Television Production And Camera-II
Television lens has three controls: iris, focus, and zoom.in a fully automatic camera it is not required to adjust the focus or iris of the camera, they are automatically adjusted accordingly.sometimes they are also required to be adjusted by you.
i. 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
ii. 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 of the camera.
iii. 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.
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