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Focusing and Depth of Field (DOF)

Focus Mode Settings     Separating Focus from Exposure     Where and How To Focus     Summary and Caveats

In this tutorial, I deal with auto-focus modes, focusing routines, where to set focus and depth of field.

As my tutorials are intended for most makes and types of digital camera, I will refer broadly to focus mode, menu and button control options, and nomenclature.

Focus Mode Settings (Autofocus)

Single Point of Focus     What are You Shooting?

Focus mode settings vary from camera to camera, but most enthusiast and pro models offer similar options.

Single Point of Focus

In most circumstances, it's best to set focus with a single focus point; there is one plane of sharp focus, and ideally you should choose where to place it yourself. Multi-point/ auto-area/ wide allows the camera choose one or more near-field and sharply contrasting objects to set focus on; such objects are often not the subject of the photo, nor the point for best depth of field (more on this later). Unless it helps to laterally track a moving subject, forget multi-point/ auto-area/ wide - choose single / flexible spot.

Most cameras allow you to move the single/ flexible spot around with the left/ right/ up/ down arrows of a control dial (or joystick); and with touch screens, the focus point can be set with a single touch. Moving the focus point is most useful with cameras that have contrast detection or hybrid focusing (CSCscompactssuper-zoom / bridge) where you can place it almost anywhere in the frame. DSLRs usually only give you a grid of focus points around the middle of the frame, and whichever one you choose (the centre one is usually most responsive), you may still need to move the camera to set focus and re-compose to take the shot - more on this later.

What are You Shooting?

We often need different settings for stationary and moving subjects so the camera will focus as required:

For sports photography, or shooting anything that moves quickly, you'll benefit from a focus mode that will continuously track (AF-C) or lock-on to the subject. Camera options vary with this; just try each tracking option and use the one that works best for you. DSLRs are usually best at this, but technology moves on, and some compact system cameras (CSCs) - such as the Olympus OMD-EM1, Fuji XT1 and Sony a6000 - are very good at continuous focusing and object tracking.

For landscape, portraiture and everything else, where both you and your subject are stationary, it's mostly best to switch object tracking off and use AF-S / one-shot focusing so the camera can easily find focus and hold it. Again, this depends how the focus modes are oriented on your particular camera; you might have to toggle each option off or change to a defined AF-S/ one-shot/ single focus setting.

Cameras often have an auto mode that tracks the subject if it detects it's moving or holds focus if it's stationary (AF-A) - ideal, if it works reliably. However, this may not work reliably for the focus and recompose technique. Check to see if it holds focus; if it doesn't, use AF-S / one-shot for stationary subjects.

Separating Focus from Exposure

How to Check     Remedy     Workarounds

Some cameras, by default, lock focus together with exposure when you half depress the shutter button.

This is fine if you shoot in manual exposure, or if you're able to correctly position the focus point without tilting the camera away from the scene. But if you're using a DSLR (all the focus points around the centre) in programmed auto, aperture priority or shutter priority, and you need to focus towards the bottom of the frame, you'll have to tilt the camera downwards to set focus. When you then re-frame with the shutter button half depressed and take the shot, the image is likely to be incorrectly exposed, because what's now in the frame is different from when you locked the exposure.

Other cameras, by default, continue to adjust exposure as required with the shutter button half depressed.

How to Check

To check what your camera does when you half depress the shutter button, just point your camera at a dark area, half depress the button and keep it held while you move the camera to face a brighter scene. When you do this in aperture priority, the shutter speed should rise; if it doesn't, the exposure was locked.

In shutter priority, the aperture would decrease (go to a higher f/ number). However, shutter priority is often used with auto ISO, so the f/ number may stay fixed and the ISO could change instead. Similarly, in programmed auto, either/ both aperture and shutter speed (and perhaps ISO too) could change.

It's best to test this in aperture priority.

Remedy

To remedy this, look through your camera's menu settings to see if you can set the shutter button to just lock focus when half-depressed and continue to automatically adjust exposure as required (this doesn't apply when shooting in manual exposure - of course). If there isn't a specific option in the menu, try switching to centre weighted metering. This usually fixes the issue on Canon cameras; it also dispenses with other idiosyncrasies (more later).

