Used correctly, exposure lock saves time and headaches
The exposure lock function on your camera does exactly what it says. It will take an exposure reading at any point and lock it into your cameras memory once you hit the "exposure lock button". Normally the reading stays locked for a period of around 10 - 15 seconds before re-setting itself. This should be enough time for you to re-compose and take the shot.
This feature is actually one of the most used buttons on any of my cameras. There are times when I just don’t have the time to mess about with:
However, I still need to know I have the right exposure there and then.
How does exposure lock work and when to use it?
As I mentioned in the previous chapter, this function works in a similar way to the spot metering that many cameras have. When faced with a large area that you wish to photograph, you may have many differing light readings in the scene meaning confusion for your light meter. Some could be overly bright and some overly dark.
Let's say you are photographing through a dark arch for instance, as in the image below. (Please excuse the web quality).
Your camera's natural instinct, if using the "evaluative" or standard metering, is to meter for the largest area in view. In this case, that is the interior of the arch. As it is dark it will overcompensate by giving a slow shutter speed or large aperture. This is to allow more light in and therefore "overexpose" the outside (see fig.1).
What I would do in this situation is:
You could also do this with a zoom lens which does the same job but allows you to stay in the same place. Great if the area you are shooting is inaccessible.
Now we have an image that is well exposed outside and underexposed inside (see fig.2). Remember, the golden rule is that you can pull details from a darkened or underexposed area but may struggle to put them back to an overexposed or overly light area (as done in fig.3).
What about shooting in RAW?
This is the case even in RAW sometimes. Bad news for brides and their gorgeous dresses so get it right. Therefore, you are better off having dark areas that you need to work on rather than overly bright areas.
In some cases, the dark arch may be quite effective as a silhouette. However, if you really want to include the details, you have 3 options open to you;
- 1Take the reading from outside, lock it in, step back and shoot using fill in flash or some other form of lighting. Maybe a reflector, a portable studio light with diffuser etc for the interior of the arch. You will end up with both areas perfectly exposed. The Pocket Wizards are excellent for this as they allow for radio-controlled, off-camera flash.
- 2Use a tripod. Take 2 images being careful not to move the camera at all in between shots. One is exposed for the exterior, one is exposed for the interior. Then merge the 2 in Photoshop or similar editing program later on. A bit tricky and time consuming, but quite effective. You can do this in a number of ways. The most effective being to mask the lighter areas in one image using the pen tool, and paste the new, darker areas into it. Try it to see which works best for you.
- 3As number 1 above but perhaps you either do not have a flash or the time to use it and no tripod. In that case, leave the arch darkened and pull out the details later on in Photoshop. Do this using the shadow/highlights tools or similar. If your camera has RAW capabilities, use them. It is much easier to manipulate this kind of shot with RAW. Pulling details from dark areas in a JPEG image can lead to some nasty noise or grain that is difficult to remove.
It takes practice and experience
For me, I could come across a situation during any kind of photography that warrants the use of this handy "locking" feature. Whatever part of the scene I want to be well exposed, I will aim the camera at it, press exposure lock, re-compose and take the shot. Whatever happens to the rest of the image, I know that the most important part, the subject, will be exposed correctly.
As a test, the next time you are out set your camera to Av or aperture priority. Have a play with the exposure lock function. As a rule, try to aim the camera at the lightest part of the scene and set the lock. Then practice pulling out the details later but watch your shutter speeds when in Aperture Priority.
Also aim at the darkest area and see the difference. Which is easier to manipulate and "save" later on? Once mastered, you will find this technique invaluable in many circumstances.
So, the next time you see a professional photographer wildly swinging his camera up, down and left to right, you have a pretty good idea what he is doing!