The Exposure Triangle: Shutter Speed, Aperture and ISO Explained
The relationship between shutter speed, aperture and ISO (or the so-called “exposure triangle”) is the most essential and most boring part of photography. This relationship sets the basis for EVERY single type of photography and not just landscape photography. Briefly, the exposure triangle determines the exposure and aspect of a photo. You can have the most expensive and cutting-edge camera equipment of the entire globe, but if you don’t know how to play with the exposure triangle then all those big bucks you have spent on photography gear are worth nothing. NOTHING!!! If you are new to photography and don't know where to start, this is definitely the post for you. To better understand this triangular relationship, let’s start to separate the three main elements and then see how they work together. Shall we?!
The shutter speed indicates for how long your shutter (or mirror) is open and, therefore, it determines the time your sensor will be exposed to the light. A fast shutter speed (i.e. 1/500, 1/1000, 1/2000 and so on) allows your sensor to collect light for a limited interval as the shutter exposes the sensor for a very tiny fraction of a second, while a slow shutter speed (i.e. 1/4, 1s, 10s and so on) lets your sensor to be exposed for a longer period of time. As everything in photography, your shutter speed value always depends on the scene and the subject you are about to capture and if you are using a tripod or shooting hand-held. As you can see from this high-tech chart here, if you want to “freeze” moving objects in your scene you would need a fast shutter speed to have your moving subjects in sharp focus. Another reason to have a fast shutter speed is when you shoot handheld. In this case, the shutter speed must be fast enough (usually up to 1/50 and beyond) to avoid camera shakes from your hand and breathing, especially if you are using a tele-photo lens. If, instead, you want "smooth out" moving water to get that soft and silky effect, you would need a longer shutter speed and a tripod.
What’s the ideal shutter speed for landscape photography? The correct answer would be: it depends on the scene. Most of the time, the elements of a landscape picture are still and the shutter speed isn’t very relevant, since you are shooting on a tripod. Hence, the shutter speed is the last thing you worry about. Nonetheless, this can change when in presence of water or fast moving clouds. For example, a slow shutter speed (1/4 to 1s) creates a very pleasant effect when shooting streams, waves and waterfalls. The prolonged exposure time makes the flowing water silky and dreamy, which I personally find very compelling and artistic as you retain a nice texture in the water. You can see an example of a slow shutter speed in the picture on the right, where the shutter speed was set to 1/5 of a second. Using a very slow shutter speed (between 10s to 30s) in the presence of water movement will also smooth the water element out, but this time you’ll lose the texture and the water will look like a milky and foggy surface. This slower range is ideal for adding texture to your sky. If you have well-defined clouds in the sky, you can add more interesting texture by using a very slow shutter speed (30s or longer). This will make the clouds streak through your image and add some drama in your picture. The image on the left was captured after a 244s exposure and you can see how there's no texture in the water (which look like a smooth surface) and that also the clouds in the clouds were smoothen by the very long exposure.
The aperture is the measure of how open your lens’ iris is; therefore, the aperture indicates the amount of light passing through the lens and hitting the sensor. Aperture is measured in f-numbers (or f-stops): a wide aperture (low f-number such as f/1.8, f/2 or f/2.8) allows a great amount of light through the lens, while a narrow aperture (high f-number such as f/14, f/16 or f/18) allows a limited amount of light in. Usually, lenses are classified by their focal length range and by the lowest aperture available on the lens such as the famous 16-35mm f/4, which means that the lens can go as low as f/4 at all focal lengths or the 80-400mm f/4.5-5.6, which means you can go as low as f/4.5 at 80mm and as low as f/5.6 when zoomed in at 400mm. Another important factor to consider with aperture is depth-of-field. The depth-of-field determines what portion of your scene will be in focus and this portion changes depending on the f-number you choose. Confused?! Here’s a cheat sheet for aperture as well. A wide aperture, for example, gives you a so-called shallow depth-of-field, which means that just a small portion of your scene will be in focus. As you can see, at f/2.8 your flower in the foreground will be in focus, but your mountain in the background will be blurred due to the shallow depth-of-field. A narrow aperture, on the other hand, gives you a deeper depth-of-field and a bigger portion of your image will be in focus. Roughly at f/8 and beyond both your flower and your mountain will be acceptably in focus. While a shallow depth-of-field is not always ideal for landscape photography, it can be useful for portrait, wedding, street and wildlife photography to isolate your subject and have that nice soothing blurred background (also known as bokeh) like in this picture below off my brother's dog.
