When you press the shutter release button, a few things happen. The camera will focus onto the subject, measure the light and take a photo. To make sure the focus is on the right subject and that the light is measured correctly you may want to set these two values yourself. Straight out of the box most, if not all, cameras are set incorrectly.
In your viewfinder or on your display, you may see several dots or squares lighting up, or just one. When there are many, you are in big trouble. That is where the camera is searching for a subject and so it may choose the wrong one. So instead of uncle Bob, a tree could be sharp.
To tell the camera where to focus on, change all these dots/squares to just one. Only then you can aim this single spot at your specific subject or part of your subject. So change this immediately! If you keep it there you will always know where the focal point (or square) is and it will become second nature to aim it straight at your subject. If you change these focal points all the time you never know where you left them the day before and you may lose valuable time when focusing on your subject (and therefore miss the shot).
From time to time you may want to move it to any location in the viewfinder if that makes it easier to focus. Make it a habit to move it back to the centre, so next time you know where it is!
When shooting sports photos you may want to change it back to multiple spots, as it may be easier to lock onto your fast moving subject. The same goes for a bird in the sky. If you can find one in Vietnam.
The second thing your camera does is checking (metering) the amount of light. Depending how you have set up your camera, it will give you a shutter speed, aperture and/or ISO. If you’re shooting in the auto mode (I am warning you, stay away from that!), it will be all three. Otherwise it will only change the one which is set to auto. In the A mode it will change the shutter speed, in the S mode it will change the aperture. If your ISO is set to automatic, it may change that one too.
If all three are set manually, you have blocked the camera’s options to improve or screw up your photo. The only thing it can do is to silently scream that you are either under- or over exposing your photo. You can see this at the horizontal line with – at one side and + at the other. If the indicator moves towards the + it means overexposing, towards the – means underexposing. This does not mean your photo is going to become bad. If you know what you are doing you can safely ignore these warning signs.
For measuring the light, you can set how big the area is where the camera is actually looking. Most cameras have three or four choices.
On my tours I always tell to ignore the metering function completely, for a good reason. Apart from maybe spot metering it is never 100% sure how big the area is where the camera will measure the light. So if you choose one and your photo is too dark/bright, you would change it and take the photo again. The next photo may still be too bright or too dark and then you change it again. So you lose valuable time. The subject may be gone, the moment may be gone. So from that point of view, choose a setting and leave it there. There is a much faster way to change the light: Exposure Compensation. Check the chapter about Exposure Compensation and see why this is the preferred way to go.
Cameras usually have three or four metering modes.
It measures an average of the whole photo, but marks where the camera focus point is set as more important than all other areas.
This is generally not the best option. If your subject is much brighter than the background, you don’t want to measure the light in the background, only on your subject. If that is the case you must narrow the measured area down. But it does have its benefits. When there is too much contrast, the camera will give you an average reading. In post processing this may be to your advantage. If an area is heavily over exposed you cannot get the details back. With a more average reading you have a higher chance to recover some of them.
The metering is weighted at the center and then averaged for the entire scene. So it evaluates the light in the middle of the frame and its surroundings and ignores the corners. This works good for close-up portraits.
It measures a smaller area, around that single focus point
A pretty good choice. You aim at the subject, the camera will measure the light on the subject (and ignore the light behind), meaning that it will be more accurate.
It measures only at a tiny part, the single focus point. This is good when the subject or important area is very small.
There is no holy grail here. Determine what works best for you and realise that huge contrasts of light are potentially fatal for your photo.
Remember that photo of your friends, where they all look dark and the background looks wonderful? This is typically a situation where a camera cannot deal with the huge contrasts of light. The foreground needs a slower setting (because there is less light) and the background needs a faster setting (because there is more light). You can’t have both. Only measure the light on your friends, so at least you can see them well in the photo. You may want to use a fill-in flash to add some light to the subject in the foreground.