Focal LengthThe focal length of your lens effects the field of view and the magnification of the view.Field of View & MagnificationField of view is the part of the scene in front of the photographer that is visible through the camera. As your focal length gets higher (28mm, 35mm, 50mm), your field of view gets smaller.Magnification is the detail of your subjects as seen by your camera. As your focal length gets higher, you gain more magnification.
Here’s a look at how this affects different focal lengths…Wide (16-40mm)Shorter focal lengths give a wider field of view, but less magnification. Normal (40-70mm)A normal range of magnification with a field of view that’s close to what a human eye would see.Long (70-100mm)A long focal length gives less field of view, but provide greater magnification. You can shoot things a little further away. Great for portraits!Telephoto (100-400mm)Telephoto lenses allow the most magnification, but the smallest field of view. The magnification allows you shoot photos and “reach” subjects that are far away.
Zoom LensesA zoom lens can operate over different focal lengths. An example of a zoom lens is a 24-70mm. This lens can shoot both wide (towards the 24mm side) and normal (towards the 70mm side) focal lengths.A Prime LensA prime lens shoots at only one focal length. Also called a fixed focal length.Example: A Prime/Fixed Lens - A 50mm f/1.8 lens.The numbers mean the lens has a max aperture of f/1.8. There is NO zooming (using different mm), so 1.8 represents the maximum aperture value of the lens.Zoom Lenses with Variable Maximum AperturesA zoom lens that operates with different focal lengths AND different maximum apertures.Example: An 18-55mm f/3.5-5.6 lens.This is a common kit lens available with many entry level cameras (the lens that comes with the camera). The max aperture at 18mm is 3.5, and the maximum aperture at 55mm is 5.6. Meaning you can only shoot with f/3.5 at 18mm. Once you start zooming, you max aperture changes!
Zoom Lenses with A Fixed Maximum ApertureA zoom lens that maintains the same maximum aperture throughout its entire focal range.Example: A 24-70mm f/2.8 lens.Meaning that the maximum aperture at 24mm is 2.8 & the maximum aperture at 70mm is also 2.8.This is an important feature for professional photographers. Keeping that f/2.8 maintains the same depth of field at any focal length on the lens.
Different Price Points - Big Bucks!Walk into a camera store and you will notice that fixed aperture zoom lenses are more expensive then variable aperture lenses. Here’s why…Simply put, the reason is its design. More lens elements, more glass, more hardware, and more complex engineering. All of this means higher production costs and a higher price tag for you!