5.
Identify the positive and negative lenses from the illustration below:
Positive lenses _______, ______.
Negative Lenses ______, ______.
SECTION II
FOCAL PLANE AND FOCAL LENGTH
2-6.
GENERAL.
a. When a lens projects an image, the plane in which the image is sharply
formed is called the focal plane.
b. The distance from the optical center of a lens to its focal plane,
when the lens is focused at infinity, is called focal length.
This distance
can be changed in some modern lenses by increasing or decreasing the distance
between the front and rear lens elements.
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