NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
RES: Achromatic Telescope
From: Jos? Otavio O. de Almeida
Date: 2003 Oct 7, 21:54 -0300
From: Jos? Otavio O. de Almeida
Date: 2003 Oct 7, 21:54 -0300
Andrew, an achromatic lens, be it a telescope, a microscope, binocular,
or camera lenses, means that the lenses are corrected for chromatic aberration
(partially true). It means that the colored fringes you see around a bright
object over dark background are held to a controlled level. An apochromatic lens
is more corrected and more suitable for the more critical aplications, wich
doesn`t necessarily means that you need it.
As to the other question, most simple binoculars will
enable you to see some Jupiter`s moons. The selection of a telescope is not
trivial, and will depend mostly on other factors, not magnification. The most
important factor is quality of construction, and you better stick to Zeiss, or
Takahashi if you can spare the money. The russian Intes is a much cheaper
alternative with high quality. Then come the Meades and Celestrons, wich have
models for all budgets. You won´t regret having any one of these. Then comes the
choice of the diameter of the objective. If you want to see the
moon and planets, where light gathering capacity is not an issue, you may look
into a small refractor or Maksutov. But if you want to see deep sky objects such
as nebulas and galaxies, you need a large diameter objective, say a minimum of
200 mm.The refractors become too expensive in these sizes, but you have a choice
of Maksutovs, Cassegrains and Newton reflectors. Also, don´t forget the mount.
The telescope orientation must compensate for the earth`s rotation, and the
telescope mount should do this. You have a choice of mounts to do the job,
depending on the size and weight of your telescope. In short, I recomend you
find the local astronomical club, see the plethora of equipment choices, get
some eyes on experience with them, and then make your choice. José
Almeida.
-----Mensagem original-----
De: Navigation Mailing List [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]Em nome de Andrew Corl
Enviada em: segunda-feira, 6 de outubro de 2003 18:46
Para: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
Assunto: 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
