Advanced Tutorial 4
An underused function on modern digital cameras is the ability to lock automatic focus, automatic exposure or both, during a shoot with several images taken in quick succession, or where it would otherwise be useful to repeat the exact same settings for several shots in a sequence. Here’s how.
Using AF/AE Lock mode
As we have discovered in previous tutorials, there are two common factors of photography that are constantly changing – focus and exposure. More often than not, it will be necessary to keep changing settings on your camera to compensate for a changing focus point or light level.
In some shooting situations, however, it can be useful to fix a focus distance or a level of exposure in order that a number of shots can be taken with these factors remaining consistent. This is where the Auto Focus (AF) and Auto Exposure (AE) ‘Lock’ modes come into their own.
Some cameras have a dedicated ‘AF/AE LOCK’ button, usually on the rear, other models assign one of the function keys.
Either way, most modern digital cameras require a preliminary setup in the menu, as shown – allowing the function to be set according to your preference.
The first thing you need to decide is which function you want to control with the lock button.
There are usually three options: Exposure Lock only, Focus Lock only or a combination of the two – as you can see from the LUMIX G6 menu options below.
Once you have selected which option you want to use, you can then move on to the second setting: Lock Hold.
With this switched off, the lock button must be pressed and held with your thumb in order for the focus or exposure to be locked. As soon as you release the button, the setting is lost. By setting Lock Hold to ‘On’, however, once a focus or exposure is then locked (by pressing the button), you can release your thumb and the settings will remain locked until you switch off or change modes on the camera.
How to use the feature in practice
Having decided on which parameter it is you want to lock in the menu, you are now ready to start using the function.
Firstly let’s take AF Lock. It can be used in P (Program), A (Aperture Priority), S (Shutter Priority) or M (Manual) exposure modes, but remember it is an automatic function and so will not work in ‘Manual Focus’.
In effect, this is an alternative to the ‘half shutter press’ focus-locking function, where you compose, half-press and then hold before fully pressing to take a shot. Instead, you set focus on the subject by pressing the ‘Lock’ button, not the shutter button.
If focusing is successful (indicated by the green focus light and ‘AFL’ indication on the display), you can now recompose at your leisure and press the shutter button to take the shot at any time. The focus point will remain ready, locked at the original target distance until you do.
AE Lock works in a similar way, except it can only be used in P, A or S exposure modes (not M). Target your subject and compose your shot. Press the ‘Lock’ button and the camera’s metering system will select the correct exposure settings and lock them in.
Now you can relax, recompose and take the shot – the locked exposure settings will be used whenever you are ready. Don’t forget to use the ‘Lock Hold’ function if you know you will need to take several shots continuously with locked settings – it saves you getting cramp in your thumb.
When to use AF Lock
Using the half-pressed shutter button to lock focus on a subject, then recomposing the shot to the side of the frame is a useful and common method. But what if you need to repeat the shot, or take several from the same angle and location? Using AF Lock with Hold enables you to take many shots without having to refocus every time.
As an example, consider the shots below of vehicles; these use a fixed focus point, but have different subjects (the next vehicle) coming into position at different times.
Here we can lock focus at a fixed point (pick a point on the tarmac or the curbing) and capture moving subjects as they come in to the frame.
When to use AE Lock
Whenever you are using fully or semi-automatic exposure modes, AE Lock becomes very useful to ensure the exposure doesn’t change between shots.
A good example is when shooting a series of pictures in order to combine them into a panorama. The software for this relies on stitching together several shots taken from different angles at the same location. In order for a seamless composition, it is important that the exposure remains the same across all shots.
In the first panoramic example, without AE Lock, the change in exposure is visible – but you may not want that effect.
The second panoramic picture was taken with AE Lock on, so there is no change in brightness levels.
Hopefully, this tutorial has explained how these under-used functions can be used to make your photography a little easier.
The LUMIX Advantage
LUMIX G cameras offer an ‘AF-ON’ option in the menu (as do some top-end DSLRs) that turns the lock button into a quick AF button. Instead of half-pressing the shutter button to acquire focus, the lock button is assigned to operate the same function.
This is a useful option for users who prefer to use the shutter button solely for activating the shutter. Note: with ‘AF-ON’ mode set, it is not possible to also use ‘AE LOCK’.
So, before you move on to the next tutorial, familiarise yourself with these functions. Then try the ‘panoramic picture’ test for yourself and see how AE LOCK makes a difference to the end result.
Not sure what something means? Read our glossary