When is a 102mm tube ring not.........

[Merlin66 (Ken)]

The SW tube rings are advertised as 102mm, BUT the internal diameter measures 100mm!!!!!!!!!!!!
I ordered them to mount a new 4" (102mm) refractor for a SHG.
OK, what should I have ordered?????

[iborg (Philip)]

Hi Ken


From https://www.optics-pro.com/tube-clam...ng-set/p,16103


It says Internal diameter max. (mm) 10.


Could it be that the metal has an ID of 102mm, but, usable ID reduced by padding?


Philip

[astro744]

Ok. 4” = 101.6mm. Is the 4” lens also in a 4” tube?

Sky-Watcher call them 102mm rings.

Saxon call them 102mm rings with 101mm I.D.

Orion call them 100mm I.D. rings.

They look like they all come out of the same factory but perhaps not. Could also be quality control issue.

Do you not have enough length in the captive screws to be able to lock the rings around the tube?

[Merlin66 (Ken)]

The aluminium tube for the OTA arrived. Outside diameter measured 101.7mm.
This JUST (!!!!) fitted into the SW 102 rings. The locking nuts had to be removed from the screw and some (significant!) pressure applied to close the rings before the nut could be screwed on....
Definitely at the limit for these rings. As mentioned they should be sold as 100mm or 101mm rings NOT 102.

[iborg (Philip)]

I'm glad it worked, even if only just.


Philip