In the preceding section, we talked about the television camera. An important production element of the camera is its lens. The lens produces the light image that the pickup tube of the camera converts into video signals, and affects greatly how we perceive an environment as shown on the television screen.
This section is, therefore, devoted to two main aspects of lenses: (1) their optical characteristics, including focal length, focus, f-stop, and depth of field, and (2) their performance characteristics, including the field of view, lens settings in respect to particular production effects, and how to work lenses, and the manual and automatic units that control their operation.
Lenses are used in all fields of photographic art.
Their function is mainly to produce a small, clear image of the viewed scene on the film or, in the case of television, on the camera pickup tube. The particular lens used determines how close or how far away an object will appear, assuming a fixed distance from camera to object. One lens will make an object or action look far away although the camera is relatively close to it; another will show the object or action at close range, even though the camera is some distance from it.
A zoom lens can duplicate the characteristics of several lenses; in effect, it is many lenses in one.
It can show an object far away or at close range, and make far objects appear to move continuously closer, or close objects continuously farther away.
As mentioned earlier, all broadcast-type color cameras and many black-and-white cameras use zoom lenses, or, as they are called in technical language, variable-focal-length lenses. Other studio cameras have up to four fixed-focal-length lenses attached to a turret. Although zoom lenses are much more prevalent in television than fixed-focal-length lenses, we will use the latter as frequent reference in our discussion of optical and performance characteristics of lenses because the basic optical principles are more easily explained and understood this way. We will transfer the basic principles from the fixed lens to the zoom lens whenever necessary.
Optical Characteristics of Lenses
To determine when and why you should use a particular lens, or zoom-lens setting, you will need at least a basic knowledge of (1) focal length, (2) focus, (3) f-stop, (4) depth of field, and their interrelations.
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Back Focus
The distance between zoom lens and camera pickup tube at which the picture is in focus at the extreme wide-angle zoom position. In monochrome cameras, the back focus can be adjusted by moving the pickup tube through the camera focus control.
Depth of Field
The area in which all objects, located at different distances from the camera, appear in focus. Depth of field is dependent upon focal length of the lens, f-stop, and distance between object and camera.
Fast Lens
A lens that permits a relatively great amount of light to pass through (low f-stop number). Can be used in low lighting conditions.
Field of View
The extent of a scene that is visible through a particular lens; its vista Focal Length The distance from the optical center of the lens to the front surface of the camera pickup tube with the lens set at infinity. Focal lengths are measured in millimeters or inches.
Short-focal-length lenses have a wide angle of view (wide vista); long-focal-length (telephoto) lenses have a narrow angle of view (closeup). In a variable-focal-length lens (zoom lens) the focal length can be changed continuously from wide angle to narrow angle or vice versa. A fixed-focal-length lens has a single designated focal length only.
Focus
A picture is in focus when it appears sharp and dear on the screen (technically, the point where the light rays refracted by the lens converge). Front Focus
The proper relationship of the front elements of the zoom lens to ensure focus during the entire zoom range. Front focus is set at the extreme closeup position with the zoom focus control. Color cameras have a front-focus adjustment only because the pickup tubes cannot be moved.
f-Stop
The calibration on the lens indicating the aperture, or diaphragm opening (and therefore the amount of light transmitted through the lens). The larger the f-stop number, the smaller the aperture; the smaller the f-stop number, the larger the aperture.
Lens Format
A somewhat loose term for the grouping of lenses that have focal lengths appropriate to a particular size of film or camera pickup tube. There is a lens format for 35mm film, another for 16mm film; one for 3-inch I-O pickup tubes, another for 1-inch Plumbicons.
Normal Lens
A lens with a focal length that will approximate the spatial relationships of normal vision when used with a particular film or pickup tube format.
Range Extender
An optical attachment to the zoom lens that will extend its narrow-angle focal length.
Selective Focus
Emphasizing an object in a shallow depth of field through focus, while keeping its foreground and background out of focus.
Servo Controls
Zoom and focus controls that activate motor-driven mechanisms.
Slow Lens
A lens that permits a relatively small amount of light to pass through (high f-stop number). Can be used only in well-lighted areas.
Telephoto Lens
Same as long-focal-length lens.
Gives a closeup view of an event relatively far away from the camera.
Turret Lens
A lens that is mounted on the turret of a camera. Usually in contrast to a zoom lens.
Zoom Lens
Variable-focal-length lens. It can change from a wide shot to a closeup in one continuous move.
Zoom Ratio
The zoom range, from the widest angle position to the narrowest angle position, expressed in a ratio, such as 10:1 (wide angle 17mm to a narrow angle 170mm).
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Focal Length
3.1 Focal Length.
In general, we can group lenses into (1) short, or wide-angle, lenses, (2) long, or narrow-angle, lenses, and (3) zoom, or variable-focal-length, lenses. The long lenses are sometimes called telephoto, or (quite ambiguously) closeup lenses.
The "short" and the "long" in this connection refer to the focal length of a lens; that is, the distance from the optical center of the lens (often the midpoint between the front and back lens elements) to the point where the image as seen by the lens is in focus (see 3.1). A thorough knowledge of how to measure focal length is not too important for proper usage of camera lenses. Fortunately, since short lenses usually look short and long lenses look long, it is easy to tell whether the camera operator is using a short--or a long--focal-length lens.
With a short, or wide-angle, lens you can see more; you have a wider vista. What you see looks comparatively small. With a long, or narrow-angle, lens you see less; you have a narrower vista. But what you see is greatly magnified. A short lens creates an effect similar to looking through binoculars the wrong way. A long lens is similar to binoculars used correctly.
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3.2 In the discussion of focal length, it is important for you to realize
that there are lenses of various formats, which, although they may be identical
in focal length, nevertheless will give you different angles of view.
In order to project a clear image of its view upon the photoconductive (light-sensitive) front surface of the camera pickup tube, the basic lens format must match the size of the pickup tube. The large front surface of the image-orthicon tube, for example, requires lenses of a larger format than for the small vidicon tube. I-O cameras use lenses that fit a 35mm film format, and the 1-inch (25mm) vidicon or Plumbicon tubes generally use lenses that fit the 16mm film format.
