Last time, we talked about the different types of lenses based on their focal lengths. We also discussed special purpose lenses that help you capture shots you couldn’t otherwise shoot with conventional lenses.
Today we’ll talk about prime and zoom lenses, which is another way of distinguishing various types of lenses. But what’s the difference between the two really? There are a number of them, so let’s use the magic of tables to illustrate it for you.
|Maximum Aperture||Could be up to f/0.95||f/2.8|
|Image Quality||Varies by lens||Varies by lens|
Now let’s make sense of what I just put up there, starting with the focal length.
The focal length is the major distinguishing factor between prime and zoom lenses.
Because of their variable focal lengths, people who are after convenience often prefer zoom lenses since you could easily zoom to a particular focal length without moving an inch from where you’re standing. Thus, zoom lenses are popular among photojournalists.
Prime lenses, meanwhile, can be quite limiting in this aspect since you only have on focal length to work with. However, prime lens users simply “zoom by foot”, to counter this limitation. What it means is that you simply move closer to your subject if you want to zoom in, or back up when you want to zoom out. Simple.
Weight and Size
Zoom lenses have a more complicated design than prime lenses. The primary reason is that a zoom lens needs to cover several focal lengths, while a prime lens needs only one.
The design gets even more complicated if a zoom lens has a constant maximum aperture* (often found in professional-level zooms), and additional lens elements to prevent flares, distortions, and other problems that could be encountered in such a complex design. Because of its complexity, a zoom lens tends to be bigger and heavier than a prime lens of the similar focal length.
* – Constant maximum aperture is found in many professional-level lenses. What it means is that the aperture does not change even if you zoom in or zoom out your lens. So if you are shooting at 24mm at f/2.8, the aperture size will remain the same even if you zoom in at 70mm.
The Canon 17-55mm f/2.8 IS USM. The fact that it is a zoom lens, and that it has a constant maximum aperture of f/2.8, it has image stabilization and an ultra-silent motor makes this a pretty heavy lens.
On the other hand, prime lenses have simpler designs relative to zooms. Because of that, they tend to be smaller and lighter than zoom lenses of similar focal lengths.
Keep in mind that I’m making generalizations here for the sake of brevity. Of course you’ll be able to find zoom lenses smaller and lighter than prime lenses (for example, compare the Canon EF-S 18-55 f/3.5-5.6 to a Canon 50 f/1.2L and you’ll get what I mean). The actual size and weight depend on a number of factors, including the additional lens elements, maximum aperture, and the presence of autofocus motors, to name a few.
Due to the nature of zoom lenses, they are often limited to a maximum aperture of f/2.8. Why? Because making the maximum aperture bigger than f/2.8 would also increase the size of the lens significantly.
Prime lenses, meanwhile, could have a maximum aperture of f/0.95! This is made possible because of the fixed focal length design of a prime lens.
Now this can be quite a touchy subject. Some people would argue that prime lenses offer better image quality compared to zoom lenses. This is true up to some point, however, the truth is that it all depends on the lenses that you’re comparing. Newer zoom lenses can sometimes outperform prime lenses, and vise versa.
Thus, if you’re after high image quality, I would recommend that you don’t skimp and buy the best lens that you could get your hands on, be it a zoom or a prime.