Rotating secondary cage

[madtuna]

Has anyone made a rotating secondary cage for an EQ mounted Newtonian?

I've seen a ball baring ring system for rotating the entire OTA but was wondering if anyone has made or knows of some links to a rotating SC only

cheers!

[Ian Robinson]

Thinking about that with my upcoming OTA rebuild , just a matter of splitting the PVC tube and coming up with a solid means of rotating the upper 1/4 say without loosing colimation.... shouldn't be that hard , .... my tube clamps are a wee bit tight on the tube, might be easier to mod the tube clamps slightly (so I get another 2 or 3 mm and less snug grip on the tube though).

[Omaroo]

Steve - have a look at my binocular telescope gallery. It shows Paul Shoppis' design that incorporates rotating secondary cages in order to be able to adjust the interocular distance for different observers. I'm basing my design on this one with some material modifications.

http://www.omaroo.com/index.php?option=com_g2bridge&view=gallery&Itemid=2&g2_itemId=2211

As you can see, the cages are built with an OD slightly smaller than the support platform they sit on, and are held by a simple flange. This flange has a lower bearing surface made of Laminex (akin to the altitude bearings on a Dob) and it rotates on teflon pads attached to the platform interface. This is all held in place by a simple roller bearing whell arrangement as show. Rotating the cage results in almost zero image shift.

Hope that helps....

[Starkler]

The challenge here is maintaining collimation with the rotation of the cage.
The optical axis has to align exactly with the mechanical axis which is no mean feat. I know of one scope like this and alignment is a problem.

[PhilW]

Bob Royce (notable US mirror maker) has a design with a rotating UTA here:

http://www.rfroyce.com/newtonian8f8.htm

I copied Paul's approach for rotating UTAs for my bino. But in this case the UTAs only rotate a few degrees, just to adjust interpupillary distance. Geoff's point about the challenge of maintaining collimation for tubes moving through larger arcs is well taken.