aperture's!

Ok, so i am trying to learn as much as i can about photography, and i am having trouble understanding what exactly the listing that cannon or sigma or tamron means when they say for example"F/4-5.6". Does this mean that the aperture can only be controlled from 4-5.6? I am reading a book on photography and they are talking about apertures from 1 all the way to 18 and beyond....can anyone shed some light? Thanks!!
Tim

They are the maximum apertures of the zoom range. A 28-135 f/3.5-5.6 has a maximum aperture of f/3.5 at 28mm and a max.aperture of f/5.6 at 135. The minimum apertures are not present in the name, but they usually are between f/22-f/36

Hi Tim,

F/4-5.6 means that 4-5.6 are the largest aperatures that particular lens has. I have a 75-300 mm 4-5.6 lens. That means at 75mm the maximum aperature I can shoot at is f4, at 300mm the max aperature I can shoot at is f5.6.

Take a look at DPReviews explanation of aperature. It will help. http://www.dpreview.co​m/learn/?/key=aperture
You can also do a search on basic photography and find sites that explain aperature well.

Jackie Boyd

That helped a bunch. Thanks!
Tim