Baffling quastion on Mak scopes.

Hi All, looking at the designs for Mak scopes it seems that the length
of the primary baffle is so long that light rays coming from the
primary must collide with the outside of the baffle . I did a ray
trace diagram on a couple of scopes and was surprised to find that a
circular area almost 1" wide around the tube is affected.If this is
the case, wouldn't it be better to mask off this area of the mirror to
stop the stray light produced. Can anyone "shed any light" on this
problem and is there a book that gives any info on the baffle design
for a Rumak Mak Cass.?
Cheers Brian Morse.

Part of the problems with any of the Cassegrain designs. If you don't have
access to a baffle on the secondary, the problems become even worse.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works every time it is tried!

"Bob May" wrote in message ...
Part of the problems with any of the Cassegrain designs. If you don't have
access to a baffle on the secondary, the problems become even worse.
The only real solution to the baffling problem for
Cassegrain-type telescopes that I know of is to place a field lens
near (but not coincident with) the focal plane followed by a set of
transfer lenses with a stop between them. The final image is formed
by the transfer lenses. The field lens forms an image of the primary
mirror (as seen through the secondary) on the stop which has exactly
the same diameter as the image of the primary mirror. All rays which
do not come from the primary mirror are eliminated by the stop. The
field lens and transfer lenses are mounted on a tube similar to the
usual baffle tube mounted through the hole in the primary and can be
completely contained in the converging beam from the edge of the
central hole of the primary. No lost light. The final image formed
by the relay lens is completely free from extraneous light, and the
secondary mirror can be made much smaller than that of a 'normal' Cass
which achieves the same final focal plane behind the primary. The
only disadvantage the trans-Cass (as I call it) has is stronger
curvature of field, an unavoidable consequence of the additional
positive lenses in the system.
Horace Dall did something similar to this with a transfer lens
on a folding Gregorian telescope reported in one of the ATM books (I
think book III). In this case, the concave secondary already formed
an image of the primary so the field lens was not necessary and the
transfer lens itself served as the stop. So effective was the
elimination of extraneous light that no outer tube was needed for this
telescope.
A friend of mine, Roger Tuthill, built a 20" trans-Cass and
demonstrated it at one of the Stellafane conventions in the late 60's.
He used a pair of 2-1/8" diameter ~f/8 (as I remember) Jaegers
achromats with the crown elements facing one another on opposite sides
of the stop. The telescope had a very dark contrasty field. I
remember seeing the Veil Nebula with it when he demonstrated it on
Breezy Hill. It is presently being refurbished at Sperry Observatory
by AAI members.
Clif Ashcraft

(Clif) wrote in message . com...

@nethere.com wrote in message ...
Part of the problems with any of the Cassegrain designs. If you don't have
access to a baffle on the secondary, the problems become even worse.
The only real solution to the baffling problem for
Cassegrain-type telescopes that I know of is to place a field lens
near (but not coincident with) the focal plane followed by a set of
transfer lenses with a stop between them. The final image is formed
by the transfer lenses. The field lens forms an image of the primary
mirror (as seen through the secondary) on the stop which has exactly
the same diameter as the image of the primary mirror. All rays which
do not come from the primary mirror are eliminated by the stop. The
field lens and transfer lenses are mounted on a tube similar to the
usual baffle tube mounted through the hole in the primary and can be
completely contained in the converging beam from the edge of the
central hole of the primary. No lost light. The final image formed
by the relay lens is completely free from extraneous light, and the
secondary mirror can be made much smaller than that of a 'normal' Cass
which achieves the same final focal plane behind the primary. The
only disadvantage the trans-Cass (as I call it) has is stronger
curvature of field, an unavoidable consequence of the additional
positive lenses in the system.
Horace Dall did something similar to this with a transfer lens
on a folding Gregorian telescope reported in one of the ATM books (I
think book III). In this case, the concave secondary already formed
an image of the primary so the field lens was not necessary and the
transfer lens itself served as the stop. So effective was the
elimination of extraneous light that no outer tube was needed for this
telescope.
A friend of mine, Roger Tuthill, built a 20" trans-Cass and
demonstrated it at one of the Stellafane conventions in the late 60's.
He used a pair of 2-1/8" diameter ~f/8 (as I remember) Jaegers
achromats with the crown elements facing one another on opposite sides
of the stop. The telescope had a very dark contrasty field. I
remember seeing the Veil Nebula with it when he demonstrated it on
Breezy Hill. It is presently being refurbished at Sperry Observatory
by AAI members.
Clif Ashcraft