Understanding Camera focus modes. Focus Area Clusters

Ultimate Guide to Understanding Camera Focus Modes

In Tutorials, Ultimate Guides by Stefano CaioniLeave a Comment

With particular attention to AutoFocus modes, this guide will help you understand all the Camera Focus Modes. It is part 3 of my series The Ultimate Beginner’s Guide To Landscape Photography

In part 1 I’ve introduced fundamental concepts such as exposure and depth of field.

In part 2 You’ve seen the most important camera settings such as camera shooting modes and metering modes.

In part 3 I’m going to walk you through the different AutoFocus modes and introduce you to the “intimidating” art of Manual Focus.

Part 1: Depth of Field and Exposure Triangle
Part 2: Understanding Your Camera Settings
Part 3: Understanding Camera Focus Modes

What you will find:

  1. Camera AutoFocus
    1.1 Introduction To AutoFocus
    1.2 Main AutoFocus Settings
    1.2.1 Single AutoFocus
    1.2.2 Continuous AutoFocus
    1.2.3 Hybrid AutoFocus
    1.2.4 Tracking AutoFocus
    1.3 Back Button AutoFocus
    1.4 Focus Modes by Manufacturer
    1.5 AutoFocus Points and AutoFocus Areas
    1.6 Face and Eye Detection
    1.7 Depth of Field and Focusing
  2. Manual Focus
    2.1 When To Use Manual Focus
    2.2 How To Use Manual Focus
  3. Conclusion

1. Camera AutoFocus

Today’s digital cameras are equipped with outstanding autofocus to achieve sharp photos. Also, cameras have many focus options you can choose from and it can be pretty confusing. Understanding how autofocus works if crucial to become an excellent landscape photographer.

I’ll go over some of those options in this article, talk about the most important techniques and then discuss the rarely used manual focus mode.

1.1 Introduction To AutoFocus

I won’t pretend I have the scientific knowledge to explain the exact technicalities and theories behind this, but it’s enough for me if I can at least give you an idea of how your camera and lens work together to create in focus images.

All your eyes and even your camera are able to see and capture is merely light reflected by the objects surrounding you.

Thanks to some amazing properties, light is able to carry information about the color of each object. This is a bit out of scope so if you want to know more about how light transfer information about color and how we perceive it you can read this short article. Make sure to come back after you finish. How do we see color

So what about focus?

An image is in focus when the light reflected by each point of the area that we want to be in focus converge precisely at the plane of the camera sensor. Wait it gets more complicated.

Your camera works together with the lens to change the lens distance from the digital sensor to make sure that the captured light converges exactly at the plane of the sensor.

So focusing your camera means physically moving the lens focusing group, to change the distance from the sensor and have control of where the light converges in your camera.

To simplify things and give you a more direct example take a look at the image below. The lens job is more or less similar to what your eyes do. An image you want to capture is way bigger than the sensor. For this reason the lens has to “transform” the captured image and make it much smaller to reproduce it in your photo. It does so by bending the light that enters the lens.

The inner technical details of how the autofocus system works in your camera is very complex, out of the scope of this guide and many photographers don’t even bother going that deep into the knowledge of this technical aspect. But in the future I’ll try to write an article about it for nerds like so stay tuned!

So for this article let’s focus on your camera autofocus settings. Pun intended! 😀

1.2 Main autofocus settings

DSLRs and Mirrorless camera bodies and lenses have motors to move the focusing elements toward or away from the sensor film.

Two are the main autofocus settings available on each camera then you can have other peculiar modes depending on the camera model.

Main settings you need to know:

1.2.1 Single AutoFocus

Single AutoFocus is the focus mode cameras come out of the box and it’s the first setting you should learn how to use. In this mode, when you press the shutter button halfway you will activate the focus and your camera will attempt to focus automatically on your subject. This is called locking the focus.

The camera will maintain the focus at the point as long as you maintain the shutter button pressed halfway and it will do so only once, it will not release focus until you either press the button all the way down to take the photo or release and press the shutter button halfway again. Rinse and repeat for the next shot.

1.2.2 Continuous AutoFocus

This mode is specifically designed for moving subjects. Same as for single autofocus, as long as you keep your finger halfway down on the shutter button the focus will activate and continue to follow the moving subject and move with it while you are tracking your subject. To take the photo you press the button all the way down and if you half release the shutter button after shooting, the continuous autofocus will keep following the subject until you either press all the way down again to take the photo or you fully release it.

