Understanding Exposure

In order to create and capture the picture that you have in mind when you look at something you need to understand exposure and what it can do for you to enhance and give the exact effect you are searching for with your picture. Having a good grasp on what you want your picture to look like is an important part in taking the picture that you are aiming for and being able to manipulate it in an authentic and artistic way.

Exposure Triad

There are three things to consider when taking a picture.1. Aperture is what controls the amount of light reaching the sensor in your camera lens. 2. Shutter Speed is what control the length of time the sensor is exposed to light. 3. ISO is what controls the sensitivity of your camera’s sensor to a given amount of light. These three things are very important because they are what control the way your picture will turn out. Understanding these three things will help you be able to have the perfect exposure in order to give the desired effect.


This is what controls the area over which light can enter your camera. It can also be defined as exposure which is the amount of light that falls onto the camera’s light-sensitive surface. Aperture is the size of the opening in the lens. Like the pupil in your eye, the aperture diaphragm opens and constricts to control the amount of light passing through the lens. The ratio of the opening of a lens aperture when compared to the size of the lens, not a measurement, but a ratio, is referred to as an f/number, f/stop, focal ratio, f/ratio, or relative aperture. The formula used to assign a number to the lens opening is: f/stop = focal length / diameter of effective aperture (entrance pupil) of the lens. The smaller the number, the wider the opening.

The amount of light or exposure with vary because of these four basic factors: intensity, duration, distance between light source and subject, and modifications to the light.

Intensity, the brightness of the light: A brighter photograph is created from a sensor that has been hit by more photons which are the fundamental particle of light. When it is a darker image that means it was exposed to a lower quantity of photons.

Duration: If you increase the amount of time that a given light is emitted from a light source, you can increase the number of photons that are collected by the camera. This is going to give you a brighter picture because you have a longer time before the shutter closes.

Distance: The closer to the light source, the more photons you can capture with a camera. The further you are away, the fewer photons you can collect. According to Inverse Square Law, you get 1/4 of the light when you double the distance. This is because we are talking about area, not just distance. As light is emitted from most sources, it spreads out giving us more space to factor in.

Modifications: Changing your angle so that the light is different can give you a different feel and view. You can have your subject move into the shade or you can even create shade. There are now tools that you can purchase to create shade or more light such as reflectors, diffusers, and gels. You can measure the light’s intensity, adjust your camera settings accordingly, and then adjust them further to brighten or darken your image.

Depth of field is a function of lens aperture size, lens focal length, the distance between the subject and the camera, and something called the circle of confusion. Depending on your camera and lens, by opening your aperture to its widest settings, you will narrow the range of the focal plane to a very small distance. This can be used in photography for creative compositions with close-up photography and, most popularly, for making distant backgrounds blurry when taking portraits. Deep depth of field techniques are used commonly in landscape images.

Not only does the aperture control the amount of light passing through the lens, it affects the angle of the light rays as they transit the lens. Aperture not only serves to control the amount of light passing through a lens, it also affects the performance of a lens in terms of depth of field and sharpness.

Shutter Speed

Shutter speed is similar to blinking and it controls the duration of the exposure. When the shutter is opened or closed the sensor determines how much light is allowed to reach the sensor and the amount of time the sensor is exposed. The faster the shutter speed the shorter the exposure time. The longer shutter is open there is more light exposure which is going to give you a brighter picture.

Shutter speeds are listed as whole seconds or as fractions of a second. They are also set up so that the bigger the fraction the slower the shutter speed which means the more exposure to light. A 1/4 shutter speed with have more light exposure than a 1/200 shutter speed

It is nearly impossible to hold a camera perfectly steady for any length of time, especially for a few seconds. Therefore, an image taken with a handheld camera that covers any length of time will have some amount of blur from camera shake. You will want to keep this in mind when shooting with slow(er) shutter speeds.

A slow shutter speed will allow moving cars, runners, animals, and such to change position inside the frame of the image. Fast shutter speeds, however, are used in the opposite fashion. They are designed to freeze action versus letting it blur across the photograph. Things can become frozen in time with a fast shutter speed.

The two biggest factors in how movement is seen by the camera are: speed and distance When you double the distance from the camera to the moving subject, you will cut in half its speed through the frame. Therefore, to get the same blur, you can use cut in half the shutter speed. If the moving subject is the same distance away each time you photograph it, but you double the speed of the subject, you will have to halve the speed of your shutter to get the same amount of blur.

ISO Speed

ISO stands for International Organization of Standards is a measure of the sensitivity of a sensor to light that controls the sensitivity of your camera’s sensor to a given amount of light.

ISO is similar to the sensitivity of the rods and cones at the rear of the human eye. With your camera you can change the sensor’s sensitivity while you are shooting which is not something you can do with your eye. This a neat feature because you can get a depth of field which is when you can focus on the background or the foreground depending on how high or low your light sensitivity is.

When you adjust ISO, you are not changing the size of the pixel of your picture. You are increasing its sensitivity electronically by increasing the voltage to the sensor. The unfortunate side effect of this is called noise. The higher the ISO, the more digital noise is introduced into your image making it look grainy.

In the digital realm, there are three types of ISO: native, amplified, and simulated.

Native ISO is the ISO setting that does not require the camera to increase the voltage to the sensor

Amplified ISO is an ISO that requires an increase in voltage to the sensor.

Simulated ISO is when the camera uses a software algorithm to simulate even higher ISOs.


You have two physical controls that you can utilize inside your camera—aperture and shutter speed. You can further control the sensitivity of the sensor by adjusting the ISO on your digital camera. You can adjust exposure value up or down by doubling or halving the amount of light (aperture and shutter speed) and by doubling or halving the sensitivity of the photosensitive surface (ISO). When you allow more photons into the camera, or increase the sensitivity of the film or sensor, you will need to compensate in the opposite direction with the other camera controls.

One key to getting the photographs you want is to know how the different variables not only affect each other when exposing an image, but also knowing the different side effects of adjusting each variable (depth of field, motion blur, noise, etc).

Be sure to experiment in changing your camera settings so that you can achieve the desired objectives of your artistic vision. Take multiples of the same picture with different exposure settings until you get the exact picture you are searching for. Don’t be afraid to take what you’ve learned and try it out to better understand what you like best.

The goal in creating an exposure is to allow a specific amount of light into your camera and lens to capture your subject in a way that matches your artistic vision. Photography is art, and if you want to alter the image to be brighter (overexposed) or darker (underexposed) to better express your vision, then never think that every frame you shoot needs to meet the definition of proper exposure. It’s all about what best suits you and what you desire to capture.

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