Workarounds

Some cameras simply won't let you separate focus from exposure with the shutter button half pressed, so you'll have to use a workaround method when required. These methods include Exposure Lock, Back Button Focus, using manual exposure or manual focus.

Exposure Lock:  To do this, you'll have to check/ alter a few settings in the menu:

  • Make sure the exposure lock button (usually marked AEL, AF/AE or * on Canon) is set to lock exposure only (not both exposure and focus). This is the default on Canon cameras.
  • Select your preferred action for this button. Options often include the following: Press once to lock and again to unlock exposure; press and hold down to lock exposure and release to unlock; and timed lock where exposure is locked a number of seconds (usually timed with the metering - default on Canon).

Once setup, just use the exposure lock button (in your chosen configuration) with the scene framed for the composition before moving the camera momentarily to set focus.

Back Button Focus:  To do this, go to the menu and set up the AEL, * or AE/AF button to only lock focus; and, as with exposure lock above, select your preferred action for the button. Exposure will adjust automatically until you press the shutter button.

Alternatively, some cameras have a separate AF-On button; this could be used for the above technique leaving the AEL, * or AE/AF button free to use with other configurations. If you decide to use this, be sure to make any necessary changes in the menu settings to ensure that focus cannot be reset with the shutter button.

What I do

CSC/ Compact:  With a live view camera (CSCSLTsuper-zoom / bridge, compact), I shoot in manual exposure, or aperture priority with exposure compensation (if I can get exposure lock off the shutter button), and use the live histogram to optimise exposure for most shots.

For focusing, I usually use the centre focus point and move the camera to focus and recompose, as this is quicker (and more accurate for depth of field focusing). This way, exposure is either safely locked in manual, or continually adjusted in aperture priority.

DSLR:  With a DSLR, I would shoot in aperture priority, initially as metered because there is no opportunity to preview the exposure as there is with a dedicated live view design. (Any exposure optimisation can only take place after reviewing [AKA "chimping"] the shot and reshooting.)

For focusing, again I would mostly use the centre focus point and move the camera to focus and recompose. If necessary, I would use the exposure lock method, because it more easily transfers from one camera to another at the default settings; it also deals with the issue of focus weighted metering (See Summary and Caveats at  the bottom).

Where and How To Focus

Subject Priority Focusing     Quickly Moving Subjects     Depth of Field Focusing

So now you have a single focus point working independently from exposure; where should we position it?

Subject Priority Focusing:

If you have a single subject, it's easy: Just frame-up the shot as you want it, move the focus point directly over the subject, half depress the shutter to set focus, and once it's confirmed (usually a green light and/ or beep), take the shot. Easy!

I call this "Subject Priority Focusing" because you're simply making sure your subject is directly at the plane of focus irrespective of magnification, aperture, camera to subject distance and consequential depth of field.

In fact, photographers often use wide apertures and arrange the subject a suitable distance from background elements in order to separate the sharply focused subject from the out-of-focus background. The out-of-focus area is often referred to as "Bokeh", and the subjective quality and smooth appearance of this can be a consideration when buying a lens.

Alternative Routines:  If you don't have a movable focus point or the available focus points don't cover where you want the subject in the frame, use the following "focus and recompose" routine:

Move the camera so the focus point is on the subject, half depress the shutter button to lock focus, then move the camera back to the desired framing / composition and take the shot. Again, this is easy, and you may prefer to use this routine rather than move the focus point.

If your camera's exposure locks with the half-depressed shutter button and you can't disable this, you will have to use the Exposure Lock method or Back Button Focusing (covered in the previous section). Alternatively, you can shoot in manual exposure so the exposure isn't affected when you tilt the camera to set focus, or set focus manually.

Isn't the subject usually in the centre of the frame?  In a snapshot perhaps; but when you put some thought into a composition, it's seldom the case.

Subjects are often better given some space to look or move into, so if they're facing or moving in a particular direction, it's better to give a little more space on that side. With a stronger, more meaningful composition, the subject's eyes, or wherever is priority for focus, are unlikely to coincide with the centre of the frame.

Quickly Moving Subjects

Sports, animals and playing children are examples of where moving subjects require special consideration.