Most color cameras use either the 1-inch (25mm)
or the slightly larger 1%-inch (30mm) vidicon or Plumbicon pickup tubes. Even this slight variation in tube size requires different formats of zoom lenses.
For lenses of a larger pickup tube format (such as the 35mm film format), a focal length of 50mm constitutes a short, wide-angle lens. For the smaller format lenses (such as the 16mm film format), a focal length of 50mm is considered a rather long, narrow-angle lens.
When using zoom lenses, you really don't have to worry too much about this lens format difference.
Hopefully, the attached zoom lens has been purchased to match the pickup tubes inside the cameras. However, if you have to work with cameras that have pickup tubes of various sizes-such as an I-O and a vidicon monochrome camera with turret lenses, and a 1.25-inch Plumbicon color camera with a zoom lens-you may want to remember this simple formula: the larger the lens format is, the wider the angle of view (the larger the vista) of a lens with a given focal length (or focal-length setting on a zoom) will be.
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Turret lenses have a fixed focal length-you cannot change the angle of view-and therefore you need several lenses on a turret. Turret lenses are usually marked according to their focal length, which is given either in millimeters (mm) or in inches (in). There are 25mm to one inch. The smaller the focal-length number, the wider the angle of view.
Contrary to the turret lenses, the zoom lens with its variable focal length allows you to change the focal length of the lens from long to short or from short to long in one continuous operation. A complicated series of interacting lenses keeps the object in focus at all times during the zooming operation, assuming that the zoom lens focus has been preset for this particular zoom. To "zoom in" means to change the lens gradually from a wide-angle lens (faraway view) to a narrow-angle lens (close view). On the television screen, a zoom appears as though the object is gradually getting larger and, therefore, coming toward the viewer.
Through a zoom-in, the scene is brought closer to you. To "zoom out" or "zoom back" means to change the lens from a closeup to a distant shot.
The scene seems to move away from you.
The degree to which we can change the focal length (and thereby the angle of view, or vista) of a zoom lens is its zoom range. This is often given in a ratio, such as 10:1. A 10:1 zoom range indicates that you can increase your focal length ten times, from 17mm to 170mm for example. When you are zoomed all the way out, your lens has a focal length of 17mm, which represents a rather wide angle of view for most television pickup tubes. When you are zoomed all the way in to 170mm, you have narrowed your angle of view to a tenth of the original one. You will now have a rather big closeup of the scene. Of course, you can stop anywhere within this zoom range and operate your lens at any focal length between 17mm and 170mm.
Focus
A picture is "in focus" when the projected image is sharp and clear. The focus depends on the distance from lens to film (in a still or movie camera) or from lens to camera pickup tube or tubes (in a television camera). Simply changing the distance from lens to film, or pickup tube, brings a picture into focus or takes it out of focus.
In television photography, the pickup tube takes the place of the film. To keep in focus, you must adjust the distance between the lens and the single pickup tube (for monochrome cameras) or pickup tubes (for color cameras). You can change this distance in two principal ways: (1) When using turret lenses on monochrome cameras, you can move the camera pickup tube toward and away from the lens by turning a special focusing knob on the side of the camera. (2) When using a zoom lens, you can focus anywhere within the zoom range by moving certain lens elements within the lens through mechanical or electrical focus devices attached to it and to the camera.
Because the basic principle of focusing the television camera can be explained more readily through the operation of a monochrome camera with a turret lens (fixed focal length), we will first take up the focus procedure of moving the pickup tube, and then progress to the more common television practice of focusing a zoom lens.
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3.3 When using fixed-focal-length lenses in still photography or in motion
pictures, you adjust the focus by turning the ring on the lens barrel with
the distance scale imprinted on it. By turning the ring, you can move the
lens either closer to the film or farther away from it. The closer you hold
the camera to the object, the farther the lens must be from the film. The
farther away the object is, the closer the lens can be to the film. A typical
35mm film format lens on a still camera might show two distance scales on
the distance ring: one in feet, ranging from 1.5 feet to infinity, and the
other in meters (m), ranging from 0.45m to infinity. At the infinity setting,
the lens is turned all the way in, closest to the film. Since most television
cameras have a device that moves the pickup tube rather than the lens, the
lenses-except those for small industrial-type cameras-do not have a distance
calibration on them but have their distance setting fixed at infinity.
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3.4 Focusing the Turret Lens Camera.
Moving the Pickup Tube You focus monochrome turret cameras by moving the pickup tube toward or away from the lens, a procedure accomplished simply by turning the focus knob or crank on the side of the camera. When you "dolly in" (move the camera toward the object), you generally crank the focusing knob counterclockwise, toward you. This pulls the pickup tube back in the camera toward you, and thereby increases the distance between the lens and the pickup tube. The closer the camera gets to the object, the farther back the tube has to travel in order to stay in focus. When you "dolly back" (move the camera away from the object), you crank the focusing knob clockwise, or away from you, pushing the pickup tube toward the lens and thereby decreasing the distance between the tube and the lens.
Because the travel of the pickup tube is obviously restricted within the camera, there are limitations to focusing, especially when long lenses are used. For example, you cannot take an extreme closeup of a postage stamp with a long lens, because you cannot rack into focus when you are close enough to the object to fill the screen with it. The reason for this dilemma is that long lenses have a long focal length; that is, the picture comes into focus relatively far behind the optical center of the lens. Operationally, you must rack the pickup tube back a considerable distance to align the sharp image from the lens with the front surface of the pickup tube. The closer the camera gets to the object, the farther back the tube has to travel in order to stay in focus. If the pickup tube cannot go back any farther, the picture will be out of focus until either the object or the camera backs up (see 3.4). So an extreme closeup of a very small object requires a wide-angle lens, which has a shorter focal length and for which the tube travel within the camera is sufficient. Of course, extreme closeups with wide-angle lenses cause lighting problems, because the camera blocks out the light when it is close to the object.
Closeups of this nature must be carefully planned before the show.
