Exposure – Photography 101

What if someone asked you, ”what is the first thing to learn in photography?” What will be your answer, it is obviously the ‘exposure‘. Whether you have a DSLR, or a mirror-less camera, or a compact camera or just a smartphone, if you are going to learn photography, the first thing you will have to understand and master is the exposure. It doesn’t matter how beautiful the scene you are capturing, if you couldn’t give the correct exposure, you are lost. (It is not true always, the post production may save your life up to some extent. But just pretend there is nothing called post production.)

What is Exposure?

In simple terms, ‘exposure’ is the amount of light that your sensor (or the film) exposed to, when you take a photograph. To be more precise, it is the amount of light that your sensor gets recorded. There is a difference, I’ll come to that later. The amount of light decides the brightness of your photograph. By letting the correct amount of light get recorded in your sensor, you can capture a photograph with correct exposure, in other words, a correctly lit up photograph.

As a photographer, you will have to take photographs in various places with various light conditions. That can be either natural light or artificial light. What you have to master is giving the correct exposure to your photograph in these various light conditions. Once you master it, you have a strong foundation in photography.

How to Control Exposure?

To control exposure, there are three main features in a DSLR camera (and in any type of today’s cameras). They are,

• Aperture
• Shutter Speed
• Sensor Speed.

Now let’s take one by one and see how they work and what their outcomes are.

Aperture

Aperture is the opening that controls the amount of light enters to the camera body (intensity of light). Aperture is placed inside the lens, between lens elements. The size of the opening can be regulated, and the amount of light enters to the camera is controlled accordingly. So, it is obvious that, larger Apertures take in more light which leads to higher exposures and smaller Apertures take in lesser light which leads to lower exposures. The opening is also referred as ‘pupil’, since its functionality is exactly same as the functionality of pupil in human eye. As an additional note, the entire camera technology is based on the functionality of human eye.

f-number

‘f-number’ is the measurement of aperture (ex. f/2.8, f/4). But don’t be mistaken that f-number indicates the aperture diameter, it does not. Instead, f-number represents the ratio of focal length to aperture diameter.

To understand f-number clearly, please read the extensive article on ‘Aperture’.

So you must be clear that, higher the f-number, lower the exposure and lower the f-nmber, higher the exposure. Also, do notice the way I wrote the f-number. It is always written as f/N (with a hooked f), where N is the f-number (Ex. f/8, f/2.8). I have explained why it is written that way in the Aperture article. Make sure you understand it properly. Some do not follow this way, but this is the accepted way of writing f-number.

Below is the standard series of f-numbers.

f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45, f/64, f/90, f/128, etc.

With each stop increment, light gathering power of the lens drops to half of the previous one. But in most of modern cameras, there are number of intermediate f-numbers in between the standard f-numbers.

Effect of Aperture

Even though aperture is used to control the exposure, it has its own side effect, which can add an expressive photographic value to the image. It is called the ‘depth-of-field’.

Depth-of-field is the distance between the nearest and the furthest objects giving a focused image.

Let’s see some examples.

Here you can see that all the objects in this image is well focused (almost) in equal state. This is called a ‘wide depth-of-field’ in photography. Distance between the nearest and the furthest objects giving a focused image is high in this one. But now check this image.

In this photo, only the apple is focused. Both foreground and background is de-focused. Even the rear area of apple is also de-focused. The distance where objects are focused is very small, hence this is called ‘shallow depth-of-field’.

Both these photos are taken with same camera, same lens, same lighting conditions and in the same distance. Then what caused this difference? It is the aperture. When you go for larger apertures (lower f-numbers), you will get a shallow depth-of-field, and when you go for smaller apertures (higher f-numbers), you will get wide depth-of-field.

Read the article on Aperture to see a demonstration on how aperture affects depth-of-field.

Shallow depth of field is widely used by photographers to create artistic photographs. Because, a de-focused background can strongly focus the viewers attention to the subject. See the below photograph.

Not only aperture, there are some other factors affecting the depth of field. They are,

• Focal length
• Distance between camera and the object
• Sensor size

Depth of field is a whole another topic to discuss. Let us discuss that in another article. Just keep in mind that if you have enough light sources (and you don’t have to worry about exposure), you can play with aperture just to adjust the depth of field to create stunning images.

Shutter Speed

Let’s come to the second feature that regulates the exposure. Shutter is the gate that regulates the amount of time, that light rays are allowed to hit the sensor. You know in every camera, once you press the shutter button, shutter opens for a limited period of time and light rays are allowed to move towards the sensor (or the film). Shutter speed can be controlled electronically, so the amount of light hits the sensor can be regulated accordingly.

It is pretty simple understand how the shutter works. When you use slower shutter speeds, the shutter is open for a longer period of time, allowing more light rays to hit the sensor, creating a higher exposure. On the other way, if you use higher shutter speeds, the shutter is opened for shorter period of time, allowing lesser light rays to hit the sensor, thus create lower exposures.

In all the present cameras, shutter is situated inside the camera body in front of the digital sensor (or film). They are called focal plane shutters. But there were older cameras where shutter was situated inside the lens, and in some, in front of the lens. The earliest and most primitive shutter was the mere lens cap. The photographer had to open the lens cap, allow enough time to get the film exposed and close the lens cap, all by himself.