You will mostly benefit from using continuous/ servo focusing so focus is carried with the subject as it gets nearer or farther from the camera. Also, some cameras offer a form of lateral/ 3D or dynamic area object tracking which can be useful for subjects moving unpredictably.

Panning:  Panning is the technique of following a moving subject with the camera, and it creates great action shots! When you move your camera laterally, following the subject, the resulting image should feature a subject that looks mostly sharp against a motion-blurred background. You'll need an appropriate shutter speed - too fast and everything will be frozen still. Experiment; take a few shots at different shutter speeds to compare.

Focusing Problems:  If your camera doesn't have phase detection or hybrid focusing, you may find that your camera's focus tracking doesn't work so well. If this is the case, try to bear in mind the following in order to achieve decent shots:

  • Try to position yourself so the distance between you and the subject is constant whilst panning (such as with the subject travelling round a bend/ curve); this way, you're tracking laterally and the subject remains at the same distance thus in focus.
  • Use a smaller aperture to give greater depth of field. This makes focus precision less critical.
  • Sometimes you can plan your shot by pre-focusing on an object before the subject arrives, holding focus, panning with the subject and taking the shot when the subject passes the pre-focus point.

Successful action shots require practice and experience.

Train and Station at Grange-Over-Sands

Freezing a Subject: Sometimes we might want to freeze a moving subject in a photograph rather than depict movement.

With this train shot, I predicted that the train would stop further along the station platform than I wanted for the photo, and the camera I was using at the time didn't continuously track moving objects well, so I planned the shot in advance of the train entering the station.

Firstly, I planned the composition. The bright sun and ISO 200 allowed optimised exposure of 1/400s at f8, so I was confident of freezing the slowing train and depicting as if it were actually stationary.

With a focal length of 23mm (APS-C) at f8, I set and held focus on the platform near where the front of the train would be, as an element of subject priority whilst ensuring acceptable sharpness throughout the composition (segueing to Depth of Field Focusing below). I then waited for the train to reach the desired position and took the shot.

Depth of Field Focusing

Lots of genres of photography, such as landscape and architecture, require everything in the frame to be acceptably sharp from near to far. What's required here is a little less obvious because there is no subject, as such, to set focus on.

This is where we need to use what I call "Depth of Field Focusing".

There is a particular point at which to set focus where everything, from near to far, will be acceptably sharp. This varies with the distances involved and compositional priorities, but pragmatically, the distance at which to set focus is as follows:

  1. One-third into the depth of the scene for close quarter shots when there are no distant objects in the frame;
  2. and the "hyperfocal distance" where scenes have near-field objects and distant objects (virtual infinity) in the frame.

Scenario 1 could include interiors, gardens, courtyards or anywhere that has a defined outer boundary that you cannot see beyond. In these situations, we don't need infinity or anything beyond the boundary in focus, and the whole depth of field can be brought closer to the camera.

Scenario 2 could be a typical landscape where you have close foreground from around 4 feet away, mid ground trees, and distant mountains at infinity. Here, we need to set focus at the hyperfocal distance, and it's best to memorise a few figures for regularly used focal lengths. You can study online depth of field calculators, and you should find various apps available for your smartphone.

Here are some guide figures for popular camera formats and focal lengths.

The 8 Foot Rule

At the wide end of most standard zoom lenses, the typical hyperfocal distance is approximately 8 feet / 2.5 metres. This applies to all formats at the following equivalent apertures and focal lengths:

  • For 35mm / FF / FX format cameras - 27mm at f11
  • For APS-C / DX format cameras - 18mm at f8
  • For Micro Four Thirds (M4/3) format cameras - 14mm at f5.6
  • For 1" format cameras - 10mm at f4
  • For compacts and super zooms - 5 to 6mm at f2.8

The above 8-foot rule will give acceptable sharpness to infinity starting 4 feet back from the focus point - half the distance between the camera and the focus point

But I need more depth of field ...

If your composition has a foreground element at just 3 feet from the camera, then the focus point will need to be twice that - 6 feet.

