On May 1st, 2004, I've acquired a new Vixen Sphinx mount. In this review I will take a critical look at the mechanics, operation, and practical use of this medium-duty equatorial mount.

Mount and Mechanics: First impression

The Vixen Sphinx mount looks futuristic and distinctly "Japanese". With its white finish and dark blue transparent parts, it has a remarkable appearance. It might not be to everyone's tastes, but I personally find it refreshing. One thing about this mount that you will immediately notice is the complete absence of RA and declination setting circles and the absence of outside cables and motor housings. The SXW version that I own has a retractable counterweight axis that allows to make the mount compact for storage. There is also a lighter SX version of the mount that lacks a counterweight axis as well as a declination clamp.

The mount looks and feels massive and it gives the impression of high quality we have come to expect from Vixen mounts. Although this mount looks heavier than the GP-DX mount, Vixen places its maximum load capacity at the same level (10~11 kilograms; 22~24 lbs). This is probably a conservative value, and I expect the mount will still perform well when carrying loads near its maximum capacity. My own C8 (circa 7 kilograms) feels right at home on this mount. Any vibrations disappear within less than a second.

I have not yet been able to determine the mount's Periodic Error (PE), but several sources, most notably the Vixen_Sphinx Yahoo group state that the basic PE is a bit better than that of the GP/DX without Periodic Error Correction (PEC), possibly because of the new 180 tooth worm wheel. Unfortunately the current software version of the mount does not yet provide for Periodic Error Correction (it does now, see below).

The mount has a standard and widely used Vixen GP/GP-DX dovetail mounting mechanism, so almost any OTA can be made to fit. A polar axis finder is, unexpectedly for a mount in this class, missing. The RA clamp works as expected, but only the SXW version of the Sphinx mount has a declination clamp. The declination clamp has a handle that screws tight, which can get in the way when an OTA is mounted.

There are practical knobs for azimuth and altitude adjustment, to facilitate exact polar alignment. This is certainly an improvement over the awkward way this was done in previous Vixen mounts. An approximate polar alignment is okay for visual use and still produces accurate GoTo's.

The only electrical connections present are a 12V power connector and a 9 pin D-connector for the Starbook controller. The motors are relatively quiet while slewing. When tracking, a soft ticking noise can be heard.

Tripod

The tripod mounting surface has a larger diameter than the GP(-DX) mounts, so a GP tripod will not work with the Sphinx mount without modifications. At the moment the aliminium SX-HAL110 tripod is the only tripod available for the Vixen Sphinx mount. The SX-HAL110 tripod is a good platform that has none of the drawbacks of the cheaper Chinese tripods. Strangely, and accessory tray that mounts atop the leg spreader is missing. I've fitted an accessory tray that came with my EQ3 tripod. In addition to providing a place to put eyepieces and other tidbits, adding an accessory tray has a positive effect on the stability of the tripod.

The most innovative component of the Vixen Sphinx system is the Starbook controller. It has a 4.7 inch color LCD screen with a 320x240 pixel resolution. Underneath the display are two groups of five keys, both arranged into "Up", "Down", "Left" and "Right", and a key that usually has an "OK" function.

On the underside are four connectors: Power (12V), the connection to the mount (9 pin D-connector), an Autoguider connector (more on that later), and an Ethernet LAN connector. Unfortunately there are no provisions to attach the controller to the tripod, except for two eyelets to string a cord through.

Using the controller

When turning the powering on the unit, a brief Vixen "splash" screen is visible, followed by a menu from which things like local time, the observers' coordinates and time zone can be set. With the current software version that I had at the time of this review (version 24), only one observing location can be stored.

Before the mount can be used, it has to be put in a pre-defined starting position. This is done by pointing the telescope at the western horizon, aligning the markers on both the RA and declination axes. The mount software tells the user to point the telescope at the “right” horizon, but off course this depends on where you are standing with respect to the mount. Take care here.

After confirming this screen, the mount will do a short calibration. After this, the navigation screen (Scope mode) appears, with a real time star chart. From Scope mode, the mount can be manually moved with the directional buttons.

Finding and moving to objects

Before the mount can accurately find objects, alignment must be performed on a few known astronomical objects (usually bright stars). There is a maximum of 10 alignment points, but 3 are usually sufficient for good GoTo accuracy. During alignment a medium to high power eyepiece should be used, preferably with a reticle (crosshairs).

Setting an alignment point is a simple procedure:

1. •Enter Chart mode
   

2. •Choose a bright star or another easy to find object from the Object menu
   

3. •Choose GoTo; The mount will move the telescope to the location where it expects the object
   

4. •The mount wil return to Scope mode
   

5. •Use the RA+/RA-, DEC+/DEC- keys to move the chosen object as accurately as possible in the center of the field of view of a medium to high power eyepiece
   

6. •Choose Align
   

The mount will now refine its internal "view" on the sky to account for the new alignment point.

