Lenses

Lenses
"A photographic lens (or more correctly, objective) is an integrated system comprising one or more simple optical lens
elements, used for a camera or microscope. It may be fixed to the camera body, or interchangeable.
There will usually be an aperture selection mechanism for adjusting the amount of light through the lens, and a focusing mechanism.
Depending on type of camera, there may also be an integrated shutter. ..." Source: wikipedia.org

Types	Descriptions
Normal	This is the lens that most retailers sell along with the body of the camera. The most commonly sold are the 50 mm. They have an f-stop range of between f/1.2 to f/2.8. ( some are faster but more expensive)
Wide Angle	This lens are usually between 20 mm to 28 mm. They are used to take pictures with a large number of subjects or scenic views. They have a wide depth of field.
Zoom	This lens has a range of focal lengths you can use to move from one type of lens to another. You can have a wide angle, normal and telephoto lens all in one package.
Telephoto	This lens is used to photograph a distant subject such as a bird. They bring the subject closer to you like a telescope. They can run to over 500 mm
Macro	This lens is used to photograph near small objects such as a flower or insect. They have a very narrow depth of field.

The focal length is the distance between the center part of the lens and its point of focus on the subject.
An excellent addition to any lens system is a teleconverter, sometimes called teleextender.
This handy device fits between the body and the lens and doubles or triples the focal length of the lens.
For example a 50 mm lens becomes a 100 mm lens. Its easy to install and saves a lot of room in the gadget bag.
Below is a chart that will show the advantages and disadvantages of this equipment. Teleconverter

Advantages	Disadvantages
Cheaper	The effective aperture becomes smaller. A 2x (Doubles focal length) reduces the f-stop by 2. A 3x (Triples focal length) reduces the f-stop by 3.*
Increases your focal length	Can not be used with Canon EOS system.
You get a larger image for close-up pictures.	The view finder image appears dimmer. Though it does not effect the picture

* A TTL system will automatically adjust to the teleconverter.

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