Usually for landscapes the “go-to” aperture is between f/8-f/11, which gives you a good depth-of-field to get most of the landscape in focus and it’s usually the sharpest range for most lenses. I know there are guys out there that preach that the absolute sharpest f-number must be scientifically calculated in order to get the best out your lens, but that’s just gear-head poppycock. And I am no gear-head. I personally use between f/8 to f/14 as my “go-to” aperture, because it is a good compromise for my actual lenses and it has always worked fine also for printing. The picture here on the right was taken at f/14 and both the first tree and the last one at the end are in focus. You are probably asking yourself: Why don’t you go higher than f/14 so everything will be in perfect focus? Well, the answer is diffraction, which is the biggest trade-off of using narrow apertures. Light beams tend to disperse and interfere with each other when travelling through small openings such as f/18, f/20 or f/22. In this case, light will hit the sensor unevenly and this translates into loss of resolution. In other words, shooting with very narrow apertures will give you smudgy looking pictures, even if you have 100 trillion megapixels. So, if you want to go to higher f-numbers (f/18, f/20, f/22) you surely would get the whole scene in focus, but your subjects won’t be as sharp as the one at f/8 or f/11. Now that you despise narrow apertures, I can tell that these f-numbers are usually helpful to get the dramatic sun-star effect when shooting directly into the sun, but this topic will be discussed later on. To sum up, aperture determines the amount of light passing through the lens and the depth-of-field (sharpness) of your scene.
The ISO (pronounced I-SO) is the last but not the least element of the exposure triade. It determines the sensitivity of your sensor to the light and, if increased, the ISO allows you to work with low to very low amount of light. An ISO of 100 makes your sensor very insensitive to light, which means that more light will be required to properly expose your picture. An ISO of 6400, instead, makes your sensor very sensitive to light and allows you to properly expose your frame even when the light is very dim. There is also a trade-off when using high ISO, which is the introduction of noise (or grain) in your RAW file. An ISO of 100 or lower results in minimal noise in your photo, while a high ISO (i.e. 4000, 6400 or 12600) introduces a lot of grain in your picture (see the cheat sheet below).
At this point you are asking yourself: “why would I want to increase my ISO then and deliberately introduce noise when shooting landscapes?” Well, high ISOs are particularly useful with low light situations such as astrophotography or handheld indoor shooting. An ISO of 100 usually is the best value for landscape photography as it gives you inexistent noise in your picture and, assuming you are on a tripod, always go for ISO100. There will be times though, when you will want to increase the ISO a tad to achieve the perfect shutter speed: for example when shooting waterfalls or waves to get your exposure right in that sweet range of 1/4 to 1s. The picture above in the Shutter Speed paragraph is an example as I shot that with ISO125, instead of ISO100 to compensate the fading sunset light. Note that the introduction of noise by ISO settings also depends by the camera you are using. Most full-frame and high-end crop sensor cameras handles high ISO very well, while entry-level crop sensor DSLRs and point-and-shoot cameras may be limited in this area as high ISO may introduce a lot of grain in your picture. Cameras that can handle high ISOs well are very popular amongst night photographers as they always shoot in extremely low light situations, when the camera "sees" more than the human eye. These new age cameras are able to achieve extraordinary results of the starry sky and Galactic core, such as the image below, with an more than acceptable noise introduction.
A combination of a specific shutter speed, aperture and ISO is called exposure value (EV) and any modification doubling or halving the amount of light reaching the sensor or its sensitivity is referred to as adding or subtracting 1 full stop. For example, adding 1 stop to your basic EV (EV+1) translates to doubling the amount of light or sensor sensitivity of your basic EV, hence creating a brighter or over-exposed image compared to the one taken with your basic EV. Subtracting 1 stop (EV-1), on the other hand, halves the amount of light reaching the sensor, therefore generating a darker or under-exposed image. Take these three straight out of the camera shots below. The one in the middle is my basic EV, while the right one has my basic EV plus 1 stop, resulting in a brighter image. The shot on the left, instead, has my basic EV minus 1 stop and consequentially is a darker image. In this case, I modified my shutter speed to add and subtract 1 full stops, but, of course, the modification of either shutter speed, aperture or ISO can be used to modify your basic EV or adjust your EV according to the light changing in your scene.
How do we know how many stops we are adding or subtracting to our EV? Stay sharp here as it gets a little tricky. As you can see from the previous cheat sheets, shutter speed, aperture and ISO don’t follow an intuitive scale, but they follow a so-called standardised scale introduced by camera manufacturers. For example, aperture goes from f/4 to f/5 to f/5.6 to f/6.3 to f/7.1 and then to f/8, the same goes for the ISO that skips from ISO200 to 250 to 320 to 400 and finally shutter speed values go from 1/5 to 1/6, 1/8, 1/10, 1/13 and to 1/15 and so on. Fair to say that all 3 scales are less than straight-forward at first glance and, unfortunately, you should try to remember all them as they are by memory. Don’t worry yet though, as they get intuitive with practice. All these scales are based on thirds, which means that every change of value in either aperture, shutter speed or ISO roughly corresponds to add or subtract one third of a stop. To simplify things out, I have already divided all the previous cheat sheets in thirds to help you visualise how to add or subtract the correct amount of stops to your EV.
