Back To Basics: Exposure Triangle


My wife, Amanda, approached me a few weeks ago and asked that I teach her photography. I was honored, and, really, I was hoping that this day would come. She’s creative and has an interest in art, but she’s never had a fascination with the camera. I’ve always tried to include her, one way or another, in my photographic pursuits. To say that I’m happy that we can do something photographically together would be an understatement. I’m thrilled to teach her photography!

One thing that I realized is that the Fujifilm X100F is an excellent camera to learn photography on. It has easy-to-access manual controls. If you want to learn how to use a camera, the auto functions need to be disabled. You learn by doing. You learn by messing up. You learn by practice. Each exposure is an educational opportunity. My wife is learning photography on the X100F one frame at a time, in a similar way that I learned photography one frame at a time on a Canon AE-1 two decades ago.

Her first lesson was on exposure and the exposure triangle. I thought it might be helpful to some Fuji X Weekly readers to bring my wife’s lessons to written words and share them here. Even if just one person finds it useful it will be worth the time it took to type this out. If you’re the person who keeps everything in “A” because you’re not sure what it all means, I invite you to continue reading.

In photography, exposure is the amount of light that reaches the sensor or film combined with the sensitivity of the sensor or film to light. There are three aspects that determine exposure: aperture, shutter and ISO. In a moment we will look at all three in-depth, and how they affect each other, working together to make an exposure.


The goal is to achieve a correct exposure. Not enough light and the frame will be underexposed. Too much light and the frame will be overexposed. The window for a correct exposure is actually very narrow. It doesn’t take a whole lot of variance to move outside of a properly exposed photograph.

That brings up the question: what exactly is a correct exposure? The answer is subjective, and there is a bit of grey area. One picture might look good dark, or what some may call “low key” and what some might consider underexposed. Another picture might look good bright, or what some may call “high key” and what some might consider overexposed. Due to the limitations of the sensor or film, there is an issue where highlights can become overexposed and lose details, and this is known as “clipped highlights.” And there is an issue where shadows can become underexposed and lose details, and this is known as “blocked shadows.” Camera sensors and film have a limited ability to capture the full spectrum of tones, and this is known as dynamic range.

Exposure is a balancing act, where the picture is appropriately bright for whatever the subject is, and clipped highlights and blocked shadows are kept to a minimum, except in cases where they are purposefully included for effect. What exactly that is must be determined by the photographer. It’s the photographer’s job to decide what exposure is most appropriate for the subject.

There are tools to aid the photographer in determining the correct exposure, and the main one is a light meter, which reads the light and displays what settings it thinks would be good for a proper exposure. All modern cameras have a light meter built-in. There are usually a few different options: spot, center and matrix. The Fujifilm X100F has spot and center meter options, and two different matrix options called multi and average.


Spot metering reads the light in just one location of the frame and ignores everything else. Center metering reads the light in just the center of the frame and ignores the edges. Matrix metering takes readings at different places within the frame and determines what would be the correct settings based on what it finds all over. There are reasons to use each of these, and in different situations one option will produce better results than the others.

Even if one doesn’t have a light meter, there are rules of thumb that could help determine the correct exposure, such as the “Sunny 16” rule. If the scene that you are photographing is in bright sunlight, then the ISO and shutter speed should be (roughly) the same number (e.g. ISO 100 and 1/125) if the aperture is f/16. From there you could figure out the approximate correct exposure no matter the lighting conditions. It’s not important to remember this rule, I simply wanted to illustrate that with knowledge and experience it’s possible to be able to fairly accurately guess proper exposure even without the assistance of a light meter.

Many cameras, including the X100F, have a histogram, which is a graphic display of the luminous tones in an image. It shows exactly where the highlights and shadows fall. Some photographers use this to determine if an image is or will be exposed correctly. Many cameras, including (again) the X100F, have the ability to give a clipped highlight warning, and some people use this as an aid to determining correct exposure.

