The Twenty Five

The assembled scope is easily moved on the wheels which can be left on
during observing or removed in seconds.

Side by side comparison of the Twenty Five and the Sweet Sixteen Telescopes.

 25" f/3

The f/3 scope with Argo Navis, ServoCat, and Starlight SIPS coma corrector/focuser system. It features a 1.7" thick Lockwood primary and matching 6" secondary. The eyepiece height is 70" at zenith, but the remaining dimensions other than overall height are the same as the F4 specifications listed below.

 
The Twenty Five shares the basic design concept of the sweet Sixteen, but has a number of new features I wanted for this larger telescope.

Dimensions and weight:
Height at zenith ..........................................   103"
Eyepiece height at Zenith .........................   95"
Rocker box footprint..................................    31.5" square
Weight complete with Servocat etc. .......    288 pounds
 
The following photographs taken at various stages of the construction of this, the first of three telescopes built, best illustrate the new features. Please contact me if you have questions about the construction or availability of the Twenty Five.

 

Rear view showing the JP Astrocraft 18 point mirror cell and the Mike Lockwood 1.7"  thick primary optic. This is a tilt down / lift out type cell which is secured by the four black knobs at the four corners of the frame.  The five round ventilation holes in both the front and rear faces of the mirror box allow passive airflow across the front surface of the mirror. These can be fitted with fans if additional boundary layer cooling is desired.

 

Removing the four knobs allow the cell to tilt down for easier insertion or removal of the Lockwood Primary. The cell also simply lifts out of it's "U" shaped support brackets.  This cell features spherical bearings at the triangle supports and a 45 degree wiffletree edge support. Robert Houdart has a nice analysis of edge supports on his Cruxis telescope web page.
 

 

 

Bottom view of the flotation triangle showing the mounted spherical bearing and triangle positioning pin.

 

 

The mirror installed.

Electrical contacts at the upper right of the frame engage as the cell is closed to provide power to the cell fans.

 

These are the parts that make up the truss system . The ball shaped recesses milled into the two lower inserts and the upper cage mounting angle provide a positive alignment system when the ball shaped end of the knob is tightened. The two 1 1/2" poles end at a common point forming a true triangle for optimum strength. The poles are connected by a brass tee nut  which provides both a bearing and a connection. The spot faced recess in the right ear allows everything to clamp up solid when tightened. This system allows fast easy assembly of the telescope.

 

The lower end of the truss showing how the lower insert fits over a 3/8" stainless mounting stud in the 3" x 3" x 1/4" aluminum corner angle.

 

 Side view of the top showing how the knob draws all the parts tightly together. The top ears on the poles are 3/8" thick aluminum bar.

 

A massive 4 vane spider featuring a center hub milled from a 2" solid bar. Note how the big hub has the square plate holding the four collimation screws  tightened securely to it.  This keeps the secondary mounting stud from bending under the weight of the large secondary.
 

 Power to the upper cage is routed through a truss pole and plugged into a junction block mounted on the bottom cage ring.  Strut tubes are located directly above the truss anchor for maximum rigidity.

 

 

A switch block mounted on the finder board distributes power to the anti-dew devices. The right hand switch controls the Astrosystems secondary heater while the other two provide switched junctions for finder and eyepiece heaters.
 

 

 

Even though the assembled scope weighs 288 lbs, the integral wheels allow me to move it out of the shop to my observing site about 200' away. The wheels detach quickly if desired . Slide bolts lock the mirror box to the rocker for moving. Integral wheels are nice if you have facilities to store the assembled telescope as it's over 8' high.

 

The rocker has inserts to attach wheelbarrow handles for loading into a vehicle. Normally, however I will have a friend help me lift the lower assembly into my van using the two handles on the rocker.

 

This picture of the scope was taken just after I had mounted the ServoCat and Cattail stalk.

 

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