On Most cameras these days there are at least three different options when it comes to choosing the types of light metering system you use. These are typically ‘Matrix/evaluative’, ‘Centre weighted’ and ‘Spot metering’ modes.
Usually your camera is set to the Matrix/evaluative metering out of the box and 8/10 times this usually does a pretty good job. This mode takes a reading from the entire scene and does its best to give an exposure to suit all of the elements within that scene. Centre weighted is the next option. This mode takes a reading from, as its name suggests, the middle proportion of the frame. Old school photographers tend to like this mode, myself included, as it gives fairly predictable results. I find that it is also very useful when you are shooting nature, when the animal (such a a deer for example) will typically fill the middle part of the picture, hence using the centre weighted light meter will make sure that animal will be correctly exposed for.
Now we come on to the spot metering mode (on some Canon models I believe this can be called ‘Partial’. I’m a Nikon chap so don’t quote me on that!). This mode takes a light reading from only a very small percentage of the scene, typically 2% and on most cameras it will take the reading from where the centre focus point is. I don’t tend to use this mode too much but in certain situations it can be a real bonus. For example, you could be taking a picture of a small bird that you choose to be relatively small in the frame, and by using the spot meter you can take a reading off the bird ensuring that your main subject will be properly exposed for. You may want to use the exposure lock button found on the back of your camera if you want to recompose your image once you take the reading.
For the picture above I decided to use it to achieve a slightly different result. This flower was shot at around midday and in bright sunlight, but I noticed that there was a tree above casting its shadow around the flower, plus there was a wall behind also slightly in shadow. The sun on the flower was very bright but I knew that by choosing the spot meter mode and taking a reading from the yellow centre of the flower it would correctly expose for that keeping the detail, but also it would have the effect of darkening the rest of the flower and the shadows in the background. The scene was far brighter to look at than what you see here.
These are just a couple of examples of how to use the spot meter, I’d be interested to know what your experiences are too.
I hope this has been of some use. Thanks for reading and happy shooting.