Another method that is popularly used is exposure bracketing. Typically one will set up the camera to make three exposures (with one press of the shutter release button), with exposure compensation set to -1, 0 and +1. It can be customized to be different than that, but the idea is to underexposure and overexpose (as well as properly expose) what you believe is the correct exposure, just in case you got it wrong. One of the three will most likely be right.


In my opinion, the single best tool for achieving correct exposure is to review the image on the back of the camera. Take a picture, and if it’s too dark increase the exposure and if it’s too bright decrease the exposure. It doesn’t have to be complicated. The fact is that most cameras nowadays have phenomenal light meters that will give you the correct exposure 95% of the time. It’s just a matter of verifying that it is indeed correct, and making adjustments if it’s not.

I mentioned earlier that aperture, shutter and ISO work together to make the exposure. All three of these functions will change the brightness of an image. The value settings of each are called “stops” and adjusting them one way or another will either double or half the light from that feature. To make things more complicated (and precise), many cameras also have intermediate stops (usually 1/3 stops, sometime 1/2 stops) in-between the regular stops.

The aperture is an opening in the lens that controls the amount of light that’s allowed to enter the camera. On the X100F this is adjusted by a ring around the lens. Common settings, known as f-stops, are f/2, f/2.8, f/4, f/5.6, f/8, f/11, and f/16, although some lenses also have larger and/or smaller apertures. The smaller the number (for example: f/2) the larger the opening is in the lens and the larger the number (for example: f/16) the smaller the opening is in the lens. Obviously the largest opening will allow the most light in and the smallest opening will allow the least light in. Aperture f/4 will allow half as much light to enter the camera as f/2.8 and twice as much light as f/5.6.

The aperture does more than just regulate light. It also controls the depth-of-field, which is the amount of the image that’s in focus, and can effect things like sharpness, chromatic aberrations and vignetting. For a large depth-of-field (lots in focus) choose a small aperture such as f/11. For a small depth-of-field (little in focus) choose a large aperture such as f/2.8. Typically, although not always, the middle apertures tend to be the sharpest. Oftentimes the largest apertures will be less sharp away from the center of the frame, and the smallest apertures suffer from diffraction, which softens the entire image.


Amanda & The Boys, Bonneville Salt Flats – Wendover, UT – Fujifilm X-A3

When setting the exposure, it’s important to consider what aperture you want in order to achieve an appropriate depth-of-field and maximize image quality. For some images a large aperture may be required, for others a small aperture might be necessary, and for some a middle aperture could be best. It’s up to the photographer to determine this.

The shutter is like curtain that briefly opens and closes, and it controls the length of time that light is allowed to hit the sensor or film. Most of the time it’s a tiny fraction of a second. On the X100F this is controlled by a knob on top of the camera. Some typical settings are 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, and there are many others, including “B” which allows you to control a long shutter speed. Yes, those numbers are fractions of a second, and you’ll notice that they double or half the length of time that light is allowed to enter the camera.

A quick shutter will freeze motion while a slow shutter will show things that are moving as a blur. If you want something that’s moving fast (kids, pets, automobiles, etc.) to be sharp and not blurry, a shutter speed that’s also fast must be selected. How fast exactly depends on the speed of the object and its proximity to the camera, but 1/500 is a good starting point. You might find that 1/250 or even 1/125 will work, depending on the situation. If you want something to be blurry, such as a flowing river or panning (which is when the subject is sharp but the background is streaked), then something slower must be selected, and 1/15 or 1/30 might be appropriate.

The slight movement of the photographer holding the camera can cause blurring, known as camera shake. To prevent this, the slowest shutter speed that one should choose is the same number of the lens focal length. For example, the lens on the X100F is 35mm (equivalent), and so the slowest handheld shutter speed should be no slower than 1/30. For anything slower than that a tripod should be used. Using good techniques I’ve been able to achieve sharp results handheld using the X100F with a shutter as slow as 1/4, but I’ve also experienced camera blur when not using good techniques with the shutter set to 1/60. It’s important to use a steady hand, brace yourself if possible, and regulate breathing when using a slow shutter in order to prevent camera shake.


