Light is the most important part to a photograph – we judge, compensate, and even manipulate our light sources in order to create the image we see in our minds. In order to get an accurate exposure, we need to choose what settings work best for the lighting situation we’re in: what aperture, how fast a shutter speed, etc. The built-in light meter in a digital SLR camera automatically chooses what settings are needed to expose an image properly. However, light meters can’t predict what kind of photo we want. What if we want to underexpose an image by a stop, or expose the entire photo based on the meter settings of a small part of your viewfinder? To help, there are several options that still allow you to use the auto-metering, but with more accuracy to compensate for the kind of photo you’re aiming for.
The three universal metering choices are evaluative, center-weighted, and spot metering. Your camera manual will tell you how to change and activate these modes so I won’t go into that specific detail. Instead, I’ll explain what each of these modes do, what photos to use them for, and how they benefit you as a photographer.
The most popular metering mode for landscapes (at least for me) is evaluative, which is quite straightforward. Your camera’s built-in light meter will scan the entire area of your viewfinder at certain points – making note of the right combination of aperture, shutter speed, and ISO needed to get a proper exposure – and then average all those points out to give you a final setting. In short, your camera will “evaluate” the scene and tell you what is needed to expose your photo, taking several areas into account.
While it’s fantastic that you can meter a scene without actually purchasing a separate light meter (remember: the less gear needed, the better for a landscape photographer), it’s not always accurate, especially in high-contrast situations:
What if you’re taking a photo of the moon? If you average out the exposure between the dark sky and the bright moon, you’re going to get a photo with a moon that looks more like the sun. For sensitive situations like these, there’s a quick fix for DSLR cameras: spot metering mode.
When you choose spot metering to get a read on your scene, your camera will take a small percentage of the center of your viewfinder (around 5% roughly) and meter ONLY for that area – the rest of your image will not be taken into consideration when calculating your exposure.
Spot metering is used often in landscapes, but more often for portraits and macro photography since there is usually a subject you want exposed correctly with the background being of lesser importance.
It’s ideal for situations where you have a lit subject (such as a leaf in the sun above) and a darkened background where you want the subject to stand out – to be in the spotlight with an accurate exposure. If you were to take this photo in evaluative mode, your light meter would average the exposure needed for your lit subject (the leaf) against the exposure for your darkened environment (with more weight given for the background since it covers more area than the leaf).
In short, your end result would be an image with a blown out subject and a not-so-dark environment. In my example above, the leaf would be horribly overexposed and the soft, dark background would now be quite ugly. Spot metering for a specific subject would avoid this metering mistake.
However, spot metering is not good for a dark subject and a lighter background, such as backlit images. Your camera will try to expose a backlit object out of the shadows which is counterproductive to what you want (usually). Additionally, the bright background will be exposed even more, which will certainly give you blown highlights.
In cases like these, it’s best to spot meter for the background – not for the subject. This way, your camera will get a reading on how to expose the brightest part of your image, leaving your subject in shadow.
However, there is a problem to this method: if you have autofocus on, you’ll be focusing on the background and not your subject, which can cause some unwanted blurring depending on your aperture and distances.
To fix this, do a pre-focus with your spot meter and make note of what shutter speed/aperture/ISO is needed to expose the background. Then switch into manual mode and input those settings. This will allow you to use the proper exposure you just metered for a silhouette image and also still let you use the autofocus on any focal point you want – much more convenient.
So spot metering is greatly beneficial when one part of your image needs to be exposed correctly while proper exposure for the remainder of your photo isn’t too important. The example images above illustrate instances where this works successfully: a correctly exposed subject/dark environment compared to a silhouette subject/correctly exposed environment.
This type of metering mode works like evaluative, however it gives dominance to the center area of your viewfinder – much like the name implies. This is good for situations where the contrast isn’t so dramatic throughout your image, but you still would like to ensure that the exposure for the center of the photo takes precedence over the remainder of your image (for example, a tight crop of a portrait). Think of this as a balance between spot metering and evaluative, where the “spot” is much wider and has a softer transition.
Personally, I rarely use this metering mode in landscapes as I can use spot metering to achieve roughly the same results. Either I want my entire photo to be evaluative or I’ll just use spot metering to get a reading and recompose my shot if necessary. However, that’s not to say that you won’t find use for center-weighted metering in the field- it’s just that I haven’t as of yet.
A great tool for photographers is the exposure compensation feature, which allows you to instantly adjust the exposure in either direction without having to input the changes manually. You can select to adjust your metered exposure by 1/3 of a stop increments (whether you’re in a priority mode or in full-auto) by simply turning a dial. This won’t work if you’re in full manual mode though.
I use this very often because it’s so much easier than adjusting your settings manually. I mostly shoot in aperture priority mode and there are times when my light meter will over or underexpose my photo a bit. Instead of making note of my settings, going into full manual mode and inputting a different exposure, I can simply adjust my exposure compensation dial and get a different exposure.
When in full-auto mode, your camera will use a combination of your aperture, shutter speed, and ISO to change the exposure by how many 1/3rd stops you select.
If you’re in a priority mode, exposure compensation is a great way to avoid full manual while still retaining some control over your settings. Adjusting your exposure compensation in aperture priority mode will increase/decrease your shutter speed easily by turning the dial; same with shutter priority mode – you can keep the shutter speed you want, but adjust the exposure by changing your aperture.
So basically, this is a way to instantly override your light meter. Your camera will meter your image and give you an exposure based on it’s own calculations, and exposure compensation allows you to trump this function without having to go into full manual. It’s very handy, especially since my camera will often overexpose an image by 1/3 of a stop. However, there is a limit to how far you can adjust your exposure this way – usually two full stops. Anything beyond that will have to be done by adjusting your settings manually.
You can also use this for autobracketing a scene. For example, let’s say your camera picks an exposure that it thinks will work, and you autobracket the image by one stop. Upon investigation, the underexposed image still has a large amount of blown highlights. You can then use your exposure compensation to underexpose the metered base image (your middle exposure), allowing you to instantly decrease the overall exposure of your auto-bracketing. Otherwise, you’d have to bracket it manually which can be time consuming.
I typically shoot in evaluative mode, but as noted with my images above, I do find use for spot metering as well. When I’m in spot metering mode, I almost never have my subject dead-center…which doesn’t sport well since this mode takes the exposure from the center of your image. How do I make this work?
I typically capture my freehand photos (whether or not I’m using spot metering) by doing a pre-focus – basically, I center my viewfinder on the subject I want in perfect focus and press the shutter button down half way. This will not only get a focus lock, but will record the exposure needed for your image. Without letting up on the shutter button, I then recompose my image to how I want it to be framed. In addition to getting a solid focus lock on your subject (always important), it also locks in the correct exposure via spot metering without always placing your subject dead center in your image.
If you’re in the market for a new DSLR, remember that some intro-level cameras do NOT have this feature. I consider this a deal breaker because I love how you can instantly expose a high-contrast scene accurately based on where I point my viewfinder. Instead I could take some test images, manually adjust the exposure, and take another test image…but that’s time consuming and unnecessary with spot metering. However, if it comes down to spending more money on a body and less money on a lens…I would go for the lens since the quality of your glass should be your top priority – this will determine the quality of your photos more than anything else.
Establishing a solid workflow is important to every photographer, and knowing when to use the correct metering should definitely find a place in your routine.