back into my photography. One other thing comes to mind though – with recent sensors the dynamic range is now larger, but is also dependent on the ISO. Has anyone thought about the number of suitable zones at a given ISO for RAW capture?

    I never really went for incident light metering as most of what we photograph is reflected light, with few exceptions – what is your view on this Ming?

    This is a great, informative site; I enjoy the information as much as viewing your images. Equally important are the useful comments from your readers, not the awful opinionated tirades that frequent on many photography blogs. Great job!

    • The spot always meters about zone 5-6 in my experience. So if you’re using spot on the highlights, then you’ll have to add two stops or so to put it in zone 9. Alternatively, I just move the spot around so it lands on something that I want to average out to zone 5.

      Base ISO for the D800 has about 13-14 stops recoverable from an optimum RAW file. The base two don’t have a lot of tonal gradations – that’s just the nature of digital – but they’re there.

      I’m all for incident metering, but most of the time it isn’t practical so I hardly ever use it except in studio with reflective objects – this is where it shines over reflective.

  16. Thanks Ming for Part 2. On my OMD I have a Fn2 set to AEL and have spot metering set up. But am I missing something. Do a I need to select the specific area in composition I want the spot metering to focus on or does the metering system do this automatically in conjunction with AF? If I need choose this area how do I literally do this?

    This brings me to my next question. If shooting in full manual mode and your spot metering is determined by AF, what happens in this case?

    Thanks for any help or clarification. The above may come across as very silly questions for many but I’m a novice!!

    Given you have the OMD thought I’d check but if too long winded no worries. I’ve looked on google and can’t really find an answer to this question.

    • The spot meter follows the AF sensor – I put AEL on the shutter half-press.

      In full manual, the meter is a guide only – unless auto ISO is active (actually, I can’t remember if auto-ISO works in M or not – it does on some cameras, not on others.)

      • Doesn’t seem to when trying it out today (Auto ISO that is.)….M looks to be a meter by eye. I turned on the highlights/shadows tool last night, tried the histogram……to be honest i think I just prefer the eye in live view over both options.

        • Ah, I guess the Olympus doesn’t do it then. My Nikons do, which is why I always get confused between the two. The OMD has a handy live highlight overexposure guide which helps you to get perfect exposure, too.

  17. Many thanks for the very informative post, Ming. Your blog is the number one on my daily reading list.

    There are some complaints that Nikon’s matrix metering systems are not very good at recognising situations with spot lights or back light in the frame and tend to under-expose the subject much often than other systems. For example, this guy complained about the matrix metering of his D600 on DPR.

    http://forums.dpreview.com/forums/post/50505363

    http://forums.dpreview.com/forums/post/50587515

    I have no experience with Nikon but am interested in switching from Canon 40D to Nikon D600. What is your opinion of D600’s matrix metering accuracy compared with those in other systems like Olympus or Sony RX100 that you use? Is the miss rate much worse? Thanks for your help.

    Wayne

    • The newer Nikons tend to be very heavily weighted towards the AF point – this might or might not have something to do with it. I felt the most infallible meters were the D3/D700 generation; the newer ones often require quite a bit of compensation. The Olympus is actually very good – probably because it uses the imaging sensor to meter. The RX100 isn’t, and I default to spot metering most of the time.

  18. This series has been very educational so far; it has changed the way I look at and the importance I associate to metering. I wonder now how to make metering in the film world more predictable. I suppose experience with camera and type of film are probably the most important when shooting in the field?

    As usual, I very much enjoy reading your lucid articles, always giving me food for thought every time I think of photography—thanks again for the writing!

    • Very much so. For instance, I’m finding that the film I use – Delta 100 – has an odd response curve in bright light, which means one has to underexpose quite a bit to get the tonal values you want – as much as a stop, I think. Lens transmission matters too – the Zeiss lenses on the 501C tend to be about a stop hotter than the RX100 (which I sometimes use as a meter)…learned the hard way on the first roll.

  19. You could also use incident metering in some of those cases, which would avoid the “where to meter” problem.

  20. John Prosper says:

    Another interesting read! I tend to favor spot metering (SM) for almost everything, save flash photography. I learned to use SM using the OM3/OM4(T) camera bodies, which precluded matrix metering (MM). I haven’t played with too much MM since I prefer to know exactly what is being metered. One can get very fast with SM if one knows what area(s) to consider for metering, especially if one becomes adept at SM very early before actual exposure. I can see where MM can come into its own for fast changing situations where one has little to no time to employ SM beforehand. However, I would really have get very familiar with a particular MM scheme before I could trust it,

    John in Atlanta, Georgia/USA

    • Agree totally – which is why it’s either centerweight or spot for me most of the time, unless it’s on a camera that I’ve used extensively and am intimately familiar with – which is basically only the Nikons and the OM-D.

  21. Wonderful article Ming. Very instructive and informational. Fantastic. Many Thanks! – Eric

  22. Interesting, I just shot at the bird park last weekend. I went full manual, as the lighting in the park is too extreme (4-6pm): shades in one area, bright sun in another. I’d love to read your opinion on artistic value/approach on shooting animals, eg: do we still follow the conventional rule of third? golden spiral and etc.

    Regards,
    Kelvin

    *is that a smiley at the right bottom corner of this blog or am I seeing things?

    • Whatever looks right – personally, I tend to treat animals much like people in terms of composition; there’s got to be some emotional engagement in it for the viewer.

      I think the smiley was part of the theme, I remember seeing it before too.

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