imaging optics (zoom lens system)

My question is about imaging optics. I will explain it if someone faces difficulty in understanding my question. I want to know about zoom lens system. I also want to calculate the zoom positions in a "zoom lens system".

Hi aasif

No double posting. You may re-edit the first post for more clarity and requests.

well, everytime you post, please especify well your question.
zoom location could be calculate, using focus point of lenses, and the ditance between focus point and the center of lens. do you have just convex lens or concave and other types (astigmate, cylinder, spherical...) too? take a look at Balanis standard antenna book.

and, please do as ramesh sed. edit your post as i do here :),

marti

the details of the question are the following:
1.we have two focal lengths
2.we want to design the zoom lens using the both focal lengths
3.how the no of lenses used will be calculated?
4.how the zoom positions will be calculated?
5. how the zoom ratios will be calculated?
6.what is the procedure for zoom positions greater than two?