Focusing at 6 feet away, the aperture would have to be 1 stop smaller (larger f/ number) for each format:

  • For 35mm / FF / FX format cameras - 27mm at f/16
  • For APS-C / DX format cameras - 18mm at f/11
  • For Micro Four Thirds (M4/3) format cameras - 14mm at f/8
  • For 1" format cameras - 10mm at f/5.6
  • For compacts and super zooms - 5 to 6mm at f/4

If your lens goes a little wider, then you could focus at 6ft and have acceptable sharpness back to 3ft at the following focal lengths and apertures:

  • For 35mm / FF / FX format cameras - 24mm at f/11
  • For APS-C / DX format cameras - 16mm at f/8
  • For Micro Four Thirds (M4/3) format cameras - 12mm at f/5.6
  • For compacts and super zooms - 4 to 5mm at f/2.8

Closer still ... to have sharp objects from just 2 feet away, all the way to infinity, the following figures would apply when setting focus at just 4 feet away:

  • For 35mm / FF / FX format cameras - 27mm at f/22
  • For APS-C / DX format cameras - 18mm at f/16
  • For Micro Four Thirds (M4/3) format cameras - 14mm at f/11
  • For 1" format cameras - 10mm at f/8
  • For compacts and super zooms - 5 to 6mm at f/5.6

At these apertures, however, you've introduced diffraction which could significantly degrade the image; so consider the composition and see if you could move back a little and use a stop or so wider aperture.

Again, if your lens goes a little wider, the following figures would apply when setting focus at 4 feet:

  • For 35mm / FF / FX format cameras - 24mm at f/16
  • For APS-C / DX format cameras - 16mm at f/11
  • For Micro Four Thirds (M4/3) format cameras - 12mm at f/8
  • For compacts and super zooms - 4 to 5mm at f/4

The above scenarios apply to wide-angle focal lengths where there's lots of things in the frame. For medium focal lengths and telephoto (including macro), the depth of field distribution is nearer 50:50% in front of and behind the focus point, so you should bear this in mind with focus point placement. There's usually a greater element of subject priority focusing with such focal lengths anyway.

Summary and Caveats

Hyperfocal Obsession     Focus Weighted Metering

So, in short, you need to be able to place your camera's focus point on the subject, or at a distance that makes everything in the frame acceptably sharp (whilst maintaining the correct exposure), and that's how it's done.

Hyperfocal Obsession

Don't become obsessive with the 8-foot rule.

If your wide-angle shot has mid-distance and infinity in the frame but no near field elements, then give the benefit of sharpness to the actual content. In other words, don't focus at 8 feet if the nearest element in your composition is further away.

The 8-foot rule applies compromise for acceptable sharpness from just 4 feet from the camera to infinity. But infinity will be much sharper if you focus 16ft away, and a little sharper still if you focus 60 feet away.

So what should I do?  Look for the nearest element in the frame of your composition and estimate its distance from the camera. Then look for a distinctive object that's just less than twice that distance away from you/ the camera, and set focus on that.

If there really are no near field elements in your wide-angle shot, then focus on a point just a little beyond the nearest element.

Focus Weighted Metering

Some cameras weight metering to the focus point in their default evaluative/ matrix/ pattern metering mode. Not only can this be unexpected, but for Depth of Field Focusing, it can adversely affect exposure. Basically, if you focus on a dark object, the exposure will be brighter, and if you focus on a light object, the exposure will be darker.

Personally, I think this is wrong, although I can see it can be useful for Subject Priority Focusing in auto/ point-and-shoot modes.

Manufacturers who persist in this must be predominantly portrait photographers, because they assume where you set focus is always the subject; this is clearly not the case for landscape and many other genres.

When taking more control of our camera, we need reliable and consistent metering.

Canon are one manufacturer who persist with focus weighted metering in their evaluative mode despite having "partial" which is where you'd expect such behaviour. If you have a Canon camera, simply switching the metering mode to centre weighted will eliminate focus weighted metering; it also takes exposure locking off the shutter button too Smile

Nikon applied this to the D80, and it was widely regarded as a mistake. As far as I am aware, Nikon DSLRs haven't had focus weighted metering in matrix mode since.

Remedy:  The remedy for this, on the cameras where I've witnessed it, is to switch to centre weighted metering.

The problem is also eliminated if you use the exposure lock method described above.

Please Leave Comments

I may have missed or overlooked something. I work alone; there's no proofreader, and I would appreciate positive input.

Please leave any comments in the section below.