For example, there’s a full stop difference between f/5.6 and f/8, meaning that at f/8 I have halved the amount of light hitting my sensor than f/5.6, creating a darker image. In this interval, f/6.3 subtracts the first third stop (also called -0.3 stop) to my EV, f/7.1 subtracts the second third stop (or -0.7 stop) and then f/8 subtracts a full stop (-1 stop). Similarly, there is a 2 full stops difference between ISO100 and ISO400 as the scale goes ISO100, ISO125 (+0.3 stop), ISO160 (+0.7 stop), ISO200 (+1 stop), ISO250 (+1.3 stops), ISO320 (+1.7 stops) and ISO400 (+2 stops). And again, there is a whopping 4 full stops difference between a shutter speed of 1/2 and 1/30 of a second, as 1/30 of a second will allow a significant less amount of light into the camera (more precisely 2^4-fold less light). Intuitively, whenever we want to slow down our shutter speed to our basic EV, we then need to compensate the exposure by closing the aperture or decreasing the ISO or even the two combined as a slow shutter speed allows more light in. Same goes when we want to use a wide aperture such as f/2.8, we need to dial in a faster shutter speed or decrease the ISO to compensate the huge amount of light entering the camera from a very wide aperture. I know this can be a little confusing, but hopefully the following examples will clear all your doubts and your headache.
As a practical example, let’s have a look at this super-high tech graph below that I stole from a top-classified NASA database called: the scale example. In the first example, let’s assume that my basic and perfect EV is ISO400, f/11, 1/60 (EV=0) and I would like to keep my aperture at f/11 to get my whole scene sharp, therefore aperture will remain unchanged for depth-of-field purposes. Now, I want to reduce the noise in my picture, so I am going to lower the ISO400 to ISO100, which means I am subtracting 2 full stops to my perfect EV, hence darkening (under-exposing) my picture (EV=-2). To balance this, I need to add 2 full stops with my shutter speed and, since I am shooting on a tripod, this shouldn’t be a problem. Adding 2 full stops with the shutter speed setting means that I have to slow down my 1/60 to 1/15 of a second to compensate the ISO decrement. In this case, the use of the exposure triangle allows me to keep my aperture constant, reduce the noise in my picture and have the same exposure than my initial settings.
To really wipe out any doubt left, let’s consider another example. I am shooting a seascape scene like the one below and my perfect EV is ISO100, f/8, 1/5 (EV=0). I like to shoot at 1/5 of a second as this shutter speed gives me amazing textures in the water, so, in this case, the shutter speed is the most important setting and cannot be changed otherwise I’ll lose the texture. The ambient light is fading and suddenly my perfect EV is giving horribly under-exposed frames (EV=-2) as you can see from the second picture. At this point, I can either increase the ISO or open up the aperture or a bit of both. This always depends on the scene but I would probably increase the ISO first to retain a good depth-of-field. Let’s assume the light has faded by 2 full stops, I will then increase the ISO100 to ISO400. This value compensates the light decrement and it still allows me to have acceptably noise-free images without changing my shutter speed. As you can see from the third picture, increasing the ISO to 400 resulted into the same EV (EV=0). After a while, the light has faded by another full stop, so in this case I can open up the aperture from f/8 to f/5.6 (+1 full stop) to still get a well exposed and relatively sharp image. Now my final settings in the sixth picture are ISO400, f/5.6, 1/5 and I still have a nice texture in the water and the same perfectly exposed picture despite the lower light.
Since we are focusing on landscape photography, I can say that I rarely touch my ISO (always at 100) exceptions made for seascapes, waterfalls, trees in high winds or when shooting hand-held. I also use an aperture value between f/8-f/14 and I don’t usually go lower than f/8 with my aperture. When on a tripod, I generally change the shutter speed only to tune my EV as the light changes in my scene, since it’s the least important setting for that situation. I also always use the live view exposure metering mode to dial in my initial EV and then adjust it according to the situation (the exposure meter mode is only available in Manual Mode). When shooting water (i.e. waterfalls, streams or seascapes) or handholding the camera, the shutter speed becomes the most important setting for the texture, if I shoot water, and for the sharpness, if I shoot hand-held. In this case, I will first change my aperture or ISO if my picture is getting over- or under-exposed or blurry.
Well done!!! You have officially survived the most boring part of landscape photography and photography in general. I hope this topic didn’t cause you any migraine and you now have a better understanding of the exposure triangle. I suggest you to practice these settings and their relationship in order to be comfortable with them because you’ll need to act fast and without thinking when in the field. They should be second nature and I am sure they’ll become very intuitive after a while. This is also a good exercise for becoming familiar with your camera and lenses. For example, you can figure out what is the highest ISO value of your camera you can use without introducing too much noise or when diffraction kicks in causing loss of resolution in your pictures. Now you should be an expert of the exposure triangle and how to modify the shutter speed, aperture and ISO for the perfect exposure. Therefore, you should not be afraid to shoot in Manual Mode anymore as this mode gives the greatest degree of freedom with the camera settings. The question is: how do you know you have achieved the perfect exposure for your scene? And how can you tell if your picture is over- or under-exposed in order to tweak your settings? The answer is: the Histogram and this little dude is a complimentary topic of the exposure triangle.