What does an astronomer do when it is cloudy and very cold? Not much astronomy to be sure.
So instead of observing the stars with telescopes, lets do some disassembly!

This is our Meade DS90 refractor, purchased from Costco in 2008 for approx $190. It had a computer controlled mount until the main plastic gear ground away. So we put the mount away awaiting spare parts and have used the Optical Tube Assembly (OTA) on other mounts since then.

We noticed that there had developed some dirt/cloud/scoring on the primary lens… so over the holidays, it came apart for a cleaning. This is the DS90 OTA. The cap comes off by friction as does the dew shield. The primary lens assembly had 3 screws and was marked with ink before it came apart. 3 screws for the focuser as well, with ink markings made.

The 5/4″ 90degree eyepiece holder, mostly plastic


The Rack and pinion focuser, fully extended

The dew shield and end cap, all plastic

The primary lens assembly. The stuff on the primary is hard to see but it looks like a water level flood line about 1/3 of the way up/down.

The Optical tube itself, coated black on the inside with a baffle

Reattaching the primary lens assembly, to the marks made *before* disassembly! Three screws.

Adding the dew shield, not so critical but why not put it back together exactly? THis is strictly a friction fit, no screws.

Reattaching the focuser, matching the alignment marks. Three screws

After the OTA came apart, the primary lens was cleaned using glass cleaner on the inside and outside and lint free tissue wipes. That certainly fixed the problem that started this whole process.
Putting it back together went much faster than taking apart, as that was a learning experience with note taking.
I did take measurements when it was apart… but do you think I can find them right now? They will be added in later.

Updated: 2018Jan21
Found the measurements!
Primary lens 3 5/8″ at one end, 3 1/2″ at the other and 4″ long
Optical Tube Assembly Length=20.5″, Inside diameter= 3 5/8″. There is a baffle with a 2 1/4″ hole, located 4 3/4″ inside from the focuser end and 15 1/2″ from the other end.
The dewshield is 6 3/4″ long and 4 1/2″ diameter at one end and 4 5/8″ at the open end.
The focuser travel is 5 1/2″ with a total length of 10 1/2″