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Re: [Phys-l] optical center : real-life physics

On 06/11/2007 05:24 PM, alex brown wrote:
What principles did you use to find the optical centre of the lens

1) Turn on laser. Set it on the table. Aim it at a reference mark,
in this case the crack between a pair of kitchen cabinet doors.

2) Put the lens in the beam. Move the lens around until the beam
lines up with the aforementioned reference mark.

3) Mark the place where the beam is hitting the lens. That's the
optical center.

How would this apply to an optical system, say a telescope?

That depends.

-- If the telescope is axially symmetric, the question never arises.

-- I've seen telescopes so asymmetric that the optical center of
the primary was an abstraction, not within the diameter of the
actual mirror. For sure my method of finding the optical center
would not work in such a case.

-- In intermediate cases, I reckon the general idea ought to work.

Does it even make sense to talk
about an optical centre of a system of more than one lens?

Good question. I'm not 1000% sure.

In many cases, a lens system can be modeled as a thin lens
plus an offset-distance. In such cases, you ought to be
able to /define/ a notion of generalized optical center,
and go from there.

I have to think about this some more.

There are folks on the list who know more about optics than
I do; maybe they know the answer.