Darker, medium and brighter image of a chair.

Exposure Basics Tutorial – Part 1

In Photography Basics by Kareem Alahdab Photography0 Comments

Hello everyone, I hope you’re enjoying the weekend.

Our first article is part 1 of the Exposure Basics Tutorial, which is one of the fundamentals of photography. If you’re shooting in Auto mode all the time and want to know what the camera is actually controlling, or want to better understand a major part of your toolkit as a photographer, read on below.

What is exposure?

A simple way to define exposure is how dark or bright the image is, after it has been captured by the camera. In most modes other than Auto, your camera will display an exposure bar that looks like the image below.

The middle point of the bar (zero point) denotes a balanced exposure. Going towards the right side into the positive numbers means the exposure or brightness is increasing. While going towards the left negative side means the image is going to be darker. To quantify things, every +1 to the right means a doubling of the light captured by the sensor (+1 stop), while every -1 to the left will result in the light captured being cut in half (-1 stop).
The exposure bar on the LCD screen of a Canon 5D Mark 3

The exposure bar on the LCD screen of a Canon 5D Mark 3.
شريط التعريض على شاشة كاميرا كانون 5دي مارك 3

The Exposure Triangle

If you’re shooting most of the time in Auto mode, you may not be aware that the camera is silently controlling three variables, referred to as the exposure triangle to produce an image that is neither too dark nor too bright. As a photographer understanding these variables is very important as they become a part of your creative toolkit. They can alter the mood of an image, give a sense of movement -or lack of- and sometimes they can help you take an image that would otherwise be too dark. Below is a brief explanation of these variables and how they can effect exposure.

Left: under exposed photo of a flower taken at a shutter speed of 1/800th of a second. Right: Corrected the exposure by shooting at 1/400th of a second.

Left: Under exposed image of a flower taken with a shutter speed of 1/800th of a second. Right: Corrected exposure of the same flower by reducing the shutter speed to 1/400th of a second.
اليسار: تعريض ناقص لصورة زهرة أخذت بسرعة غالق 800 جزء من الثانية. اليمين: تم تعديل التعريض بعد خفض سرعة الغالق الى 400 جزء من الثانية.

The amount of time the image sensor is exposed to the light.
The shorter the duration, the darker image.
The relationship here is a positive one. For example, if you double the amount of time the sensor is exposed to light, the image will be twice as bright (+1 stop).
Sequence: 30sec 15sec 8sec 4sec 2sec 1sec 0.5sec 1/4sec 1/8sec 1/15sec 1/30sec 1/60sec 1/125sec 1/250sec 1/500sec 1/1000sec 1/2000sec 1/4000sec
To the left, an under exposed flower shot at ISO 100. To the right, a correct exposure of the same flower when increasing the ISO to 200.

Left: Under exposed subject shot at ISO 100. Right: Correctly exposed subject at ISO 200. يسار: تعريض ناقص عند التصوير بحساسية 100. يمين: تعريض مناسب بعد رفع الحساسية الى 200.

How sensitive the image sensor is to the light.
The higher the ISO, the brighter the image.
The relationship here is a positive one. For example, if you double the ISO, the image will be twice as bright (+1 stop).
Sequence: 100ISO 200ISO 400ISO 800ISO 1600ISO 3200ISO 6400ISO 12800ISO 25600ISO
A side by side compairson of the same subject, photographed once under-exposed with an aperture of F4 and correctly exposed at an aperture of F/2.8

Left: Under-exposed subject shot with an aperture of F/4. Right: The exposure was balanced by opening or widening the aperture to F/2.8
يسار: تعريض ناقص لوردة تم تصويرها بفتحة عدسة F/4.0. يمين: تم تعديل التعريض عن طريق توسيع فتخة العدسة ل F/2.8.

The opening through which the light passes through to reach the sensor. You can control the blades within the lens to make this pathway wider or narrower via the camera.
The wider the aperture (lower f-number), the brighter the image. The narrower the aperture (higher f-number), the darker the image.
The relationship here is a negative one between the f-number and the exposure. For example, an image taken with an aperture of F/2.8 will be twice as bright as one taken with F/4.
You might have noticed that F-numbers do not increase in sequence in a normal fashion, so it is best to familiarize yourself with the sequence below and you’ll memorize it over time with enough practice.
Sequence: F/1.4 F/2 F2.8 F/4 F/5.6 F/8 F/11 F/16 F/22

Exposure increases if you

The Takeaway

The camera silently controls the brightness of an image by altering shutter speed, ISO and Aperture. Exposure is a combination of these variables, so this means you have several options to achieve any given exposure value. For example, an image captured at ISO 100, F/2.8and a shutter speed of 1/100th of a second will have the same exposure as an image captured at ISO 100, F/4 and a shutter speed of 1/50th of a second. I recommend you go over how these variables interact with exposure by putting your camera in Manual mode and testing first hand how changing each setting affects the exposure of your photo.

You will often find yourself in situations where you will have to shoot in a mode other than auto to take control of one or more of these settings to get your desired image. Part 2 of the Exposure Basics Tutorial will give examples of such scenarios and explain how you could get your desired image.

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