Something that is often a point of confusion for newbie photographers is concept of light metering. The cameras of old had fairly simple ways of helping you determine the exposure, but now with digital it's become a complex topic with so many options that it's easy to become confused.
I'll try and take some of the mystery out of metering with this article explaining the two methods you can use to measure the light, and set your exposure.
What is metering?
Metering is simply taking a measurement of the amount of light, so your camera knows how to make the correct exposure. There are two different types of metering: reflective and incident. Let's look at reflective first, which is how your in-camera meter works.
Reflective metering measures the amount of light hitting the subject and bouncing back to the meter (which in many cases will be in your camera). It is affected by the color or brightness of the subject itself. So, if the subject is dark, less light bounces back to the meter. With a light colored subject (white shirt) more light is bounced back to be measured. This presents a problem because it doesn't always give an accurate reading of the amount of light.
The following scenarios may fool your in-camera meter:
- A light colored subject
- A dark toned subject
- A backlit subject (light is behind them) – read Three Ways to Fix Dark Backlit People Photos for a solution to this problem
- An overly bright background or high contrast in the scene
Important things to note in regards to metering and exposure:
- Your camera wants to make gray
- For more information on why the meter gets fooled and how to solve that issue, read: Why is the Snow Gray in my Photos?
- Zero on your camera meter = gray
- Use exposure compensation to adjust and correct
- NOTE: Exposure compensation does not revert back to zero by itself. If you find all your images are too dark or too light, check that the setting is put back to the default of zero.
- NOTE: The exposure compensation setting does not apply when using manual mode on a Canon but it does if you are using a Nikon. Make note!
- Manual mode will let you make a really bad exposure; you need to watch the scale carefully.
- Using aperture or shutter priority the camera sets the exposure to zero for you (unless you have exposure compensation set to + or -).
Learn to read your histogram
Something I highly recommend learning, is how to read the histogram. Your camera provides a graph of the exposure for you in the form of this graph called the histogram. Check your menu settings to turn it on during image playback (some of the newer cameras even display it while you're shooting). It will show you if you have a “good” exposure or not. For more on this, read my article on Digital Photography School, How to Read and Use Histograms, which explains it in a lot more detail. Here are a few quick tips for you:
Tips for reading histograms:
- Watch for gaps on either side of the graph, which indicate either under (a gap on the right side as in the screenshot on the right) or overexposure (gap on the left side)
- Watch for clipped highlights or “blinkies” which means you will have no detail in that area (you get to decide if that area needs detail or not i.e. if it's your friend's face I'd say that's pretty important, if it's a bright spot in the background probably not).
- Does it represent the scene accurately? It may be a nice arch and in the middle but if your subject isn't gray it's not the best exposure.
Using a gray card for metering
You can also purchase a gray card (or a reflector that comes with one on the back of the case) and use that to meter. Just remember to use spot metering, and target only the gray card area. Make sure the card isn't tilted, and getting more or less light than the actual subject. Set your exposure using manual mode to the setting you get when you meter off of the gray card. Have your subject hold it in the scene like this:
List of the type of gray cards recommended:
- DGK set of 3 gray cards (2 sizes)
- PhotoVision target-style collapsible gray card
- Also note that many manufacturers make their camera bags gray on the inside – this is NOT a coincidence! You can pull out a removal panel from your bag and use that in a pinch.
Incident meter reading
The second method of measuring the light is called incident metering. This is where you use a handheld light meter to measure the amount of light falling on the subject. It is not affected by the brightness or tonality of the subject and will give you a more accurate reading right off the bat.
Incident metering is done by placing the meter by the subject, pointing it at the light source and taking a reading. Each brand or model of incident meter is slightly different, but basically what it will tell you is what to settings to use on your camera to get a good exposure. You plug the ISO in, and the meter tells you the shutter speed/aperture combination to use. You can also scroll up and down to see different pairings – for example:
- ISO 400 is entered and the meter says f/8 at 1/30th
- You can adjust to f/5.6 and it will then read 1/60th which is the same amount of light or Exposure Value (EV)
- f/4 at 1/125 is also the same
- As is f/11 at 1/15th
ONE STOP OF LIGHT IS DOUBLE THE AMOUNT OF LIGHT
Which method do most professional portrait photographers use for metering?
Most professionals use incident metering for portraits and things that are stationary, like studio work or still life subjects. It is more accurate, and also allows you to measure things like off-camera flash (set to manual exposure) and ratios.
Just know that it's really handy to have an incident light meter. If you don't have one now here are some of the options available:
- Luxi for all – this is a slick little device that for only $21.95 turns your iPhone into an incident meter. I've tested it side-by-side with my regular meter and it was pretty close (within a third of a stop) most times. If a full handheld meter is out of the budget for now, you might want to consider this option.
- Sekonic L-308S – I have the predecessor to this model (a similar one is in the photo above) and it works great. This is about the simplest version of an incident meter you can get. It doesn't do fancy stuff like store things in memory, or calculate ratios though so if you want advanced features look at one of the more expensive models.
- Sekonic LITEMASTER PRO L-478DR Light Meter: with PocketWizard Triggering and Flash Power Setting for ControlTL Radios – slightly more upscale model with more bells and whistles.
- Gossen Digipro F2 Light Meter – a model from another manufacturer that's been making these things for decades.
- Sekonic L-758DR DigitalMaster, programmable digital flash and ambient exposure meter – top of the line. Probably more than you need if you're just starting out, but there it is if you want to check out the cream of the crop.
So I hope that sheds some light on the different ways you can measure, or meter the light. Both will be effective if you understand what the camera or meter is telling you, and adjust accordingly. You get to decide the look of your image, so remember the meter reading is just a starting point.