If you can fill a cup from a faucet, you can master exposure "Exposure": perhaps one of the most misunderstood, poorly taught, and confusing words in photography. What -- exactly -- the heck is exposure, and how do you nail it? How do you know settings to use for whatever you're shooting, without having to guess or pull up a guide, or have a mentor there to show you? Some would say exposure is the settings you use to take a picture. "Hey, what's your exposure?" And the answer he may hear is, "ISO 200, 1/500 second at f/8." Is that really exposure?
A bigger nerd might say "Exposure = Aperture x Time x ISO." Are you supposed to have a physics degree to master photography? What does that mean for a landscape? Sports? When I first started learning photography, I actually read those equations and tried to understand exposure. I couldn't!
Well, scientifically, mathematically, those are ways of describing the formula for exposure, but how does that really translate to making a photograph in the field?
First, let's settle what exposure is so you have a framework to hang the rest of your understanding on.
Exposure is nothing more than the total amount of light recorded. It translates visually to brightness. And you need not think of it as any more for the length of your photographic career.
If you remember nothing else, exposure is the amount of light recorded, which in visual terms is brightness. Whenever you hear "exposure," no matter how technical the method or explanation, that's it.
Start from the roots
Wait, recording light? That sounds sciency. I thought we were just taking pictures!
Turns out, recording light doesn't have to be sciency, but to really get on top of photography, and ultimately exposure control settings, I had to shift my entire perspective on what photographers actually do -- and it's not "take pictures."
Let's quick drop back in time to how photography came about. Long ago, some say in ancient China, it was discovered that if light shone through a small hole in a dark room, it would project an image of the outside world on the opposite wall! This phenomenon is known as "camera obscura," Latin meaning darkened room.
Initially, all one could do was trace the projected image, or marvel at it. But over time people sought not just to trace the image but record it directly. So the search began for light-sensitive materials. These materials took many forms, from metal plates that took a long time to absorb and thus record the light, to large pieces of film, to small pieces of film, to the variety of digital sensors we enjoy today.
The concept of photography has never changed. The dark room has simply been shrunk into a handheld box. And the hole in the box has become a sophisticated lens. And, rather than a large metal plate, we have a small digital sensor arrayed with light-sensitive cells called pixels. And all of these things have a lot more controls and features than early cameras.
"Photography" as we know it is from the Latin "photo" and "graphy," which means to draw with light. That's key, as we're not just projecting a wash of light but recording an image with it.
Today, the development of new light recording technologies continues, with vastly improving equipment. As of this publishing, perhaps the biggest departure from traditional photography is the shutterless camera, which Nikon pioneered. Instead of a mechanical shutter, parts of the sensor just turn on and off to start and stop exposure.
That's where photography comes from and what it is, but what's the shift in perspective that makes understanding exposure so much easier? It's that you've never actually taken a picture of anything, nor can you. Oooh, creepy. Nope. All you can do is record what the light is telling you about that thing at that moment.
Take for example an apple. You can take a snapshot of that apple, but what is an apple, really? It's a concept. No two are the same. Different apples have different colors, shapes, sizes, textures, leaves, seeds inside. Even the same apple appears differently depending on the direction, color, quality and quantity of light. And, without light, you don't see the apple at all, but it still exists.
So, you can never take a picture of ”an apple” in its entirety. Again -- and this is the key shift in thinking -- all you can do is record what the light is telling you about that apple at a given time in a given way. That's photography!
The faucet analogy (that will change your understanding of exposure forever)
The best framework I can teach to hang your understanding of photography on -- the one I practice -- is one that I unfortunately didn't learn until much later, that would have saved me years of struggle and advanced my photography at lightning speed:
Light behaves like water, and the camera is like a faucet.
For some of you, a lot of things might have just clicked, pun intended. But let's delve in.
Let's say you have a cup and a faucet. You turn on the faucet, and the water comes out. When the cup is filled to your desired level, you turn off the faucet. That, my friend, is exposure! Mind blown, I know. The primary difference with photography is that the camera controls light coming in, whereas a faucet controls water going out.
Remember exposure is nothing more than the total amount of light recorded. So when you push the button, you're setting in motion a controlled flow of light that fills the little cups of the sensor called pixels and then stops. A photograph is the result of a measured amount of exposure to light. Without light, no photography is possible.
