What is Exposure | Tips from a San Antonio Wedding Photographer

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If you've been following my blog for long you know that wedding photography is my passion, my obsession even. You also might know that film photography is a big past time of mine. What you might not know, however, is that I love teaching others about photography. It's not just about having all of this information in my head - it's about sharing and spreading it so others can experience the amazing world of photography!

Today's post is going to focus on exposure - one of the most important fundamental elements of photography. If you've already read the "How to Use Your New Camera" blog post then you know what the word exposure means, and understand the basics. Over exposure is when a photo is too bright and under exposure is when it's too dark. You also know that the exposure of a photograph is determined by three factors: shutter speed, aperture, and ISO.

Why should I bother learning about how the camera controls exposure when I can just brighten or darken the image later with editing software? A few reasons. You will save a bunch of time by learning how to properly expose your images in camera instead of just trying to fix it after the fact, and depending on the file type your camera is creating, you might not be able to adjust the images very much. As a wedding photographer I need to be as smart and efficient as possible when shooting so I have less time to spend fixing things in post-production, but I also absolutely have to be in complete control of the look and feel of my images. 

The most important reason for new photographers to learn exposure is because the three factors that go into creating the exposure, shutter speed, aperture, and ISO, all effect the look of the final image in different ways. As a photographer, I'm willing to bet that you're not JUST interested in capturing a moment, but you also are wanting to achieve a certain look. You want your viewer to feel a certain way when they look at your image. Understanding exposure and being able to control it will put you, the artist, in control of how your work looks. 

As photographers, we measure light in stops. A photo can be two stops over exposed, it can be 1/3 stop under exposed, etc. For now don't worry too much about what a stop of light is, just be aware of the term. The second thing you want to keep in mind is that shutter speed, aperture, and ISO all impact the exposure of an image equally. If you increase your shutter speed by one stop, your image will be one stop of light brighter. If you want to increase your shutter speed but keep the image at the initial exposure (brightness), you'll need to decrease the aperture and/or ISO a combined total of one stop. If you're really confused right now that is completely normal. Don't sweat it, we'll pick this "stop" stuff up later. Just be aware of the term for now.

 

Shutter Speed

Dragonfly captured at 1/250th of a second (aperture f/4, ISO 500) with a 210 mm lens.

Dragonfly captured at 1/250th of a second (aperture f/4, ISO 500) with a 210 mm lens.

Inside your camera is either film or a digital sensor. This is what the light coming into your lens hits and records an image onto. The shutter stands between your lens and your sensor (or film) and every time you "press the button", your shutter opens and shuts - letting light into your camera. This is basically how all cameras work. The length of time the shutter stays open, aka: the length of time light is pouring into your camera, is your shutter speed. The longer your shutter stays open, the more light will come in. The shorter it is open, the less light. 

So what does shutter speed control in the image? Well it controls how big of a sliver of time you're including in your image. You can freeze time, or you can slow it down. You can freeze a football being thrown through the air, or you can show the blurred movement of it with a slower shutter speed. You can create a beautiful image of cars going down a busy city road at night with using a slow shutter speed to capture just the tail lights / headlights. 

Shutter speed is measured in seconds and fractions of a second. A shutter speed of 1/250th is where your shutter is opening and closing at 1/250th of a second - a rather fast shutter speed. Sports photographers frequently rely on VERY fast shutter speeds, sometimes over 1/1000th of a second, to catch crisp and clean action photos of fast moving subjects without blur. With these fast shutter speeds, it's a very short amount of light that is being let into the camera so the photographer will have to adjust their aperture and ISO so the photograph isn't under exposed. Landscape photographers will sometimes use very slow shutter speeds, 5 to 10 seconds long, to blur the movement of water and create a smooth surface. With slow shutter speeds you're letting in a lot of light, so again the aperture and ISO will need to be adjusted accordingly so the image isn't over exposed. 

 

Aperture

Leaves captured at f5 (1/500th of a second, ISO100) with a 100 mm lens.

Leaves captured at f5 (1/500th of a second, ISO100) with a 100 mm lens.

The aperture is how wide open, or how narrow, the opening inside the lens is that is letting light into the camera. The wider open it is, the more light is coming in. The narrower the hole, the less light is coming into the camera.  You know how when you step outside everything is so bright until your eyes adjust? Your pupils are narrowing, creating a smaller hole to let light in, so your eyes are able to see everything at the correct exposure. Same thing when you step inside after being outside, everything is way too dark until your pupils widen, letting more light in. 

In regards to how it changes the look of your image, aperture controls your depth of field - the amount of space in front of and behind what you're focused on that will also be in focus. This concept is easier to explain in pictures, so check out below. The image on the left has a shallow depth of field. The camera is focused on the subject and nothing else is in focus. In the image on the right, the camera is focused on the subject, but as you can see a lot of the foreground and background are also in focus - not just the subject. Shallow depths of field are often sought after in portrait photography because a soft blurry background helps isolate your subject, but be careful. If your depth of field is too shallow, only part of your subject will be in focus! Please note that there are other factors that impact the depth of field, we'll go over them in additional posts.

The openness and closeness of the aperture is measured in f-stops. Unless you're a huge nerd it's not worth looking into where the name came from, but when you hear "f-stop" we are referring to the aperture. Aperture measurements are counter intuitive. The smaller the number, the wider open your aperture is. The higher the number, the more closed your aperture is. f2.0 is a very wide-open aperture, where virtually only your subject will be in focus. f22 is a very closed (sometimes referred to "stopped down") aperture where your subject, and virtually all of your foreground and background will be in focus. f8 is somewhere in the middle. 

 

ISO

Path captured at ISO 100 (1/80th of a second, f/10) with a 28 mm lens.

