large aperture (the lens is wide open).
The higher f-stop indicates the
smaller opening. These numbers may seem confusing; however, they represent
the ratio. In this sense f/2 is actually f-1/2 (read: f one-half).
c. The quality of a lens is based on how much light it lets through the
lens. A lens that lets in a great amount of light is called a fast lens,
thus a slow lens lets in a relatively small amount of light (fig 2-2).
Figure 2-2.
F-stop and lens aperture
d. One additional feature to a zoom lens is the automatic iris control.
Most cameras, especially the ENG/EFP systems, can be switched over to
automatic iris mode.
The camera then senses the amount of light entering
the lens and adjusts the iris automatically for optimal pickup tube
performance.
(1) Although this procedure seems ideal for ENG/EFP systems, it does
not always work to the operator's advantage.
With a fairly even
illumination the auto iris closes down when it sees an extremely bright area
in your scene, or opens up when sensing a rather dark set area.
(2) The automatic iris responds to whatever light it receives,
regardless of the lights' origin.
Some cameras are equipped with an auto
lock which prevents the automatic iris from drifting in and out.
3.
One very important thing to remember about a lens is depth of field.
If you place several objects at different distances from the camera, some of
them will be in focus and some of them out of focus. The area in which the
objects are seen in focus is called depth of field.
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