Faucet on. Faucet off. That's the basics of exposure. A faucet gives you control over the flow of water -- specifically volume and the amount of time the water is on. Imagine not having those controls. Water would be flowing out of the tap continuosly, day and night! That's very much like the world around you, in the sense that there's generally some light always bombarding you. Therefore, you can't just have a sensor that's always open and active. That sensor needs to be kept in a dark box -- the camera.
Of course the camera gives you more control over the flow of light to the sensor than just on and off, and that's where the three settings aperture, shutter speed and ISO come in.
Aperture: The Pupil of Your Eye
As you move the knob or handle on your faucet, you notice you can change the volume of water coming out. If you nearly close the faucet, the water slows to a trickle. If you open it fully, the water flows out in a forceful stream.
Aperture is the valve in our faucet analogy. The aperture is located inside the lens and is a diaphragm of blades that opens and closes, expands and contracts, kind of like the pupil in your eye. The wider you open it up, the greater the volume of light. The narrower you close the valve, the lesser the volume. That concept is simple enough.
Indeed, in early examples of the camera, lenses had only one aperture -- one fixed, constant volume of light, some as simple as the size of the hole in the box. Although technically this was a control over the volume, it wasn't adjustable. Only through advances in technology were selectable apertures developed to adjust the volume of light and put into smaller and smaller lenses.
In the camera, aperture is represented by an f-number, such as f/8, f/4, f/2.8. The "f/" portion may or may not be displayed.
The range of available f-numbers is generally as follows: f/1.2, f/1.4, f/1.8, f/2, f/2.8, f/4, f/5, f/5.6, f/8, f/11, f/16, f/22, f/32. There are some in between. There's even an f/0.95, the widest aperture available in a lens, which is on the Nikon 58mm f/0.95 Noct.
The smaller the f-number, the larger the opening. The larger the f-number, the smaller the opening. That's because the f-number is like a fraction: 1/2.8 of the opening is larger than 1/16 of the opening. I have no easy way to remember it other than that. Over time, with practice, you'll have it memorized.
The Need for (Shutter) Speed
When you turn your faucet on, it takes a certain amount of time to fill a cup. If there's more volume of water, you need less time to fill the cup. If there's lower volume, it takes more time to fill the cup. Can you guess how that relates to shutter speed?
Shutter speed is essentially how long the faucet is on -- the time between when the flow of light starts and stops. In other words, shutter speed is duration. It's how long you expose the sensor to record enough light. The longer you have it open, the more light fills the pixels. The greater the volume of light, the shorter duration you need (or faster shutter speed) to record enough light.
The shutter itself is like a floodgate, basically a thin mechanical curtain that opens and closes, situated between the lens and the sensor. Regardless of how the aperture is set, the shutter starts and stops the exposure. As long as photography has existed in the form we know today, there has been a shutter or curtain. Photography requires some way to start and finish the flow of light to the sensor. However, in some mirrorless cameras, the function of the shutter is created by simply activating and deactivating pixels on the sensor. In flash photography, the shutter has additional modes and effects.
Shutter speed appears as a fraction of a second. For example, 1/2 is a half second and will appear as a fraction in the viewfinder. Whole seconds or longer will appear with a quotation mark after, such as 1" or 10". Common shutter speeds are 1/60, 1/125, 1/500, 1/1000, 1/2000.
ISO: In Search Of: Sensitivity
Volume and time aren't the only factors in filling a cup, are they? What about the size of the cup? You need more water to fill a bigger cup, and less water to fill a smaller cup. What if there's something already in the cup -- perhaps a drink powder? That affects the amount of water you'd need to fill the cup to the same level.
ISO is the sensitivity of pixels to light. The higher the number, the more sensitive. I teach ISO two ways, and you could think of it either way. One way is like the size of the cup. A high ISO would be like a small cup, requiring less light to fill, and a lower ISO would be like a large cup, requiring lots of light to fill. But what's a little more accurate (scientifically) is that ISO is a bit like some gravel already in the cup. A high ISO is like a lot of gravel already in the cup, requiring less light to fill it, and a low ISO is like very little to no gravel already in the cup, requiring more light to fill to the same level.
