Exposure in the Context of Digital Photography

Exposure is one of the most fundamental concepts of photography that all photographers struggle with or had to struggle with. In digital photography, you may entirely rely on your digital camera to make a good exposure decision for you. But certainly, it doesn’t know about your artistic tastes and no automation technology can reach your vision. Camera’s automatic features ignore the emotional qualities of a scene.

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“Choosing the exposure for a photograph is both alarmingly simple and infinitely complex; in fact, it’s one of photography’s most absorbing paradoxes.” – Michael Freeman

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A fully automated camera is called a “point and shoot” camera. It was just a commercial interest to make cameras available to all and that interest brought “Kodak Brownie” in 1900. Later people found it as a tool to document their own stories with a very little effort and cost. But artists wanted more control over this medium. Often you will find it necessary to override the camera’s automatic exposure settings to achieve the desired result. Understanding it properly gives you full ability to control and override your camera’s exposure settings to achieve the desired image that you have in your mind.

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Exposure is the understanding between the image seen by the human eye and the image seen by the camera.

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What is exposure? Or, What is a good exposure?

Exposure is the amount of light hits the camera sensor exposed for a certain amount of time determined by the shutter speed of your camera.

Exposure = Intensity x Time

A perfectly exposed photograph will render the scene as you see with your naked eye. That means if your subject looks gray it should exactly render that gray in the captured image. But there is no such technology currently available that can reproduce the full range of tones that our eye can see, or is capable of capturing the full visible electromagnetic spectrum.

Making an exposure can be considered as making a compromise in recording luminous data unless it’s a cloudy or overcast day when dynamic range naturally gets lowered. In the domain of artistry, this compromise is totally subjective.

There is no right or wrong exposure recipe unless the photograph gets too dark considered as underexposed or washed away which is an overexposed scenario where you usually risk losing data in shadow or highlight areas. You have to make this artistic judgment as you interpret a scene.

There are only three things in a digital camera that defines a photographic exposure; Aperture, Shutter Speed and ISO. I’m going to be a bit brief about the definitions of these things.

I suggest that you start with your camera’s user manual to be comfortable with all the buttons and controls specifically designed for your camera model. Because what’s more important about those buttons and controls is the relationship between them and how they manipulate the light.

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The better the exposure in camera the easier the work in post-processing.

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Aperture

An aperture is a hole that lets the light get into your camera all the way to the sensor chip. A series of blades designed in a special way inside your lens that adjusts the size of this hole. How wide or small it will open depends on the lens you have chosen.

Because the angle of projected light on the image sensor gets altered as you make the size of your aperture larger or smaller the aperture defines the Depth of Field (DOF). The depth of field defines how much of the scene should be in focus.

This aperture adjustment greatly impacts the exposure of a scene as it also determines the amount of light that gets into the camera. The smaller (technically larger f-numbers, e.g. f/22 < f/16 < f/11 < f/8 … ) the size of your aperture is, the larger the depth of field will be or vice-versa.

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Here in this intimate landscape photograph Creek in Twilight I was interested to capture the motion and the groups of rocks and stones across the riverbed. To achieve the result I had to keep the foreground in focus as well as the distant background.

So I set the aperture value to f/22─which was the maximum f-number for that particular lens─to include everything from the foreground rock─which was probably 1.5 feet away from my camera lens─to the distant background.

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In the photograph Little Red Flowers I wanted to remove the distractions in the background to simplify the composition. The leaves, stems, and other dark patches caused by the shadows would compete with each other if I had kept them all in focus. Then your mind had to struggle to find what’s more important about this picture.

So, I set it to the smallest aperture value my 50mm prime lens offered to blur out the background. Where I also had to carefully choose the plain that I wanted to keep in focus.

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Major f-stops

There are some aperture values that we use more often than the other ones and considered to be the major f-stops. They are f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32.

Lens Focal Length / Stop = Diameter of the Diaphragm

When you look through the viewfinder the aperture of your camera is entirely open due to the complexity of its design. So you may not see the difference between the DOF that was previously set to your camera and the DOF that you have currently set to. To get the actual DOF through the viewfinder you may take help of DOF Preview Button (if available in your camera) that will give you the simulation of actual DOF currently set to your camera.

What is a good aperture?

There is no such thing as good or bad aperture. It is an artistic choice. Your composition will dictate what aperture value is necessary for that scene. In other words, how much and what part of your scene you want to keep in focus.

