Hobbies And Interests
Things You'll Need
Instructions
Create the plywood base of the telescope, cutting all pieces to exact lengths and widths per the charts located in the San Francisco Sidewalk Astronomers plans. The sizes must be measured based on which size of telescope you have chosen to build: the 8-inch diameter telescope or the 10-inch diameter telescope at a fixed f/7 focal length. Be sure to follow the recommendation that each piece is marked with a pencil or crayon, so the parts may be assembled in order as they are given. Since several pieces are close in size, many first-time builders experience difficulty if the parts weren't marked as they were cut.
Determine the actual focal length of the objective mirror purchased. According to the plans on which this article is based, a partner should be present. Find a flat, level vertical wall on which you may reflect a star or the moon, using the mirror.
Instruct your partner to catch the light of a star or the moon and reflect the light onto a location on the wall, moving backwards and forwards slowly while you watch for when the reflected dot of light is at its smallest on the wall, given the location of your partner. With the smallest point visible on the wall, use a measuring tape to measure the exact distance from the image to the mirror and write this down as it will be needed for trimming the cardboard tube and the eyepiece tube.
Trim the sonotube per the charts listed in the plans based on the measurement taken above. Although most mirrors will come with near exact focal length as ordered, there can be some variance. For the most optimum performance the tube length must be trimmed according to the actual focal length of the objective, or primary, mirror.
Peel the plastic liner carefully out of the sonotube gently, so the interior maintains a smooth and even surface. To ensure all of the captured light of a celestial object is reflected by only the mirror and not the interior of the tube, tape a paint brush to the end of a long 6-foot stick and use it to paint the interior with flat black paint to eliminate any interior reflectivity of the tube itself.
Build the secondary mirror mounting assembly (called the "spider") using the piece of dowel, shingles, glue and leather scrap. Once the assembly has been built according to the San Francisco Sidewalk Astronomers recommendations, apply a generous amount of white craft glue to the slanted portion of the dowel you created. Allow the glue to dry until sticky, but not wet, so that the back of the secondary mirror will stick without sliding from its position once it has been placed. Allow the assembly with mirror intact to dry for 48 hours undisturbed.
Prepare the eyepiece holder by applying glue around the outside of one end of the short piece of cardboard tube and insert that glued end through the hole in the piece of prepared Masonite (the piece which the hole was drilled in the middle) and allow to dry until firmly in place. Once dry, slide the piece of brass tubing inside of the cardboard eyepiece tube. The fit should be snug. If too tight to insert the brass tube, peel out a thin layer from inside of the cardboard tube. If too lose, glue a thin strip of cardboard to the inside of the tube.
Cut (or drill) the eyepiece hole into the sonotube. For a sonotube that is 10 inches in diameter, the hole should be cut 5 inches from the front end of the sonotube. For a tube that is 12 inches in diameter, the hole should be cut 6 inches from the front. Once cut or drilled, apply glue to Masonite on which the eyepiece tube is glued to, applying it to the side on which the length of the tube is located (not the bottom). Slide the eyepiece tube through the hole by doing so from inside of the sonotube. Press against the interior of the sonotube and maintain pressure for several minutes allowing the glue to set.
Install the secondary mirror and spider into the inside of the sonotube near the eyepiece tube previously installed. Follow the plans to ensure it is aligned for optimum performance.
Build the objective mirror "tailgate" and mount the mirror to it, fastening per recommendation in the plans, and install it to the back end of the sonotube.
Assemble all parts of the tube mounting box and install the completed telescope to this box. Paint if desired.
Install an eyepiece into the eyepiece mounting tube and make adjustments by carefully following the procedure outlined within the San Francisco Sidewalk Astronomers plans, which go into much detail about proper alignment and maintaining that alignment.