But, do you really want gravel in your water? I hope not! ISO doesn’t just give you the free gift of greater sensitivity in low light without any drawbacks. It introduces a factor called noise, or unwanted signal (remember the analogy of gravel in your cup of water). It shows up in pictures as grain, or color aberrations, and obscures detail.
How you might use ISO is if you have less light to work with, one option is to increase ISO, thereby requiring less light to achieve the same brightness but also introducing more noise to the image. Conversely, when you have plenty of light to work with, you can reduce ISO, thereby filling the pixels with more signal and preserving more detail.
In terms of raw exposure, ISO is a bit different than aperture and shutter because it doesn't affect how much light is recorded. It affects how sensitive the pixels are to light, and affects the amount of noise in the image, but it doesn't increase or decrease the light itself. It only affects the aperture or shutter speed needed to render the same brightness.
In early photography, the light-sensitive plates were not very sensitive and thus required long exposures to record an image. You've probably heard of people in the early 19th century having to be held still in a brace so they didn't move during an exposure that could have been a couple of minutes long -- just for one portrait. Thank God for modern sensors and adjustable settings!
In the film days, a roll of film was produced in a given ISO, so everything you shot with that roll had one sensitivity. With digital cameras, photographers could finally change ISO on the fly, which believe me is a miracle taken for granted today. Digital cameras do this by applying gain to the pixels, which incresaes sensitivity but also introduces the noise.
The ISO appears as a whole number, generally as a multiple of 25 -- so, ISO 50, ISO 100, ISO 800, ISO 3,200, with cameras allowing steps in between. The numbers are straightforward: the higher the number, the higher the sensitivity to light.
The Exposure "Triangle"
In the words of my daughters, "ugh." Exposure isn't a triangle, except conceptually.
Aperture, shutter speed and ISO together constitute what boring ancient professionals refer to as the "exposure triangle" because it's a triad of settings that work in combination to affect brightness. Yay. How creative. Other than that, there's no real-world application to "triangle" in exposure.
Unfortunately the diagram of a triangle connecting the three settings has been overtaught and rarely understood -- a poor aid for most, especially evidenced by the multitudes of people continually confused by the topic despite no shortage of explanations of the diagram and thus reaching out for courses and in Internet forums for help on what should be a quickly-mastered fundamental. It's so bad, I almost wonder if this has been done on purpose to gatekeep professional knowledge.
I hope thinking of exposure like filling a cup from a faucet makes much more sense when you stand behind the camera than some silly triangle diagram that exists nowhere in photography other than a crusty slideshow or YouTube video.
Your camera isn't an exposure triangle, nor does it contain one, but in a real, practical way it does work very much like a faucet controlling light coming in, and that's why I love and teach that analogy -- and I'd say darn well was the first to flesh out such an analogy.
How do you know the right exposure?
Throughout the water analogy, I've been referring to recording "enough" light. For example, a certain shutter speed requires a certain aperture to record "enough" light. But what's enough, and how do you know?
Well, what's the correct amount of water in a cup? It depends on what you decide in the moment, doesn't it? Nobody can tell you how much water you want in your cup. You have an idea, a desire, a goal, and you make the decision -- a little more, or a little less, until it's just right for you. It's subjective -- a little less subjective in print competition, but still somewhat subjective.
But I can show you how to get the exposure you want. Just like there are different combinations of volume and time to filling a cup with water, there are different combinations of aperture and shutter speed to get the same brightness in a photo.
Let's say there's a desired brightness you want for your photo. If you want longer duration (shutter speed) but the same amount of light (brightness), compensate with lesser volume (close down aperture). If you pre-fill the pixels with more noise, you need less volume and duration. The more grain you pre-fill them with, the less light you need to get the same brightness. And you can vary the combination of those settings any way you want to get the same amount of total light, just like you can vary the controls of a faucet and still get the same amount of water in a cup.
How do you get the right exposure?
One of the most common questions I get is "What settings should I use for this situation?"
One way is through lots of experience finding what works for common situations, like sports, portrait or landscape. That's where things get somewhat personal. Generally, I think about the faucet analogy, like filling a bucket. First, how much light do I have to work with? Do I have a lot of light, like a bright sunny day? Then I'd start with a big empty bucket, like a low ISO.
Next, I decide my main storytelling priority. Is it showing movement, or depth of field?