When this procedure has been followed for three objects, GoTo accuracy will usually be sufficient to put any object within the view of the eyepiece. With the current firmware, the mount has a database of more than 22.000 objects to choose from.

Choosing and slewing to objects is an easy and intuitive process, thanks to the star chart and the large screen menus. By using Chart mode to zoom in and out, the speed with which the mount moves varies according to the scale of the display (it will move slower with higher zoom). With maximum zoom, the directional buttons can be used for manual guiding.

Firmware version 1.2, build 24

On september 30, 2004, Vixen issued a new firmware version for the Vixen Sphinx mount. This firmware had a number of improvements over previous versions, most notably the speed and responsiveness of the graphical user interface and improvements in motor control (but, see below). This firmware also added the possibility to control the Vixen Sphinx mount by PC via its ethernet interface. Two advanced features were added that had to be paid for by purchasing a key code. These advanced functions were Backlash Compensation and the long-awaited Autoguiding support. The purchasing process is quick and painless.

After doing a few tests under the stars, I can say I definitely like the new software. Computer control works. However, some Vixen Sphinx users are reporting irregular axis movement and issues with manual guiding in the lowest speed settings. It seems Vixen has yet to iron out some bugs in the Starbook software.

Firmware version 1.2, build 26

On december 19, 2004, Vixen issued another new firmware version for the Vixen Sphinx mount. This software adds a very useful time-out function for the Starbook display backlight. In addition, Comet C/2004 Q2 Machholz has been added to the object list. At least this shows that Vixen is still paying attention to their Sphinx users by continuing to add functionality to the mount’s software. The new firmware can be downloaded here.

Many users on the Vixen Sphinx Yahoo group are also reporting a considerable improvement in the mount’s mechanical behaviour and pointing accuracy after upgrading to build 26.

Firmware version 1.2, build 27

On june 23, 2005, version 1.2, build 27 of the Vixen Sphinx software was issued by Vixen. There were some minor bug fixes, as well as support for more languages. The chart now also displays more stars (up to about magnitude 7.0), while the responsiveness of the user interface is still very good.

Firmware version 1.2, builds 28 to 31

Some minor software updates followed, with no major functionality added.

Firmware version 1.2, build 34/35

On may 18, 2007, version 1.2, build 34 of the Vixen Sphinx software was released by Vixen, followed by version 35 on the very same day. This software version appears to be the same one as the version that is on the new Vixen SXD mount (which is a version of the Sphinx that can carry a heavier load).

This is another major upgrade that adds the long-awaited PEC functionality (Periodic Error Correction) to all existing Sphinx mounts. Other major improvements are the inclusion of bright star labels on the Star Chart display and GOTO speed limiting. This Starbook software version can be downloaded from here.

Firmware version 1.2, build 40

Vixen briefly placed this version on their web site on october 27, 2007. Immediately afterwards reports started coming in from users that, after having upgraded to the new version, started having problems with unusual noises and autoguiding. Consequently, the new version was taken down from the site and disappeared for a few months until februari 2008. Personally I am still using this version and have not found it to be particularly unreliable. This software build can be downloaded from here. Please Note this page also contains a few warnings about using this software with older Vixen Sphinx mounts.

Starbook Connectivity

1. 1.Power connector (bus). This port is normally not connected (the Starbook is powered by the cable that runs from the mount), but enables the Starbook to be used as a standalone interactive star chart.
   

2. 2.Autoguider connector (RJ12). This port can be used to connect an SBIG or Vixen autoguider.
   

3. 3.Mount connection (9 pin D-Sub). This port is used to connect the Starbook to the mount (a normal straight-through serial "modem" cable can be used). During normal use (not autoguiding), this is the only cable that needs to be connected.
   

4. 4.Ethernet connection (RJ45, 10/100Base-Tx). This port can be used to control the mount from a computer. The ethernet connection is also used for upgrading the mount's firmware. This port can be directly connected to a computer's ethernet port using a crossover network cable, or it can be connected to an ethernet switch or router using a straight-through network cable. At the moment the Vixen Sphinx mount is supported by TheSky. Peter Enzerink (see the link below) made an ASCOM driver that can be used with many other astronomy PC programs.
   

Conclusion

Despite a few oddities and ommisions, the Vixen Sphinx mount and its associated Starbook is a solid product. The excellent mechanical quality of the mount, its innovative design, and its easy to use Starbook controller, make this mount worth recommending to everyone that is in the market for a midrange, computer controlled equatorial mount. Fortunately Vixen has listened to its customers and continues to improve this mount by (slowly) adding major functionality. The addition of PEC has (finally) made the Sphinx into a mount that should be seriously considered not only by visual observers but also by more advanced astrophotographers.

Please send me an e-mail if you have any questions or comments about this review or the Vixen Sphinx mount. I also keep an archive of all the older Starbook software builds.