My Ultima spotting scope zoom eyepiece isn’t threading on the scope. What’s wrong?

Most likely it's because you accidentally unscrewed part of the zoom eyepiece assembly while removing it from its case.

Here is the eyepiece case.
eyepiece case

 

Here it is with the top of the case removed.
top off

The eyepiece should screw off, leaving the case bottom.
bottom of case

 

Instead, it may screw off and look like this:

bottom plus part of eyepiece

If this has happened, then this ring has come unscrewed off the eyepiece and is at the bottom of the case.
eyepiece ring part

The eyepiece without the ring will look like this:

eyepiece without ring

Remove the ring from the case bottom and screw it back on the eyepiece.

Here is the correct appearance of the complete eyepiece:

complete eyepiece

To prevent this from occurring again, when putting the eyepiece in its case don’t tighten it down as firmly. This way, the ring should come out with the rest of the eyepiece instead of staying with the case.

 

Updated 12/18/13