Ann Randolph '02, Kendra Rand '02, Duane Sturino '01
The goal of this class was to have each student build their own personal telescope. The telescopes built were 6 inch f/8 Newtonian reflectors. Each student was given a mirror blank, a glass tool, the parts for a grinding stand which would later serve as the telescope stand, the grinding compounds, and a place to build the telescope hardware. Below is a diagram of a Newtonian reflector telescope.
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To start out, the students assembled their grinding stands and began to grind the mirror blanks. The mirror's surface had to be ground until it was nearly smooth. The grinding started with 220 grit sand and went all the way to 9 micron powder. This process took several days. |
| Once the grinding process was completed the polishing process began. First a layer pitch was poured onto the glass tool. The mirror, coated with polishing compound, was pressed onto the lap to make the pitch conform to the mirror curvature. After the pitch tool is created grooves need to be cut into the tool to allow the polishing compound to be evenly distributed across the surface of the glass. It also allows air between the glass and the pitch tool which is important for removing the tool from the glass. This was done using a saw to cut grooves in the pitch. |  |
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After the polishing tool was formed the students began the polishing process. This can range from 9-12 hours before the glass is completely polished out. In order to polish the glass Cerium oxide is used as the polishing compound to remove any remnants of the grinding process. |
| Once the mirrors were polished out completely, the figuring began. The method the class used for figuring is called the foucalt test. The test is used to correct the surface of a mirror, first to a sphere then to a parabolic shape. The test was conducted in a completely dark room. |  |
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The Foucault test basically contains a light source on a moving platform with a straight edge attached to it. A beam of light is projected to a fully polished piece of glass. The returning beam of light is intersected by the straight edge at a point where the straight edge evenly divides the returning light. This will allow the person who is viewing the glass to see the various defects in order to determine the methods to correct the defects. |
| Once the mirrors were finished, they were shipped off to be coated with a thin layer of aluminum. At this point the mirror mounts need to be created. The mirror mounts were created out of 3/4 inch plywood. The mirror mount consists of two pieces of plywood, the first section is a 6 inch disk and the second piece is a 7 inch diameter arc triangle. They are held together by three bolts, springs, washers, and wing-nuts. This assembly allows for adjustment in the angle of the mirror for collimation. |  |
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The stands that were used for grinding now needed to be converted into telescope stands. The grinding platform was removed from the flange and discarded. The pipe tee was then rotated 90 degrees and threaded back onto the pipe, so a cradle could be attached to allow the telescope tube to swing in both altitude and azimuth. The stand consists of a thirty inch long, two inch diameter galvanized pipe, a 2" nipple, flange, and a tee. |
| The tubes arrived and needed to be painted on both the exterior and interior. The outside of the tubes could be painted at the discretion of the students, however the interior of the tube had to be painted flat black to prevent light scattering. |  |
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When the mirrors returned from being coated, they were glued onto their mounts and the telescopes were put together. Each student was supplied with a 20 mm eyepiece which, in conjunction with the 6 inch mirror, is a good instrument for observation of the night sky.