In this article, we will see how to get it right every time! What is focus in photography? What’s the point ? What are the different modes?
I will also explain the back button focus technique to you; essential practice to know to succeed in your focusing and have very sharp photos every time.
How to get it right? Collimators in the viewfinder of a camera.
What is focus in photography?
This is the operation which consists, for a photographer, of adjusting the sharpness of the image he wants to obtain.
Simply put, this is when you press the shutter button halfway to take a photo.
There are several ways to focus: manually or automatically.
To focus manually, it’s simple, you select the M or MF position on the lens and/or on the body, you turn the ring of your lens, you look in the viewfinder and you trigger. This obviously requires having excellent eyesight, very good responsiveness and also not shaking! We might as well tell you that we are going to leave this mode aside for the moment. Let’s take a look at the automatic mode also called Autofocus or AF.
How to get it right? Autofocus and manual focus on Canon EOS mark IV camera with EF 24 lens
Autofocus works according to two criteria: contrast detection and phase correlation.
Contrast detection consists of modifying the focus by level, until the image is sharp. Sharpness being measured by the contrast between adjacent pixels (side by side).
So avoid focusing on a plain background (white wall, etc.). Try to find a point of contrast (nail in the white wall, cloud in the blue sky, etc.)
Phase correlation consists of determining the distance between the two pieces of the image. Autofocus looks at the same image along two opposite paths relative to the center of the lens. It then reduces this difference until it gets as close as possible to a clear image.
This is the same system that was already used on film SLRs. Consequently, its effectiveness no longer needs to be demonstrated! This very rapid technique allows the lens to make the necessary correction to produce a sharp image.
Which collimators to choose for successful focusing
The collimators or AF points will allow you to select the focus area of your photo. Depending on the type or brand of your device, these small squares or rectangles are more or less numerous and more or less precise. When focus is achieved, the collimators light red. And the more focus points you have on the screen, the better your camera’s ability to focus successfully. The ideal would be to have collimators present on the entire viewfinder. Indeed, the more points you have distributed across the viewfinder, the more extensive your creative possibilities are. You can then focus on a subject positioned in a corner of the frame or located further away in the image.
Conversely, if the collimators are mainly placed in the center of the viewfinder, then the choice of focus will be more limited.
The different types of collimators
There are 3 types of collimators: vertical, horizontal or cross.
- Single vertical focus points make it easy to focus on horizontal subjects.
- Simple horizontal focus points allow easy focusing on vertical subjects.
- The cross (or star-shaped for high-end devices) collimators allow you to focus on all subjects, whatever their orientation.
The different collimators in the viewfinder of a camera
Focus or MAP is done when you see one or more points lit and permanent.
At the bottom of the screen, you have a green signal which tells you that the MAP is correct. It’s time to shoot!
Autofocus modes
Autofocus modes allow you to influence the attitude of the camera to adopt depending on the circumstances.
- Automatic autofocus (AF-A): your camera decides the most appropriate mode (AF-S or AF-C) based on its analysis of the scene. This mode is most effective when you have a lot of focus points.
- Single autofocus (AF-S): When you press the shutter button halfway, your camera focuses on a specific area of the image. Use this mode when you want to precisely select the focus area or when the subject is still.
- Continuous autofocus (AF-C): This mode allows the camera to continuously focus on a moving subject. Use this mode when the subject is moving quickly (sport, animals, etc.)
Decide on the focus area
You have two options: automatic selection or manual selection.
Automatic selection: you let your camera choose where to focus. Do you think it’s a good thing for someone to choose the sharpness area of the image for you? I bet not!
Manual selection: press the assigned button and use the dial on your case to choose the desired collimator.
This way, you choose the precise location of your focus.
Cropping or focusing technique: “Focus-Recompose”
Your device does not have enough focus points distributed across the entire viewfinder and your subject is not placed on one of the focus points (the corners for example). Don’t panic, there is a solution!
Use AF-S mode, focus on the subject by choosing the central point which is the most precise, hold the shutter button halfway (the point lights up and you hear a beep), quickly reframe where appropriate looks like you and shoot! And there it is, it’s in the box!
The cropping technique with the back button: “Back Button Focus”
This technique consists of focusing no longer on the trigger, but on a button located at the back of the camera at thumb level. Focusing is then most often done on the AF-On button.
The idea is to separate focusing from shooting. So you have a shutter button independent of the focus button, which allows you to keep the same focus each time you press the shutter button.
The main advantage of the rear focus button is that it allows you to combine all focus modes: simple, continuous, manual. This is particularly effective for wildlife photography or street photography, as subject movements are often random.
If the subject is static, you press the AF-On button to focus and release it when you feel the focus is good.
If the subject is moving, you press and hold the AF-On button to follow your subject until the shutter is released.
The “BBF” technique will prevent you from messing up your focus if, for example, a subject passes into the frame at the same time. The focus remains the same. Indeed, the focus in simple mode (AF-S) tends to slip when we have low lights in particular. The camera will start to chase the image and will not always be able to find the right focus.
Also useful in many situations. For example, you are in the street, you see a pedestrian approaching… The subject moves to the place where you focused and that’s it! Also very practical for reframing, but this time you no longer need to hold the shutter button. Release the AF-On button and the focus is locked! As you will have understood, the list of advantages of back button focus is long. That said, this technique takes some practice. We tend to get confused quickly at first. But after a few days of practice, we can no longer do without it! Faster and more intuitive.
So, I hope that this article has helped you to see more clearly how autofocus and focusing work and that it will now allow you to take sharper photos.