Cinematography Basics: How To Choose The Right Lens For The Job
In previous posts in the Cinematography Basics series, I talked about the basics of framing a shot, and the various shot types and how to use them. So now that you’ve figured out the best way to frame your shots in order to convey the right visual message for each of your scenes, what’s the next consideration you need to be thinking about in order to capture each and every frame of your film perfectly?
Lenses. It’s all to easy to get lost in choosing the latest and greatest camera system, but a terrible choice of lenses will make even the most expensive machines turn out a less-than-pleasing image. Not to mention the impact your available lenses will have on the overall shot design of your film projects.
So just how do you go about choosing a set of lenses? First of all, let’s talk about focal lengths.
For most applications, anything below a 50mm is generally considered to be a wide angle, while lenses above 50mm are known as telephoto. A 50mm lens in itself quite closely approximates the ‘ordinary’ field of view of the human eyes, and for this reason it’s widely recommended in both the film and photography worlds that this is the length you start with; this is also the reason why French filmmaker Robert Bresson famously used a 50mm lens throughout his work in order to create a ‘realistic’ aesthetic.
When choosing a wide-angle and a telephoto lens, we first need to understand how changing our focal length affects our perspective on what’s in front of the camera.
At the wide end of things, the distance between objects is increased, so that rooms appear larger and the frame has greater depth. This phenomenon is utilised by filmmakers for many reasons, whether to create a sense of scale and show off a setting, or to create a meaningful distance between people or their surroundings. The widest of lenses actually distort the image, bending light at the edges. As you can see in the below image from How The West Was Won, vertical lines become slanted and cause the top and bottom of the image to lean inwards towards the center (a process known as keystoning). Although this effect is best used sparingly, it can be effectively used to create a sense of unease and abnormality.
On the other hand, telephoto lenses compress space, making objects appear to be closer together. This is frequently used in chase sequences in order to make a pursuer appear closer than he/she actually is to their victim, in fight scenes to create the illusion of connecting punches and kicks (when in fact they land off to one side of a person) and during rapid sideways movements such as with galloping horses, to exaggerate their speed. Beyond their use in action though, telephoto lenses are frequently used to create intimate dialogue scenes and to produce beautiful close-ups such as in the below still from Bellflower.
With both of the above types of lenses, the more extreme the focal length, the greater the effect on the image will be.
As you may or may not be aware, lenses of all focal lengths come in two different types:
- Prime lenses have just one focal length which cannot be changed, whether it’s 50mm, 13mm, 200mm or any other length.
- Zoom lenses have a range of available focal lengths, which can be changed back and forth as desired.
However, a prime lens most often has a higher quality than an equivalent zoom lens, producing clearer and sharper images. In addition, their construction means that less light travelling through the lens is lost; for this reason a greater exposure can be captured than from a zoom lens (see ‘aperture‘ below).
The choice between them is a complicated one, but basically comes down to affordability, flexibility and overall quality. For more on this, check out this article from Digital Photography School.
Lastly if you’re using a zoom lens to shoot your film, there exists an unwritten rule that you DO NOT ZOOM during a shot. As mentioned above, different focal lengths change the perception of depth and distance in a scene; by changing the focal length during a shot you are doing a whole lot more to the image than just tightening the frame. The result is a very undesirable ‘home video’ aesthetic. Of course there are exceptions and in some cases a zoom in or out may produce a stylistic effect that suits the look you’re trying to achieve. For example, several filmmakers have famously zoomed while dollying in the opposite direction to produce an extraordinary visual effect (first used in Hithcock’s Vertigo; see the below example from Goodfellas:
If you’ve ever taken a close look at a stills photography or video lens, you may have noticed a series of numbers around the barrel preceded by the letter f. This is what’s known as an f-stop and refers to the aperture setting of the lens:
Inside any lens (just like in the human eye) is an iris, which opens and closes to allow more or less light to travel through and reach the film or video sensor of the camera. This iris is controlled by the aperture ring, which is measured in f-stops. The higher the f number, the more the iris closes and the darker the image will be. Conversely the lower the f number, the more the iris opens and the brighter the image will be.
Higher quality lenses tend to have a lower f-stop available, with the most desirable settings including f1.8, f1.4, f1.2 or more rarely, down to numbers below 1. As explained above, prime lenses usually have lower f-stops.
Changing the f-stop (or aperture setting) to a lower number is known as stopping up, while changing to a higher number is known as stopping down. As well as controlling the light entering the lens though, changing the aperture affects how much of the image is in focus at once, a phenomenon known as depth of field. For more on this, see my dedicated post on the topic here.
While stills photography lenses video lenses are currently marked up with f-stops, dedicated cine lenses old and new usually measure aperture using T-stops. Though there is a small difference in their measurement, their function uses precisely the same set of rules.
As you can see, there’s a lot to take into consideration when choosing which lens or lenses to buy. Above all though, it’s vital that your choices of lens when making a film are made carefully and purposefully in order to communicate meaning and to create the style you want to achieve. You can learn more about the meanings associated with different types of shots in other Cinematography Basics posts: How To Frame A Shot and The Types Of Shot And How To Use Them.
This post, as all others, has benefited from a number of key sources. This includes not only my film school education and on-set experience, but also a variety of books and online materials. In all cases, I have reworked, combined and elaborated upon found and learnt information to provide a helpful and accessible post.