Zoom Lenses
Zoom lenses (Figure 1-13) are lenses that have a range of focal lengths and angles of view available in a single lens. The zoom range refers to these lengths; for example, an 18–70 mm lens will cover the focal lengths between 18 mm and 70 mm. Zoom lenses are named based on the ratio of their longest to shortest focal lengths or their magnification factor.
Figure 1-13: Canon 70-200 2.8 IS zoom lens on the set of The Shamus in Burano, Italy
The other major factor on a zoom lens is aperture and whether the lens has a variable aperture or a fixed aperture. A variable-aperture lens means that the f-stop will change depending on the focal length the lens is set at or zoomed to. If you have a lens that is a 28–135 mm f/3.5–5.6, the range of f-stops indicates that it is a variable-aperture lens: at 28 mm wide, the f-stop can be 3.5, but when the lens is zoomed to 135 mm, it can be opened up only to f/5.6.
A fixed-aperture lens allows you to set the aperture or shoot at the lowest f-stop the lens will allow at any focal length.
One drawback of zoom lenses is that they can be large and heavy. If size and weight are of the utmost importance to you, then you might want to not use or at least minimize the use of zoom lenses on your shoot.
Categorizing Lenses Based on Angle of View
Lenses are often broken down into categories based on the focal length’s interaction with the angle of view. The angle of view, or field of view, is determined by the focal length and the dimension of the image format, which in a 35 mm film shoot is the size of a frame; for a DSLR, this correlates with the sensor size.
Extreme wide-angle lenses are typically in the 8 mm to 16 mm range.
Wide-angle lenses are typically in the 16 mm to 35 mm range.
Normal lenses are typically in the 35 mm to 80 mm range.
Telephoto lenses are typically in the 80 mm to 200 mm range.
Super telephoto lenses are typically in the 200 mm to 800 mm range.
Specialty Lenses
Specialty lenses are increasingly being used in DSLR productions. Often they were limited to big-budget feature films that had the luxury of time and budget to include elaborate shots. Now DSLR filmmakers can easily rent, buy, or borrow these lenses to achieve unique looks in their productions.
Macro Lenses These are lenses designed for close focusing and for getting close to the subjects they are recording. They are typically used for small items or items where tiny details are crucial. The depth of field is limited, which allows the subject that is the focus of the shot to be prominent.
Fish-Eye Lenses These are ultra-wide-angle lenses that result in an extremely wide hemispherical image. They are deliberately distorted and have a view up to 180 degrees.
Tilt/Shift Lenses These are distinctive because they move side to side (laterally) and up and down (vertically) while allowing for a coherent image to be captured with the sensor.
The Tilt
With a normal lens, the sensor plane and the plane of focus are parallel to each other (Figure 1-14).
Figure 1-14: Angle of standard lens to a building that cannot fit entirely in the frame
Tilting the lens and moving it to the side allows the plane of focus to be at an angle to the camera instead of perpendicular to it. This means you can change the plane of focus in relation to the sensor and you can have more control of what is in focus in a given shot (Figure 1-15).
Figure 1-15: The angle of a tilted lens to the same building; notice how the entire building is in the frame with the lens correction.
The Shift
By shifting, or moving laterally, the lens, you have control of the relationship between the image plane and the subject plane. Shift lenses allow you to move the centerline without moving the camera or changing the angle of the camera or perspective of the image (Figure 1-16).
The lens elements are still parallel to the sensor/film, but they are no longer directly in front of the sensor/film (Figure 1-17).
Figure 1-16: The plane in relation to the camera and the shifted lens
Figure 1-17: The lens is to the side of the center of the camera.
In addition to allowing for special-effect shots such as miniaturization, tilt shift lenses have a utilitarian purpose. Tilt movements allow you to obtain a wide depth of field even at the maximum aperture and still keep the entire subject in focus. Shift movements correct the trapezoidal effect seen in pictures taken of tall objects so as not to distort the subject. This can be helpful when using your DSLR camera in low-light situations.
Lensbaby, Subjectiv, and Loreo Lenses
These kinds of lenses are used for various special effects. The effects include pinhole, multi-element anachromatic, some unique tilt functions, and selective focus. These special-effect lenses are used for shots where a distinctive look is the goal, and they have specialized components and construction.
Anamorphic Lenses
Anamorphic lenses are often used with DSLR filmmaking to achieve unique lens flare and bokeh. An anamorphic lens is designed to “squeeze” a widescreen image onto the sensor and must be “unsqueezed” in post to be viewed correctly. When you use an anamorphic lens, your horizontal image will be up to two times wider than a standard 16×9 frame so you will have letterboxing on the top and bottom of your image. This process creates an interesting look and effect on the footage.
How Sensor Size and Lenses Interact
One of the major options for DSLR cameras is sensor size, and one of the factors to take note of is how sensor size affects lens choice or usage. Here we will split the sensors into two rough categories: full-frame sensors and crop sensors. The format – that is, the sensor – changes either in relation to 35 mm or because various cameras have different size sensors. The sensor size affects how a lens will work with that particular format, so lenses that you are accustomed to working with in a different format may behave differently than you think. The change can be compared to moving from a standard 35 mm still camera to a medium-format camera or moving from 35 mm film to 16 mm but still using the same lenses on each camera body.
Film movie cameras have always had lenses designed specifically for their format, but with DSLRs, the lenses can be used on different formats and in many cases interchangeably. Additionally, a 35 mm movie