Zoom-Lens Focusing
A zoom lens has several internal lens elements that move in relation to one .another when you zoom as well as when you focus. One set of these sliding elements, normally located at the front part of the lens, takes care of the focusing. The focus controls, which come in various configurations, are usually mounted on one of the panning handles, or attached close to the actual zoom control. Assuming that neither the object nor the camera moves very much, you won't have to focus while zooming in or out provided that you have properly preset your zoom. This procedure is slightly different for monochrome than for color cameras.
Since it is explained more readily on monochrome cameras than on color cameras, we will discuss pre-focusing in order of camera complexity.
When you are zoom pre-focusing for a monochrome camera-let us assume that you will have to zoom in and out on the newscaster and the map behind him-these are the steps you must take:
1. Zoom all the way out to a long shot (widest angle lens setting on your zoom lens). Now focus up on the scene with the camera focus control. In effect, you are moving the pickup tube relative to the lens, very much like focusing a turret lens.
2. As soon as you are in focus, zoom all the way in to the map, the object farthest away from the camera that needs to be included in your shot. Most likely the map will look out of focus. Do not correct focus now with the camera focus control. Rather, focus up on the map with the zoom control. Make sure that you are zoomed in all the way, to your narrowest angle lens setting.
3. Now zoom back again slowly, without touching any focus control. You should remain in focus throughout the zoom. Sometimes, when you are zoomed out all the way again, you may have to touch up the focus just a little with your camera focus control Then zoom in again, and check whether you are still in focus on the closeup of the map. If not, correct the focus again very slightly with the zoom control. By now, you should have a fairly even focus throughout your zoom range.
Because the adjustment with the camera focus concerns the "back matter" of the camera-the pickup tube-this focus is called back focus. The closeup adjustment with the zoom focus concerns "front matter" of the camera-the lens elements in the zoom lens. This focus is, therefore, called front focus.
As soon as you move your camera into a different position, you must obviously go through another presetting procedure. Otherwise, your zoom will most likely not remain in focus from the new location.
Zoom pre-focusing for color cameras is a very different process. Since the internal optical system of the color camera is extremely critical in its alignment, the pickup tubes cannot be moved for focusing. Therefore, there is no easy way of back-focusing, and indeed, the internal optical system is set in such a way that the camera is more or less permanently back-focused. The color camera has no camera focus (which you would need for back-focusing) but only a front focus, the zoom-lens focus controls.
Here is what you should do to preset your zoom on a color camera:
1. Zoom all the way in on the farthest object in your zoom range, like the map behind the newscaster. Focus on the map with the zoom focus control. In effect, you are adjusting the front focus.
2. Zoom all the way back to your widest angle lens setting. Since the back focus is already adjusted for this lens setting, your scene-the whole news set-should be reasonably in focus. If not, once again make a slight adjustment with the zoom focus control.
3. Now zoom in again. You should maintain focus pretty much throughout the entire zoom range.
Because of the preset back focus in a color camera, you may find that the wide-angle shots are slightly out of focus, at least not quite as crisp as you may like them to be. But if you have to compromise with your focus, it is better to have a crisper, sharper closeup picture of an object and a slightly softer long shot (wide-angle view) of the scene than the other way around. Also, the colors themselves help to define the overall scene sufficiently so that a slightly softer focus is generally unnoticeable on the home receiver.[1] Like long-focal-length lenses, the zoom lens sets some limitations on how close the camera can get to an object and still remain in focus. Without special attachments, the closest focusing distance for most zoom lenses lies between two and four feet with the lens zoomed in all the way to its maximum focal length, or, as it is frequently called, maximum telephoto position. In wider-angle positions, you can, of course, move the camera or object somewhat closer without losing focus.
[1. Herbert Zettl, Sight-Sound-Motion (Belmont, Calif.: Wadsworth Publishing Co., 1973), pp. 187-188. ]
3.5 Lens Iris: The lens iris, or diaphragm, consists of a series of thin
metal blades that form, through partial overlapping, a lens opening of variable
size.
3.6 J-Stop: The f-stop is a calibration that indicates how large or small
the iris, or lens opening, is.
f-Stop
Similar to photographic film, the camera pickup tube will operate properly only within a certain range of light intensity. If too little light falls on the pickup tube, or tubes, the picture quality will suffer as much as if it receives too much light.
Since you will probably use the camera not only indoors but also outdoors on remote telecasts, you will have to adjust for the extreme difference in light. There are several ways of controlling the light level. First, in the studio you can regulate the lighting itself. Second, if you are outdoors, you have recourse to a variety of neutral density filters that admit a certain amount of light. Third, and most importantly, the lens itself has a diaphragm, or iris, that can be "opened up" to permit more light to pass through the lens, or "stopped down," made smaller, to permit less light to enter. The opening in the diaphragm is called aperture (see 3.5). On a fixed-focal-length lens, there is a ring around the lens barrel (similar to the distance calibration) that, when turned clockwise or counterclockwise, will either increase (open) or reduce (close down) the iris opening. The different positions of lens (iris or diaphragm) openings are calibrated in f-stops. The smaller the/-stop number, such as f/1.4, the larger the iris opening. The larger the f-stop number, such as f/22, the smaller the iris opening. (See 3.6.) The quality of a lens is measured not by how little light it allows to enter the camera (small aperture with large f-stop number) but by how much light it lets in (large aperture with small f-stop number). A fast lens, which permits a large amount of light to enter, can be used in low-light-level conditions. A slow lens, through which relatively little light can pass, requires relatively high-level lighting conditions. In general, short-focal-length (wide-angle) lenses are faster than long-focal-length (narrow-angle or telephoto) lenses.
Zoom lenses for color cameras (for the 1-inch or 1 1/4-inch Plumbicon pickup tube formats) have a maximum aperture (iris opening) of /11.8 or f/2.0. The zoom lenses for the I-O pickup tube format are generally slower.
Since the iris opening is one of the most important video control elements, it is usually remotely controlled by the video operator. In fact, it is changed continually during a telecast in order to control and balance the light striking the camera tube, or tubes. The more sophisticated color cameras have an automatic iris control: the camera senses the light entering the lens and adjusts the lens opening in such a way as to produce an optimal picture.
