Understanding DLSR Exposure in Just 10-Minutes

If you’re a new photographer, you’ve probably felt the urge to flip the switch from Auto over to Manual mode just to see what happens. If you’re like me, then you probably felt a wave of confusion, and any photo attempts probably came out too bright, too dark, or even shaky. You may have even fiddled around with the dials to no avail as I did. After a few horrendous shots, I switched mine right back to my comfort zone in auto mode, determined to make the best of it and learn manual “another time.”

So, Why Bother With Manual?

Contrary to what many professionals would like you to believe, manual mode is actually quite simple to learn. In fact, by the end of this post, you’ll understand exactly how manual functions work. There are only 3 settings in manual mode: aperture, shutter-speed, and ISO. Varying any one of these simply makes the resulting photograph either brighter or darker. Your only job is to balance them to get the best possible exposure, and as you’ll see right now, it’s very easy. Manual controls also produce some visual effects, which you’ll also learn about in just a minute. Just like composition and lighting, shooting in manual mode will take some time to master, but with practice, manual shooting is something you can start creating with right now.

There are good reasons to learn how to shoot in manual mode. Ansel Adams said it best:

“You don’t take a photograph, you make it.”

In automatic mode, the camera makes all of the aesthetic decisions for you. You can only control where to point the camera. You’re taking the photo.

Manual mode gives you the freedom to create stronger compositions by making conscious aesthetic decisions about your photograph. You get to control things like the softness/sharpness of the background in relation to your subject (depth-of-field). You could also choose to express degrees of motion in your shot, or freeze any fast-moving action in the scene (shutter-speed). You gain more control over the narrative of the scene, and you can manipulate the scene to better express your vision for how you want to tell the story. You make the photo.

The Tool Itself Is Easy!

Learning how to use a hammer or screwdriver is easy – building something with those tools is the challenge. The same is true for photography. As a photographer, your job is to build compelling photographs using the camera as your tool.

Regardless of how many digital features, bells and whistles, and technical specs the manufacturer packs in, your camera is just a box that captures light through a small hole. Light enters the camera and hits a sensor for a certain period of time, and that’s it. Too much light and the photo will be over-exposed (too light). Not enough light and the photo will be under-exposed (too dark).

DSLR Exposure Over Vs Under

Before we begin, I’d like to address something quickly. In addition to auto and manual modes, your DSLR includes other shooting modes including shutter priority and aperture priority. These two have tremendous time-saving advantages – but they also have limitations. They exist solely for efficiency and we will explore these modes in another article. It’s vital to first understand manual controls so you’ll know exactly when is the appropriate time to use the other modes, and when they will simply not work to translate your vision.


The size of the “hole” through which light enters your camera is called the aperture. Mechanically, the aperture is a little diaphragm inside the lens that you can widen or narrow by telling your camera what f-stop you would like to use.

The f-number is a funny measurement because a small f-number (like f/1.8) equates to a wide opening, whereas a large f-number (like f/32) equates to a small opening. A wider opening allows more light into the camera resulting in a brighter photograph. A smaller opening allows less light into the camera, resulting in a darker photograph. Pretty basic so far right?

The Side Effect: The aesthetic effect of varying the aperture causes changes in the level of focus between the foreground and background elements in your photograph. Light that enters through a wide aperture (small f-number) translates into less focus between the foreground and the background. This is how photographers throw backgrounds out of focus while the subject remains sharp. If you want to isolate a subject by blurring out the background, use a wide aperture.


Alternatively, light that enters through a smaller, tighter aperture is more focused than light entering a wide aperture, and light that is more focused translates into sharper focus through the foreground-to-background depth in a photograph.


So if you want everything as sharp as possible through the depth of your scene, you would want to use a small aperture (higher f-number).

The above example shows how varying the apertures from f/2.8 (wide) to f/16 (small) has an effect on the background. Also, to maintain the same overall brightness (the exposure), notice how the shutter speed needed to be adjusted. With a wide aperture (f2.8), the shutter needed less time to capture the light since the opening was wide. A narrow aperture (f/16) requires a longer shutter speed to allow more time for the sensor to capture the available light.

