Philips VCM1976 - Manual (Page 8)

The lens
Caution: Do not touch the glass of the lens. This could damage the
delicate coating on its surface, if the lens has to be cleaned, use a
special lens cleaning tissue, available at any good camera store.
Focus range: The camera supplied with a CS-mount lens does have a
manual focus adjustment. This allows you to find an optimal image
sharpness for objects between 0.3 metre and infinity by rotating the
front ring with the text FAR NEAR. You should be aware that the
most FAR position does not always gives you the best image
sharpness for an object far away.
Using a different lens: The CS-mount of the camera allows you to use
any one of a wide range of both C-mount and CS-mount lenses with
a fixed-iris or manual-iris mechanism. When choosing a C-mount
lens you should use a C/CS adapter ring. An auto-iris connector at
the back of the camera (fig. A-11) enables you to choose for a
passive (or DC-controlles) auto-iris lens.
Caution:
The back side of a CS-mount lens (fig. A-14) should not protrude more
than 6mm outside the flange of the CS-mount (11mm for a C-mount
lens) otherwise the lens might touch the filter glass in the camera.
You may want to use a lens with a different angle of view and thus a
different focal length than the lens supplied with your camera. The next
diagram will help you select the focal length, required to cover the ob­
ject of area you want to be monitored. It shows the width of the scene
visible on the screen with lenses of different focal lengths at given
distances (camera to object). You can extend the scope of the diagram
by simply mulitplying the values at both axes with ”x".