1.2.3 Hybrid AutoFocus

This mode is not present in all camera. It combines Single and Continuous AutoFocus mode and it’s able to recognize if the subject is still or if it’s moving. If the subject is still, the camera behaves as if in single autofocus mode, otherwise if the subject starts moving the camera will automatically switch to continuous autofocus mode and attempt to follow the subject.

1.2.4 Tracking AutoFocus

Please note this mode is not present in all cameras.
This is an enhancement of Continuous AutoFocus. With this system the camera tries to identify automatically the moving subject you want to focus and it will follow that subject, attempting to ignore any other moving objects in the scene.

1.3 Back Button AutoFocus

This technique can really change the way you take photos. Basically it separates focusing from the shutter button.

As I described, normally when you press the shutter button halfway, the camera focuses and then you push it all the way to take the shot. But that means that the camera will try to refocus each time you press the shutter button even though you might not want that.

You can set one of the buttons on the back of your camera to be your autofocus button so that whenever you decide to shoot, you’re in total control and you decide if the camera is focusing or not. The benefit of delegating focus to a button other than the shutter is that you can shoot compose, focus and shoot a photo and then shoot another photo without the need of focusing again in-between focus. You could even re-compose your photo without worrying that the camera is going to try to re-focus.

This is especially useful if you’re shooting wildlife.

If for example you have a bird in a tree and it’s surrounded by branches. Without back button focus the camera will try to re-focus again and again each time you shoot and with all the branches surrounding the bird it will struggle to find the subject. With back button focus you’ll lock the focus once and won’t worry about losing it in between shot.

1.4 Focus Modes by Manufacturer

As I said each camera manufacturer calls the different autofocus modes differently, here’s a useful list for you to identify those modes in your camera.

Olympus

Single Shot: S-AF
Continuous: C-AF
Hybrid: N/A
Tracking: C-AF+TR

Nikon

Single Shot: AF-S
Continuous: AF-C
Hybrid: AF-A

Canon

Single Shot: ONE SHOT
Continuous: AI SERVO
Hybrid: AI FOCUS

Panasonic

Single Shot: AFS
Continuous: AFC
Hybrid: AFF

Pentax

Single Shot: AF.S
Continuous: AF.C
Hybrid: AF.A

Sony

Single Shot: AF-S
Continuous: AF-C

Fuji

Single Shot: AF-S
Continuous: AF-C
Hybrid: AF-A

1.5 Autofocus Points and Autofocus Areas

I haven’t talked yet about the combination of settings you can use for focusing together with the modes introduced above. Your focus modes can work with focus points and focus areas.

To understand focus points you can think for a moment of the explanation I gave you about the different metering modes in part 2 of this series.

When you look at a scene you know that of all the view in front of you, your camera has to choose one particular distance in your scene and hope that that distance is on your subject in order to have a sharp image.

Cameras have a number (different for each brand and model) of focus points spread across the field of view. By default your camera autofocus tries to automatically identify which one of those points is falling on your subject to bring it into focus. Usually the camera will do a decent job, but it will mainly try to focus on the closest object near the center of the frame.

So there will be times when you’ll need to override that automatic mechanism, because it might have chosen the wrong point and so you’ll need to manually set the focus point yourself to force the camera to focus to a particular spot. This Manual AutoFocus (Manual AF) point selection is very useful for landscape photography especially if you have time to set the camera properly.

You can move a single autofocus point around on the screen and the camera will focus on that point. Depending on your camera you can use the arrow buttons you normally use to navigate your camera menu.

This is a really precise autofocus mode since it lets you choose a single point on your scene and allow you for great control. It’s also pretty good because it works well with almost any situation, unless your subject is moving.

In the image below you can see the viewfinder of my Olympus OM-D EM-1 Mark II. Each of the empty squares represents a different focus point. The camera can either use all of them, or part of them or even one.

Understanding Camera focus modes. Focus Areas
Image Courtesy of Olympus Australia

A good example of when you could use a single point autofocus is for a bird that is resting quietly and you can focus on the eye.

