Spacing of tube rings?

[TheThing]

Just wondering if there is any reasoning or prefernce for the spacing of tube rings at all - i.e. does it matter how close or far apart they are as long as the scope is well balanced?

I want to put the SW 200 onto a Tal motorised pier for webcam work, but it will mean moving the tube rings much closer together - from about 280mm apart currently to about 185mm apart. Will I notice any change? Is it likely to put added stresses on the tube walls at all?

[Bizibilder]

The rings themselves will be Ok it is the connection from them to the dovetail that will have to "take the strain". The closer they are together the greater the "moment" of the tube - you have a heavy mirror at one end and equally heavy bits and bobs at the secondary end. Imagine the scope with just ONE, central, ring, it would twist and probably pull the ring off the mount! Two very close rings would not be much better! So the further apart they can be placed the better! The actual distance used will always be a compromise. Most scopes have the rings 280mm apart because that's the size of the dovetail supplied!!!!!

Hope this makes sense.

[John]

I've gone for rings spaced closer together than standard with my 6" F/8 refractor because the longer dovetail bar introduced more vibrations than a shorter one (I need to invest in a better quality dovetail bar !), You could use more than 2 tube rings of course - I've seen 4 used with a long dovetail bar - that put more rigidity into the whole setup.