Exposure in photography is what defines how bright or dark a photo is. It is the amount of light allowed into the sensor, within a certain amount of time (usually defined in milliseconds or seconds). It is often compared to a bucket and rain, that is, the size and wideness of a bucket, vs. how long it rains into the bucket vs. how much rains falls at a given moment. The wider the bucket, the more rain can fall in it at any given moment, the longer it is allowed to rain into the bucket, the longer the rain will be poured into the bucket, and the stronger the downfall the more it will fill the bucket for each raindrop. These three things are equal to aperture, shutter speed, and ISO.
When you decide on the exposure, there is no default exposure you should obtain. It depends on the photo, what you want to show in the photo, etc. But these three things you have to consider:
The shutter speed
The aperture controls the hole, which the light comes through. The lower the aperture number, the larger the hole, and the more light comes through. The lower the number, the more shallow depth of field, which creates the blurry background (known as the bokeh or bokeh effect).
If a photo is too bright, you can choose to make the hole smaller, to allow in less light. This will however broaden the depth of field (DoF), so if you want a blurry background, be aware that the higher the aperture number, the larger the DoF will be, and the less blurry background. You can change this by moving the camera closer to or away from the subject.
The shutter speed controls how fast the photo is taken. 1/4000 is fast, allowing less light in, while slower numbers, such as 1/60 and above, allow more light in, but also creates motion blur. If you’re shutter speed is too slow, you will need a tripod to stabilize the camera. If you for example want a blurry background, but there is too much light, you can make the shutter speed slower, while keeping the aperture large (that is, a low aperture number).
Finally, the ISO. This is the light sensitivity of the camera. The higher the number, the more sensitivity. However, the higher the number, the more grainy the photo will be. I suggest using ISO 100 in sunny outdoor shots, since there will be enough light anyway. Only use automatic ISO or adjust it to higher levels, when shooting indoor or during night.
These three settings control your exposure. I suggest that you get to know them and how they work. Try using the aperture mode (AV) and the shutter speed mode (TV), in order to really getting an understanding of how they work. The first will allow you to decide on the aperture, and then adjust other settings to compensate the exposure (except ISO, if it isn’t in auto), the second will let you decide how fast the shot should be, and then adjust the other settings to compensate for the exposure.
So to give some examples:
Let’s say that you want to take a portrait with a blurry background. If you don’t feel comfortable with the manual settings, put the camera in AV (aperture value), and put the aperture down as low as possible, preferable between f/1.2 and f/3.2, depending on the lens and how blurry the background should be. Be aware though that the smaller the f-stop, the shallower the depth of field. Put the f-stop too low, and you risk having most of the face out of focus. This is also depended on how far you are from the subject. The closer you are, the shallower the DoF will be. The further away, the deeper the DoF will be.
|An example of a low f-stop of f/2.8, on a 50mm lens, close to the cat. Notice the shallowness of the Depth of Field, leaving only a very small part in focus.|
In another example you wish to add motion to your photo. You can do this by adjusting the shutter speed, for example by using the TV settings (time value). The higher it is, the longer time the shutter will stay open, allowing for more motion to be visible on the photo. This is typically often used for night photos with the light trails from cars on the road.
|An example of a photo taken with a shutter speed of 5 seconds. The longer shutter speed allows more light to come in, as well as capturing the movement of the cars passing by, creating light trails.|
The ISO should only be used, when you can’t obtain the required effect with the shutter or the aperture. In case of a low-light shot, where you already have the lowest f-stop, but you don’t want motion in the photo, you will need to adjust the ISO. Just be aware that putting the ISO too high, will add noise to your photo. This can be an intended effect, in cases where you want to add a feeling of an older photo, but as a rule of thumb, always keep the ISO as low as possible.
|This photo was taken with a too high ISO. It was only on ISO 400, which normally isn’t considered high, but in this case, with direct sunlight, an aperture of f/2.8, and a shutter speed of 1/500 the ISO was simply too high.|
Personally I’m mostly focused on the aperture. In daylight I have it between f/5.6 and f/8, depending on the shot, in order to have as much in focus as possible, without having to put the shutter speed too high. It is my experience that if I put the f-stop too high, I will need a longer shutter speed, which then will create motion and make the result seem unfocused.
In night time I put the f-stop down, opening the lens as much as possible. I like the effect it gives with the blurry background, because you have the lights being blurred out, giving a special mood to the shots.
How do you make your exposure?