How to control exposure in photography

A bit of theory to start with. The concept of Exposure Value (EV) is quite simply just a common base to measure the variations of light related to the settings of your camera, in terms of shutter speed, aperture, and ISO sensitivity.

As a side note about photographic jargon, if you talk with a professional photographer, they will use the terms “EV” and “IL” (luminance index) interchangeably, or even the terms “aperture” and “stop” to mean the same thing. There is actually a slight nuance between these terms, but they essentially mean the same thing.

For example: you are at a speed of 1/250s with an aperture of F2.8 and a sensitivity of 200 ISO. If you decide to go to 1/500s, you then lose one EV/stop with your shutter speed, and will therefore need to add one EV of aperture (so go to F1.4) or one EV of sensitivity (400 ISO).

• Shutter speed (in seconds)
• Aperture (f-values as in “focal”)
• ISO sensitivity (ISO values)

Each setting affects not only the brightness of your image, but also its visual rendering (blur, depth of field, noise).

While photography is largely a didactic discipline, there are still some theoretical principles to know and a few rules to learn by heart. The EV/stops for each setting are part of this. I personally memorized them during my photography training like multiplication tables and ten years later I still know them by heart, so let me tell you that the effort pays off!

Let’s look at the theoretical steps for aperture, shutter speed, and ISO sensitivity. Depending on your camera, you will have subdivisions of half a stop (for example, aperture of 1/125s then 1/200s and finally 1/250s) or a third of a stop (1/125s then 1/160s then 1/200s and finally 1/250s) but these are not the “real” steps.

• Aperture: F1.4, F2, F2.8, F4, F5.6, F8, F11, F16, F22, F32
• Shutter speed: 1/60s, 1/125s, 1/250s, 1/500s, 1/1000s
• Sensitivity: 100 ISO, 200 ISO, 400 ISO, 800 ISO, 1600 ISO, 3200 ISO

How to visualize exposure during shooting

The beauty of modern digital cameras is that they allow real-time visualization of exposure with clear indicators. In other words, no more excuses if you “blow out” (overexpose) or block up (underexpose) your images!
Two tools available via the LCD screen or in the viewfinder enable this: the histogram and the blinking highlights (or zebras).

Understanding histogram curves

A histogram is a graph showing the distribution of tones in your photo, from black (on the left) to white (on the right). It is available for each photo and simply needs to be activated in your camera’s setup menu.

This may seem complex at first, but it is your best ally for checking exposure. When I start a photo session, I constantly check the histogram. For example, in broad daylight, it is easy to blow out the highlights (white areas with no detail). I look at the histogram to ensure that the highlights remain under control.

Pro tip: if you have a DSLR or mirrorless camera, configure the histogram so you can display it using the up/down arrows. Always check once at the start of a shoot if the lighting conditions are extreme (either very bright areas like the sky or very dark areas like shaded parts). If the histogram is cut off on the right or left, then adjust your settings accordingly.

Composition of a histogram: highlights, midtones, and shadows

A histogram is a fairly simple graph that is divided into three sections:

• The left side corresponds to the shadows
• The middle/center of the graph corresponds to the midtones
• The right side corresponds to the highlights

From this organization of the graph come the expressions “expose to the left” meaning to darken the photo, or “expose to the right” meaning to let in more light.
The ideal histogram as taught at university is a bell-shaped curve, without spikes and that covers the entire width of the graph.
A bell-shaped histogram simply means a technically balanced photo, but it does not guarantee that the photo is readable or creatively interesting.

Zebras and blinking highlights

Modern cameras have zebra patterns or blinking areas indicating the overexposed parts of an image. These areas will appear directly on the image when you view it in your camera.
Pro tips: I always activate these warnings in tricky lighting situations, such as backlit portraits. If a few meaningless areas are slightly overexposed/underexposed, it’s not a big deal; just make sure there are no zebras around your subjects and main elements.

The role of exposure in the photographic process

From a technical point of view, good exposure ensures that your image retains as much detail as possible in both the highlights and shadows. This gives you more flexibility during the editing phase (also called post-production), especially when shooting in RAW.
Pro tip: save your images in RAW format rather than JPEG. The main drawback here is the much larger file size and the need for post-production software to convert these RAW files into universally understood images (JPEG, PNG for example). However, the huge advantage is having all the available data in both the shadow and highlight areas. The RAW format allows you to retain all the data captured by the sensor, whereas JPEG reduces it considerably (notably by compressing the image, choosing the white balance for you, reducing dynamic range, and removing other information deemed non-essential). The RAW format is non-destructive, unlike JPEG.

