12.5" RC Optical Systems Ritchey-Chretién

The 12.5" RC Optical Systems Ritchey-Chretién telescope is the largest aperture scope I own. Used in either its native f/9 or reduced f/6.9 configuration, the
corresponding focal lengths of 2800 and 2150 mm respectively make this instrument perfect for imaging a wide variety of astronomical objects.
The optical tube assembly is 15.3 inch diameter x 40 inches long and is a hefty 55 pounds, making it a handful to hoist atop the mount.


Looking down the barrel. The ribbon cable for secondary
mirror positioning and dew heater are seen in this
image. The small black probe with blue wire is the
ambient air temperature sensor.
The rear cell is the older RC design with the cooling fans on
the exterior. Primary mirror collimation is accomplished
by adjusting the three bolts sets at 120° spacing. I added
two additional handles at the 9 and 3 o'clock positions.
RCOS Telescope Command Center (TCC) shown mounted on
rear tube ring. The TCC connects to the telescope via a MIL
style plug and controls cooling fan speed, secondary mirror
positioning and the secondary dew heater.


The primary mirror baffle tube has a total of seven baffles of
ever-decreasing aperture running down its length for
maximum contrast and performance.
I've added a few enhancements to my RC telescope as shown above. First, I installed an aperture mask around the outer circumference
of the primary mirror to cover the bevel at the mirror's edge in order to reduce "flaring" on brighter stars. The precision ring and
three mounting feet were supplied by RCOS. I did my own machining to fit the mask to the rear cell, which involved drilling and
tapping operations. Secondly, I added two chrome handles to the rear cell (one visible in the above image) to make handling
this telescope a little easier. Drilling and counterboring operations were required for this add-on. Having these two extra
handles has proven to be a handy thing.
Here you can see a close-up of the aperture ring foot mounting. The foot fastens to the inside surface of the rear cell with two #10-32 Allen
head cap screws. Also visible in this image is a countersunk hole with a #10 Allen head cap screw in place, fastening one end of the two
extra handles I added to the rear cell for ease of handling.