The Camera
We're well on our way to the world of fully automatic "point and shoot"
television cameras. Smart cameras are great most of the time and they
certainly cut down on the common mistakes most people (even pros) make
from time to time. When automatic operation doesn't work, though, the
results can be pretty bad. Knowing what the conditions were that fooled
your "smart" camera will help you to know when to turn these features
off and do it the old-fashioned way. But before you do, you need to
know what cameras do and how they work.
The television camera changes light into an electronic signal that can
be stored (using video tape, optical disks, or computer memory,
transmitted, and displayed on a television receiver or monitor.
Television cameras are probably easier to operate well than film or
still cameras because you can watch and control the camera output as
you record. There are few electronic controls, and the manual controls
on the lens will be familiar to anyone who has used a good still or
motion picture camera. Since video cameras can, as a rule, produce
sharper, clearer pictures than the recording media they were designed
to work with, the quality of your camera is seldom an excuse for fuzzy
pictures. Understanding how to use the camera correctly will help you
avoid poor results.
Lens Controls
The modern television lens has three controls: iris, focus, and zoom.
On a fully automatic camera you may not have to adjust the focus or
iris except under unusual conditions, but you should know what's going
on so you can use manual settings with confidence.
Iris
The ring closest to the camera body controls the amount of light
passing through the lens to the light-sensitive surface of the pickup
tube or chip. It is called the iris, aperture, or f-stop control and is
marked off in f-numbers. The lowest f-stop lets in the most light, and
the highest f-stop lets in the least. Some lenses even have a "C"
setting after the highest f-stop which means the lens is completely
closed, letting no light through at all.
More light------------- Less light
1 1.4 2 2.8 4 5.6 8 11 16 22 32
STANDARD F-NUMBERS
Each standard f-stop lets half as much light through the lens as the f-stop below it.
If the camera gets too little light, the image will look fuzzy and
drab, even though it may be in focus. The camera image may lag behind
quick changes in the picture and the picture will be grayish, with
little contrast.
Too much light will produce too much contrast. Details in both the very
bright and the very dark parts of the picture will be lost. Bright
spots may grow "halos" or "bloom." So-called "point sources" of light
may cause light vertical stripes on CCD cameras.
The correct setting is between these extremes, generally about one
f-stop higher than the f-stop at which the bright parts of the picture
lose details and grow halos, or "bloom." To find this point, begin with
the lens in the closed or highest f-stop position and open it slowly
until you start losing details in the brightest parts of the picture.
Then reduce the amount of light coming through by going down to the
next highest f-stop.
Indoors it's often necessary to add light to get a good picture.
Outdoors on bright sunny days it may be necessary to reduce the light
reaching the pickup tube even more than the lens will allow. This is
done by adding a neutral density filter between the lens and lens hood.
A two power (2X) filter has the same effect as using the next highest
f-stop, while a four power (4X) filter gives the effect of going up two
f-stops.
Zoom
The center ring on most lenses is the zoom control. Most cameras use a
rocker switch beside the lens. This allows you to change the focal
length of the lens through a range from wide angle (short focal length)
to telephoto (long focal length). It's common for inexpensive zoom
lenses to have a range of about six to one. That is, the longest focal
length is about six times the shortest. Zoom lenses for television
cameras with two-thirds inch pickup tubes or chips range from about
12mm to 75mm, with a normal focal length of about 33mm.
A wide angle setting makes the subject smaller as the angle of view is
increased. Distances from the camera are exaggerated, with objects
nearer the camera appearing abnormally large. This is especially true
of people who are too close to a wide angle lens. Straight lines near
the edges of the picture are often bent with an effect known as barrel
distortion.
A telephoto setting makes the subject larger as the angle of view is
reduced. Distances from the camera are compressed. More than one
feature film director has used this effect to make an action (like
running toward the camera) seem to take much longer than it should.
The normal lens settings offer the most natural perspective to the viewer.
It's possible to change the focal length of a zoom lens during a shot
by "zooming" in or out. Inexperienced camera operators often over-use
this capability. The main value of the lens is in controlling the field
of view of the camera when it's inconvenient or impossible to change
the distance from the subject to the camera.
Focus
The focus control is the ring farthest from the camera body, on the
front of the lens. Distance settings are marked in meters and in feet.
While a non-zoom (fixed focal length) lens is focused simply by turning
the ring until the image is sharp, the zoom lens must be zoomed in to
the smallest angle of view and the largest image size to adjust focus.
The lens should then be zoomed out to the widest angle of view and the
smallest image size to make sure the image stays in focus through the
entire zoom range. If the image stays sharp, the lens will remain
focused at any focal length as long as the distance from the subject
does not change.
Depth of field is the range of distances in front of the lens in which
objects appear to be in acceptable focus. It's longer for short (wide
angle) lenses than for long (telephoto) lenses, and it increases as you
use higher f-stops. It is often wise to use a higher f-stop when
lighting conditions permit, if you expect the distance between the
camera and the subject to change often while you're taping, since
you'll have less trouble keeping the subject sharply focused with
greater depth of field.
While all cameras with zoom lenses must control iris, focal length, and
focus, the functions of the three rings described here may be automated
or provided by remote control.
Most lenses also have a "macro" setting on the zoom ring. This changes
the characteristics of the lens to let you focus on objects right up to
the front of the lens.
Electronic Controls
Some or all of the following controls may be automatic or preset and thus not adjustable by the user.
Pedestal
Also called the "set-up" control, sets the level of the darkest parts
of the picture. On portable cameras it's generally automatic or totally
absent.
Gain
Also called "level," this control sets the level of the brightest parts
of the picture. It can be used to reduce the level when too much light
is striking the pickup tube, but it will not make the picture brighter
without making it grainy or snowy if the pickup tube or chip isn't
getting enough light. Automatic gain controls can be extremely
sensitive to even small bright parts of the picture, driving medium and
darker parts into black. They may also bring dark parts up into the
medium range if there's not enough light for a good picture.
White Balance
If you use outdoor film with normal indoor lighting (no flash)
everything comes out orange. The color temperature of sunlight is very
different from an incandescent light bulb. Most consumer cameras now
sense the overall color temperature and adjust color electronically. In
older or professional cameras it may be necessary with each change in
location or lighting to "tell" the camera how to interpret color. This
is done by showing the camera a white card, which represents the total
absence of color. Controls on the camera are then used to minimize the
color output of the camera.
Viewfinder
There are often controls to adjust a camera viewfinder. To state the
obvious, these controls have absolutely nothing to do with the actual
output of the camera. It's helpful to adjust the viewfinder under
controlled conditions so it shows a faithful representation of actual
camera output. Otherwise, if you want viewfinders to tell you the
truth, they should never be adjusted just to make a "pretty" picture.
See the camera forum at http://tv-handbook.com/discussion/
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