Hi, so I purchased a old orange Celestron C90 back a couple months ago, it's a great scope that's super fun to use, but the previous owner had lost the dust cap that goes on the back, and replaced it with a pink pill bottle cap that only kind of fits. The stupid thing is driving me nuts, and doesn't even screw on right in the first place. I was looking at replacing it with one of the 3D printed dust caps people in the classifieds sell, but realized that I have no idea what sized thread that is on the back of the scope. Does anyone know what size it is?
Thread Size on Back of C90
Posted 20 October 2020 - 10:56 PM
How accurate does it need to be? You could measure the width of the threads and count them, that'll give TPI.
Posted 21 October 2020 - 01:53 AM
The hole fits a .965" diagonal so you might plug it with a junk eyepiece, until you find a decent cap.
- GreyDay likes this
Posted 23 October 2020 - 08:40 PM
The C90's rear external thread, is: 1.375" * 24TPI and was used for mounting photo accessories such as the tele-extender for eyepiece projection AP.