5 Reasons Why Prime Lenses Are Better Than Zooms

INTRODUCTION

If you’re into cinematography, photography or capturing images at all you’re probably aware that there are two types of camera lenses - prime lenses and zoom lenses. 

Primes have a fixed focal length, which is measured in millimetres. This means that when you put this lens on a camera, the angle of view of what it sees, how wide it is, or how much the image is magnified is set at one distance and cannot be changed.

Zooms have a range of variable focal lengths. So by moving the zoom ring on the barrel of a lens you can change how wide an image is - in some cases all the way from a very wide angle to a close up telephoto shot.

As is the case with all film gear, there are a number of reasons for and against using prime lenses. In this video I’ll go over five reasons that make primes superior to zooms - and follow it up with a later video from the other side of the argument about why zoom lenses are better than primes. So if you like this content, consider hitting that subscribe button so that you can view the follow up video. Now, let’s get into it.

1 - CONSIDERED PERSPECTIVE

We can think of the width of a frame, or a focal length, as offering a perspective on the world. 

This close up, shot with a wide focal length, sees a lot of background and places us, the audience, within the same world as that of the character. This close up, shot with a longer focal length, isolates the character more from the background, blurs it, and compresses, rather than distorts the features of their face.

The great thing about a prime lens’ fixed focal length, is that it also fixes the perspective or feeling of an image. When you choose what prime to put on the camera you are therefore forced into making a decision about perspective. 

This isn’t to say that you can't do the same with a zoom, but when you work with a variable focal length lens it’s far easier to just plonk down the camera at a random distance from the subject and then zoom in or out until you get to the shot size that you want.

If you’re using a prime, you need to first decide on the focal length you want and then are forced to reposition the camera by moving it into the correct position. As they say in photography, it makes your legs become the zoom. This is especially useful as a teaching device for those learning about lens selection and camera placement. 

So, prime lenses force you more into thinking about the focal length that you chose, which may elevate the visual telling of the story by making it a deliberate decision, rather than an incidental decision.   

2 - OPTICAL QUALITY

The practical reasons behind choosing a lens are important, but so too is the look that the lens produces. Due to their design, prime lenses are considered to possess a higher quality optical look than most equivalent zooms. This is mainly because the construction of primes is much simpler and the design more straightforward than that of zooms.

Inside a lens you’ll find different pieces of curved glass. Light passes through this glass to produce an image. Because prime lenses only need to be built as a single focal length they can use less of these glass elements - and, the glass elements inside the lens don’t have to move in order to zoom. 

Less glass means less diffraction of light, which usually means sharper images. Also, prime lenses only need to be corrected for optical aberrations like distortion and chromatic aberration for a single focal length. Zooms need to do this for multiple focal lengths, which is trickier to do. 

Therefore, your average prime lens will be sharper with less distortion, or bending of the image, and more minimal colour fringing between dark and light areas. 

I should add as a caveat that modern, high-end cinema zooms are constructed to a high degree of optical quality that is comparable to many prime lenses, but you pay a pretty penny for that level of cutting edge engineering. When you’re looking at zooms and primes in a comparable price range, primes usually have the winning, optical edge.        

3 - APERTURE

A lens’ aperture is the size of the round opening at the back of the lens that lets in light. A large opening, which has a lower T or F stop number, like T/ 1.3, means that more light is let in, while a smaller opening, with a stop such as T/ 2.8 means that it lets in less light.

Once again, because of the extra glass and more complex design required to build zoom lenses, primes tend to have a faster stop. 

When it comes to cinema glass, each extra stop of light that a lens can let in is precious and demands a higher price tag. Shooting with a wide aperture comes with a few advantages. It means you can expose an image in dark, lower light conditions. It allows you to create more bokeh - the out of focus area that separates the subject from the background and is generally considered ‘cinematic’. 

This allows you to also be more deliberate about what is in and out of focus and is a way of guiding the audience's gaze to a certain part of the frame. So, for those cinematographers or photographers that want fast lenses, primes are the way to go.      

4 - SIZE

If you’re working in wide open spaces, with a dolly that holds a heavy cinema camera, then the size of the lens is less of a concern. But the reality is that more often than not that’s not the case and having a physically smaller lens attached to the camera makes things much easier.

By now we know that zooming requires extra glass and extra glass requires a larger housing. This means zooms are heavier, longer and wider than primes. 

Cinema rigs that need to be precariously balanced - like drones, a gimbal or a Steadicam - are often unable to take longer cinema zooms because of their excess weight and length. Some of the bigger zooms are so large that they can’t be effectively operated as a handheld camera on the shoulder and are limited to only being viable for use on a dolly or a tripod.

So, if you need to work in a confined space, want to move the camera on a lightweight rig, or shoot with a handheld camera then a big zoom lens may not be for you.   

5 - FOCUS

The fifth and final reason not to use a zoom lens is because of its focusing limitations. Every lens has a range of distances that can be rendered in sharp focus and a range that will fall out of focus. 

Cinema and photo lenses can focus on objects far away up to infinity, but they are limited as to how near they can focus on an object. This limit is called close focus or MOD - minimum object distance. Generally, zooms have inferior close focusing capabilities. 

For example, the closest that an Angenieux 24-290mm zoom can focus, set at a 50mm focal length is 4’. A Zeiss Master Prime 50mm lens on the other hand can render objects in focus up to only 20” away. 

So, if you want to shoot a close up of a face or a detail, you can get much tighter with a prime lens than with a zoom lens before you lose focus.

Additionally, when it comes to many zooms built for photography, because the glass shifts when you zoom in, the focus also changes. So if a person is in focus at 70mm and you then zoom into them to 200mm without touching the focus ring, the shot may go out of focus and be soft.

Most cinema zooms are able to remedy this and maintain sharpness across the entire focal length range, however for simpler, pin sharp focus that doesn’t shift, and a superior MOD - primes beat zooms.