Explore Landscapes #43

So much has been written about exposure, metering, and camera metering modes, but much of it overcomplicates the subject (in my humble opinion).

In Explore Landscapes #28, I outlined some essential photography terms I believe every photographer needs to understand. Exposure is one of the most overly complicated topics of all these various terms, abbreviations, and techniques. So much has been written about exposure, metering, and metering modes, but much of it overcomplicates the subject (in my humble opinion) for people starting off on their photographic journey.

In my workshops and mentoring sessions, I always strive to simplify photography to the essentials, i.e., what you need to know to make the progress you want with your photography.

In this post, I will try to simplify the concept of exposure down to its basics so that you have a strong foundation to build upon when you’re out shooting. Let’s start by defining what we mean by Exposure:

Exposure - is a term used to describe an image's overall lightness or darkness and how the amount of light reaching your camera’s sensor (or film) is measured. Most of you will likely be shooting with a DSLR or a Mirrorless camera, so the rest of the article will concentrate on digital images.

To make a photograph that we can see, we have to adjust the amount of light that the sensor is exposed to. An image that is too bright is overexposed; an image that is too dark is underexposed. Exposure is controlled by aperture, shutter speed, and ISO (commonly known as the exposure triangle).

These three camera/lens settings work together to regulate the amount of light that reaches the sensor. Aperture and Shutter speed regulate the amount of light reaching the sensor, and ISO amplifies the light signal that reaches the sensor.

An image is said to be ‘properly exposed’ when the image is neither overexposed (too bright with some areas pure white) nor underexposed (too dark with some areas pure black). Please note that there’s no such thing as ‘proper exposure’ - you can choose to expose an image as you see fit to suit your artistic vision.

When I’m shooting, I try to capture as much of the available light data as I can for the scene I’m photographing. For me, this means shooting in RAW and using my histogram to capture the widest dynamic range of light I can.

Then, when I come to edit the photograph, I can determine how I want to expose the image (i.e., what I believe to be the proper exposure) and give myself maximum artistic latitude.

Anyway, back to the exposure triangle of aperture, shutter speed, and ISO. You (or the camera) can choose different combinations of aperture, shutter speed, and ISO that will produce an equivalent exposure, i.e., an image of consistent brightness.

Selecting which of the three settings you choose to increase or decrease (to achieve the ‘proper exposure’) is a decision the photographer takes based on the scene they are photographing and their artistic intent for that image. Each of the three settings affects the light reaching the sensor and has specific side effects you must be aware of. These side effects are identified in the exposure triangle diagram above. Let’s go through each of them in turn.

Aperture - is the size of the hole in your lens through which light passes to the sensor (DSLR or Mirrorless camera). The larger the aperture, the more light is allowed through; the smaller the aperture, the less light is allowed through. Aperture is measured in f/stops (which mathematically is your lens focal length/aperture diameter). A small aperture number (e.g., f/2.8) represents a large aperture size, and a large aperture number (i.e., f/22) represents a small aperture size. The aperture also determines the depth of field in an image.

Depth of field (DoF) - refers to the area of a photo that is in acceptably sharp focus. When you focus the camera, you select a point in the scene that you wish to have the sharpest focus. This sharpness of focus also extends in front of and behind the main focus point. The depth of field is influenced by several factors, including the aperture (the larger the size of the aperture, the shallower DoF becomes), the distance from your lens to the subject (the closer you are, the greater the depth of field), and the distance from your subject to the background (the larger the distance, the greater the depth of field).

For landscape photography, depth of field (and, therefore, aperture) is normally the first (and most important) of your three exposure settings. Do you want to have sharp front-to-back focus in your image? Do you want your foreground subject in focus and then through the mid and background out of focus? You need to make this artistic choice as you’re composing your image.

Shutter speed - is the time (measured in fractions of a second or seconds, e.g., 1/4s or 15s) that the camera shutter stays open, exposing the sensor to the light in your scene. Shutter speed allows you to control the appearance of motion in an image, such as blurring the movement of a river or waterfall or freezing the movement of an animal or person in the scene.

For landscape photography, assuming that you’re shooting on a tripod, you can choose your preferred aperture (for required depth of field) and maintain a low ISO (to minimize digital noise) by selecting a slow shutter speed. However, you have another artistic choice to make while composing your image. Do you want to show motion in your image, or do you want to freeze any motion?

Shutter speed is (typically) the second most important of the three exposure settings, but that depends on the scene you’re shooting.

ISO - refers to the sensitivity of a camera’s sensor to light (for DSLRs and mirrorless cameras). Commonly used ISO values range from 100-6400, where 100 is not very sensitive to light, and 6400 is highly sensitive to light. However, one thing to note about ISO is that the higher its value, the more likely the image is to have digital noise, which gives the photo a grainy look. This noise comes from the amplification that records the light falling on the sensor. Typically, in a landscape photograph, you want to keep the ISO as low as possible but as high as required to use the aperture and shutter speed you selected.

So, how do you know if you’ve selected the right combination of the three settings to achieve a ‘proper exposure’? You use the histogram (see Trust Your Histogram).

Histogram - is a graphical representation of the number of different toned pixels in a scene (from dark to light). The LH edge of the histogram represents pure black, and the RH edge of the histogram is pure white. There are 256 tones between black and white (in an 8-bit RGB image). The histogram shows how many pixels of each tone are in the scene. The shape of the histogram is not important - it’s simply a function of the tones present in the scene you’re photographing. However, it is important to avoid clipping the histogram's LH (black) or RH (white) edges. Try to keep a small gap at the base of the graph on both sides of the curve. If you cannot position the histogram to avoid clipping, you have exceeded your camera's dynamic range and should bracket your exposure (the subject of a future post). The histogram can be viewed on your camera’s LCD screen (live with a mirrorless camera or DSLR using live view), or when reviewing a image already shot.