Depth of Field
If you place objects at different distances from the camera, some of them will be in focus and some of them out. The area in which objects are seen in focus, called "depth of field," can be shallow or great. When it is shallow, only objects in the middle-ground will be in focus; the foreground and background will be out of focus. When the depth of field is great, all objects (in the fore-, middle-, and backgrounds) will be in focus.
If the depth of field is great, you will find it rather easy to keep the performer in focus, although he or she may move rapidly toward or away from your camera. If the depth of field is shallow, he or she will have to move very slowly toward or away from your camera in order to stay in focus.
The same rules apply, of course, when the camera moves. A great depth of field makes it easy for you to stay in focus while dollying. A shallow depth of field makes it extremely difficult to dolly without getting out of focus (see 3.7). It seems as though a very great depth of field would be the most desirable condition in television studio operation. But a medium depth is often preferred because then the in-focus objects are set off against a slightly out-of-focus background. Thus, the object will be emphasized, and busy background designs or the inevitable smudges on the television scenery will receive little attention. Foreground, middle-ground, and background will be better defined. 2
You can control the depth of field by coordinating three factors:
1. The focal length of the lens used. Given a fixed camera-to-object distance, short-focal-length lenses, or wide-angle zoom positions, have a great depth of field. Long lenses, or narrow-angle zoom positions, have a shallow depth of field.
2. The lens opening (f-stop). Large lens openings (small f-stop numbers) cause a shallow depth of field.
Small lens openings cause a great depth of field. A low light level will necessitate the opening of the lens diaphragms and a subsequent decrease in the depth of field. More light will permit you to stop down your lens (decrease the lens opening) and thereby increase the depth of field.
3. The distance between camera and object. The farther away the object is from the camera, the greater the depth of field. The closer the object is to the camera, the shallower the depth of field.
[2. Zettl, Sight-Sound-Motion, pp. 188-191.]
In a closeup with a wide-angle lens, or a zoom lens zoomed out (wide-angle position), for instance, your distance from camera to object will be small; the initially large depth of field (wide-angle lens) will become quite shallow (distance from camera to object is small). If a similar closeup is taken with a long lens, or a zoom lens zoomed in (narrow-angle or telephoto position), the distance from object to camera may be comparatively great (great depth of field); the long focal length of the lens, however, will reduce the depth of field considerably.
When you are zoomed in, you have a shallow depth of field; when zoomed out, you have a larger depth of field. In general, we can say that closeups have a shallow depth of field, long shots a great depth of field.
Quite frequently, a shallow depth of field can work to your advantage. Let us assume that you are about to take a quick closeup of a medium sized object, such as a can of dog food. You don't have to bother to put up a special background for it. All you need to do is to move your camera back and zoom in on the display (or use a narrow-angle lens). Your zoom lens will now be in a telephoto (narrow-angle) position, decreasing the depth of field to a large extent. Your background will now be sufficiently out of focus to prevent undesirable distractions. This technique is called selective focus, meaning that you can focus either on the foreground, with the middle ground and background out of focus; or on the middle-ground, with the foreground and background out of focus; or on the background, with the foreground and middle-ground out of focus.
You can also shift emphasis from one object to another quite easily with the help of selective focus. For example, you can zoom in on a foreground camera, thus reducing the depth of field, and focus (with your zoom lens at the telephoto position) on it. Then, by simply "racking focus"-that is, by refocusing-on the person behind it, you can quickly shift the emphasis from the camera (foreground) to the person about to take a picture (middleground). (See 3.8.) The advantage of a shallow depth of field also applies to unwanted foreground objects. In a baseball pickup, for example, the camera behind home plate may have to shoot through the fence wire. But since your camera will most likely be zoomed in on the pitcher, or other players performing at a considerable distance from the camera, you will work with a relatively short depth of field. Consequently, everything fairly close to the camera, such as the fence wire, will be so much out of focus that for all practical purposes it becomes invisible. The same principle works for shooting through bird cages, prison bars, or similar foreground objects.
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3.7 Depth of Field.
3.8 Selective Focus: (a) In this shot, the camera (foreground object) is
out of focus, drawing attention to the woman (middleground); (b) here, the
focus is shifted from the woman (middleground) to the camera (foreground).
A large depth of field is necessary when there is considerable movement of camera and/or subjects. Also, when two objects are located at widely different distances from the camera, a great depth of field will enable you to keep them both in focus simultaneously. Most outdoor telecasts, such as sports events and other remotes, require a large depth of field, the principal objective being to help the viewer see as much and as well as possible. Fortunately, during daytime remotes, there is usually enough light to stop down the lenses considerably, an arrangement which, as we have seen, will help to increase the depth of field. In night telecasts, make sure that there is enough light so that you can work within a reasonably great depth of field.
Performance Characteristics
The performance characteristic of a lens refers to what it can and cannot do, and how it generally behaves in common production practice. Since the camera will process only the information the lens can see, a knowledge of the performance characteristics of lenses will aid you greatly in many production tasks. As a director or associate director, for example, you must know which lens or zoom-lens position to use in order to let the viewer see the important parts of an event. Or you may want to use a specific zoom position or lens in order to achieve an important aesthetic effect. As a microphone boom operator, you must know how lenses function so that you can keep your microphone out of the picture yet as close to the sound source as possible. As talent, your knowledge of lenses will aid you in where to look, how to move, or how to hold an object so that the camera can see it as well as possible.
Three topics especially pertinent to the discussion of performance characteristics of television lenses are: (1) field of view, including focal length and zoom range, (2) relationship of focal length to performance, and (3) operational controls.
3.9 10:1 Zoom Range: (a) Zoomed out: at 20 feet (or approximately 6m) away
from the camera, the field of view is 15 feet (or approximately 4.5m) wide.
(b) Zoomed in: at 20 feet from the camera, the field of view is now only
1.5 feet wide (1/10 of the wide-angle field of view).