Still, there are photographers who may argue that some aperture values produces a sharper and better result than the other ones. But they are not so significant and the result is tolerable to me. For example, they might not use f/22 for the photograph Creek in Twilight. Instead, they may bracket their focus to blend them later in post-processing.

Yes, the maximum aperture value or the smallest aperture hole of a specific lens introduces a little softening effect caused by the diffraction of light. However, you notice the difference only when compared side by side at a 100% or 200% magnification level.

Shutter Speed

The shutter is a kind of curtain placed before the image sensor that controls how long the image sensor should remain exposed to the light coming through the lens. The shutter speed of a particular scene is measured in seconds or a fraction of a second.

We vary this shutter speed to achieve different results. Here are some examples that demonstrate the reasons we may want to capture our photographs in some specific ranges of shutter speed.

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The photograph Morning Birds introduced a few exposure challenges. First of all, I captured it during the time of sunrise when the light was very low and I was shooting handheld from a bridge. Another challenge was the flying birds.

I was shooting it at a wide angle and I also had image stabilization feature with my lens. So I would be okay with relatively slower shutter speed than 1/200 sec. in this low light situation if there was no bird or if I didn’t want to freeze their motion.

But here in this example, a shutter speed that was fast enough to freeze the movement of the birds was one of the critical exposure decisions that I had to make during the capture.

To keep the shutter speed high and everything in the scene in focus I had to boost my ISO sensitivity. Which I generally avoid to minimize digital sensor noise. I usually set the ISO as low as possible in a specific photographic situation.

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There are situations when all that is interesting to you is some moving things in your scene and you want to capture it to let your viewers experience that sense of motion. We often see this motion effect in photographs of waterfalls, river creeks, sea waves, and night photography.

This is usually done by slowing down your shutter speed either by putting an ND filter in front of your lens or choosing a time or place where the light is naturally very low. Because the goal here is to achieve a shutter speed long enough to represent the desired motion.

In the case of the above image Morning Stream, I took a few shots to figure out the particular shutter speed which was able to produce these fine details. Longer shutter speed would make the motion smoother and I would lose the textures and lines created by the motion.

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Long exposure photography doesn’t necessarily mean capturing some motions or trails. It can also serve you very well in a low light situation where you cannot go beyond a certain aperture value and ISO speed for any creative or technical reason. Long exposure typically means your exposure time is set to either 1 sec. or more than 1.sec to record enough light.

I took the long exposure photograph Fading In Fading Out in 2016 on a foggy day. The fisherman and the boat on the left were undesired when I composed the shot. I was annoyed when they entered in my composed frame; where I already locked the shutter for 30 seconds. Initially, all I wanted was the poles on the left as something static. Since everything else was moving in the scene that would make the whole photograph render blurry.

Eventually, this one turned out to be the best of the series and the most significant for the vision I had in my mind. As a matter of fact, the ghostly man on the left added more drama to the picture.

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Although there is a shutter priority mode in DSLRs modern photographers don’t seem to use it so much. Since we can manipulate the speed of the camera’s shutter─in other shooting modes say aperture priority or manual mode─by adjusting the other two exposure parameters.

The only reason you might want to shoot in shutter priority mode is when you want to capture some motions of any moving objects in your scene and you happen to know the speed that will produce the effect you’re looking for. Which is very rare unless you’re shooting the same thing again and over again where the speed of the moving objects is very consistent.

ISO Sensitivity

ISO defines how sensitive your image sensor should be to the light in a particular exposure scenario. It’s similar to photographic film sensitivity.

Technically, ISO boosts/amplifies the signals coming to your camera to give you enough shutter speed for handheld shooting to protect you from a camera shake or to freeze motion in a low lighting condition. Remember, you have to make this choice with cautions. Because higher ISO generates noise─which is random colored pixels generated from a camera.

You should consider the minimum ISO possible for the particular scene. If you have a tripod with you I would say adjust your aperture or shutter speed values to get the desired exposure rather than, boosting your ISO up. But there will still be a time you have to increase ISO where adjusting aperture or shutter speed will just spoil the desired shot.

You must experiment with your camera to ensure the maximum number of ISO that generates a noise you can deal with, before running into those situations.

