Michael Weinstein wrote:
On 2005-02-15 13:14:39 -0500, (R.Satish) said:

can anybody tell me the difference between an ordinary zoom lens
and a teleconverter lens. what makes a teleconverter cost 4 times that
of an ordinary zoom lens.

A Canon EF 1.4x or 2x extender (teleconverter) costs $279.95
at bhphoto.com. Please show me a zoom lens for $70 with an
acceptable image quality.

also please tell me what is the difference
between a macro lens and an ordinary lens

A teleconverter is an add-on that fits between the camera and the lens
and multiplies the focal length (usually doubles it).

Usually, you can get 1.4x teleconverters and 2x teleconverters.
They enlarge the image (and thus any fault in the lens itself,
too).

The 1.4x gives you 40% more focal length for 1 step of apperture,
e.g. a 70-200mm f/4 lens becomes a 98-280mm f/5.6 lens. With
quality lenses the quality degradation is reputedly slight ---
especially if the sensor/film and not the lens is the limiting
factor.

A 2x teleconverter doubles the focal length for two steps of
apperture, e.g. a 70-200mm f/4 turns into a 140-400mm f/8.
The quality degradation is very noticable and you don't want to
use them outside exceptional situations.

You can combine teleconverters for even more degraded images.

-Wolfgang