Exposure lock

The exposure lock is the simplest way to consciously influence the exposure. It requires no prior technical knowledge, can be carried out instantly and is nevertheless so effective that even many experts and professionals use it.

The sensible idea behind it is to measure the exposure in a suitable section of the picture and to retain it for your photo with a different section. The exposure is locked in for a moment, so to speak.

Here is a typical candidate for the use of the exposure lock: A subject in backlight, the automatic exposure metering reproduces the main subject too dark because of the bright background. But I want to have Freddy nice and bright in the photo and accept a very bright or even overexposed background for that.

So a pan to the right, next to the window is a green plant. With this image detail, I switch on the exposure lock. To do this 

• either tap the shutter release or, 
• with advanced cameras, press a separate button.

More about this below. The only important aspect for the exposure is that this section has approximately the same brightness as the main subject; it doesn't matter if there is a floor, a wall or a plant.

The only thing to watch out for is if your camera focuses at the same time, then after panning back the distance might no longer be correct and you should take the exposure at a point that is at the same distance as your main subject. More about this below where I write about how to handle it

Pan back, release the shutter. And: The photo has become much brighter, now the camera has applied the exposure from the darker wall and green plant to the new section of the picture. Freddy is similarly bright and appears well exposed. The much brighter background is overexposed; this is the unavoidable consequence of exposure onto the darker parts of the picture when contrasts are high.

On compact cameras and entry-level camera models, the exposure lock is active as long as you hold the shutter button halfway down.

It is easy to try out whether your camera is one of them:

• Point the camera at any subject, press the shutter release lightly and hold it down.
• Pan the camera to a much brighter or darker frame while still holding the shutter button down.
• Press the shutter button all the way down to take a photo.
• Keeping the frame unchanged, briefly take your finger off the shutter button and take a second picture.
• Compare the two pictures:
• If they are equally bright, your camera did not lock the exposure when you pressed the shutter button, no automatic exposure lock.
• If the second picture is clearly brighter or darker, your camera has frozen the exposure after the first exposure, as long as the shutter button was pressed down - automatically activated the exposure lock.

Note: It is also possible that exposure lock is possible at all in a camera's full automatic mode. I have observed this with a Canon camera. In this case, you have to switch to the advanced modes P, S, A, M in order to use the exposure lock.

And: If your camera does not automatically activate the exposure lock when the shutter release button is pressed, it may be possible to change this in the menu settings.

If your camera activates the exposure lock while holding the shutter-release button down, it is to be used as follows:

• Point your camera at a part of the picture that has approximately the same brightness as your main subject and is at the same distance.
• Press the shutter release button halfway down.
• Compose the final image and press the shutter release button all the way down.

Advanced and professional cameras have a different behaviour, at least in their standard settings. There, even with the shutter button pressed halfway down, the exposure adjusts when you pan the camera. Then the camera will have a button accessible with the right thumb and labelled AE or AE-L, Canon has a -button. AE-L stands for ”auto exposure lock“.

Exposure lock works the same as before, except that you press the dedicated exposure lock button:

• Point your camera at a section of the picture that has the same brightness as your main subject.

It depends on your camera whether it also focuses with the exposure, you can tell if an autofocus mark lights up or not. If it does, the selected section must also be at the same distance as the main subject.

• Press the exposure lock button. With Nikon you have to keep it pressed until the shutter is released, with Canon a short press is enough and the exposure is saved until the shutter is released. Please try out how your camera behaves.

In addition, there are settings for the exposure lock in the camera menus, so that it behaves as you prefer. The full selection for this, found at least on Nikon and Canon, is:

• whether exposure and autofocus should be locked at the same time
• whether exposure can also be locked with the shutter release button
• whether you have to keep the exposure lock button pressed or not
• whether the exposure lock remains active until the next exposure or until you press the exposure lock button again.