Alt Az, goto's and zenith
Posted 22 April 2013 - 07:23 AM
Posted 22 April 2013 - 09:05 AM
Posted 22 April 2013 - 09:41 AM
Am i right in saying that with an altaz mount as you goto objects near the zenith then the goto accuracy deteriorates?
That's generally been my experience, yes. "How much" depends on the mount: NexStar 11 GPS "a little"...ETX 125 EC "a lot."
Posted 22 April 2013 - 10:42 AM
No problems like a fork with space for face or camera
Posted 22 April 2013 - 04:06 PM
Posted 22 April 2013 - 04:14 PM
My refractors on my DM6 using a 12 inch pier extension can pivot at the zenith without problems. I have 2nd handle on my mount for pushing at near the zenith. Its hard to get leverage when the scopes straight up without it.
That's cool, but the DM is not a go-to mount...
Posted 22 April 2013 - 04:58 PM
So, any coordinate/computer-guided alt-azimuth mount will become more tedious near the zenith. The issue translates to DSC-guided manual mounts as well as to GoTo Mounts -- although worse for a GoTo mount because the issue is compounded by the problem of rapidly varying the motor controls.
The underlying problem has nothing at all to do with "how easily" a mount turns on its axes. It's strictly about the fact that alt-azimuth coordinates change rapidly with respect to the rate at which celestial coordinates change near the zenith. Of course, the mathematics is reflecting the physical nature of an alt-azimuth mount.
Note also that this same problem affects alt-az TRACKING near the zenith -- not just aiming.
It's interesting to note the differences in comparing an equatorial mount near its "hole" at the celestial pole. Although perhaps awkward to aim near the pole, an equatorial mount will not have analogous aiming/tracking issues because it points in terms of celestial coordinates. Of course, there is something of a singularity at the pole itself -- where movement across the pole produces a discontinuous jump in coordinates.
Posted 22 April 2013 - 09:20 PM
Posted 22 April 2013 - 09:38 PM