Intro to Photography- Exposure
As with last week, this post is a continuation of my intro to photography series. If you haven't yet, I would encourage you to read the previous posts first.
With that being said, once you have chosen a subject to take a picture of, the next question is typically: how should I expose this image? If you don't know what that means, that's ok! This is an intuitive question if you know what it's asking. Exposure, in photography, technically has to do with how much light the image sensor is exposed to. In lamence terms, the exposure could be referred to as the brightness of the image. An overexposed picture means that it is too bright, while an underexposed image would be too dark, relative to what you, the photographer, wants. We'll talk about this more in later weeks, but intentionally making a dark or bright picture can be an extremely powerful artistic tool! Stay tuned for that.
So how do you go about exposing an image, exactly? Well, it depends on what kind of camera you have and how you want to use it.
Phone Cameras
If you're shooting with a phone camera, it is likely to be in a fully automatic mode, meaning that the exposure is done for you. While this can be limiting, most phones allow you to choose which part of your composition to base the exposure on. For example, in the picture below, the automatic exposure made the snow closer to white, which completely blew out the highlights in the sky (blew out, in this case, means that it made the highlights so bright that they became pure white with no discernable detail). I wanted to focus on the beauty of the sky during this sunset, so I tapped on the sky instead. A small, yellow focus box appeared around where I tapped and the photo's exposure readjusted to be based on the sky.
This is one of my favorite pictures that I've ever taken with a phone (taken with an IPhone 16 pro)
While this made the snow a little darker than it was in reality, I didn't mind this sacrifice as it gave so much more detail to the sky. This is also something that I easily addressed in post processing by boosting the shadows and whites.
Dedicated cameras
If you're shooting with a dedicated camera, on the other hand, you have a lot more to worry about, but also a lot more flexibility. Some lower end camers are still mostly automatic, so the same advice above applies. However, as you get more advanced equipment, you will likely have the ability to shoot fully manual, if you choose. In manual photography, your exposure is controlled by three factors: the shutter speed, the aperture, and ISO. These three factors are sometimes collectively referred to as the "exposure triangle", and I think that that is a helpful way to see them all.
The exposure triangle (diagram from action camera blog)
To get your ideal exposure for a photo, you have to balance these three main elements. Let's start by talking about shutter speed.
shutter speed
Shutter speed is the length of time that the camera's image sensor is exposed to light. This can be an extremely short amount of time (1/2500 of a second is a common shutter speed for me during hockey games), a long period (some exposures can be minutes long for astrophotography; the longest I've ever done is 30 seconds), or anything in between. The amount of time that you choose will be dependent on a couple of things. First off: the lighting. If your sensor is exposed for less time, less light will be captured, leading to a darker image. Second: motion. With a fast shutter speed, motion will be captured and frozen in time, as opposed to a long shutter speed, where any quicky moving objects will blur in the shot. While exposure is a primary concern with shutter speed and more of what I am emphasizing this week, it is worth mentioning that both long and short exposures can be used intentionally for different effects, sometimes even in the same situation. For an easy example: hockey. Most of my shots are taken with a high shutter speed to freeze the action (pun intended!).
taken with a nikon z6 & nikon 70-200 mm f/2.8 @ 82 mm, 1/2500 sec, f/2.8, iso 1600
However, in anything with moving subjects, you can intentionally use a long exposure to highlight the motion and add a blur effect.
taken with a nikon z6 & nikon 70-200 mm f/2.8 @ 160 mm, 1/30 sec, f/7.1, iso 100
If you want to get extra fancy, you can do this with subjects that produce light (cars, fireworks, etc.), to make what are called light trails. As opposed to the whole image being blurred with an in focus subject, here, the background and landscape is static, while the subject(s) is (are) blurred and moving.
taken with a nikon z6 & nikon 70-200 f/2.8 @ 82 mm, 2 sec, f/22, iso 50
In all of these example images, though, the other two facets of the exposure triangle came into play. With the faster shutter speed, I had to shoot with a wide aperture (f/2.8 is considered "wide open", or as far open as possible, with my f/2.8 lens) and raise my ISO. This is in contrast to the longer exposures, in which I had to stop down my aperture and shoot with an ISO as low as possible. So what do these other two things mean?
aperture
Aperture, like shutter speed, is a physical attribute that affects how much light the sensor is exposed to. Aperture, however, has to do with the lens. Lenses have a collection of blades, collectively referred to as a diaphragm, that can be adjusted to inhibit the passage of light.
Different apertures in an f/1.4 lens (image from wikipedia)
Somewhat confusingly, the lower the f-stop (aperture is denoted with the letter f, a slash, and then a number (ex. f/2.8)), the larger the aperture. This is because the number in aperture is the ratio of focal length to aperture diameter. Therefore, the larger the aperture, the closer its diameter will be to the focal length, and the ratio will be smaller (a lens of f/1 would have a diameter equal to its focal length, so a 50 MM f/1 would have a maximum aperture diameter of 50 MM).