Shutter speeds are indicated as numbers like 60, 125, 200. But what they really mean are their inverse value in seconds. As an example, 60 means 1/60 seconds, 125 means 1/125 seconds and 200 means 1/200 seconds. That means 60 will give you higher exposure than 125 or 200.

Effect of Shutter Speed

Unlike Aperture, we can’t change shutter speed at liberty. The desired shutter speed depends on what type of object you are shooting. If you are shooting a moving object, slow shutter speeds may result in ‘motion blur’. Motion Blur occurs when a moving object gets recorded on more than one place in the frame, due to its motion. When the shutter speed is not sufficient enough, that can happen.

Not only the motion of the object, but also jerks of the hands may result in motion blur. Higher the focal length, higher the motion blur due to jerks. Because, when you are in high focal lengths, even the tiniest motion of camera will result in large deviation of the frame. So, even if your object is a still one, you can’t lower the shutter speed too much if you holding the camera by hand. In that case, you have to use a tripod or at least a mono pod to go for lower shutter speeds.

Above photograph is taken at a very low shutter speed, 1/2 seconds. The subject is still but the image is blurred due to the jerk of the hand.

But don’t forget, motion blur can also be used as a way to create beautiful images.

This is a masterpiece from veteran photographer Mr. Henry Rajakaruna (MFIAP). He has experimented on slow shutter speed photography for decades and developed his own style called ‘Rajakaruna Style’.

This is another application of motion blur to create beautiful images. It is called panning.

Using slow shutter to create artistic images is a vast area to discuss, let’s talk about it in another article. What you have to remember is, when you use the shutter speed as a way to control exposure, you have to take motions of the object also into the account and come a optimal value that suits both the requirements.

Sensor Speed

Sensor speed is the third and last feature to control the exposure. Literally, it has to be the last option to adjust the exposure. I’ll come to that later. Now, if you remember, I told at the very beginning that there is a difference between ‘the amount of light the sensor exposed to’ and ‘the amount of light the sensor gets recorded’. Obviously there is a difference, and that is where ‘sensor speed’ comes into action.

While the amount of light the sensor exposed to is fixed, the exposure can be changed by adjusting the sensor speed. Sensor speed means the sensor’s ability (speed) to record light. By adjusting the sensor speed, different amounts of light can be recorded with same given light. When sensor speed is high, the amount of light recorded is high, hence the exposure is high. And when the sensor speed is low, the amount of light recorded is low, then the exposure is low.

That is why I told you that there is a difference between ‘the amount of light the sensor exposed to’ and ‘the amount of light the sensor get recorded’. So, when you cannot the control the actual amount of light furthermore (due practical reasons and artistic requirements), you can adjust sensor’s speed of recording light.

Sensor speed or sensitivity is measured in ISO. In the past, there were numerous methods to measure sensor speed, but for the last decades ISO is the accepted way of measuring the sensor speed. In modern DSLR cameras, ISO series would look like

100, 125, 160, 200, 250, 320, 400, 500, 640, 800,1000, 1250, 1600, 2000, 2500, 3200, 4000, 5000 etc.

In the era of film cameras, people didn’t have the luxury to change the ISO value just by rotating a dial. At the time, ISO value is a property of the film, so you would have only one ISO value with a given film. To change it you would have to change the whole film.

Effect of Sensor Speed

You have to well understand that, in both the other features we talked about above, we adjust the exposure optically (in simple terms, by adjusting the actual light). Using Aperture, we control the intensity of light and using Shutter Speed we control the duration of light. But here, we adjust the exposure digitally, by enhancing the light signal within the sensor. Simply we record the light which is not there actually. So there has to be a cost. And that cost is Noise (also called Grain). Higher the sensor speed, higher the amount of noise. Check the below images.

You might not be able see the difference clearly. Let’s zoom into these images and check the difference.

These photos are captured in day light. But, when you shoot in low light, the amount of noise increases drastically with sensor speed. But today’s many high end cameras have reduced the amount of noise considerably, even in higher ISO values. But if you have an entry level or mid range camera, you don’t have that luxury, still.

That is why I told you earlier that, sensor speed has to be the last option to adjust exposure. Only, if you can’t increase the exposure optically (by aperture and shutter speed), you have to consider increasing sensor speed as the last option. Otherwise you will have to pay for it with picture quality. Some say that noise can also be used to create artistic images, but I don’t buy it, still.

Final Verdict

To summarize, what we have discussed, Exposure means the amount of light the sensor (or film) gets recorded when you take a photograph. That decides the brightness of the image, so we have to keep it perfect. There are three features in your camera to control exposure, namely, Aperture, Shutter Speed, and Sensor Speed. Apart from controlling exposure, they all three have their own effects to the photograph, if used wisely, which can add artistic value to your photograph.

Two of them, namely Aperture and Shutter Speed control the exposure optically, where the other, Sensor Speed, control the exposure digitally. Therefore sensor speed has to be used as the last option to adjust exposure, when you can’t do it furthermore by aperture and shutter speed. Otherwise you might have to pay off with picture quality.

So that is about exposure, the most important thing to master in photography. If you have any questions or if you need further explanation, just leave a comment below.

References:

https://en.wikipedia.org/wiki/F-number

https://en.wikipedia.org/wiki/Shutter_speed

https://en.wikipedia.org/wiki/Film_speed