November 15, 2014

A Primer on Focal Length: Why Lenses Are One of the Most Powerful Tools at Our Disposal

Focal Length, Field of View, Depth of Field
Of the many complex aesthetic decisions that cinematographers make, lens choice is one of the simplest, most powerful, and most misunderstood.

There are several different factors that determine the aesthetic of any given lens, but today we're just going to be focusing on the basics. Focal length is one of the more straight-forward aspects of lens design. In the simplest sense, focal length is the physical distance between the imaging plane (ie. the sensor) and the optical center of the lens. Focal length values - which are expressed in millimeters - are basic measurements of how wide or zoomed-in a particular lens is. Easy enough, right? Where things start to get more complicated, however, is with all of the different aesthetic implications that the focal length of a lens has on the the final image.

The easiest to understand of these implications is field of view. When combined with a certain sensor size, the focal length of a lens is what determines field of view, or how much/how little of an image is actually being captured by the sensor. Here's an excellent and in-depth tutorial from Tuts+ on the topics of focal length and field of view that explains all of these concepts and explores how they're related.

Obviously field of view is a basic, albeit incredibly powerful tool for cinematographers, as it allows them the ability to directly manipulate the mise en scène of any given shot by including or excluding certain elements from the frame. Take a look at just how many aesthetic possibilities there are when focal length drastically changes and the camera stays in one position. Here we see everything from an extreme telephoto focal length of 580mm all the way down to an extreme wide of 8mm (from Vimeo user Pixine).

Outside of determining field of view, however, the focal length of a lens can produce a wide range of aesthetic qualities that can have drastic effects on how an audience perceives an image. First and foremost is the issue of depth. Depth cues - or differences in light, shadow, and spatial relation that trick our brains into perceiving a three-dimensional space in a two-dimensional medium - are rendered differently by different focal lengths. Say you frame up a medium shot of your subject. With wider lenses, the depth cues in the scene become elongated and are seemingly pushed farther apart. In a sense, wider lenses artificially add depth to a scene. The wider the lens, the more dramatic this effect becomes.

When you frame up the same medium shot with a telephoto lens, however, the exact opposite happens. The depth cues within the scene become compressed, which creates the illusion that everything in the scene is much closer together than it is in reality. Additionally, where wide lenses tend to add depth, telephoto lenses tend to flatten images and the individual elements in those images.

For one of the best (and most quirky) rundowns and examples of the aesthetic properties of different focal lengths, here's a wonderfully educational video from the University of North Carolina Wilmington and YouTube user HorrorOldSchool:

Last, but certainly not least, is the issue of depth of field, something with which all of us are familiar. Depth of field is defined as the distance between the nearest and farthest points of an image where that image is in focus. Put into visual terms, wider depth of field results in images where everything, or most things, appear in focus. Shallow or narrow depth of field, on the other hand, results in images where only a small portion of the image is in focus, and where everything else falls out of focus to varying degrees.

Although lens aperture is widely considered to be the most important factor when trying to achieve a narrow depth of field, the focal length of your lens actually plays the most significant role. Wider lenses inherently reduce depth of field, creating images where more elements are in focus at once, whereas telephoto lenses enable shallower depth of field. Of course, if you're hoping to achieve a certain depth of field, whether it be wide or narrow, there are several other technical factors to consider including the minimum and maximum apertures of the lens, the sensor or film size that you're shooting with, and the distance between your lens and your subject. The closer your subject is to the lens, the more out of focus their background will be. The closer the lens is to infinity focus, the wider the depth of field will appear to be.

What are some of your favorite focal lengths to shoot with and why? How do you guys use different focal lengths to effectively tell a story? Let us know down in the comments!     

Your Comment

30 Comments

Wish I could've seen this when I started shooting a couple years ago!

November 15, 2014 at 1:00PM

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Tommy Plesky
Director / D.P / Editor
1943

I'm a film student and I've always had a hard time understanding cinematogrpahy. For some reason i can't get my head around these technical things...

November 15, 2014 at 1:01PM, Edited November 15, 1:01PM

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Pretty cool post, especially the last video. I never thought that focal length could influence perception of movement. That's great for giving a chase that little extra "humpth" to it.

