Telescope Reviews: Cassegrain

Hello Folks,

** Reiner,
Thanks for the nice photo of your great folded Newtonian.
Yet, those do lower the height of the EP and you height and scope
seem to be made for each other. And thanks for the links so others
can enjoy more info.

** Sallies,
Thanks for the link to the other Gregorian style of Dob thread.

I believe, the Gregorian light-path allows the image to go past the
focal point before being reflected back down the tube off the
secondary mirror.

In the Nasmyth light-path, the image is reflected off the secondary
before the focal point is reached and the light goes back down the
tube to a third mirror to be reflected left or right through the altitude
shaft to the focuser and EP where the focal point is reached. This
makes for a far shorter OTA and allows the observer to stand on
the ground or sit in a chair which could be easily attached to the
telescope and pivot with the telescope through the azimuth.

In a so-called "modified Nasmyth" design, some ATMers have made
the light-path the same as the Nasmyth above, however the third
mirror is placed close to the primary and reflects the image up
through the rocker-box to the focuser and EP on the top of the
rocker-box.

If you make a mount slightly higher, then you can have the light-path
continue through the center of the primary mirror (Cassegrain --
SCT/MAK style) and have a regular diagonal on the end of the tube
(the bottom of the rocker box). This may be too low for Zenith
viewing unless the scope is mounted higher.

Thanks for the great links to some good information.

** George N,

Sorry George, the link didn't seem to work for me, even after a
couple attempts. Seems if Mr. Novak won a couple prises with the
scope, there must be something goos about it, or was it the
quality of construction?

* * *

Thanks for all the posts. Lets see if we can get a few more photos
showing the placement of the focuser and the EP. A description
of where the secondary and third mirrors are and how they are
mounted with some measurements would be great too.

Thanks everyone.
Cheers,

--------------------
Clear skies...
Duncan

"Watch the skies, everywhere! Keep looking. Keep watching the skies!"
-- Closing line in movie spoken by newspaper report Ned "Scotty" Scott (Douglas Spencer) in the Sci-Fi movie
"The Thing From Another World", RKO Radio Pictures, 1951.

Antares (refractor) 127mm f/6.45. w/2-spd Crayford
Orion (Maksutov) 150mm f/12 w/2" EP adapter
Giro 3 (twin), 18" pier, EQ5 tripod.
Garrett 20x80mm, 410 head, 055 tripod.