Just What the Heck is the Exposure Triangle??
Those who understand the exposure triangle have greater photographic creativity, no longer fear the dreaded ‘M’ mode, wake up earlier, and are guaranteed to regrow years of lost hair! Well, maybe not quite all that.
Before we can begin to discuss exposure, we must understand how your camera gathers light. When we talk about exposure for a scene, we are talking primarily about three distinct components to a camera. These parts consist of the aperture, the shutter speed, and the ISO. These three settings work together to capture the light coming in through the camera’s lens. Balancing these elements gives the camera’s sensor (or film) the widest range of light without over or underexposing the image. Learning what each of these elements do and how each impacts an image will increase your ability to create images.
We’ll start with aperture. This is the iris within your camera’s lens system that controls the amount of light passing on through to the sensor. This iris may be a mechanical series of “leaves” that physically increase or decrease an opening, or it may be a digital system compensating for a fixed opening such as found on mobile phone cameras. The size of the opening is measured in what are called f-stops. And, while the f-stop numbers do have significance as being a ratio between the opening size and the lens size, what you need to know is that the bigger the number the smaller the opening. So, an f-stop of f22 is signficantly smaller than the opening of, say f1.8.
Click on this image to watch a video where I try to explain aperture while being stuck inside after months of pandemic lockdown. It’s a riot.
Basically, as one would expect, the larger the opening the more light is going to pass through. This ability to adjust the amount of light getting to the sensor becomes increasingly important as the environment’s light reduces. Say, for example, you’re attempting to catch all the colours of an evening sunset. As the daylight diminishes, opening your aperture will allow more of the remaining light to pass into your camera allowing your camera to expose the image.
Now before you decide to just take every image with as large of an opening as you can, aperture has secondary impact on your images. The size of the opening also has a direct relationship to how much of your image is in focus. Both your lens and your eye can only focus on a range of distance at any one time. While your eye can change focus so quickly as we look about that we rarely notice when something is out of focus, the camera is slower to focus and captures the image while focused at one particular distance. The larger the aperture opening (the lower the f-stop) the shallower the range of depth that will be in focus. This is called depth of field and can be used to create wonderful images that creatively blur the background from the subject. Conversely, decreasing the opening expands that range to where the ground a few feet in front of the camera is just as sharp as the mountains miles away.
Starting to see the challenge? Let’s move on to the shutter speed.
Shutter speed is comparatively simple to aperture. It is quite simply the speed at which the shutter opens and closes again exposing the sensor to light. This also has an impact on the exposure as a slower shutter speed (the shutter is opening longer) will allow more light on to the sensor. In our sunset example from earlier you could set a longer shutter speed to let more light in getting you the shot you want. If that’s a bit muddy, think about it as herding cats in from the rain; the longer you hold the door open, the more cats with make it through. However, shutter speed also has a secondary effect on images and that is motion blur.
If you click on this image you can watch me try to explain how a photograph is really a span of time compressed into a single moment. While still in lockdown.
Motion blur is the result of something moving across the frame faster than the shutter activates, essentially allowing the sensor to record that element over a range of space in one frame. Sort of like how all those cats streak in the door the moment it is open. This technique can be quite useful in making flowing water seem smooth or purposefully introducing a sense of motion to your images. However, when unwanted motion blur is captured, it can become a distraction from the image you are trying to create. Birds flying across our sunset scene could become blurred lines in the sky. Now, it is possible to have your shutter open so long that moving objects are effectively erased from the image through a technique called long exposure photography. However, that is generally not an area that people start in and often requires additional equipment on cameras with that capability, so I won’t be going into that here. What you need to know about shutter speed is that faster settings will freeze motion more while limiting the cameras ability to gather light and slower settings will blur moving objects but let more light in.
Is your head spinning yet? Don’t worry, we’ll connect everything in the end and hopefully it will all start to make sense. Now, on to ISO.
Yup, did an ISO video too but with bonus exposure triangle stuff. Had to keep productive….
The International Standards Organization (ISO) is an industry scale to measure the sensitivity to light. ISO is notated in a numerical for that, for cameras, typically doubles as it increases in sensitivity. For cameras the scale typically starts at 100 (although some do go a bit lower) and moves up through 200, 400, 800, 1600, etc.… As the ISO increases the sensor’s sensitivity, exposure time can be decreased. The technology in modern digital cameras has greatly increased the usable ISO range. Why do I say usable? Because, as the sensitivity increases the sharpness and clarity of the images decreases. This is rather like playing electric guitar, turning it up to 11, and being blown back like Marty McFly to the distorted, feedback cacophony of noise. High ISO also has another minor drawback in that it becomes harder to capture all the wavelengths of light. Again, technology has combatted this with great success but there can be a loss of the red and orange (the slower wavelengths) with high ISO.
It is now that we find ourselves armed with just enough information to stand bewildered before the next scene we want to take a picture of. You’re now thinking about the light, motion blur, meowing cats, and a souped-up DeLorean. Do you open the aperture and risk losing the shape of the mountains in the background to depth of field? Will your nephew hold still long enough to get a clear image with a longer shutter speed (unlikely) or do you need to push up the ISO and hope technology can clean it up later? Maybe you’re wondering if it’s too late to take up whittling instead.
So, hopefully you’re starting to see what goes into properly exposing the sensor for the composition you wish to photograph. You should be starting to see how these three adjustments both work together and how changing one can affect the others. Getting proper exposure is kind of like a 3-way teeter totter, adjusting one element means compensating another to keep in balance. To really master an understanding of this takes experimentation and practice. What I recommend is taking multiple pictures of a scene while adjusting only one parameter at a time. Find a place with consistent, stationary light to take a series of pictures. Keep everything outside of the camera the same and go through the range of each point in this triangle. See how the images increase in brightness as you open the aperture but also look at how the foreground and background begin to blur. Do the same with ISO and shutter speed. Admittedly, you’ll want to experiment with something moving to really see how motion blur is recorded but, you’ll get the idea. If you need a starting point, take your first image with your camera in full Auto mode and look at what those settings are. Duplicate them and start your journey. When you’ve done this, be sure to look at the images side by side on your computer screen. Really dig into them, zoom in and see when you lose detail and at what point do you no longer think it’s sharp. Digital images record in their data all the settings so you can go back at any time to these reference pictures and recall what your settings were.
