Telescope Reviews: TV-102 + Gibraltar with Sky Tour Report

Last night was the Off Fisher Lane Irregulars (O.F.L.I.) last organized star party of 2009. As usual the session was hosted by the ever generous O.F.L.I. founder CNer cuzimthedad (aka "Dan") at his farm in Sonoma, CA. IN addition to a handful of O.F.L.I. regulars, many members of the "Nameless Napa Astronomy Association" (seriously, they are very organized, have been at it longer than O.F.L.I. and as of yet have no official name; so until they pick one, I'll call 'em N.N.A.A.).

It was also first light for my new Gibraltar Walnut with Sky Tour. I purchase the mount as an easy travel option for my near and dear TV-102 (as compared to the Orion Altas that scope usually rides on).

So here's the deal. Earlier in this forum I reported the "Enc Error" issues I was having with the azimuth encoder. By backing out the encoder shaft set screw and re-tightening it a little less firmly, I was able to eliminate the error message and obtain full 360-click rotation in each direction on the azimuth axis.

Initial alignment was a breeze. I used Vega then Polaris right at sunset. I used a cross-hair reticle 12.5mm Lumicon Orthoscopic, and still the Warp Factor was around +2, which surprised me. The manual suggests that you really want Warp factors < 1.0. Nonetheless for the early part of the evening the alignment was sufficient to put targets in a low power field of view. So far so good.

After a couple of hours, however, targets were considerably outside of the low power field. I used the "Align" feature to synch up the computer on each centered target, and that allowed me to place targets within 10 or so degrees of the synched target in the low power field, but targets on the other side of the sky were not even close, sadly being outside of a 2-degree field. Candidly, I am (a) not particularly happy with this level of accuracy (I expect better) and (b) have lingering concerns that I have some encode slippage or defect, even though the azimuth encoder no longer throws error messages. I will readjust the azimuth set screw tension today, but several times during the night I used the Encoder function to check both encoders and they seemed perfectly fine.

It could be me. It could be the electronics. It could be a combination of these things. I will be patient, but at present I give the Sky Tour a "C-/D+) as DSCs go. The lowly Orion Intelliscope system I've used on two different Dobs performs better. On the other hand, I've had worse issues with an Argo Navis/High Res encoder system.

Beyond the electronics, here is how I would rate the Gibraltar mount itself for use with the TV-102. It is relatively easy to adjust axial tension, but I found the azimuth motion to be consistently smoother when tensioned than the altitude motion. There's a bit of stiction in play in azimuth when you have enough tension to hold the OTA in position. Not bad, but not great either. I give it a solid "B" for axial movements.

The last performance-related item I would like to comment on is vibration dampening. I am a stickler for vibration dampening. I like to use higher magnifications and expect ~1 second dampening or better at ~140x in the TV-102. At magnification of over ~80x the Gibraltar displayed considerable vibration after focusing, taking more than 2 seconds to stabilize enough to check the focusing adjustment. It higher magnifications, the vibrations were even more pronounced. I should note that I did not use Vibration Suppression Pads on this first outing, and will do so next time to see if there's improvement in this quarter. I would give the Gibraltar a "C" for VSP-less vibration suppression.

The final item isn't related to performance, but rather to fit and finish. The Gibraltar with Sky Tour runs about the same as a GOTO-less Losmandy GM-8 or Celestron CGEM. The head is nicely machined; as nice as either of those mounts in build. The tripod is likewise well-made, but...the stain/oil on the wood leaves something to be desired. I forked out a little extra for walnut and shouldn't have bothered. The stain/oil is unevenly applied; there are several ares where the wood is extremely light due to thinly applied color/oil. Certainly easily remedied, but frankly for the price I expect a little better finish on the woodwork. Overall fit and finish (head plus tripod) I give it a "B-"; the score being brought down by the woodwork.

As I said, I will give it some more time and troubleshoot both user-induced variables (like my newness with this mount) and mechanical and electronic issues (like axial stiction which may be balance- or tensioning-related, and the accuracy problems with the Sky Tour setup). I am a little disappointed thus far though.

I am very curious about the accuracy issue in particular. I used a fairly high magnification eyepiece with cross hairs, and centered targets precisely in rapid succession, yet the unit lost alignment accuracy within a couple of hours. I suspect this is NOT standard or typical.

Report Card Summary:

Electronics: C-/D+
Axial Movements: B
Vibration Control (with TV-102): C
Workmanship and Finish: B-

As a boy, had I brought home a report card like this, I would have been in deep water.

Regards,

Jim

--------------------
"I do not always view with "low glass" eyepieces, but when I do, I prefer Brandons. Stay simple and sharp, my friends!"

- The Most Interesting Astronomer in the Universe