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What is Exposure in Photography? - An Introduction

Exposure is an extensive subject and something that can be talked about for a long time. However, in this first blog about exposure I want to simply explain it and the different elements of exposure that are essential.

When you take a photograph, you can control the amount of light that enters your camera. If you let too much light in, you will be overexposing the image, meaning it’s too bright and washed out. On the contrary, if you don’t let enough light in, you will be underexposing it and therefore it will be too dark.

In both cases, all the details of the photograph are lost. And this balancing act is what we call exposure. To obtain the light you want in an image and make it your own, you have to control the shutter speed, aperture, and ISO (International Organization for Standardization). This trio is inseparable, as each member is responsible for something different. They rely on each other.

  • Shutter speed: controls the length of time that light enters your camera.

  • Aperture: controls how much light enters your camera.

  • ISO: controls how sensitive your camera is to light.

Shutter speed is connected with the movement. The values of shutter speed range between 1” -slow- to 1/2000 - fast- (these values are indicative, depending on your camera make and model, it can be slower and/or faster). The slower the shutter speed is the more light enters your camera and the more chance you have of blur movement. 1/60 is really the limit, any slower than this and you risk camera shake if you don’t have a tripod. On the contrary, the faster the shutter speed is the less light enters, and the more you can freeze an image.

The aperture is related to the focus, it’s what we use to gain more or less depth of field in our image. The values of aperture vary from f/2.8 -wide- to f/22 -narrow-. The wider the aperture the more light enters and the shallower the depth of field will be (less in focus). The narrower the aperture, less light enters and we have a deeper depth of field (there’s more in focus).

In both the shutter speed and aperture, the lower the number, the lighter our image is, whereas the higher the number, the darker our image is. This means that in order to get a balanced image, we must combine a slow shutter speed with a narrow focus or a fast shutter speed with a wide aperture.

Lastly, the ISO is related to sensitivity. It ranges from 100 -low- to 3200 (or more) -high-. The lower the ISO, the camera is less sensitive to light, therefore it should be used in brighter conditions, when we have a lot of light. Also, this means we have less image noise in our photograph. The higher the ISO, the more sensitive to light our camera is. We will then use a higher ISO in darker conditions, although keeping in mind that we may have more image noise.

To help us with this balancing act we have the Exposure Compensation. This is a dial that we have on our camera screen that usually ranges from -3 -darker- to +3 -lighter-. This is there to guide us. An image is correctly exposed when the dial is bang in the center, on 0. If the dial is on the left side of the dial, in the negative numbers, it’s indicating that our image is too dark and therefore there are fewer details in the shadows and more in the highlights. On the contrary, if the dial is on the right side, in the positive numbers, it’s letting us know that our image is too bright. There will be more details in the shadows but less in the highlights.

With this dial as a guide, we will vary the shutter speed, aperture, or ISO to obtain the image we want. The ISO works opposite to the shutter speed and aperture in the sense that the lower the number, the less light there will be in our image:

Shutter speed:

1” ½ ¼ 1/15 1/30 1/60 1/125 1/250 1/500 1/1000…

+light ----------------------------------------------------------------------------------> -light


f/2.8 f/4 f/5.6 f/8 f/11 f/16 f/22...

+light ---------------------------------------------------------> -light


100 200 400 800 1600 3200

-light -------------------------------------------------------------------------> +light

Although exposure might seem complicated at first, once you get the hang of it your don’t even have to think about it. It’s like driving a car, at first you have a lot of different things to think about, but with enough practice, it becomes second nature. To really master these skills I highly recommend purchasing the book Read this if you want to take great photographs by Henry Carroll:

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