We’ve just learned how images are recorded and about the cameras that make this possible, but how do the images arrive in the camera in the first place? Every camera, whether digital or film, relies on light coming through a lens. The lens is a piece of specially shaped optical glass at the front of the camera. It is the most important part of any camera (see Action Steps: Taking Care of Your Camera and Lenses, below). Everything else on the camera is called the camera body. The lens is the camera’s eye; without the lens, the camera cannot see. It is important to note that there are tools and techniques for altering the color, intensity, and quality of the light passing through the lens using various types of lens filters that are widely used around the industry. We will discuss those during our discussion on light in Chapter 9. For now, let’s focus on the basic kinds of lensing systems, and there are a great variety of them, although they are all controlled the same way. Four elements establish the “vision” of a lens: focal length, focus, aperture, and shutter angle; together they determine the qualities of your images, including how you manage the depth of field. We’ll look at each of these in turn.

Focal Length

When light enters the front of the lens, it is curved based on the lens’s shape and then focused onto the optical sensor or piece of film. The distance between the end of the lens and the point at which it focuses on the optical sensor or piece of film is called the focal length and is measured in millimeters. A lens with a shorter focal length bends light more strongly; it brings closer objects into focus and allows a wider view of the scene. A lens with a longer focal length bends light more weakly; it is able to focus on objects that are farther away and shows a smaller area of the scene.

For professional filmmaking, using 35mm cameras or their digital counterparts, a normal lens has a focal length between 35 and 50mm. This is because the human eye has a focal length of 43mm, so lenses in the 35–50mm range closely represent the way we see the world. A lens shorter than 35mm is called a wide-angle lens because it captures a wider-than-normal field of view. A lens with a focal length of 85mm and above is called a long lens or a telephoto lens because it magnifies the scene and lets the camera see things that are farther away.

All professional cameras (and many DSLR and prosumer cameras) allow you to change lenses. Interchangeable lenses are important for cinematographers because different lenses allow for greater creativity in capturing images. Let’s take a look at how each of these lenses affects what the camera sees (see also Figure 6.3, below).

Wide-angle or short-focal-length lenses

Normal-focal-length lenses

Telephoto or long-focal-length lenses

The types of lenses described here fit into two categories: prime and zoom. A lens with only one focal length is said to have a fixed focal length and is called a primary lens, or prime lens. If you want a different focal length, you must replace one prime lens with a different prime lens. However, primes are useful because they are relatively lightweight, extremely sharp, and allow a great deal of light to come through even in low-light conditions. For this reason, most primes are considered fast lenses that may require less light on set or at your location.

A lens with a variable focal length can zoom in and out and is therefore called a zoom lens. All consumer and most prosumer digital cameras have the ability to zoom, but they do so differently. Optical zooms actually use the optics of a movable lens to make the subject appear closer. Conversely, a digital zoom uses internal software to enlarge a portion of the image, making it appear larger. With a digital zoom, there is degradation of quality, and the picture may seem to break apart. Use an optical zoom for the highest quality image.

You can also take advantage of special lenses to produce unique imagery:

Finally, if you’re using certain DSLR cameras, you can take advantage of the Four Thirds (4/3) standard, which consists of interchangeable lenses that work on several different DSLR camera bodies. These lenses are thinner and lighter than their traditional counterparts, and are specifically designed to produce the optimum image on the digital sensor of compliant cameras (the sensor on these cameras is a 4/3” sensor). Olympus, Leica, and Panasonic are the major manufacturers of cameras that work within this standard.

Focus

The term focus has two related meanings. The first is attention—what you want the audience to concentrate on. The second is technical and has to do with clarity—what has sharp edges and what is blurry? At its most basic, mechanical level, the focus of any lens is set by turning the focus ring to make sure the most important part of an image is sharp.

If you’ve never used a manual focus control before, now is the time to turn off the automatic focus and learn how to do it yourself. Automatic focus is acceptable if you’re not very experienced or if you are in an in-the-moment documentary action situation, but manual focus is usually preferable because it allows you to demonstrate your creative intention of where each shot’s focus should be. Autofocus also has some significant drawbacks, especially in low-light situations.

To focus your camera manually, adjust the focus control ring; a follow focus attachment will make it easier on your hand. Most digital cameras with pull-down view screens have magnifying focus functions, which allow you to magnify an area of the shot and focus precisely on it. This may be helpful, although many view screens are difficult to see when you’re in a high-light situation, such as broad daylight. In these cases, you may want to drape a black cloth over your head, enclosing the screen so you can see it more clearly.

Focus is a function of the distance between the lens and the subject. To get precise focus, camera operators often use a tape measure to get an exact number by measuring from the focal point on the lens to the object. Most focus rings have distance markings on them, which correlate to the distance at which a subject will be in sharp focus.

When photographing people, the sharpest focus should generally be on the center of the eye closest to the camera. If you shift the focus in a single shot, in order to draw the audience’s attention first to one thing and then to another, this is called a rack focus. Rack focus is often used to generate suspense; for example, you might focus on a person who’s hiding in the foreground, and then rack focus to reveal a predator lurking in the background. (See Action Steps: Rack Focus and Depth of Field.)

Key Factors: Aperture and Shutter Angle

Focus is also affected by two other factors: the aperture, or amount of light permitted through the lens, and the shutter angle, or the duration the lens is allowed to capture light. The interplay between aperture and shutter angle affects the way an image looks. Lighting also comes into play, especially the white balance on digital cameras, and you’ll learn about that in Chapter 9. Aperture, shutter angle, and other camera functions can seem confusing and counterintuitive—this chart has everything in one place and should make it easy for you.

Aperture is controlled by adjusting a variable ring that sits behind the focus ring. This ring is also called the iris, and like the iris of your eye, it can get larger or smaller. On automatic settings, the iris adjusts its size automatically. In motion picture and television productions, the DP determines the desired iris setting, or shooting stop, and relays it to the first camera assistant, who sets the iris on the lens to the desired aperture. The size of the aperture is measured in f-stops. F-stops typically range in number from 2.8 to 32, and the larger the f-stop number, the smaller the amount of light allowed through the lens; for example, an f-stop of 32 is practically a pinhole.

Shutter angle is the amount of time during each frame that light is present for image capture. It is the same as exposure time for each image frame, or the shutter speed on a still camera. It is called shutter angle because the shutter is a circular disc, and the open slice of that disc—like the slice of a pie—can be larger or smaller. A shutter angle of 180 degrees is typical; that means the pie is half-open and half-closed, and the image will be exposed for 1/48th of a second.

Depth of Field

Skinnier shutter angles allow quickly moving action to be shot without blurring. Big apertures allow a lot of light into the camera but also reduce the sharpness of the image. If you want every object in the frame to be in focus, use a great deal of light (much more than you could stand in daily life) and a very small aperture opening with a skinny shutter angle. The quality of this focus is called depth of field. When everything in a frame is in focus, it is called deep focus. When only one specific plane is in focus, it is called shallow or narrow focus. Adjusting the depth of field is an effective way to make a storytelling point in your film, because deep focus puts a character in the context of the scene as a whole, whereas shallow focus emphasizes a subject’s importance while everything else around it is blurry. (You’ll learn more about what this and other techniques mean for story and emotion in Chapter 9.) In stereoscopic 3D photography, the variables are multiplied because you are using two lenses and recording two images. (See Action Steps: Rack Focus and Depth of Field, below.)