Re: [ATM] Tri-shiefspiegler

["Martti Koskimo" <martti.koskimo@kolumbus.fi>]

David,




The Optical Design of TriSpiegler is based only on those 3 mirrors. Optical
window is not needed.

There are 3 mirrors to make and they all have very long focal lengths making
the optics relative easy to make. Surprisingly the ( in 400 mm Telescope)
the tertiary 150 mm diameter mirror was the difficulties mirror to make . It
has almost 100 meter long radius of curvature. I had to use a Telescope to
test the optics . Can't even see the mirror with the naked eye !

One advantage usually not mentioned from unobstructed Mirror Telescopes is
that  when the secondary mirror is outside of the primary light path  then
also bad thermal effects from secondary mirror are much reduced.

Surprisingly the TriSpiegler is excellent telescope for deep sky
objects....... long focal length and fully baffled system

With the 400 mm TriSpiegler Airy disk  can be seen very often and planetary
and lunar details are incredible.

The disadvantages of TriSpieglers are:

Awkward structure: More difficult to attach to Telescope mount.
Collimation : Not symmetrical system making collimation time consuming .
Focal Plane: tilted  focal plane also a disadvantage.

I do not want to start discussions about the assumed bad effects of
obstructed  Telescopes. My Opinion probably differs from that of most of the
list.
I only say that in my extensive practical experiments the effect of Central
obstruction ( 1:5 or smaller) in planetary and lunar detail is very small.
Mostly the many forms of thermal effects are the ones that spoil the image
in reflecting telescopes:

I have made two TriSpieglers one  200mm and the other  400 mm Diameter
optics and use them regularly.
I made 450 mm diameter optical window to close the tube but that is an other
matter.

Picture of the 400 mm Telescope  is hosted in
http://www.astro-electronic.de/trispieg.jpg
                                                        and
http://www.abilitysystems.com/koskimo.html


 Martti Koskimo





----- Original Message ----- 
From: "David Williams" <dwilliams1128@earthlink.net>
To: <atm@atmlist.net>
Sent: Friday, May 21, 2004 11:28 PM
Subject: [ATM] Tri-shiefspiegler


Hello

Does anyone know of the advantages of the Tri-shiefspiegler telescope
besides that there is more consentration of light in the first few rings in
the difration patern of a star?  And therefore better resolution at the same
power.  It apperently has 3 mirrors, but do you know if it has an optical
window too?  How difficult are these instruments to make?  Are they pretty
heavy (like their density ratio compared to other telescopes)?

Thanks
David Willliams
dwilliams1128@earthlink.net
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