Over a decade ago, I started to see low power wide field of view telescopes build by fellow ATMer's that used the lens from an old copier machine as the objective lens. Hence, the name for scope became known as a "CopyScope".
2.52" or 64 mm
Focal Length f/4.6
11.6" or 300 mm
Magnification with 20mm Plossl 54° FOV
True Field of View (TFOV)
How I got started: I brought a copier lens from the Surplus Shed years ago. It is a 64mm f/4.6 lens. It came in a metal housing. Attached to it was a removable bracket held on by two threaded retaining rings. I loosen the rings and threw away the bracket. The diameter of the threads around the cell is about 80 mm (3.15 in). Due to the weight of the lens and its cell, I decided to go with PVC pipe for tube for strength. Unfortunately, the threads were too big to fit in a 3 inch PVC pipe. The next size up is the 4 inch pipe. Moving up to next size also allowed me to use the retaining rings.
Mounting the lens: I decided to use the retaining rings to hold a donut made from PVC pipe. This donut will hold the lens cell in the 4 inch pipe. But how? Lucky, I discovered that a 3 inch PVC coupler will fit neatly inside a 4 inch pipe. So, I purchased two couplers and cut each one of them in two. Then, I took a piece of 3 inch pipe and epoxy it into one 3 inch coupler halves. After letting it to dried, I use a wood turning lathe to trim the ends and enlarge the inside diameter of the donut to allow the lens cell to slide into it. By turning the retaining rings, the lens cell and the donut are locked into place. I took the other half of the 3 inch coupler and epoxy it into the 4 inch pipe. It acts as backstop for the lens cell assembly and keeps it from sliding all the way through. I used another half to make a retention ring and which locks the whole assembly in place. The lens cell is removable by pressing against the lens cell from the eyepiece end (back end) and sliding it out the front end. Friction between the retention ring and the tube keeps the lens assembly in place.
The optical design: The challenge was the fact that the focal plane was only 8.5 inches from the back of the metal lens cell. After some quick light ray tracing, I determined that internal baffling was not needed. Another complication with this short distance is that a low profile focuser is needed to keep the draw tube from cutting into the light cone from the lens. After considering a half of different focuser designs and their costs, I decide to build a simpler Crawford style focuser.