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How to Build a Telescope Eyepiece

Telescope eyepieces basically magnify the image made by an objective lens or telescope primary mirror. Eyepieces usually increase, but may also decrease the size of the image sent through them in order to widen the field of view or improve detail of the object in the scope. In building an eyepiece, remember that the greater the magnification, the dimmer the image becomes. Higher magnification also reduces the quality of the image due to air turbulence, flaws in the objective or movement of the telescope. Good eyepieces can be made inexpensively using a two-lens surplus lens kit.

Things You'll Need

Telescope eyepiece lens kit from a surplus optics supplier or lens manufacturer
Fine-tooth small hacksaw
2-inch OD PVC pipe
2-inch PVC pipe endcap
Black marker
PVC glue and cleaner
Drill
Epoxy glue
Thin cardboard strips
Soft linen cloth
Superglue
Black electrical tape

Instructions

- 1
  Check the spacing requirements for your lens elements to help you determine the length of your tube. This information will come with the lens set. The kit should also tell you which lens goes on top and which on the inside of the tube. Good eyepiece kits come with two or more lenses. Multiple lenses reduce color aberrations and the rainbow effect.
- 2
  Cut the tube with the hacksaw to the proper length for your two lenses as determined in Step 1. Blacken the inside of the PVC tube with a large marker to reduce light reflection. Blacken the inside of the endcap as well
- 3
  Clean one end of the open tube and glue the endcap on with PVC glue. Allow to set for two hours.
- 4
  Drill a hole in the center of the endcap. The size of the hole should be a little bit larger than the outside lens so that the lens slips easily through the hole you've made. Run the drill bit back and forth till the hole is large enough.
- 5
  Cut a 0.25 inch wide strip of thin cardboard large enough to match the circumference of the hole you just drilled. Trial fit the cardboard inside the hole until it just fits the inside of the hole and presses tightly against the side. Test the lens to see if it fits inside the cardboard liner. You may have to enlarge the drilled hole a few times till the lens fits snugly into the cardboard sleeve inside the hole in the endcap.
- 6
  Use superglue to secure the cardboard sleeve strip around the inside of the endcap hole. Allow to set for an hour. Holding the lens with a soft linen cloth, carefully slip it into the cardboard sleeve. Once the lens is seated, apply three small drops of superglue evenly spaced around the edge of the lens.
- 7
  Lay a long strip of black electrical tape flat up on a table. Starting at one end, roll the edge of the inside lens along the strip of tape and let the tape roll up around the outside edge of the lens. Don't let the sticky side of the tape touch the lens. Roll up enough tape around the lens to make a tube of tape with the lens in the middle. The tube should fit snugly inside the PVC eyepiece tube at the open end opposite the endcap. Push the tape and lens assembly up inside the tube so that the inside lens is where it should be in relation to the outside one. The black tape should be entirely inside the eyepiece tube.
- 8
  Slip the eyepiece into the focuser and try it out.

Astronomy