Most beginners don't get this but once you know, controlling your camera becomes very easy. There are several elements that controls the exposure of a photo:
1) ISO
ISO (also refer to as the film's speed) determines the light sensitivity of the camera's sensor or film, the higher the number, the more light sensitive the light sensor (or film) is. You might ask, if that is the case why don't people just use high ISO settings such as ISO 3200 or above; you have to bear in mind that the higher the ISO, the more grainy the photos will look. Therefore, unless you want to make your photos very grainy, best to choose the lowest ISO possible given the lighting condition. Usually, if the environment is very bright (such as a sunny day and you are outdoor), best to choose the lowest ISO setting possible. For some camera, the lowest ISO setting is ISO 200 (or ISO 100). A lower ISO will means that the photos will be smoother, and it's suitable for portraits and landscape.
2) Aperture
Apertures is basically the hole on the lens where lights gets through i.e. the smaller the hole, the less lights can get through to the sensor given the same amount of time. Different lenses will have different apertures, generally a standard lens can have size f/3.5 to f/32, more expensive lenses usually have bigger aperture such as f/1.4 to f/16. The lower the number, the larger the aperture i.e. f/1.4 is a bigger hole than f/32.
The natural question followed will then be "When should I use a bigger aperture, and when to use a smaller one?" Generally, you would want to use a bigger aperture when you want to take portrait i.e. a f/2.8 or below depending on your lens. People generally want to use a smaller aperture when they want to take landscape (i.e. f/9 or above).
A larger aperture will give a "shallower" depth of view i.e. only the object in focus will be clear and the background will be blurred out. A small aperture will give a "deeper" depth of views i.e. both the object and the background in the photo will be in focus i.e. as you may seen in many landscape shot (usually f/9 or smaller aperture such as f/16)
You may now turn your camera to "A-mode" i.e. aperture priority mode, where you can set your preferred aperture size (by rolling the wheel) and do some test shots with different aperture sizes. While in "A-mode", you can choose your preferred aperture size and the camera will automatically choose the appropriate shutter speed to give the correct exposure. You may not be clear on the notations that cameras use for shutter speed, so please see below:
1" = one second
2" = two seconds
30 = 1/30th seconds
125 = 1/125th seconds etc
please note that 1/125th second is faster than 1/30th seconds; and 1/30th seconds is faster than 2 seconds and so on...
It is important to know that 1/30th seconds is the slowest shutter speed that you could chose if you are hand-holding your camera, anything slower than that e.g. 1/15th sec will create shaky photos. So most people will turn the camera to "A-mode" and choose their preferred aperture size and let the camera to determine the correct shutter speed that is faster than 1/30th seconds. If you find that the shutter speed is slower than 1/30th second even after your used the largest aperture size, then you could increase the ISO (you may now try a few test shots)
3) Shutter speed
Shutter speed is the length of time that the aperture is opened. As mentioned above, the lowest shutter speed that you can choose when you are hand-holding your camera is 1/30th seconds (i.e. reading 30 in your camera's setting screen). For shutter speed slower than 1/30th seconds, you will need to put your camera on a tripod in order to create sharp but not shaky photos.
"When will people use slow shutter speed?" Sometimes, people will use a slower shutter speed for landscape photos because the landscape won't move. i.e. they could put the camera on the tripod and set a very low aperture size and low ISO setting. In that case, the photos will contain the most details of the landscape (see "deeper depth of views" mentioned above)
See my samples photos above, the one with big aperture has a blurred background while the one with small aperture is very clear through the photo.
I hope this will be useful : )
KC
