Celestron 20mm erecting eyepiece

[sjj1805]

I “accidentally” took apart my Celestron 20mm erecting eyepiece. How do I put it back together?

Answer
Normally you should not need to remove any lenses from an eyepiece for cleaning, since only two lenses – the eye lens closest to the eye and the field lens (at the opposite end) closest to the telescope – are exposed to dust and contact from fingers, etc.

Care must be taken to keep the disassembled pieces clean and lenses unscratched while reassembling the eyepiece. Prepare a clean surface on a desk or table for the reassembly.

The disassembled eyepiece will consist of six parts. Here top, up or uppermost will mean the eye end of the eyepiece. In the order of assembly from bottom to top here are the pieces.

The largest part is the main body (barrel) of the eyepiece itself. The name of the eyepiece is on the top of the eyepiece barrel.

The second piece is a spacer. It is round and stepped and about 3/4" high. The narrow end will eventually go down into the eyepiece barrel.

The third piece is a lens. It is the bigger of the two lenses from the disassembled eyepiece. (If you look closely you'll see that it's actually two pieces of glass cemented together.) One side is flat and one side is curved.

Take the stepped spacer and place it on the table, narrow end down. Place the big lens with the curved side up into the larger diameter end of the spacer.

Next, place the spacer and lens into the eyepiece barrel. The narrow step end of the spacer will go down into the eyepiece barrel. Be sure that the lens is correctly in place on the spacer and not tilting at an angle after you drop it into the eyepiece barrel. Double check that the curved surface of the lens is uppermost.

The fourth piece is another spacer. It is not stepped on the outside. On the inside, one end is stepped and one end is bevelled. Put the spacer down on the table so the bevelled end is upright.

The fifth piece is the second, smaller lens. It also has a curved and a flat surface. Place this lens on top of the spacer (part four) so that the flat surface is uppermost.

Now take the smaller lens and spacer together and place them over the larger lens already in the eyepiece barrel. The inside step on the smaller spacer will fit over the larger lens. Be sure it is seated on this lens.

The sixth and final piece for reassembly is the eye-cup. Gently place the eye-cup threads onto the eyepiece barrel and screw the eye-cup into the barrel. Be careful not to shift any of the previously assembled parts out of position as you reattach the eye-cup. Avoid cross-threading the two pieces. Tighten the eye-cup with moderate but not excessive turning force.

NOTE: disassembling an eyepiece may void its Celestron warranty.