ISO is also measured in stops. For example, ISO 100, 200, 400, 800, 1600, 3200, 6400 or more. Each of these value is one stop lesser than it’s succeeding value or higher than its preceding value. If you are shooting in aperture priority mode where you get a shutter speed of 1/100th part of a second at an aperture value of f/8 and with an ISO 100, doubling (increasing by one stop) the ISO from 100 to 200 will yield a shutter speed of 1/200th part of a second. Or if you are in the shutter priority mode with the same settings mentioned above will increase the aperture value, from f/8 to one stop higher at f/11 keeping the shutter speed unaltered. I hope you got the idea.

The Concept of ‘Stop’

In order to understand the relationship between aperture, shutter speed, and ISO the term “stop” comes in between. A stop is a unit; an amount of light in the realm of photography. It sounds complex to amateurs but the idea of “stop” is to simplify the complexity of the relationship between aperture, shutter speed, and ISO.

What is a stop?

A stop is simply doubling or halving the amount light in an exposure. For example, increasing a stop means doubling the amount of light and decreasing a stop means halving the amount of light your image sensor will be exposed to.

The Relationship Between Aperture, Shutter Speed, and ISO Sensitivity

The modern digital SLRs have a built-in light meter. For most cameras, as you half-press the shutter release button it measures the available light that is illuminating the subject and gives you an exposure setting; which is a combination of aperture, shutter speed, and ISO values.

For example, let us assume an aperture of f/8 at a shutter speed of 1/250th part of a second with an ISO 100 gives you a proper exposure of a particular scene. Now if you increase the aperture by one stop means from f/8 to f/11 the very setting has to be readjusted by altering other parameters shutter speed or ISO or both of them (if necessary) to achieve the same exposure that the previous setting yielded.

In this scenario if you keep the ISO unaltered you have to double the amount of duration of this exposure as the amount of light is halved and your new shutter speed will be 1/125th part of a second. Or if you don’t want to alter the shutter speed to avoid camera shake you have to increase ISO by one stop to ISO 200 to achieve the same exposure.

The following table illustrates the above example where each exposure settings yields the same exposure. Meaning they will record the same amount of light.

Exposure Compensation (EC)

Your camera light meter gets dumb when it meters off something white or black. This is a designing flaw as it is calibrated to assume 18% reflection from all the objects in the real world. It will always yield an inaccurate exposure when it is metering off something lighter or darker than middle gray.

Exposure Compensation (EC) is a technique of correcting in-camera metering errors. So to successfully meter white (which reflects more than 18% of incident light) and black (which reflects less than 18% of incident light) subject you have to overexpose or underexpose intentionally.

RAW and JPEG

Digital cameras produce digital files and that are saved in different file formats. If you do not know the differences between them, for now, I would strongly recommend you to shoot raw and completely ignore jpeg.

Histogram

The histogram represents the tonal distribution of photographic exposure. The darkest values are presented on the extreme left and lightest values are presented on the extreme right and midtone values are presented in between. It gives you a quick overview of what exposure you are going to achieve.

Dynamic Range

The concept of the dynamic range must be understood if you’re shooting outdoors. Quickly scanning through a scene gives you an idea of the darkest and the lightest part of it. For example, if the lightest part of that scene emits a luminance of 50,000 cd/m2 (candelas per meter squared) and the darkest part of that scene emits .5 cd/m2 then you are in a 100,000:1 dynamic range situation/challenge.

The dynamic range is the difference between the lightest and the darkest part of a scene. And you must know how much of it your camera can actually capture. Modern SLRs have 12 stops of dynamic range and some manufacturers claim 14 stops of dynamic range where our visual system has a dynamic range of arguably 18 to 20 stops.

The Zone System in Digital Photography

If you are a digital shooter then you should not be so concerned about zones, the classification of gray tones in your composition. The Zone System was invented by the greatest photographer Ansel Adams to pre-visualize photographic prints. This technique is long gone with the invention of digital photography; it is even more obscured with color photographs and raw capture.

Still, this old technique may give you some insight into photographic tones and help you develop some interesting tonal relationship in post-production.

Sunny 16 or Sunny f/16

Of course you’re not just bound to stay with f/16; you can increase or decrease aperture settings in your camera to adjust the desired depth-of-field. In order to have an equivalent exposure you have to multiply or divide the base Shutter Speed or ISO with how many stops you increase or decrease.

The following table shows the equivalent exposures when base settings is set to f/16 at 1/200 sec, ISO 200.