November 15, 2014 at 1:40PM

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...and on the flip side, focal length can create a supernatural flatness that nearly removes z-axis motion perception from composition. Look at some of the deep street scenes from a Scorcese movie, and maybe hit pause. Realize that you're looking at NYC blocks (which are huge) and humans who are hundreds of feet apart seem to be walking right behind each other, in relatively similar focus...crazy stuff.

November 15, 2014 at 4:59PM

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Might be crazy to people coming from the photo world, but most films are shot between 21mm-40mm. Many directors never go above a 50mm.

November 15, 2014 at 6:38PM, Edited November 15, 6:38PM

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Indie Guy
844

That's incredibly untrue.

November 16, 2014 at 1:41AM

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Jacob Floyd
Writer / Videographer
1318

Oh dear, that's not even remotely close to the truth

November 16, 2014 at 12:22PM, Edited November 16, 12:22PM

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Michael Van Ostade
Director
206

uuuuuugh, I give up on this site, does no one read AC, DPs talk about their lens selection for each major film that comes out, you see the same thing over and over 21mm-40mm for most of the film. Ask guillermo del toro or martin scorsese. Del toro doesn't like anything over a 50 because he feels it doesn't look real. Scorsese says he wants to see space in each of his shots. roger deakin scouts with just a 40 because its his favorite mm. Read any cinematography book, it says use the widest angle that can achieve the desired framing in most cases. Obviously there are instances like The Conversation where telephoto helps define the story, but for the most part most shots are 50mm or under for films. My point was it is not like photography and its a mistake that many people do coming from photography lenses. Filmmaking is more about subject in space than just subject in photography.

November 16, 2014 at 1:30PM

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Indie Guy
844

You give up on this site and want to delete your profile because two people disagreed with your internet comment?

November 16, 2014 at 5:54PM, Edited November 16, 5:54PM

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Robert Hardy
Founder of Filmmaker's Process
4299

That's three specific directors who like wides. I can do that too. Ridley Scott loves to use lenses 75mm and longer, Kurosawa often used lenses between 100mm and 500mm, even for indoors work, and James Cameron uses a telephoto for an action scenes all the time.

If you ask any director or cinematographer, they'll have lenses they prefer to use, but they'd also tell you about all the other people that do things different. In film, you don't always need to create space, eliminating it can be just as effective.

November 16, 2014 at 8:46PM

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Jacob Floyd
Writer / Videographer
1318

this

November 17, 2014 at 7:00AM

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Michael Van Ostade
Director
206

Anyone who shoots action scenes uses longer lenses. At 20mm, the actors would actually be hitting each other!

November 17, 2014 at 7:37AM

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Richard van den Boogaard
Freelance filmmaker & editor
74

Completely agree. Lens choice is almost like the filmmakers' signature. Terrence Malick loves wides, from 14-28mm, which is pretty rare for non-comedic or non-fantasy films. If you like the compression of space that a 100+ mm lens gives you, then do so with a purpose - not just because it looks pretty; same for going super wide. It all comes down to making the right choices for the right reasons and remaining dedicated to that vision.

November 17, 2014 at 3:56PM

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Jason Blevins
Director / Producer / Videographer
161

Guylookingtodeleteprofile, you're absolutely right. I can't believe how misinformed people are about this.

Malick and Kubrick tend to shoot much wider than most other directors, but yeah, the 24mm, 28mm (27mm with Panavision), 35mm, and 50mm are the most common cine lenses, sometimes a 21mm when you're in a tight location. Someone mentioned Ridley Scott liking longer lenses, which is generally true...but until recently, he's mostly been working in anamorphic, where a 75mm lens has the width of a 37.5mm lens, so he's not really shooting that long.

When I bought my first PL mount lens, I started with a RPZ 17mm-50mm because I knew I'd never upgrade to PL lenses if I had to buy all at once and it covers the most focal lengths commonly needed. It covers everything I've ever been asked to do on steadicam, or handheld. My second lens was an 85mm CP...which I rarely use, but is nice for close ups.

