Why Your Camera’s Light Meter is (often) Wrong Understanding Exposure

It doesn’t matter how advanced your camera’s meter is, or which metering mode you use, all camera meters work the same way – by measuring reflected light.

So, why is this. It’s down to the way your camera’s meter works So, why is this? It’s down to the way your camera’s meter works. It measures the light reflected from the subject, and then calculates what it thinks the best exposure is accordingly. If you rely only on your camera’s meter, it may get the exposure wrong, leaving you with under or overexposed images.

So you have a white dog and black dog lying next to each other So you have a white dog and black dog lying next to each other. If you move in close and take a photo of just the white dog, your camera’s meter will give you a very different suggested exposure setting than if you had chosen the black dog. That’s because the fur of the white cat dog reflects more light.

So if you expose to get more detail in the shadows (black dog) you will blow out the highlights (top). Do the opposite to bring out more detail in the white dog and the black dog loses detail. This is a difficult dilemma.

Why can’t a light meter figure out how to expose both highlights and shadow accurately? The reason is that the camera expects all the tones within the scene that it is metering to average out to a mid-grey tone (also known as 18% grey).

Why would they design a light meter to average out the exposure to an 18 percent grey? It turns out that Caucasian flesh (Germans invented the light meter) renders to a light-mid grey in black and white. Inventors/engineers made an assumption that the “typical”subject would reflect back at about 18 percent grey.

Now, if that’s not complicated enough, let me confuse you a little more. Since the advent of digital, some camera designers say they actually reading is 12 percent grey. It appears the 18 percent takes into account that most photos were viewed with reflected light (on paper), but now they are viewed with transmitted light (monitors)

Either way, here’s the issue Either way, here’s the issue. What you are pointing at and how you are pointing it may/will change your light meter reading and create over and underexposed pictures. Let’s look at a couple examples.

In a "simple" lighting situation - for example, a portrait of your friend taken with typical flat, cloudy Oregon sky (hazy white), the traditional aim-your camera-and-trust-the-meter method works just fine. But when the lighting is more complex, you often need to use a different method to get the right exposure.

So if your subject has a lot of dark tones, your camera light meter reading will overexpose the image because it is trying to render the dominant darks as a lighter grey, resulting in overexposure of lighter tones by up to 2-3 f-stops.

Conversely, if your subject has a lot of lighter tones, your camera light meter reading will underexpose the image because it is trying to render the dominant lights as a darker (average 12-18 percent) grey, resulting in underexposure of lighter tones by up to 2 f-stops.

Bright/harsh outdoor sunlight Bright/harsh outdoor sunlight. (Can give very contrasty images, with a loss of shadow detail and burnt out highlights). Sunrise/sunset photography. (Lighting can be problematic due to being low. May also give flat results). Low light / nighttime photography. Dark building interior. (Shadow details can be difficult to capture). Chiaroscuro lighting (strong shadowed areas with bright highlights can lead to a dilemma—what to meter?) Strong illuminations - signs / artificial lights. (Exposure errors may arise, and image end tones may alter). Water. (Can lead to unsharp subject - if a polarising filter is not used). Skies. (Can lead to an overall lack of sharpness - if a polarising filter is not used). Mountains. (Haze / unsharp end images can be an issue). Snow, white sand, light concrete (The effect of vast areas of white can affect the exposure and result in burnt out highlights. Exposure errors may arise). Above are potential lighting problems that can cause your light meter to be wrong. Your assignment: Using the internet, research light metering techniques that will help you solve difficult lighting situations

Examples of search terms that may produce useful information problematic lighting photography Difficult lighting situations photography Selective metering techniques selective metering photography exposure ansel adams Zone system (very advanced but the gold standard) Bracketing exposures light metering modes Remember, this is about exposure control inside the camera. Don’t include PhotoShop techniques or HDR (we will get to that later). The methods we are looking for work equally well with film and digital. Find solutions to three of the 10 problems listed on previous slide, write them out in a simple handout and be prepared to instruct others in how to use the techniques. Demonstration is also helpful.