[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]

[ATM] Tri-shiefspiegler


I lack the mirror making experience needed to address the 
optical issues so it's best I leave that domain to others. 

However, I've spent a lot of time developing a building method for 
OTA's for both 4.5" and 6" variants of the two mirror Schief.

I used the math generated by David Grotsky for correcting 
aberrations and modeled the OTA for his 4.5" variant as built by 
Bill Cheng. The only difference being I chose a medium I am 
more familiar with: composites.

Bill brought his 4.5 to the annual Mirror Making event hosted by 
the DelMarva StarGazers earlier this year and it was an instant 
hit with all who used it.

Perhaps it's inappropriate to make comparisons between the two 
designs. Still, the physical geometry of the two telescopes are 
structurally quite similar me thinks and do not, in my opinion, 
represent any significant obstacle.

Listening to Dave Grotsky speak on the subject of making the 
mirrors left me with the impression that they too are not a 
significant challenge.

The biggest challenge, it appears, is carefully testing the optical
performance mathematically BEFORE you cut the first piece of 
carbon fibre or grind the glass. The second is to insure, as Martti 
Koskimo 
suggested, that the system has sufficient latitude in adjustments 
to
support proper collimation.

Art Bianconi

There are JPG's of both designs enclosed.




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.
Not symmetrical system. 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>
Subject: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


Attachments:
  D:\MAIN GRAPHICS\Astro-E-Mail JPG's\Schiefspiegler E-
Mail\EM-Bill
  Cheng's Telescope@Mallard Lodge 04--03-08 016.jpg D:\MAIN
  GRAPHICS\Astro-E-Mail JPG's\Schiefspiegler E-Mail\EM-Bill 
Cheng's
  Telescope@Mallard Lodge 04--03-08 010.jpg D:\MAIN
  GRAPHICS\Astro-E-Mail JPG's\Schiefspiegler E-Mail\EM-4.25
  Schief-Slide Mount.jpg D:\MAIN GRAPHICS\Astro-E-Mail
  JPG's\Schiefspiegler E-Mail\EM-4.25 Schiefspiegler
  telescope-TOP-Quarter.jpg
------- End of forwarded message -------

_______________________________________________
ATM mailing list http://www.atmlist.net/