What Is Meant By Power Of A Lens?

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What Is Meant By Power Of A Lens?

2 Answers

Answer Question

Answer 1

If the focal length of a lens is "f" then its reciprocal "1/f" is called the power of the lens.
Power of the lens=p=1/f
When "f" is measured in meters then power of the lens is in 'Dioptres'. The unit of power 'Dioptres' is defined as;
"Power of a lens is one Dioptres when its focal length is one meter". Its symbol is "D".
hyperphysics.phy-astr.gsu.edu

Answer 2

Well, A lens which has a variable focal length that can be set manually
or remotely. Unlike the varifocal lens, if the back focus is correctly
set, the image should stay in focus as the focal length is altered.

Zoom
lenses are often described by the ratio of their longest to shortest
focal lengths. For example, a zoom lens with focal lengths ranging from
100 mm to 400 mm may be described as a 4:1 or "4×" zoom. The term
superzoom or hyperzoom is used to describe photographic zoom lenses
with very large focal length factors, typically more than 4× and
ranging up to 10× and even 14×. This ratio can be as high as 100× in
professional television cameras. Currently, photographic zoom lenses
beyond about 3× are not considered to have a quality on par with prime
lenses, and constant fast aperture zooms (usually f/2.8 or f/2.0) are
typically restricted to this range.
Photographic zoom lenses should not be confused with telephoto lenses,
those with a narrow angle of view..