Basics of photography: Understanding how focusing works

Basics of photography: Understanding how focusing works

Cameras on your smartphones are great. They are convenient and they are something that you will have with you in your pocket. The best advantage is that you don’t require to carry any other extra gear! One to rule them all. Internet, phone and a camera. But just as you would want a laptop to do work(its power and tools that lets you finish your work) you would want a camera if you need a bit more power.

But when you start using your first DSLR or mirrorless, focusing can become a bit more complicated and can be easily overlooked. If you want to know about focusing and how a camera creates a picture click on this link, since that will be the base for this blog.

This post is not a difference between your smartphone and camera. This post is to help you to understand how focusing works on a camera, what kind of option that you need to choose for which scenario and how to use each option.

Note: Some of these techniques and options can vary from camera type to even what manufacturers put into the camera. Their performance can also vary(Example, Canon DLSRs are known for their quick and accurate autofocus compared to its competitors). Hence I will keep this topic general to all cameras.


A person using a mobile phone to take a photo will be all too familiar with auto focus but might have not even heard the name. Well in older cameras you would have to focus on the subject manually which means adjusting the lens so that your subject is in focus. 

But these days auto focus where the camera decides if the subject is in focus or not is more popular. Even photographers primarily use auto focus, due to its convenience and speed. 

How to use auto-focus

When it is time to focus on a subject you could either focus using the viewfinder or selecting the subject using the live view(the screen on the camera) if available. 

The viewfinder and live view have their own pros and cons. Not that one is better than the other or the viewfinder old tried and tested method.This might come to you as a surprise, both methods use two different types of auto focus, known as the phase detection auto focus or contrast detection, I have written about both below and where they are used. Modern cameras use a mix between the two to get a quick and sharp image.

Note: With mirrorless the difference between phase detection and contrast detection is becoming narrower and narrower making photographers prefer mirrorless over DSLRs.

Auto-Focus Points on camera

When you use the viewfinder there are predetermined points that generally light up when the camera is focused on that point. This can range as low as one point and can more than 40 points in more expensive cameras. 

But when you are using the live view you generally have the liberty in selecting anywhere on the screen where you want to focus. There is a reason for this and is explained later in this blog post.

How cameras autofocus – Explained

There are multiple ways that a camera can determine if an object is in focus or not. But the two commonly used methods are phase detection and contrast detection. The difference between contrast detection and phase detection and where to use them are mentioned below.

Contrast Detection

Contrast detection is the cheapest and easiest way cameras can auto focus. It is primarily or the only way that mobile phone cameras focus. Another good thing about contrast detection is that it can be quite accurate. 

Contrast detection works by adjusting the lens in different positions and the camera works to analyse contrast of each position of the lens. It finds the subject by using the point with the highest contrast. Just like a histogram that you use to know if you have the best exposure. This results in a sharp image but can be slow since the camera has to keep adjusting and analyzing to get the sharpest image. 

The result of hunting on a camera while focusing is because of this and this mostly happens when there is not enough light.

Tip: Live view will predominantly use contrast detection, since contrast detection uses the data from the sensor you have more autofocus points on the camera. That is the reason you can select anywhere on the screen and it can focus there.

Phase detection

A newer form of focusing is phase detection. This uses a separate sensor in the camera to determine if the object is in focus or not. These are more popular in DSLR than mirroless since a part of the light is reflected to the second sensor. Mirrorless cameras have the phase detection but they are behind the sensor making them less effective than the larger DSLR’s.

Phase detection is much faster in locking on the object since it doesn’t have to analyse too many images and the lens is constantly moving making it the best option for photographers who are shooting fast moving objects such as sport photography. But they can be inaccurate at times not able to get a lock on the subject.

Tip: If you’re having a moving target then it would be better to use the phase detection, you can make sure to use the phase detection focusing on the subject through the viewfinder.

Now that you understand how your camera determines how it focuses you need to understand the different types of focus

What are auto-focus points

Auto-focus points are points at which the camera can focus on. Most DSLRs or Mirrorless show these points through the viewfinder or the screen on the camera. When you half click the shutter button they light up indicating that it has locked focus on that particular point.

Tip: Some cameras help you select more than the available auto-focus points using the live view on the camera. You could also manually focus if you don’t have that option on a live view.

Some cameras even let you select multiple autofocus points. See the image for example

Different types of auto focusing Techniques 

Now that you know what is in your camera and how it works let’s move on to how to use them. There are two main ways that you can focus using the camera. They are the single autofocus and continuous autofocus. 

Note: The terms for single autofocus and continuous auto focus might differ from different brands Example: for canon it is known as Single shot and servo AI(continuous) 

Single Shot: This mode locks on to the subject and the focus will not shift after that. This is useful for subjects that are not moving. 

Servo Shot: But what if your subject is moving like a car? You will need your focus constantly focusing on the subject. This is where continuous shot works, where the camera constantly focuses on the subject even if it is moving so that you will get the best image.

Some of this might be all new to you and some you might already know. Understanding this helps you to make the wise choice on what option that you would want to use in each of the scenarios. You never want your want to be out of focused even after any 

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