Lenses anfd filters

There are basically three types of lenses. Standard,wide angle and telephoto. Standard lens has 50mm focal length, so any lens which has shorter focal length is wide angle and any lens which has longer focal length is a telephoto lens.
Telephoto lenses are used to take photos of objects of far distance, but then it covers a smaller near field. It can also be used to take portraits of animals, birds which are far and can not be disturbed. The important point using these lenses are blurring of distant objects, because of the camera shake which can be remedied by using a tripod.At present lenses of focal lengths of 300mm are available, but then they become large, heavy and bulky.
Wide angle lenses are used to take landscape photos, indoor family photos.the object being to include many people in one frame.Most commonly used wide angle lenses are of 18 or 28 mm.But then as low as 12 and 14 mm are also available, they are called fish eye lenses and they are very expensive.
Most of the present day digital SLR cameras are suitable to use different lenses.for different occasions different lenses can be used by interchanging them. Now a days to avoid this inconvenience combination of lenses of different focal lengths are in the market. Combination like 18-55, 18-105, 28-200, 28-300 are also available.Tele converters are a cheaper version of telephoto lens which are attached between the camera and the lens
Another type of lens is the macro lens which takes pictures of small objects at very close range. These lenses are usually used in taking pictures of insects, coins or any part of the body.
In the past I had used 28-200 lens, but because of the camera shake now I use 18-105 which gives a better quality pictures.
Filters
These are a kind of lens fitted in front of the lens.They are used for the purpose of increasing the contrast,reducing the glare and reflections and capturing the invisible light such as ultra violet light.
Types of filters are UV filters,skylight,Polaroid,ND (neutral density) and macro filters. These filters have added function protecting the main lens from water,dust etc.