Obviously, the larger the aperture, the more that light will be allowed to reach the image sensor, leading to a brighter image. So in low light scenarios, a lower f-stop will typically be necessary, while you may have to increase your f-stop in a situation that demands less light be captured. As with shutter speed, though, changing the aperture comes with side effects. A wider aperture will lead to a shallower depth of field in an image, while a smaller aperture will have a much larger depth of field, meaning that more of the image will be in focus. In the first image below, I was shooting wide open with my f/5.6 lens, leading to a smooth and blurry background (also known as bokeh). Take note, however, that my wide open aperture in broad daylight required a quick shutter speed and a low ISO. In the second image, I utilized a significantly more narrow f/20, keeping almost the whole shot in focus. This did require a slow shutter speed and higher ISO to properly expose, though.
Taken with a nikon z6 & nikon 200-500 f/5.6 @ 500 mm, 1/500 sec, f/5.6, iso 320
taken with a nikon d5100 & tamron 18-400 mm f/3.5-6.3 @ 18 mm, 4/5 sec, f/20, iso 800 (Featuring some motion blur from slow shutter speed!)
There is a lot of physics needed to explain why aperture affects depth of field like this, but it all boils down to the angles of the light rays when they're hitting the image sensor. A wider aperture creates wider angles, leading to fewer light rays being aligned when hitting the sensor, and hence blur in most of the image. A narrower aperture, however, does the opposite, creating more narrow angles, more aligned light rays, and a more in focus image.
diagram from Cambridge in colour
iso
Finally, we've touched on it in the other two sections, but let's discuss ISO. In contrast to shutter speed and aperture, ISO is fully digital in modern cameras. In the days of old, ISO was a measure of a film's sensitivity to light. Nowadays, ISO can be changed on the fly and is a measure of how sensitive the camera's sensor will be to incoming light. Think of the gain on a microphone: the lower the gain, the less noise will be picked up, while higher gain will conversely lead to more noise being amplified. Similarly, a low ISO will lead to a less sensitive image sensor, and a darker overall image, while a higher ISO will lead to more sensitivity to light and a brighter image.
As with shutter speed and aperture, though, changing ISO will affect more than just image brightness. Going back to our microphone gain example, a higher gain will amplify more volume, and while this will include making the speaker louder, this will also let more background noise seep into the speakers (a noisy AC, buzzing flies, etc., will be picked up and also have their sound amplified). Similarly, the higher that ISO gets in a camera, the more visual "noise" their will be. This manifests as random and uneven grain or distortion in the image.
Taken with a nikon z6 & nikon 20-500 mm f/5.6 @ 500 mm, 1/80 sec, f/5.6, iso 5000
In this shot, I had to use ISO 5000, in combination wtih a relatively low 1/80 second shutter speed and a wide open aperture of f/5.6, to get a proper exposure. This high ISO resulted in some serious grain, as you can see.
Often, when people learn that high ISO leads to grain and distortion, they get scared away from using it. However, I want to push back on this idea. I always set my ISO last. Shutter speed and aperture are much more important to me, as they have much stronger visual and artistic effects on the image with motion blur and depth of field. These effects are difficult to recreate digitially. Additionally, high ISO is becoming less of a concern in the modern day with the power of new, advanced sensors, combined with post processing. My Nikon Z6 is a relatively recent camera, released in 2018. Had I shot an image at ISO 5000 with my old Nikon D5100, I'm not sure the image would have been usable. However, with the newer, full frame sensor in the Z6, the image is grainy, but not unsaveable. In Lightroom, and many other image processing softwares, you can actually denoise your pictures. With how sophisticated these modern softwares are, using image denoise can be incredibly effective. Look no further than my edited shot below.
Taken with a nikon z6, nikon 20-500 mm f/5.6 @ 500 mm, 1/80 sec, f/5.6, iso 5000 (combined with denoise in Lightroom)
I should caution you, though. While high ISO is becoming less of a concern, there are still legitimate reasons to try and avoid it when possible. I use image denoise as a last resort. Having properly exposed, low noise images in camera will significantly reduce your workload when editing. Post processing takes time, and denoising can be a bit of a pain, so I try to avoid it when possible. However, while underexposing your image in the name of lowering your ISO may improve your image's quality, it can also cause you to lose details in the dark parts of your image that cannot be recovered in editing, especially if you don't shoot in RAW. So set your shutter speed and aperture to taste first, then worry about your ISO. Don't be too worried if it's high, but still try to keep it as low as it can be to still get a properly exposed image. You can make fine adjustments in post, but if you completely mess up exposure in camera, some images can't be saved.
conclusion
While we got technical at points, hopefully this overview of exposure will act as a guide for you in your photography on how to get properly exposed images. To summarize: phone cameras are typically fully automatic, but you can choose what part of the image to base the exposure off of, giving you more creative control. In dedicated cameras, the exposure triangle (shutter speed, aperture, and ISO) controls your exposure. Remember that each of these facets can be adjusted individually, but they each have their own unique effects on images. Shutter speed controls motion blur (higher shutter speed = less blur, but less light), aperture controls depth of field (higher f-stop = larger depth of field, but less light), and ISO controls noise (higher ISO = noisier, but brighter image). Refer to that diagram earlier in the post for a visual representation of this. As always, let me know if you have any thoughts, suggestions, questions, or comments.
We know how to choose a subject and properly expose it, but how do you know where to put it in the shot, and with what accompanying elements? Next week we'll address this question and talk composition.