If it's depth of field, which it usually is, I then dial in the aperture I want. The last option, then is shutter speed. If showing movement isn't the priority, I don't care what the shutter speed is as long as it freezes movement. If one that freezes movement isn't available given the light, I go back to the faucet analogy. Do I need to open the aperture, find more light, or introduce more light?
If the priority is freezing or showing movement, which is less often for me, then I fix my shutter speed first. I can leave the aperture to whatever the camera picks, or I can choose both my shutter speed and aperture if I have a specific idea in mind for both of them. If the shutter speed is fixed, and I want to also adjust the aperture, then I need to compensate with the ISO up or down as I close or open the aperture.
But what if there were a way to know exactly what settings to dial in, without any guessing or experimentation? You can, with a light meter!
What's a light meter? Well, if you had one chance to fill a given bucket with water without overflowing it or leaving it half empty, how would you know exactly how much to open the faucet and how long to leave it on? You could use a meter that, if told the size of the bucket, measures the rate of the water coming into the system and then calculates the precise valve opening and time to leave the faucet on. A light meter, if told the ISO and one other variable, will measure the light and calculate the third variable. You could then dial in those exact settings and get a perfect exposure.
Metering and exposure modes (P, S, A, M) are separate subjects, and not necessarily entwined. You can know perfect exposure simply through prior experience or by consulting a guide that lists exposures for known situations -- like a bright sunny day, in which case you can use the "Sunny 16 Rule."
For right now, I won't go into detail with metering or exposure modes because there are many different types and it would take some time to describe how each works as well as subjective ways to use each one. I just want you to get the feel of the faucet analogy for exposure and how each of the exposure settings affects exposure or brightness.
One thing I'll mention quickly is "exposure compensation." It's primary value is in relation to reflective metering, but all I'll say for now is that dialing in "+" exposure compensation increases brightness, while dialing in "-" compensation decreases brightness. There's more to it, but that'll be in the metering article.
Practice making exposures
If you can play around with controls on a faucet to get the same amount of water in a cup, you can figure out exposure. In all seriousness, when you're learning or experimenting with exposure, start in M for Manual mode. You're ready, my friend. I would coach you to jump right in and play with all the settings to see what they do.
Fire up the camera, turn it to manual mode and take a picture. Now look at it.
Is it too bright? OK, how would you adjust the settings to make the exposure darker? Think about all the faucet controls we just talked about. What's one you could use to cut the amount of light?
Could you... close down the aperture? Sure. That would choke down the flow of light. Less light in the same amount of time is a darker picture, which is what you're going for.
Could you... decrease the sensitivity? Sure! What else could you do? What if the ISO is already at the lowest setting? You decide how you're going to do it, and go do it and make another experiment!
As you adjust the controls, the exposure or brightness will change. Of course you'll want to read up on which exact dials and buttons change those settings on your camera; this is a conceptual guide.
STOP Right There!
There's a convention for quickly doubling or halving the amount of light recorded, called a "stop."
For example, if everything else is the same and I only change the shutter speed from 1/500 to 1/250, I've doubled the exposure time and therefore I've doubled the amount of light, even though it's still a blink of an eye. That's one stop.
If I increase the shutter speed from 1/500 to 1/1000, I've cut the exposure time in half, so I've cut the total amount of light recorded in half, so that's also one stop.
Any time you double or halve the total amount of light, that's called a stop. You can get nerdier and adjust in half stops or third stops if you want.
What effect does adjusting by stops have on the picture? Experiment and find out!
Summary
This entire lesson we've been looking at exposure in terms of brightness, but there's another side to the settings of aperture, shutter speed and ISO. Each of those settings affects the picture in a way other than brightness -- a creative way. So every time you make a picture, you want to think about two things: your settings for exposure, and how those settings affect the creative aspects of the photo. We'll explore those in another article.
We only briefly touched on metering, but it's an important topic because you can use meters to quickly figure out complicated exposures, and when you understand incident metering, it can really enhance your understanding of light and exposure and take your images to the next level. An incident meter can also calculate flash exposures and help you figure out the dynamic range of your camera.
Lastly, you can master flash faster -- and I'd suggest only -- after you gain command over exposure fundamentals. Flash adds another light source, with different properties, to the light recording equation and thus another layer of calculations and decisions, not just with brightness but color and quality.
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