Field of View
Field of view refers to how much of a scene you can see through a particular lens. The wide-angle, or short, lens-through which you can see more gives you a wider field of view than the narrow-angle, or long, lens. The same is true for a zoom lens. At the widest zoom setting, or widest focal-length position, you have the widest field of view, or the greatest vista. At the narrowest zoom set-ting, or narrowest focal-length or telephoto position, you have the narrowest field of view. But what you see is greatly enlarged, especially the middleground and background objects. Between the widest zoom position (all the way out) and the extreme telephoto position (all the way in)--the zoom range-there are innumerable gradations. Since most zoom lenses have a 10:1 or 15:1 zoom range, the field of view increases or decreases approximately tenfold or fifteen-fold. To visualize a 10:1 zoom range, imagine that you are standing twenty feet, or approximately six meters, away from the camera. Assuming that your zoom lens (for 1-inch Plumbicon) has a range of 17mm to 170mm, it will cover a field of view approximately 15 feet (or roughly 4.5 meters) wide when zoomed all the way out (see 3.9a). You will be able to move a good seven feet to either side of the stationary camera and still remain in the camera's field of view. When zoomed all the way in, however, you had better stand in one place, without moving at all (see 3.9b). The camera's field of view has appropriately enough shrunk to one-tenth of the wide-angle zoom position, to 1.5 feet (roughly 45 cm). When the camera is used outdoors, or in large indoor spaces, the normal 10:1, or even 15:1, zoom range no longer suffices. Most likely, you will find that your widest angle zoom position is too wide to be useful, and that your most extreme telephoto position does not get close enough to the event. Zoom lenses come, therefore, with a variety of range extenders, which are either attached to the front of the lens or activated automatically by a simple switch. Three range extenders usually fulfill most production requirements: one that extends the maximum focal length by 1.5 times, another that doubles the maximum focal length (2.0 times), and still another that extends the maximum focal length by 2.5 times. But as soon as you put on a range extender, you automatically lose your original widest angle, or shortest focal length, position of the lens. The lens retains its 10:1 zoom ratio. You simply start a little closer to the object with a range extender, and therefore get a little closer to the object in your extreme telephoto position. Let's use our 10:1 zoom lens, which has a range from 17mm to 170mm and see how the 1.5x, the 2x, and the 2.5x range extenders influence the focal-length range.
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3.10
The different-sized Plumbicon tubes require slightly different lens formats. Zoom lenses that fit the 1-inch (25mm) Plumbicon pickup tubes exclusively vary in size slightly from those that are made for the 1%-inch (30mm) pickup tube format. Since the optical and performance characteristics of the lenses are quite similar, we will largely ignore this difference.
3.11
The most common wide-angle zoom positions are: For color cameras: 17mm (or wider)-30mm For I-O cameras: 35mm-60mm The most common wide-angle turret lenses are: For I-O cameras: For vidicon cameras: 35mm (extreme wide-angle lens)
50mm (or 2-in, wide-angle lens on normal turret)
10mm (extreme wide-angle)
12 1/2 mm (1/2-in, wide-angle lens on normal turret)
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Normal zoom range without extenders: With 1.5x range extender: With 2.0x range extender: With 2.5x range extender: 17mm-170mm 25.5mm-255mm 34mm-340mm 42.5mm-425mm Unfortunately, range extenders are not without disadvantages. The rule that says, the longer the maximum focal length, the slower the lens, applies also to the range extenders. The f/2 of the above zoom lens is reduced with the range extenders to f/3, f/4, and f/5, respectively; so obviously the 2.5x range extender requires a large amount of light. If used outdoors in daylight, the range extenders work quite well; indoors, with limited lighting, they can present a serious production problem. The added lens elements of the range extenders, which act in effect as a magnifying glass, sometimes impair the overall crispness of the picture. Try, therefore, to move your camera as close to the event as possible, so that you can do without range extenders. If you have to use them, make sure that enough light is available for the reduced aperture.
The tables shown will give you information on the most common zoom ranges and the focal lengths of turret lenses.
Focal Length and Performance
In order to discuss the relationship of focal length to the performance characteristics of the lens, we will group the focal lengths of the turret lenses, as well as the focal-length positions of the zoom lens within its range, into (1) wide-angle (short-focal-length) lenses, or wide zoom-lens position; (2) the normal lens, or midrange zoom-lens position; and (3) the narrow-angle (long-focal-length, or telephoto) lens, or telephoto zoom-lens position.
3.12 Wide-Angle Distortion: (a) Here, the dock building appears to be much
longer than it is. Note that the mooring line is larger in the foreground
than the entire ship. (b) Even a small car, like a VW, can be made to look
like a rather powerful racer.
3.13 The length of this hallway is greatly exaggerated by the wide-angle
lens.
3.14 Ordinary gestures can become quite commanding through wide-angle lens
distortion. Note how the hand, which is relatively close to the lens, is larger
than the woman's head just a short distance behind.
3.15 Shooting through a prominent foreground piece with the wide-angle lens
creates a spatially articulated, forceful picture.
3.16 Wide-angle lens distortion of a face is generally undesirable, unless
you want to imply in the shot some psychological distortion.
The Wide-Angle Lens, or Wide Zoom-Lens Position
When speaking of the relationship between focal length of a lens and its performance characteristics, these factors should be considered: (1) field of view and object proportion, (2) dolly capability and object speed, (3) maximum aperture (iris opening), and (4) focus capability and depth of field.
The wide-angle lens gives you a wide vista. You can have a relatively wide field of view with the scene rather close to the camera. With a wide-angle lens, you can make a small room or studio look quite large, or stretch normal hallways into seemingly endless tunnels. Objects relatively close to the camera look large, and objects only a short distance away look relatively small. The proportions of the object are therefore exaggerated by the wide-angle lens. This distortion-large foreground objects, and small middleground and background objects-helps to increase the illusion of depth. Since parallel lines seem to converge faster than we ordinarily perceive with this kind of lens, you can create a forced perspective that makes objects-desks, automobiles, houses
-look longer than they actually are. (See 3.12 through 3.15.) This distortion, however, can also work against you. If you take a closeup of a face with a wide-angle lens, the nose, which is closest to the lens, is unusually large compared to the more distant parts of the face (see 3.16). In an extreme wide-angle position, or with an extreme wide-angle lens, you may notice that the vertical lines of the background appear to be somewhat curved.