Path captured at ISO 100 (1/80th of a second, f/10) with a 28 mm lens.

If you were photographing before the days of digital photography, you already know what ISO is. Perhaps you know it as film speed. ISO / film speed referrers to how sensitive the film or digital sensor is to the light that is hitting it. The more sensitive to light, the brighter the photo. The less sensitive to light, the darker the photo. ISO isn't measured any fancy way, it typically starts at 100 (or 50, depending on the camera/film) and goes up from there. The less light you have in a scene, the higher of an ISO you'll need. As digital sensors continue to become more and more advanced, available ISO's are pushed higher and higher. Most cameras being made with cutting edge sensors can reach ISOs greater than 100,000. 

ISO impacts your images not just in amount of light but also in the grainy, or nosiness, of the image. The higher the ISO you use, the more noise/grain there will be in the images. This can be annoying and require extensive editing, if you don't like the look, or it can be used on purpose. Lower quality digital sensors will have more noise at lower ISOs than higher quality digital sensors. About a year ago I upgraded to a newer camera that handled higher ISOs better, and I get the same amount of noise now at ISO 2000 that I used to get at ISO 800.

 

Light + (Shutter Speed + Aperture + ISO) = Exposure

This image was shot on film so I don't know the exact exposure settings, but its a perfect opportunity to study the exposure. The aperture has to be pretty wide open as the front flowers are in focus but the back ones aren't. I'm going to guess f/2.8. Shutter speed is virtually impossible to tell as this is a still life photograph, but it looks like window light and based on experience I'm going to guess it wasn't over 1/100th of a second. We can look at the grain and notice there is some there, but it isn't over the top so I'm going to guess ISO 400 or ISO 800.

This image was shot on film so I don't know the exact exposure settings, but its a perfect opportunity to study the exposure. The aperture has to be pretty wide open as the front flowers are in focus but the back ones aren't. I'm going to guess f/2.8. Shutter speed is virtually impossible to tell as this is a still life photograph, but it looks like window light and based on experience I'm going to guess it wasn't over 1/100th of a second. We can look at the grain and notice there is some there, but it isn't over the top so I'm going to guess ISO 400 or ISO 800.

There is one element we haven't discussed that will also impact your exposure: the amount of light in the scene! If you take a photo and it's under exposed you can either change your camera settings or simply add more light to the scene! Now it's not always possible to add more light to a scene (if you're a landscape or wildlife photographer you're usually stuck with what the sun gives you on that day) but you must take it into account. We'll cover adding light to the scene in later posts - for now let's just focus on camera settings.

So HOW do you control the exposure in camera? Remember back to the "How To Use Your New Camera" blog post? The mode dial allows you to choose how much control you have, vs the camera, in controlling the exposure. M mode, or manual mode, is where you have full control over the camera and exposure. Not only are you deciding what shutter speed, aperture, and ISO to use, you're also deciding what creative effects you want and adjusting the other elements to balance out the exposure. As you let in more light by slowing your shutter speed, you need to change your aperture and/or ISO to let in less light, or you'll have an over exposed image. If you want to explore this concept further without grabbing a camera check out this interactive tool

Switch your camera to M mode and go play around with it. If most of your images are crap, good. You're going to learn something! Okay, now take it out of M mode and breath, no need to panic, you ARE going to get this. A great way to get a foothold on exposure is to start with the Aperture Priority and Shutter Priority modes. With these two camera modes you're letting the camera make all the decisions, except you control one thing. With Aperture Priority you control the aperture and with Shutter Priority you control the shutter speed. This is a great way to explore the creative effects of both shutter speed and aperture, and get used controlling various aspects of the exposure first, before jumping in to control the entire exposure all at once.

Keep in mind, however, you're still allowing the camera to decided what is a correct exposure - as you adjust the shutter speed, the camera adjust the aperture / ISO to compensate for the changes you make so everything stays "properly exposed" according to what the camera think it should be. 

This is Lola, I'm including her for cuteness. This was also shot on film so I can't tell you the exact exposure. Notice her face is in focus but the wall behind her isn't, there is a shallow depth of field. This tells me the aperture is likely f/2.8 to f/4. She's laying still, not moving, so I can't guess much about the shutter speed, but I can tell it's indoors and experience tells me with a wide open aperture and low grain (aka low ISO) my shutter speed is likely under 1/125th of a second. There is some grain in the image, but not very much so it is likely around ISO 400 or 800 film.

This is Lola, I'm including her for cuteness. This was also shot on film so I can't tell you the exact exposure. Notice her face is in focus but the wall behind her isn't, there is a shallow depth of field. This tells me the aperture is likely f/2.8 to f/4. She's laying still, not moving, so I can't guess much about the shutter speed, but I can tell it's indoors and experience tells me with a wide open aperture and low grain (aka low ISO) my shutter speed is likely under 1/125th of a second. There is some grain in the image, but not very much so it is likely around ISO 400 or 800 film.

With the photo of Lola above notice the exposure. The left of the image, primarily the wall and her face, are properly exposed. Everything else is underexposed because it's unimportant. The image is about her so I wanted her face correctly exposed. While cameras and getting better and better at recognizing faces, and basing the exposure off the face area, there are still plenty of times it will mess up. With the image of Lola above, the camera might decide that it's the right half of the image that needs to be property exposed, so your photograph will have the subject, Lola, completely overexposed. It might not be able to guess which half you want correctly exposed so it will just go for an exposure in the middle, leaving Lola underexposed and the right half overexposed. While there are different ways you can adjust your camera to "pick" the correct exposure, there is absolutely no substitute for the human brain.

The important thing for you to know right now, as you're facing this mountain of knowledge, is that no one masters exposure overnight.

Practice, practice, practice.  

Then re-read this blog post, soak in a little more, and go back to practicing.


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