Understanding Camera Autofocus | Lone Bird

You could use a cluster of points if you are photographing an animal moving against a busy background. Objects on the background might try to “compete” with the autofocus’ attention in these situation so you don’t want to use all your camera autofocus points.

Understanding Camera focus modes. Focus Area Clusters
Image Courtesy of Olympus Australia

If your subject is moving against a clean background instead the ideal setting to use in combination to your AF mode is to use all your AutoFocus Area.

Understanding Camera Autofocus | Seagulls Flying

1.6 Face And Eye Detection

As the name says, in this fully automatic mode the camera AutoFocus chases faces to focus on. Some cameras are even able to find the eyes. If you need to shoot a video this is a particularly useful mode especially if you’re filming yourself and don’t have access to your camera settings to monitor focus. Even though this feature is becoming more common in modern cameras it’s not present in all models. Also this feature only exists in mirrorless cameras since it requires image analysis.

Portrait photo taken with M.Zuiko 40-150mm F/2.8

1.7 Depth of Field and Focusing

Precise focus is possible at only one distance. At any other distance, the object will be de-focused, and will produce a blurred image. This is where depth of field becomes involved. Depth of field describes the range in a photograph, from near to far, that appears to be in focus. The more a lens is opened up – for example, to an aperture of f/4 – the less depth of field there will be (i.e. the foreground will be in focus and the background will appear blurred). If you require all the elements of your composition to appear sharper, you should stop the lens down to an aperture with a higher numerical value, such as f/16.

When you are taking headshots of people a shallower depth of field proves beneficial, as this isolates them from any distracting background detail, whereas for a landscape shot, a deeper depth of field often ensures that every detail is brought into focus.

2. Manual Focus

With today’s digital cameras, while automatic focus almost always does the job, but there are times where no matter how many times you press that shutter button it just can’t focus properly on your subject.

For those times manual focus is the best option and it’s key to a great photograph.

AF modes are very advanced, but still have their limitations. Let’s see when to use Manual Focus.

2.1 When To Use Manual Focus

Landscape Photography. Sometimes when shooting landscapes there might be objects in your foreground such as fences or bushes and your AutoFocus will get you really frustrated, putting into focus the foreground and leaving the rest of the scenery blurred. What you can do in this case is using autofocus to focus on the background excluding the disturbing foreground object from the composition. Once you have the background in focus, switch to autofocus and recompose. Now you can shoot without worrying about losing sharpness.

Low Contrast. If there’s not enough contrast in your scene your camera will struggle and it will take more time to focus. It can also miss focus completely.

Low Light. In dimly lit environments AutoFocus suffers because the lens is not able to let enough light pass through. A wide aperture such as f/1.4 or f/2.8 will be more adapt for this light condition if compared to a f/5.6 since it will let more light pass. A problem you will encounter though is that your Depth of Field can be very shallow. Switching to Manual focus and holding steady your camera while shooting will solve the problem.

Shooting Through Glass. If for example you’re on a plane and want to take a photo out of a window your camera will most probably get confused. Manual focus will solve the problem.

2.2 How To Use Manual Focus

It can be a little bit intimidating at first if you’ve never used it, but when you get the hang of it you can really obtain amazing results with much more control over your photos.

First of all you need to switch your lens to Manual Focus mode. Your lens has a switch labeled AF – MF or A – M. Flip it to MF (or M).

Now as you know the lens has a ring dedicated to focus. Normally on a zoom lens you’ll find a second ring for the zoom. Now start by bringing the viewfinder close to your eye and start twisting the focus ring. Look how the different parts of the image come into focus.

Now look at your lens from the top and notice how the focus ring has numbers indicating ft or m. Those are distances expressed in two scales, meters and feet.

If by twisting the focus ring you align one of those numbers with the mark at the fixed mark at the center you’ll know the distance where the lens is focusing. Now this is especially important for studio photographers, but when you’re outdoor you’ll need to use your eyes.

Once you’ve twisted the focus ring and approximately put your subject into focus you can use the live view mode and look in your LCD screen to fine tune your focus. By using the magnifying button you will zoom on your subject and check from the LCD in live view mode if the image is tack sharp.

Now zoom back again and if you’re happy with your focus and composition hold the camera steady, hit the shutter button. Done!

Conclusion

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