This is called "barrel distortion," because the vertical lines look like the curved sides of a barrel.
Looking down on an object can also create undesirable distortions. A closeup of a washing machine, for instance, shows an obvious distortion when the camera dollies in and observes it from above (see 3.17). You can reduce such distortions by placing the objects on a level approximate with the lens height (see 3.18). Another negative aspect of the wide-angle lens is overshooting. The wide-angle view of the lens does not stop where the scenery ends. If you overshoot the set on top or at the sides, the great depth of field will point up the overshot areas clearly and embarrassingly.
The wide-angle lens is a good dolly lens, because its wide field of view de-emphasizes camera wobbles and bumps. The great depth of field of the lens helps you to keep in focus while dollying.
Unless you have to move the camera in quite close to the subject, you probably will have to adjust the focus only minimally, if at all.
Unfortunately, the zoom lens makes it so convenient to move from a long shot to a closeup or vice versa that dollying with a color camera has almost become a lost art. But there is a significant aesthetic difference between a zoom and a dolly.
While the zoom seems to bring the scene toward the viewer, a dolly seems to take the viewer into the scene.4 Since the camera does not move during a zoom, the spatial relationships between objects remain constant. The objects appear to be glued into position; they simply get bigger (zoom in) or smaller (zoom out). In a dolly, however, the relationships between objects change constantly.
You seem to be moving past and around them; you are enticed to participate more in the action than during a zoom. But it is just as easy to dolly with a zoom in a wide-angle position as with a wide-angle lens. There is only one problem. At the end of your dolly, you can't all of a sudden zoom in from the new position without first presetting your zoom again. Otherwise, you will surely get out of focus, or at best have a difficult time adjusting focus while zooming.
[3 Zettl, Sight-Sound-Motion, pp. 211-213. ]
[4 Zettl, Sight-Sound-Motion, pp. 194-197, 288. ]
3.17 The wide-angle lens distortion in this shot makes the washing machine
appear much too dynamic and unstable.
3.18 When shot more from eye level (either by lowering the camera or by placing
the object closer to lens height), or by using a longer lens, the undesirable
effect of distortion is greatly reduced.
The wider the lens or the zoom position, the more rapidly the objects increase or decrease in size during a dolly, and the more exaggerated the dolly speed becomes. Similarly, the movement of objects toward and away from the camera seems greatly accelerated by the wide-angle lens.
The f-stop rating of a zoom lens applies over the entire zoom range. A maximum iris opening of f/2, for example, does not decrease (to f/2.8 or f/3) during the zoom in. It will remain at f/2 even in its telephoto position because the diaphragm is adjusted automatically as the lens changes focal length.
Fixed-focal-length lenses, on the other hand, become slower the longer they get. This means that wide-angle lenses have generally a wider maximum iris opening (lower f-stop) than long, or narrow-angle, lenses. Under unfavorable lighting conditions, you may still get acceptable pictures with the fast wide-angle lens, but you may not be able to use the slower narrow-angle (long-focal-length) lenses.
As you remember, wide-angle lenses have a large depth of field. You can therefore get very close to the object with a wide-angle lens and still rack the pickup tube back far enough (in monochrome cameras) to keep in focus. Even with a zoom lens you can sometimes produce a larger screen image by zooming out to a fairly wide-angle position and moving the camera close to the subject than by simply zooming in to a narrow-angle lens position at some distance from the subject.
Be sure to check carefully, however, on whether the camera can get physically close enough to the object. Sometimes a large dolly, the zoom lens itself, or even the sunshade on a long lens mounted on the turret with the wide-angle lens, may prevent you from pushing the camera close enough to obtain the desired closeup.
The Normal Lens, or Midrange of the Zoom Lens
While the wide-angle lens makes objects seem farther apart and rooms larger than they actually are, normal lenses, or midrange zoom positions, make objects and their spatial relationships appear close to our normal vision.
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3.19 The most common midrange zoom positions are: For color cameras: 35mm-45mm
For I-O cameras: 75mm-90mm The most common normal lens on a turret is: For
I-O cameras: 75mm or 90mm For vidicon cameras: 25mm, or 1-in lens
3.20 The most common narrow-angle, or telephoto, zoom range positions for studio use are: For color cameras: 50mm-200mm without range extenders For I-O cameras: 135mm-400mm (16 in) without range extenders The most common narrow-angle turret lenses are: For I-O cameras: 135mm, 8-in (200mm), and 12-in (300mm)
For vidicon cameras: 75mm (3-in), 100mm (4-in)
For field use, range extenders are used with zoom lenses (see table). There are also fixed-focal-length lenses available:
For I-O cameras: 15-in, 17-in, and 25-in field lenses For vidicon cameras: 6-in (152mm) and 12-in (300mm)
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3.21 By using a telephoto lens, the background is greatly enlarged compared
to the foreground. The distance between the cars seems, therefore, reduced
and the impression of a traffic jam is heightened.
3.22 This shot was taken with a zoom lens in an extremely long focal length
position. Note how the runner, the pitcher, the batter, the catcher, and the
umpire all seem to stand only a few feet apart from one another. As you know,
the actual distance between the pitcher and the batter is 601/2 feet.
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3.23 Among the many manufacturers of optical equipment and lenses, there
are four whose top-quality television lenses have found wide acceptance here
in the United States and elsewhere. Their products are the Japanese Canon
lenses, the French Angenieux lenses, the British Rank-Taylor-Hobson Varotal
lenses, and the German Schneider Variogon lenses. The more expensive Angenieux
and Schneider lenses are considered the best in the field.
3.24 Most lens turrets are equipped to hold four different lenses. The most
common studio lens complement consists of a wide-angle lens, a medium lens,
and a narrow-angle lens. It is good practice to put the widest-angle lens
on your turret opposite the longest lens because then you will avoid having
the long lens show in your wide-angle picture. The problem of a lens visible
in the picture is sometimes called "cropping." If you use a standard
lens complement, cropping is no problem, whatever the position of the lenses
on the turret may be.
