Further considerations - And BTW I just finished my daily run and my head is MUCH clearer. 3.16 miles in 33 minutes- not bad for an old man, eh? ;) The equatorial platform in many of it's forms never has a true declination axis, and often has only a virtual polar axis- yet is is obviously firmly in the equatorial class of mounts. In truth it's just a split-ring, with the entire upper portion of the ring sliced-off. Whether the drive train uses conic segments, concentric ring segments, or inclined planes, kinematically they are all in the same family. Again, we see that the name is derived from the motion the mount imparts, not the presence and alignment of a secondary axis. In this case, as with the universal pivot atop the polar axis, there is no secondary axis. Declination motion is achieved in some cases by use of the altitude axis of an alt-az mount atop the platform. That motion is not true declination except when the object is on the meridian. In fact when the object is on either horizon, the altitude axis becomes a pseudo-polar axis, and the azimuth pivot becomes the declination axis! The "barn-door" mount is also an equatorial mount and can be considered a variation of the equatorial table with a true, hard polar axis. Range of motion in declination can be achieved by the methods discussed above. I am also reminded of the sphere mount as executed by James Gagin, I believe it was, about 25 or 30 years ago. Again there was no true declination axis- the telescope was essentially a huge "Astroscan" in shape, floating in a water bath. Once slewed to its target, a vacuum-pump connected suction cup, motor-driven and aligned with the NCP, engaged the sphere and began to drive the telescope in RA. Another example of a true equatorial mount with no mechanical secondary axis at all. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com