Mastering the Art of Lenses

The first time I saw a camera that wasn’t completely automatic, I thought, “What a load of faff!”

But then suddenly, I fell in love.

I could make a sliver of reality as clear as day while the rest melted away into a beautiful buttery blur. This, I’d later learn, was ‘bokeh’. And I could move the focus between points of interest, from one person to another. I was cradling cinema in my hands.

I didn’t know, or more like couldn’t have guessed, at the time how much more there was to learn about lenses alone. Most people suffer through years of trial and error and YouTube videos to learn the basics of camera lenses, but luckily for members of Sutton FilmMakers, our very own Tom McDaniel and Peter Leverick recently hosted a club night on lenses and focus pulling. This session provided a practical, hands-on exploration of how lenses work and why they are so crucial in cinematography. It really opened our eyes to the art of lenses.

Cameras can do what the human eye does, and then some. Remember this as you’re making your film, your audience will experience your movie through the filter of real life. And so, because there are more ways to manipulate that experience than you can shake a memory stick at, today we’re focusing on lenses.

But before I go any further, let’s back it up.

First of all, physics is hard. Like, really hard. You might think the movie Inception was a lot to wrap your head around, but that was peanuts compared to physics. It’s worth noting that a lot of photographers’ jargon uses metaphor to simplify how we talk about physics. I’ll be using inverted commas whenever I catch myself doing this.

Vision is possible because light is reflected off an object towards a viewing subject. For example, sunlight reflects off me towards you, which, by some miracle of human biology, you interpret as shape, colour, brightness and all sorts of other details.

The lens you use will have up to three lenses along the barrel, so let’s run through them.

The most common lens ring is the focus ring. This is what you use to select at what distance in your shot objects are most clearly visible. By turning this ring, you move the focal plane forwards or backwards.

If I’m looking at two objects, the relative distance between those objects and me changes how much I can see them clearly at any time. If the objects are relatively near to each other, I can focus on both at the same time, but if the objects are relatively far apart from each other, I can’t.

Now, if your lens is a zoom lens, its second twistable ring will change its focal length. The focal length is the distance between your camera’s sensor, or film, and the optical centre of your lens, usually measured in millimetres. In effect, this changes the perspective seen through your camera. A lower measurement gives a wider perspective, and a higher measurement gives a narrower perspective.

Shorter focal length lenses are said to ‘expand space’, often making more things in focus in a single shot, exaggerating how close to or far from me objects appear. By halving the focal length of a lens, the distance between you and me becomes twice as much.*

Longer focal length lenses make backgrounds look blurrier because they ‘compress space’, magnifying objects in the frame. If I look blurry in the background of your photo and you double my size in the frame, I will appear twice as blurry.*

Short focal length lenses are called “wide lenses”, and long focal length lenses are called “telephoto”. It makes sense then that some focal lengths in the middle are called “normal lenses”. What constitutes a normal lens will depend on the size of your camera’s sensor, but it will always equal the diagonal measurement of your sensor, 43mm on full-frame cameras or 28mm on most APS-C cameras.

Your lens’s third ring, or second if your lens does not zoom, changes your lens’s iris, also called the aperture. This affects the depth of field of your shot, meaning how thin or thick a sliver of your image is in focus, but it also changes the overall brightness of your image.

The larger the iris, marked on the lens with a lower f-stop or T-stop number, the brighter your image and the greater the amount of out-of-focus blur. The smaller the iris, or the higher f or T-stop, the darker your image and the greater the proportion of your image that will be acceptably in focus.

*Okay, not exactly 2x per se, but physics is hard.