Camera

The Camera

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.

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's important 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.