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Re: Achromatic Telescope
From: Federico Rossi
Date: 2003 Oct 7, 06:21 +0200
From: Federico Rossi
Date: 2003 Oct 7, 06:21 +0200
Dear Andrew,
the functionment of a lens is based on the physical
principle of refraction, i.e. the deviation a ray of lay shows whan it passes
between two different mediums such as air and glass. Refraction is a function of
wavelenght and this is the reason why a single lens is unable to focus the
entire range of visible wavelenghts in a single point (this is the so called
"chromatic aberration"). As a result, the image is surrounded by colored halos.
The simplest way to try to cure the problem is to couple two lenses (to form a
so called "doublet") made of different glass qualities (typically "crown" and
"flint" glass) that should correct each other's chromatic aberration. This is
what is referrred to as typical achromatic telescope. In reality, an achromatic
just bring the two ends of visible spectrum (red and violet) into the same
focus, while for the other wavelenghts the problem still exists. Many other,
more sophisticated designs were developed to solve the problems, and now we have
the so called "apochromatic" telescopes, which use many lens made of exotic
glasses and are really able to practically null the chromatic
aberration.
Hope this information will prove useful. If you
have any doubt, ask me.
Bests, Federico
----- Original Message -----From: Andrew CorlSent: Monday, October 06, 2003 11:46 PMSubject: Achromatic TelescopeI was recently reading the journals of Lewis and Clark. They mention taking several telescopes with them on their voyage. Further research told me that one of the telescopes was an Achromatic Telescope. Could anyone tell me (or refer me to a website) what this type of telescope is. If there are plans available for this I would appreciate that link as well. I am mainly interested in being able to see the moons of Jupiter (gives you an idea of the magnification I am looking for).
Andrew
