Question about lenses

Joined: 30 Aug 2004 Posts: 35

I'm always wondering what does those numbers mean behind the lenses. like 18-30mm and 3.5-4.5. what are those number. Can anyone explain me or show me where I can get explanation. Thanks a lot..

Premium Member Joined: 02 Apr 2005 Posts: 2020

Those numbers identify the focal length range of the lens, and the maximum apertures at those focal lengths respectively.

That is, for an 18-70mm, f/3.5 ~ f/4.5 lens we know that:

Its minimum focal length is 18mm and its maximum is 70mm.

We also know that at 18mm, the maximum aperture is f/3.5 and, at 70mm the maximum aperture is f/4.5.

Joined: 30 Aug 2004 Posts: 35

thanks a lot for the explanation. Now I have to find out what is aperture and focal length..he he..:-)

Joined: 18 Nov 2006 Posts: 288

It is probably time to visit the library to check out a good book on basic photography.

Joined: 30 Aug 2004 Posts: 35

Yup. I just visit the library (google :-), and I got myself a 123 photography book. Have a lot to learn, and when someday I can afford an SLR, I already know which lense I need.

Posted: Wed May 30, 2007 8:50 am

I would suggest getting a copy of John Hegecoe's book "The New Manual of Photography". He explaines all of the basic concepts in easy to understand 2-3 page sections with lots of good diagrams and photos. I highly recommend it for your basic photo library.

You can also pick up old versions of this same book real cheap. The basics haven't changed so all the information is still relevant.

You can get them from Amazon or one of the others. I like www.alibris.com for used books cheap.