Exposure Lock

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 exposure compensations or bracketing, but I need to know I have the right exposure there and then.

So how does it work and when should we 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.

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, which in this case is the interior of the arch. As it is dark it will overcompensate, and give a slow shutter speed or large aperture to allow more light in and therefore "overexposing" the outside.

What I would do in this situation is to walk to the arch, put my camera through, take a reading for the scene outside and lock in the exposure. Then move back, re-compose and take the shot.

Now we have an image that is well exposed outside and underexposed inside. Remember. the golden rule is that you can pull details from a darkened or underexposed area but never put them back to an overexposed or overly light area. Therefore, you are better off having dark areas that you need to work on rather than light areas.

In some cases, the dark arch may be quite effective as a silhouette, but it you really want to include the details; you have 3 options open to you;

1. Take the reading from outside, lock it in, step back and shoot using fill in flash for the interior of the arch. You will end up with both areas perfectly exposed.

2. Use 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 and 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.

3. As number 1 above but if you either do not have a flash or the time to use it, and no tripod, leave the arch darkened and pull out the details later on in Photoshop or your favourite editing program. 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.

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 and 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.

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!

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