Lenses come in two types: prime lenses and zoom lenses. Prime lenses have only one focal length, and are sometimes called fixed focal length lenses. The two names are interchangeable. Prime lenses are easier to make because they have to be sharp only at one focal length, making the optics a whole lot simpler than their zoom counterparts. Zoom lenses cover a range of focal lengths, giving the photographer more options than a single focal length. There was a time when having a zoom lens meant sacrificing quality for convenience because they had a reputation for not being as sharp as fixed focal length lenses, resulting in poorer image quality. They were also heavier and more expensive than prime lenses. This is not as true today, with modern manufacturing and lens design, zoom lenses that are as sharp as some fixed focal length lenses are now being produced. Modern zoom lenses are smaller, lighter, and sharper than ever. The Sony line of lenses has 12 prime lenses and 12 zoom lenses.
Prime lenses
Prime lenses have one serious advantage over zoom lenses. Due to the way that lenses are manufactured, prime lenses can have a greater maximum aperture than zoom lenses, making them much faster than most zoom lenses. Because modern zoom lenses are so much better and affordable than they used to be, many photographers don’t use prime lenses very much anymore. This is a real shame. There was a time when the lens that would come with the camera was a prime lens, usually a 50mm lens that offered a normal view. Prime lenses are great tools and should not be dismissed quickly simply because they do not offer a range. One of my favorite “walk around” lenses is the 28mm f/2.8. This prime lens is the smallest and lightest lens that Sony offers, yet it has an f/2.8 maximum aperture for great low-light shooting and amazing control over depth of field.
Zoom lenses
Modern zoom lenses have all but taken over the lens market. Why get a lens that has only one focal length when for a few dollars more (or sometimes less) you can get a single lens that covers a wide range of focal lengths? It is much more economical to purchase a single lens that can do the job of multiple lenses. The ability to cover a wide range of focal lengths makes zoom lenses very useful for today’s photographers. Instead of having to carry three or four different lenses, stopping to switch lenses every time you want a different focal length, the single zoom could be your answer. A lens like the 18-250mm f/3.5-6.3 covers focal lengths from 18mm all the way to 250mm. This makes the lens a wide-angle lens, a normal lens, and a telephoto all at the same time depending on what focal length is used.
One downside is that most zooms have a range of maximum apertures, and none of them are as fast as a good prime lens. Other than the 70-200mm f/2.8 and the 24-70mm, which both have a constant maximum aperture of f/2.8, all the other Sony zoom lenses have a wide range of maximum apertures. This can be a problem especially in low-light situations or when you want a shallow depth of field.
See also:
Lens types