The role of exposure in the photographic process

From a technical point of view, good exposure ensures that your image retains as much detail as possible in both the highlights and shadows. This gives you more flexibility during the editing phase (also called post-production), especially when shooting in RAW.
Pro tip: save your images in RAW format rather than JPEG. The main drawback here is the much larger file size and the need for post-production software to convert these RAW files into universally understood images (JPEG, PNG for example). However, the huge advantage is having all the available data in both the shadow and highlight areas. The RAW format allows you to retain all the data captured by the sensor, whereas JPEG reduces it considerably (notably by compressing the image, choosing the white balance for you, reducing dynamic range, and removing other information deemed non-essential). The RAW format is non-destructive, unlike JPEG.

Artistic aspect: Mood and storytelling through light

Exposure is one of the most effective narrative techniques in photography, as it communicates universally understood information:

• Bright images often convey a sense of joy, lightness, innocence, and softness
• Dark images evoke a dramatic or mysterious mood
• In this context, a slight overexposure or underexposure during shooting can enhance the atmosphere of the scene

Pro tip: in post-production, using the “clarity” function allows you to enhance the atmosphere created. Present in Camera Raw and Lightroom, clarity increases or decreases the contrast of details on the edges of the image. Increased, it will give hard and “rough” contours; decreased, clarity will give a soft and faded look. For example, lowering clarity is a classic technique in wedding photography to enhance the dreamlike atmosphere of the day. In sports or fitness photography, clarity is usually increased to highlight muscle definition.

The effects of incorrect exposure

Here we are talking about exposure that has been set incorrectly during shooting, not possible corrections in post-production.

Underexposure during shooting

• Loss of detail in the shadows
• Increased noise if you brighten the image in post-processing
• Reduced dynamic range

Overexposure during shooting

• Blown highlights, with no recoverable detail
• Flat, lifeless images
• Loss of realism and depth

Pro tip: if you are unsure about the exposure to use during shooting, it is better to underexpose than overexpose. A “blown out” image is a fairly common scenario if you shoot on a sunny day, and will create many white areas containing simply no information. Conversely, even if you underexpose heavily (two or three stops below neutral exposure) it will be very difficult to get pure black. You can then achieve the desired result in post-production as you wish. This adds an extra step but is much safer.

The Exposure Triangle: Mastering the Three Pillars

As controlling the light that is recorded by your camera is done using three interdependent settings, it is often referred to as the exposure triangle. The relationship between these three variables works as described below (don’t worry, it is much simpler than it looks):

Aperture

Aperture is a mechanical process that takes place in your camera’s lens. When you turn the dial on your camera, it instructs the lens to close its aperture. The aperture is a set of metal blades that come together to form a circle that lets light through. When you open the aperture this circle gets bigger, and when you close it, it becomes smaller. It’s as simple as that!

Aperture measurement index (f-stop)

Aperture is measured in F-stop, that is, in focal aperture index (F as in Focal in F-stop). As seen above, the aperture steps are as follows: F1.4, F2, F2.8, F4, F5.6, F8, F11, F16, F22, F32
A few points to remember here:

• The scale is inverted, meaning a small number indicates a large aperture
• F1.4 is the maximum aperture for most prime lenses; some go to F1.2 but this is rare. For wealthy collectors, there are even lenses below F1 such as the Zeiss Planar 50mm f/0.7, at 180,000 euros however.
• If you want to go below F1.2 some techniques allow you to achieve an extremely shallow depth of field such as the mega panorama/Brenizer method, which we discuss in another article.

Effects of aperture on your images

Aperture mainly has three effects during shooting:

• It greatly influences the amount of light entering the lens, and thus if your lens has a large aperture, this gives you more flexibility for your shutter speed and ISO sensitivity settings.
• It directly impacts depth of field, that is, the sharpness of elements on different planes (foreground, background). A large aperture (e.g., f/1.4) creates a shallow depth of field and thus blurs the background, while a small aperture (e.g., f/16) ensures good sharpness across all planes.
• It also impacts bokeh, that is, the quality of the background blur.

Pro tip: if you want to shoot portraits, favour a prime lens. It more easily offers a large aperture (zooms rarely go below F2.8) and is much more affordable than a zoom of equivalent quality.
For example, a Nikon lens (Nikkor series) 50mm with 1.8 aperture for APS-C sensor can be found for less than two hundred euros and is ideal for starting photography. If you want to take beautiful portraits with nice bokeh, choose an F2.8 aperture and do not go below that. A very wide aperture (F1.4 or F1.2) can cause blur on important elements of your subject even with good focusing. It’s simply not worth the risk.

Shutter speed

When we talk about shutter speed in photography, we are referring to the length of time the camera’s shutter remains open and therefore lets light pass through so it can hit the sensor or film, which then allows the camera to record the image.
To be more specific, the shutter in a DSLR consists of two “curtains” made of metal blades; one curtain pulls away to open while the second curtain takes its place to close and end the exposure. In a mirrorless camera, there are no more curtains and the shutter is virtual, meaning the sensor is activated and deactivated at the desired speed.

