The Power of a Lens

This is nonsense, and it almost certainly results from a glibly uninformed reading of what it says (irresponsibly, IMHO) on Wikipedia.

It's true, Wikipedia does say that "The focal length of an optical system is a measure of how strongly the system converges or diverges light;" but it goes on to say that "it is the inverse of the system's optical power."

If you follow the link that's embedded in the words "optical power", you learn that "Optical power ... is the degree to which a lens, mirror, or other optical system converges or diverges light."

The focal length is the inverse (or reciprocal, as it more scientifically says on the Optical power page) of the optical power of the lens. The greater the focal length, the weaker the lens. Not an ideal measure; much better to find something that gets bigger as the lens gets more powerful. Like the "optical power".

This was my question, and (as someone who did Physics 'A' level, and has used cameras ever since) I failed to come up with any technical term for the property that the question was asking about. I would never (literally, never) have come up with "focal length" as the answer to this question. While I struggled to come up with an answer, my thought process went something like "what's the technical term for the power of a lens?"

Turns out it's just "the power of a lens" – or, as Wikipedia puts it slightly more precisely, the "optical power". Well obviously it's the optical power; what other sort of power could it be?

Dictionary.com has two alternative definitions for "focal length": 1. "the distance from a focal point of a lens or mirror to the corresponding principal plane", and 2. "the distance between an object lens and its corresponding focal plane in a telescope."

You will note that the power of the lens, mirror or telescope, or "how strongly the system converges or diverges light" is not mentioned. I would suggest that this is because despite what it says on Wikipedia, that's not what the focal length is used to measure.

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