The standard lens complement for an I-O camera turret is (1) the 50mm lens-a wide-angle lens; (2) the 75mm or 90mm lens-the normal lens; and (3) the 127mm or 135mm lens. The standard lens turret is often referred to as the 2-3-5-inch turret (corresponding to the 50mm or 2-inch lens, the 75mm or 3-inch lens, and the 127mm or 5-inch lens). Some television stations include in their standard lens complement the 8-inch or 8 1/2-inch lens, which enables you to get fast closeups of objects located at a considerable distance from the camera.
The standard lens complement for vidicon turret cameras is a 12.5mm (1/2-inch) for the wide-angle lens, a 25mm (1-inch) for the normal lens, and a 75mm (3-inch), or a 100mm (4-inch) for the narrow-angle lens.
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The normal lens is a reasonably good dolly lens although camera wobbles become a little more noticeable than with the wide-angle lens. Also, you will find that it is harder to keep in focus while dollying with the normal lens than with the wide-angle lens.
The normal lens is still a fast lens (large maximum iris opening) and permits good closeups without your having to bring the camera too close to the object.
When shooting graphics, especially title cards, you should use the normal lens or put the zoom into the midrange position. This method has several advantages: (1) You can quickly correct the framing on the card by zooming in or out slightly, or by dollying just a little in or out without undue focus changes. (2) You will be far enough away from the easel to avoid camera shadows, yet close enough so that the danger of someone's walking in front of your camera is minimal. (3) The floor-person, by placing the easel at a standard distance from the camera, can help you frame up and focus on the easel card with a minimum of effort and time.
The most common mistake is to zoom in on an easel card from a fairly great distance. There are three major disadvantages to this method:
(1) Your focus at the telephoto zoom position is quite critical.
(2) If the director requires a closer shot when you are zoomed in most of the way already, you will have to move the whole camera closer to the easel and preset your focus again-a maneuver that can be quite time- and energy-consuming.
(3) As already mentioned, if you are too far from the easel, studio personnel unaware that you are focused on the easel card may walk right in front of your camera.
With the normal lens, you can get fairly close to the object and still be able to focus up.
The Narrow-Angle Lens, or Telephoto Zoom Lens Position
The narrow-angle, or long, lens has a narrow field of view, and it magnifies objects in the lens's field of view. Because the enlarged background objects look rather big in comparison to the foreground objects, an illusion is created that the distance between foreground, middle-ground, and background has decreased. The long lens seems to shrink the space between the objects, in direct contrast to the effect created by the wide-angle lens, which exaggerates object proportions and therefore seems to increase relative distance between objects. A narrow-angle lens, or a zoom lens in its telephoto position, crowds objects on the screen.
This crowding effect can be positive or negative. If you want to show how crowded the freeways are during rush hour, for example, use a long lens, or use your zoom lens in the telephoto position. The long focal length will reduce the distance between the cars and make them appear to be driving bumper to bumper (see 3.21). But such depth distortions by the narrow-angle lens also work to disadvantage. You are certainly familiar with the deceptive closeness of the pitcher to home plate on your television screen.
This depth distortion occurs because the zoom lens is used in a fairly extreme telephoto position, since the camera is placed far to the rear of the pitcher, on the other side of the field from home plate. Since in most sports events, television cameras must remain at a considerable distance from the action, the zoom lenses usually operate at their extreme telephoto positions or with powerful range extenders. The resulting telephoto effect of shrinking space makes it difficult for the viewer to judge actual distances and to tell with accuracy who is ahead of whom (see 3.22). You cannot dolly with a long lens, or with a zoom lens in its telephoto range. Its magnifying power makes any movement of the camera impossible.
If you work outdoors, even wind can become a problem. A stiff breeze may shake the camera to such a degree that the greatly magnified vibrations become clearly visible on the television screen.
In the studio, the telephoto position of the zoom lens may present another problem for you.
The director may have you zoom in on part of an event, such as the lead guitar in a band concert, and then, after you have zoomed in, ask you to truck (move the camera sideways) past the other members of the band. But this movement is extremely difficult to do in the telephoto zoom position. Rather you should dolly in with a wide-angle zoom position and then truck, with the lens still in the wide-angle position.
Another important performance characteristic of the long lens, or the zoom lens in a telephoto position, is the illusion of reduced speed of an object moving toward or away from the camera.
Since the narrow-angle lens changes the size of an object moving toward or away from the camera much more gradually than the wide-angle lens, the object seems to move more slowly than it actually does; in fact, an extreme narrow-angle lens virtually eliminates such movement. The object does not seem to change its size perceptibly even when it is traveling a considerably large distance relative to the camera. Such a slowdown is especially effective if you want to emphasize the frustration of someone running but not getting anywhere.
As pointed out before, the relatively slow, narrow-angle lenses usually have a smaller maximum aperture than wide-angle lenses and, as a result, need more light. Zoom lenses maintain their maximum aperture throughout the entire zoom range, but range extenders reduce the aperture rating of the lens considerably.
Since narrow-angle lenses have a rather shallow depth of field, any object that is moving fairly close to the camera is difficult to keep in focus. If someone walks toward the camera past the minimum distance you need to keep in focus, the person will go out of focus. No amount of screaming from the control room personnel will help to correct this problem. If, however, the action happens quite a distance from the camera, the lens acts more like a wide-angle lens again (since the field of view increases) and therefore your depth of field increases accordingly.
3.25 Zoom Control: With most zoom controls, you turn the handle clockwise
to zoom in and counterclockwise to zoom out. The faster you turn the handle,
the faster the zoom will be.
3.26 Servo Zoom Control: This zoom control is simply mounted next to the
camera panning handle.
3.27 Shot Box: The shot box comes in a variety of configurations, but with
similar components, such as the field-of-view meter, zoom speed control, wide-angle
and narrow-angle zoom buttons, and buttons for preset positions.
Operational Controls
You need two basic controls to operate a zoom lens: (1) the zoom control unit, which activates the variable focal length of the lens (the zooming mechanism), and (2) the focus control unit, which activates the intricate focus mechanism in a zoom lens. Both zoom controls can be operated either manually or by automatic "servo" control.