Caramel Macchiato – Sandy, UT – Fujifilm X100F @ f/4 – shallow depth-of-field

The shutter does more than just regulate light. It controls how motion will be shown in an image. Will moving objects be frozen still or will they be a blurry streak? It’s the photographer’s job to select an appropriate shutter speed that will allow motion to be shown in a manner that the he or she wishes.

ISO, which is sometimes called ASA or film speed, is a value that represents the sensitivity to light of the sensor or film. Digital and film work a little different with regards to this, but the outcome is similar. Low ISO images will look clean while high ISO images will look grainy or noisy (grainy being a film term and noisy being a digital term). On the X100F the ISO is controlled by a ring around the shutter knob.

Once upon a time ISO was a big deal, because what we now would consider high-ISO looked pretty awful, especially for color photography. Most photographers would keep the ISO as low as possible, and many tried hard to never venture above ISO 400. Those days are gone thanks to advances in digital technology, and most cameras nowadays are capable of producing good results to ISO 3200, and some cameras can go much higher than that. I find that the X100F looks good at ISO 6400 and can sometimes look fine at ISO 12,800.

Even though ISO choices aren’t nearly as critical as they used to be, the best image quality results are still found at the lower ISOs. It’s still a good practice to keep the ISO as low as the situation will allow, and only increase as necessary. But don’t be afraid to go higher when needed, and don’t hesitate to use ISO 6400 on the X100F when the situation calls for it.


Old Log In Zion – Zion NP, UT – Fujifilm X100F @ f/11 – large depth-of-field

Typical ISO values are ISO 100, ISO 200, ISO 400, ISO 800, ISO 1600, ISO 3200 and ISO 6400, although some cameras and film have ISO values that are higher or lower than those. Increasing the ISO value doubles the sensitivity to light and decreasing the ISO value halves the sensitivity to light. ISO 800 is twice as sensitive to light as ISO 400. ISO 200 is half as sensitive to light as ISO 400.

Adjusting the aperture, shutter or ISO by one stop has the same effect. It’s should be pretty easy to see how they relate to each other. If your light meter told you that the correct exposure is aperture f/8, shutter 1/125 and ISO 400, you can manipulate those settings and still maintain a correct exposure. For example, aperture f/5.6, shutter 1/250 and ISO 400 would give you the same exposure because, with these new settings, the aperture is letting in twice as much light while the shutter is open for half as long. Aperture f/4, shutter 1/250 and ISO 200 would also be the same exposure. Aperture f/16, shutter 1/60 and ISO 800 would give a correct exposure, too. You can adjust the settings any number of ways, you just have to think about how much each adjustment, either plus or minus, is changing the exposure, and then compensate with a different aspect of the exposure triangle.

Your job, then, is not only achieve a correct exposure, but to have the right depth-of-field by selecting an appropriate aperture, to either freeze or show motion through the shutter speed, and to have as clean as practical image through the ISO selection. You might have to sacrifice some things if the lighting isn’t just right. You might have to choose a larger aperture than you really want to. You might have to select a slower shutter speed than you really want to. You might have to use a higher ISO than you really want to. The photographer must decide what’s most important and what can be bent a little. A lot of times it’s not about being perfect, but about being as perfect as practical while considering what you can get away with.

If you are learning photography, this is a lot to take in at one sitting. My recommendation is to take the camera out of “A” and just take some pictures, playing around with the different settings. You probably won’t capture anything great right away, and you might even delete most of the exposures, but you’ll learn quite a bit through the process. Don’t be worried about making mistakes. This is about learning how it all works so that when the time comes to capture a great photograph you’ll have the technical know-how to do so.


Kiki – South Weber, UT – Fujifilm X100F @ 1/240 – frozen motion


Ghostly – Fort Casey, WA – Fujifilm X100F @ 1/6 – blurred


Girl By The Escalator – SLC, UT – Fujifilm X100F @ ISO 8000 – noisy image


Walking Man – SLC, UT – Fujifilm X100F @ ISO 400 – clean image


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