November 29, 2014 at 5:47AM

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Daniel Mimura
DP, cam op, steadicam op
2207

This is what confuses me:-

http://photoflex.ehclients.com/images/uploads/Blog/Jay%20P%20Morgan%20-%...

Whenever I see a film, no one's face seems particularly distorted, yet for close-ups, mid-range, wide shots etc, I'm assuming all sorts of lenses are used. Or do most directors just use a 50mm lens and move forwards and backwards accordingly ? I'd be grateful if someone could explain more.

November 16, 2014 at 6:35AM

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Saied M.
1019

The distortion in those wide shots is because the model is close to the camera. I don't imagine many directors would bring actors that close to the camera, although Wes Anderson seems to use a less extreme example of this effect.

November 16, 2014 at 8:58AM

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Bottle Rocket was entirely filmed on the 27mm (which tells you hey shot on Panavision b/c they're the only ones that use those focal lengths on primes)...the different shots were entirely achieved through framing closer and further, since there were no other lenses used.m it's pretty amazing and I had seen that film a couple times before even realizing.

November 29, 2014 at 5:53AM

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Daniel Mimura
DP, cam op, steadicam op
2207

Thats why cine lenses are so expensive, they handle distortion very very well over photo glass especially on the wider end. With a decent cine lens you can shoot a close up with a 32mm and it will look fine.

November 16, 2014 at 1:32PM

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Indie Guy
844

That last video has very good points

November 16, 2014 at 8:28AM, Edited November 16, 8:28AM

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FINALLY, some truth about the importance of lenses. The more posts i see about the new RED ULTRATITAN 12K megapixel ultraraw or the blackmagic cheapo magnifico 5K for 500 dollars crap, the more i start wondering, do modern filmmakers really think that a great image only comes from a sensor?

Light+lens= the look of your film

When i see people spending their entire budget on an Alexa and stick on some red primes on their i just want to jump out the window

November 16, 2014 at 12:27PM, Edited November 16, 12:27PM

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Michael Van Ostade
Director
206

Hold on, can I adapt my Canon FD lenses to the RED ULTRATITAN? I don't have the budget to rent more than the body for my short film right now.

November 16, 2014 at 8:50PM

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Jacob Floyd
Writer / Videographer
1318

How about not renting a red then and put more budget in your lenses? :)

November 17, 2014 at 7:03AM

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Michael Van Ostade
Director
206

What absolute silliness. Don't you need 12K RAW on your low budget short too?

(Jokes of course. I'm sick of lens choice being undervalued. It's become too easy to slap a 24mm on and go handheld rather than take your time with composition and lighting.)

November 17, 2014 at 7:58AM

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Jacob Floyd
Writer / Videographer
1318

I love wide open 135mm prime on 35mm camera :)

November 16, 2014 at 7:29PM

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Bojan Andrejek
DP / Cinematographer / Producer
229

I feel sorry for your focus puller ;)

November 16, 2014 at 9:58PM

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Robert Hardy
Founder of Filmmaker's Process
4299

On the last video they said that a 25mm lens was the “normal" on a 16mm film. Does that mean you want to use around a 50mm lens on an s35 frame to achieve the same effect?

November 18, 2014 at 3:33AM

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Somewhere between 35mm and 50mm, depending on your taste.

November 18, 2014 at 6:09AM

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Jacob Floyd
Writer / Videographer
1318

Thanks

November 19, 2014 at 2:19AM

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32mm or 35mm in super-35. 50mm is kind of mildly telephoto, which is good for close ups.

November 29, 2014 at 5:57AM

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Daniel Mimura
DP, cam op, steadicam op
2207

"Wider lenses inherently reduce depth of field, creating images where more elements are in focus at once, whereas telephoto lenses enable shallower depth of field."

This must be wrong. Wider lenses INCREASE depth of field.

November 22, 2014 at 6:29AM, Edited November 22, 6:29AM

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I believe they mean if you were to frame up the same shot size. At that distance, the telephoto lens would give the illusion of more depth of field.

http://www.film-and-video.com/dofmyth.htm

December 27, 2014 at 3:38PM

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