Give-and-Take: Generally, as you increase the aperture size, you must compensate with a faster shutter-speed to maintain the correct exposure otherwise your image would become over-exposed (too bright). As you narrow the aperture, you must lengthen the shutter-speed to obtain a correct exposure otherwise the image would be under-exposed (too dark).


The shutter is basically a tiny little curtain that opens and closes behind the aperture. As the shutter stays open longer, more light is captured by the sensor resulting in a brighter image. The shorter the shutter-speed, the less light is captured resulting in a darker image.

Side Effect: The aesthetic effect is that using a fast shutter-speed allows you to “freeze” motion in a scene, whereas a slower shutter-speed blurs any motion. For example, imagine you are taking a photograph of droplet of water as it falls. Using a fast shutter speed of 1/1000th of a second would result in the drop appearing frozen in mid-air since the exposure was being made in such a quick fraction of time. A droplet doesn’t “fall” that far during 1/1000th of a second, so to a camera, it would appear suspended in mid-air.


Alternatively, if you set a much slower shutter-speed such as ½ a second or longer, then any movement gets captured as a blur. You can see how the taillights of moving cars are translated into streaks of light when using a show shutter-speed.

Give-and-Take: Typically, fast shutter-speeds require a larger aperture for the sensor to capture enough light to produce a well-exposed photograph. Conversely, slow shutter-speeds tend to require a smaller aperture to limit the amount of light coming in over the longer duration. See how these factors are all starting to work together?


The light that enters your camera is hitting a sensor inside, and you can actually control how sensitive the sensor is to light. This brings us to the third way of controlling the overall brightness of your photograph – the ISO.

A low ISO (like 100) results in a darker photograph, while a high ISO (like 6400) results in a brighter photograph.

Side Effect: Naturally, there is a trade-off here too, and for many photographers, this is a big one. The compromise when shooting with a higher ISO is: you will produce a brighter image, which sounds good; but a higher ISO also introduces more grain (or “noise”) into a digital photograph.

In most cases, our vision for a photograph is based on our creative choices as to the depth of focus (between foreground and background elements) and how we want to capture any motion in our scene. This means you would usually decide upon your aperture and shutter-speed settings first, based on the combination of their aesthetic effects and your vision for the final image. Then you would aim to keep your ISO as low as possible. If you know that you need a certain shutter-speed along with a certain aperture and the resulting image is still too dark, that’s when you increase the ISO.

Knowing this, the general rule of thumb is that lower-lit environments (such as indoors or nighttime) require a higher ISO, and brightly-lit conditions can be captured with low ISO.

It’s about finding a balance between these settings to achieve the best exposure. You get to decide on one or two of these factors, but the camera will require a compromise on the third.

The Exposure Triangle: A Handy Visual Reference

You may have heard of this popular tool, to illustrate the relationship between aperture, shutter-speed, and ISO, called the Exposure Triangle. This is a simple guide to representing the aesthetic changes that occur as you adjust each of these settings individually.

The 3 sides of the triangle show what happens as you vary the settings of aperture, shutter-speed, and ISO. It can feel overwhelming at first, but remember the true joy of photography is the process of learning this craft and seeing your results take shape. Feel free to save this image to your computer or smartphone even, for quick reference whenever you need a refresher. You can also download a PDF version for free here.

Of course, learning how to operate your camera is the first (and easiest) step. The relationship between these exposure controls will never change, but the next step is learning how to apply them in a practical way to create photographs that are unique to your artistic voice. Photography is very much a visual language and once you learn how to use the camera, you can then communicate and translate your vision into captivating photographs.

For more detailed information on understanding manual functions, I highly recommend checking out the The Photography Starter Kit for Beginners where you’ll learn the most essential functions of your camera, enabling you to take even more memorable photographs of your travels, friends, family, or the great outdoors. Watch the free preview to learn more.

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About the author

Dave Seeram is the Editor of PhotographyBB Magazine, photographer, Canucks fan, Lostie,  fanboy, Dad, blogger, entrepreneur, and part-time superhero. Dave is the owner of this blog, Editor-in-Chief and Publisher of the PhotographyBB Magazine and CLARITY: PHOTOGRAPHY BEYOND THE CAMERA

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