Shutter speed will have three effects on the resulting image:

• Controlling the amount of light, just like aperture or ISO sensitivity
• Sharpness of moving subjects: a fast speed (1/1000s) freezes action, while a slower speed (1/30s) creates motion blur
• Camera shake blur when shooting handheld (reciprocity rule)

Pro tip: a simple rule for handheld shooting is the reciprocal focal length-shutter speed rule. This is very often taught in photography schools because it is easy to understand and apply.

Quite simply, it states that for handheld shooting, the shutter speed should always be at least equal to the focal length. So if you shoot with a 50mm prime lens on a full-frame camera (so a “true” 50mm focal length without crop factor), then your shutter speed should be at least 1/50s.
In my experience, this rule is often a bit optimistic and it’s better to choose a slightly faster speed (half a stop or a stop, so here more like 1/125s), but it gives a good starting point. If you use a 200mm focal length, you should then use a shutter speed of at least 1/200s, and so on.

ISO sensitivity

The ISO sensitivity of a camera controls the sensor’s sensitivity to light. It’s an amplification system: the higher the ISO, the more the sensor’s sensitivity is electronically increased.
Increasing the sensitivity amplifies the capture of light, but will also cause the appearance of “digital noise” in the image, that is, small coloured dots (red, blue, green) or a grain effect on the photo. With a film camera, ISO sensitivity is managed differently, that is, by the ISO sensitivity of the silver grains applied to the film; the larger the grains, the more light they captured but they were also more visible during development.
Pro tip: always try to stay as close as possible to ISO 100 to ensure optimal sharpness and minimal noise. If you have to increase the ISO, know that most digital SLRs and mirrorless cameras handle noise very well up to 1600 ISO. On a professional camera (Nikon Z7, Canon Mark IV…) you can even go up to 3200 ISO without issue. For example, I have made large format prints in 60×90 cm with photos at 3200 ISO, and there was almost no noise on the printed image.

Choosing your camera according to your needs

While most DSLRs and hybrid cameras will do a decent job in normal lighting conditions (daytime), choosing the right camera will become crucial if you want to try more challenging situations such as shooting sports events or shooting at night.

The sensor: size and dynamic range

A number of factors are important when it comes to your sensor, but the two most important when it comes to exposure are undoubtedly sensor size and dynamic range. Quite simply, the larger the sensor, the greater the overall quantity of light (= number of photons) it receives.
This physical reality of your sensor will result in better image quality, especially in low light, meaning less digital noise and better dynamic range:

• Noise is linked to the sensor’s ability to capture light without creating visual artifacts: it is therefore particularly noticeable in low light (night photography, indoor scenes, or artificial light) and when you have to use high ISO sensitivity. A full-frame sensor will in this case give you a significant advantage over an APS-C sensor. This is one of the reasons why wedding photographers “must” work with full-frame cameras – these cameras allow for working in difficult lighting situations, such as in a church or in the evening at the reception venue. For example, you will have much less noise at 3200 ISO with a full-frame sensor than with an APS-C.
• Dynamic range is the sensor’s ability to record details in both the dark and very bright areas of a scene. The greater the dynamic range, the more you will be able, in a single photo, to have nuances (information) in deep blacks and highlights. Dynamic range is one of the most important aspects of the sensor as it allows you to “recover” details in your images during post-production, for example in the sky which is often overexposed compared to the rest of the scene, or in shaded areas. Again, a large sensor will give you a big advantage. For reference, professional photographers often talk in stops or “IL” or “EV” when referring to dynamic range.

Pro tip: for me, dynamic range is one of the most important aspects when buying a new camera body. The ideal is at least 14 EV, which means the camera can record details across 14 different exposure levels, from the brightest area (just before saturation) to the darkest area (just before it becomes pure black). The darkest area can be up to 16,384 times less bright than the brightest (2 to the power of 14 = 16,384). If you are starting photography, I would recommend at least twelve EV, which most DSLRs and mirrorless cameras on the market offer. The camera is certainly a bit less sensitive than a pro camera, but you will still have the ability to get data for shadow areas that are 4096 times darker than the brightest areas of the image. Yes, between twelve and fourteen EV the difference is quite huge, due to the multiplication factor. Below twelve EV, noise really starts to become very present.

Mechanical vs electronic shutter

The type of shutter is only really important if you want to shoot with a slow shutter speed (1/50s or below).
A mechanical shutter as found in a digital SLR creates vibrations when triggered, which can cause motion blur. When triggered, the shutter curtains will quickly go down and up, which combined with the movement of the mirror will make your camera shake. For example, if you photograph a waterfall with an exposure of several seconds, triggering the shutter may create micro-vibrations that take a few tenths of a second (up to a second) to dissipate and thus may affect the sharpness of your photo.

Electronic shutters avoid these vibrations and are generally superior to mechanical shutters. They can, in some cases, create rolling shutter artifacts.