Different kinds of camera filters
Below is a list of popular filters but it is by no means exhaustive. Remember that filters can come in either square or round pieces of glass.
1. UV
Absorbs Ultraviolet rays. In sunny and outdoor photography, UV rays can sometimes makes the landscape hazy. Removing UV rays improve the clarity making the features more distinct. Photographers also like to use this filter as a permanent lens protector to protect the first piece of glass or the front element of the lens.
2. Neutral
This filter consists of an optical clear piece of glass that does not affect the colour balance. However, do remember that all type of filter will not allow 100% of the light to pass through. When using filters please take into account of your aperture and shutter speed.
3. Skylight 1B
As the name implies, this filter absorbs the excessive blue colour from skies to give the overall image a more balanced colour. Some photographers also use this filer as a permanent lens protector.
4. Polarizers
These filters only allow light which hits the glass at a certain angle and reflect the rest away. Main uses are to remove reflections and scatter light. More details are explained in the Polarising filter article.
5. Coloured filters
Such filters absorb light of certain colours. The aim is to restore the colour balance in unusual light situations. For example photos taken under fluorescent light have an unusual colour cast which can be absorb by using a FL filter. However due to the widespread use of digital photography where colour balance can easily be adjusted in photo editing software especially if photos are taken in the RAW format, very few photographers are still using these coloured filters.
6. Special effect filters
There exist filters to create special effects. For example a softener filter for portraits, or a sepia filter to recreate the effect of old photos. However with the rapid improvement on digital image enhancement, a lot of these special effects can easily be created in photo editing software.