Zoom Control Unit
The manual zoom control usually consists of a small crank mounted on the right panning handle or on a special extender at the right of the camera. A small lever next to the crank enables you to select at least two turning ratios, slow or fast. The slow ratio is for normal zooming, the fast for exceptionally fast zooms.
Some manual controls have two levers that allow four adjustable zooming speeds. When you turn the crank, a special zoom drive cable mechanically activates the zoom mechanism in the lens. Obviously, the faster you turn the crank, the faster the zoom will be. (See 3.25.) The servo zoom control unit does not activate the lens mechanism directly; rather, it signals a complex motor system that in turn drives the zoom mechanism in the lens. In actual operation, the servo control unit is quite similar to the mechanical zoom controls. It is normally mounted on the right panning handle, and you zoom in and out by moving the thumb lever either right or left.
The farther you move the lever from its original central position, the faster the zoom will be. A two-speed switch permits you to select a zoom speed four times as fast as the normal zoom rate.
With the servo system, the zoom speed is automatically reduced as the zoom approaches either of the extreme zoom positions. This reduction prevents jerks and abrupt stops when you reach the end of the zoom range. (See 3.26.) There are several advantages to the servo system: (1) Your zoom-will be steady and smooth, especially during extremely slow zooms. (2) The zoom control is easy to operate and allows you to concentrate more on other camera functions, such as panning, tilting, and focusing. (3) With the automatic zoom slowdown, you will never get caught reaching the end of the zoom range at full speed.
To make the zoom even more precise, a zoom preset system has been developed, called a shot box.
Generally mounted on the right panning handle, it allows you to preset any of a number of zoom speeds (up to twelve in some models) and several (four or five) zoom positions. By activating wide- and narrow-angle buttons or switches, your lens will zoom either out or in. A special meter indicates the angle of view of the lens. The shot box is usually combined with a servo zoom control unit that lets you override the shot box at any time. (See 3.27.)
Focus Control Unit
The manual focus control unit ordinarily consists of a twist grip, very similar to a motorcycle handle. It is generally mounted on the left panning handle. Two or three turns are usually sufficient to achieve focus over the full zoom range.
As with the zoom, the focus operations are transferred by drive cable from the panning handle control to the lens. (See 3.28.) The most common servo focus control unit is a three-spoked capstan wheel. (See 3.29.) It is generally mounted in the left panning handle or attached directly to the side of the shot box.
There are provisions for fast and slow focusing speeds and for compensating the turning of the focus control when the lens reaches long focal lengths. Remember, the tighter the shot, the smaller the depth of field. Consequently, when you zoom in for a tight shot, the focus becomes more critical as you get tighter, and you therefore have to increase the turns of the focus control.
The servo system can compensate for this change and keep the turning rate constant. Because of their experience with mechanical focus devices, however, most camera operators are already so used to the different turning ratios at close range that even with the servo system they prefer to compensate for the different close-range focus requirements themselves. The switch is, therefore, frequently left in the "uncompensated" position.
3.28 Manual Focus Control: The twist grip of the manual focus control turns
clockwise and counterclockwise for focusing.
3.29 Servo Focus Control: The servo focus control does not transfer your
movement of the focus wheel mechanically; instead, it activates a motor that
drives the focus mechanism in the zoom lens extremely smoothly.
For similar reasons, the servo focus control unit is not very popular. The preselected focus is useful only when the positions of the camera and subject are exactly the same in the show as in the rehearsal.
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3.30 Some of the portable broadcast cameras, and a number of non-broadcast
cameras, have rather simple zoom devices. Some zoom lenses are activated by
a small lever that turns part of the lens clockwise or counterclockwise, thereby
making the lens zoom in or out, respectively; or the front part of the lens
is turned directly by hand.
Some of the simpler zoom lenses on non-broadcast cameras are operated with a control rod that extends through the camera to the back. By pushing the rod in or pulling it out, you can zoom in or out. Some zoom lenses work in reverse. By pushing the rod in, you zoom out; and by pulling the rod back, you zoom in. By turning the focus wheel at the end of the rod, you can adjust focus while zooming. (See a.) You change turret lenses by rotating the lens turret with the turret control handle in the back of the camera. By pressing the inside part of the turret handle back, you will release the turret so that it can be rotated either clockwise or counterclockwise.
Once the desired lens is in the "on-the-air" position, which is marked by a dot on the camera, you should release the grip gently until it engages in a catch, thereby locking the turret solidly in its new position.
Since the turret control is spring-loaded, be sure to depress and engage the turret handle slowly and easily; otherwise the loud clicks of the engaging springs will be picked up quite noticeably by the microphone. (See b.) The focus control for turret cameras is a knob on the right side of the camera. The number of turns of the knob necessary to keep the picture in focus depends on the speed of the camera or object, the focal length of the lens used, and the iris opening of the lens. Some focusing knobs have an additional little crank that permits fast focusing (see 2.3).
a Zoom Rod
b Turret Handle
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Summary
The function is to produce viewed scene of a lens on the television camera a small, clear optical image of the on the front surface of the camera pickup tube. There are basically two types of lenses: (1) the variable-focal-length, or zoom, lens, and (2) the fixed-focal-length, or turret, lens.
The zoom lens can change its focal length continuously, which means that it can make an object appear to look far away or at close range, or make the "far" object move continuously closer, or the "close" object continuously farther away-all with the camera remaining in a fixed position.
The fixed-focal-length lens shows only one particular angle of view. In order to make an object appear at close range, or farther away than with the lens used, we need to use lenses with different focal lengths, assuming that the camera does not move.
Important optical characteristics of lenses are (1) focal length, (2) focus, (3) f-stop, and (4) depth of field.
The performance characteristics of lenses are (1) field of view, including focal length and zoom range, (2) relationship of focal length to the performance of the lens, and (3) operational control units of the lens, such as zoom and focus controls.
Turret as well as zoom lenses are dependent upon the format (size of the target area) of the camera pickup tube or tubes.
All studio color cameras use zoom lenses.