A zoom lens can operate across different focal lengths. An example of a zoom lens is a 24-70mm. This lens can shoot at both wide (towards the 24mm side) and normal (towards the 70mm side) focal lengths.
A prime lens shoots at only one focal length. Also called a fixed focal length. Example of A Prime/Fixed Lens: A 50mm f/1.8 lens. Meaning the lens has a max aperture of f/1.8. There is NO zooming (using different mm), so the number 1.8 represents the maximum aperture value of the lens.
Zoom Lenses with Variable Maximum Apertures
A 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 Aperture
A 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 than 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!
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