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The Optec Pyxis Rotator--What you really need to know!

Posted by Bob Benamati   02/13/2005 00:00:AM

The Optec Pyxis Rotator--What you really need to know!
For the user of the SBIG family of self-guiding cameras, one of the most frustrating aspects of CCD imaging is not trying to find a guide star (it's easy these days with planetarium programs such as The Sky), but really putting one ON the guiding chip. Sure, with today's modern computerized mounts or good digital setting circles, one can put the target object on the main chip without much effort. But THEN try and deal with camera angle to get the right orientation without totally losing your target! If you're lucky, you may keep it in the field of view, but then you have to recenter. Then, if you're like me, you find that the orientation is wrong, and you need to rotate yet again.

Back and forth you go, spending precious minutes in the dark trying to get everything just right.

Then there are the dreaded meridian flips for those with a German Equatorial Mount. Time to do it all over again to re-aquire that solitary guide-star, as rarely will there be another suitable one on the opposite side.

For some time now, only those lucky enough to have an RCOS RC telescope were able to do anything about it. Unfortunately, the Precision Instrument Rotator sold by RCOS is only mountable on its line of scopes--unless one really wanted to tinker with the $1300 PIR and precious scope (in my case, a Celestron C11 OTA).

Well, enter the Optec Pyxis rotator! Finally, a 'cost effective' option (about $895) for the non-RC owner.

Basics of the unit:

Mechanically, the Pyxis is fairly simple and straight-forward. As one would expect with an Optec product, the mechanical aspects are very well thought out overall.

At the heart of the rotator is a 4.156" diameter main gear riding on a 2" bearing. The main gear is driven by a set of spur gears, giving a total gear reduction of 110:1.

Driving this is a 48 step-per-rev stepper motor. All this gives one a 5280 step-per-revolution (of the camera) resolution--equal to about 4 arc-min! Plenty accurate for any conceived use.

Attachment of the Pyxis is accomplished through a dovetailed T-thread nose-piece which screws on to the face of the SBIG line of cameras or the CFW8.

On the scope-side, the Pyxis attaches to any standard 2" focuser (in my case, an Optec TCF-S), or can be direct-coupled via special adapters for the SCT back.

The Pyxis is then powered by a 110 to 12V transformer. While no battery-powered option is supplied, it is likely that one could fabricate one quite easily.

To operate the Pyxis, however, the only available option is to link via serial port to a PC. No 'manual' hand controller is available, but since the unit is geared towards the CCD imager, this should not pose a problem for the average user.

First Impressions:

Out of the box, the Pyxis is a beautiful piece of equipment. Solidly built, robust, and eye-pleasing, the Pyxis lives up to what one would expect from Optec.

One disappointment, however, is the lack of a cover for the stepper motor, giving the Pyxis a somewhat 'unfinished' appearance. While not a must-have, and by no means a danger to the motor, the sleek look of an all black anodized unit is somewhat tarnished by the silver aluminum motor.

Attaching to my ST8XE was easy and straight-forward. Simply detach the nosepiece from the Pyxis and screw onto the faceplate. Here's where the first real problem came in. Since I have a CFW8 attached, the motor cover for the filter wheel would not clear the gear cover! The nosepiece is about 1" too short. Jerry Persha, Optec's owner, assured me that a longer nosepiece is being designed and will be available soon.

Not deterred, I simply took the cover off of the CFW motor and attached. The dovetail system employed in the Pyxis is a fantastic idea. One can attach and detach the camera in seconds by simply loosening 3 set screws with the supplied Allen wrench.

From there, one inserts the Pyxis into the focuser tube. For the TCF user, there is a simple alignment screw (also employed in Optec's focal reducers, 2" nose-pieces, and other inserts for the TCF) that ensures a repeatable alignment if the Pyxis is ever removed. It also provides some leverage against unwanted rotation should the thumb-screws holding the Pyxis nose-piece be slightly loose.

The nose piece also features the standard V-groove found on Optec's other 2" inserts, as well as an internally threaded tube, allowing the use of 48mm filters. Definitely a plus!


The Pyxis is simple to operate. Plug it in, and the unit self-homes. This is extremely important so that you can accurately return to a specified angle after the power has been turned off, or if the unit slips for any reason (more on this later). This makes taking those dreaded flats much easier, too! You can image away at night, and in the event that you don't have the time to grab flat fields immediately after, you can always come back to them the next day or even later, since you can accurately return to the specific position angle where your images were taken.

Hooking up to the PC is simple as well. With the supplied adapter and reverse cable, one simply plugs it in to a serial port on your PC, link, and have at it. The software is a simple interface to the Pyxis, and if one chooses, you can even develop your own interface as the open language set is provided in the users' manual.

The Pyxis also offers the option to act as a field rotator for non-equatorally mounted telescopes (not tested in this manner). To operate in this mode, one simply sets the Lat/Long in the Pyxis control software and let it run. No interface with the scope is required--allowing it to be used on just about any alt-az scope without the need to interface the Pyxis with the scope itself.

As an aside: The Pyxis can be utilized by any software package that will support it. At this time, CCDAutoPilot has a nifty option that allows automated meridian flips and supports both the RCOS PIR and the new Pyxis rotator.

The Pyxis in action:

I wish I could say all went well with my first outing, but that wouldn't be honest. As I'm not an owner of a high-end GEM, I usually employ an AO-7 in my imaging train. This puts the main center of gravity well back and off-set from the center of the Pyxis. Unfortunately, the stock stepper motor of the Pyxis cannot handle such torque. The motor will convulse and slip, but just can't handle the weight.

So, failing that, off came the AO, and a direct mounting of the camera to the Pyxis was done. In this configuration, the Pyxis was a marvelous addition. I was able to easily keep targets at the center of my imager, as well as locate guide stars in a fraction of the time! The rotation is smooth (although a bit noisy) and efficient, and I found that the accuracy to be as promised. Additionally, once the Pyxis and camera are aligned as per the instructions in the manual, you can command the Pyxis to the EXACT position angle/camera orientation to ensure that you only have to center the object on the chip--the guide star WILL be there!


While not perfect, the Pyxis is a real value to the CCD-imaging community at large. It makes for much more efficient use of those precious dark hours, and when integrated with supporting software like CCDAutoPilot, it will allow fully unattended imaging WITHOUT having to spend a fortune for a Paramount and an RCOS!


And for those of you who are disappointed in the inability to use an AO in the system (or have an unbalanced imaging train), don't despair! If you're a tinkerer like me, there ARE solutions. I was able to modify mine for about $90 in all. It now handles the full package with ease, and has enough torque to spare! All that is required is a simple motor swap, without any further modification to the Pyxis, and takes only 10 minutes to accomplish.

Click here for more about this product . -Ed.