Lenses and f-numbers
There are a few technical terms about lenses you must understand as they affect the camera’s pictures.
Focal length
If parallel light is shone into a lens the distance to the point of focus behind a lens is its focal length.
Image size
This is the size of the image as projected onto the pick-up device (i.e. the camera tube or CCD). Most broadcast cameras use 2/3 inch, although there are some other sizes in use, particularly in miniature and high definition cameras.
Angle of view
We can use the focal length (f), and the image size (y’) to calculate the horizontal angle of view (w):
w = 2 tan−1 y’/ 2f
The good news is that I’ve never yet had to do this calculation. What is much more useful is looking up a manufacturer’s specification ...
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