|13.1" primary mirror, ground and polished by Mark Suchting
(Deep Sky Optics), Sydney.
This is a traditional conical mirror with a central plug. Normally this plug is removed and discarded but in this case the centre plug was removed, cut to 15mm depth and reinstalled before polishing.
This was done so I would have somewhere to put the centre spot, and makes collimation of this mirror a lot easier.
|Side view of mirror on its mounting plate with integrated refrigeration unit. One of the circulation fans is visible under the near edge, and the wire to the temp sensor can be seen to the left.|
|Another angle of the primary and its mounting plate|
| A side view of the primary showing the conical back and more
of the cooling unit. The mirror sits on the cold plate, and you can see
a perspex separator and then the hot plate on the outside. The three
peltier cooling units are sandwiched between these plates.|
The Mirror is attached to the cold plate with silicone bathroom sealant so it doesn't fall off. The mirror is also sitting on a metal stud that goes 50mm up through a central hole in the back.
|A last view of the primary after I attached the centre spot. The points of the triangle are aligned with the collimation adjustment screws (see the holes near the edge of the mounting plate).|
| This is the top section of the scope, all aluminium construction. It stands 600mm high and holds the
focusser, secondary and finderscope assemblies. This tube section was built
by Gary Mitchell in Sydney.|
The 3 vanes for the spider pass through cutouts in the tube and then anchor to the metal ring you see here. Rotating the secondary is done by rotating this metal ring.
The vanes are also able to move independantly in the vertical direction, to adjust the tilt of the secondary. Each vane ends in a threaded rod that is spring loaded so it holds tension but can still be moved up and down through a slit in the ring.
The focusser in the middle is a JMI DX1-M motorized unit, mounted on it's own mounting plate for easy removal.
More close-up images of the spider construction and mounting are here.
| The bottom (left) and top (right) sections shown together. The top is 600mm and the
bottom is 1200mm. The total scope length is 1800mm when assembled.|
Both tube sections were manufactured from aluminium by Gary Mitchell in Sydney.
|Another closeup of the top section. At the very top of the image you can
see inside the tube to the cutout on the far side where the rear vane passes
out and through the ring.|
When adjusting the secondary tilt it's easiest to leave the rear vane alone and adjust the two close vanes, that way you can keep your eye at the eyepiece (or autocollimator, cheshire or whatever) while adjusting the secondary tilt and rotation. The whole thing is held in place by friction so it can be adjusted by gentle nudges in the right direction.
The metal ring sits on teflon runners, you can see two of them in this image near the ends of the ring.
|Laying the bottom section over we can see the cooling unit that makes up
the mirror mount. There are many heatsinks and fans visible, this is the
hot side of the unit.|
At the edge you can see the three collimation adjustments for the primary mirror. These large triangular knobs allow for easy and precise adjustment of the primary mirror tilt.
|Looking in the other end of the bottom section you can see the primary mirror.|
|Assembling the scope in the backyard, halfway there - the bottom section is on the mount.|