Scopetronix MicroStarII+

This review has multiple parts, each of which was written at a separate time. Taken together, these parts show how I've grown with the MSII+.

Part I

I've just finished installing the new MicroStarII+ from Scopetronix, which of course brought the clouds rolling in!

I had little trouble installing the unit, since I've got some experience with electronic assembly. The components are nicely manufactured, and extra consumable parts such as belts, setscrews and double-sided tape is provided, which is a nice touch. Also included are the batteries and a small double-headed screwdriver. Installation can theoretically be done simply with what's in the kit, but I opted for a larger screwdriver to remove the ETX base and a jeweler's screwdriver to help remove the Phillips-head screws holding the circuit board in place, as both sets were pretty tightly fastened.

Ease of installation was always present in the mind of the designer of this kit, Jordan Blessing. The simple manner in which the various wires are connected and the clarity of the manual attest to this. The most difficult part of the installation was getting the coiled wires through the holes in the base plate and being able to re-attach the baseplate without getting some coils caught up between the circuit board and the plate. To simplify this, I ran the focuser cable through the N/S switch hole rather than the On/Off hole suggested by the manual. Since I have a Bogen quick-release tripod plate attached to the base of my ETX, I already knew that using the N/S hole would not interfere with the mounting of the ETX. Alternate setups may not allow for this. I also stripped another inch or two of the black coil insulation from the cable and covered the wire with shrink-tubing. This gives me more freedom to move the base plate out of the way when replacing the batteries.

Attachment of the 2 motors is straightforward. The Dec motor attaches using double-sided tape; placement was simple. The focuser motor was a bit tougher. Though it simply has a coupling that slips over the focus shaft, it took me longer than I thought it would to adjust it so that the wobble seen when the motor is running is minimized.

I also found the suggested placement of the Dec motor power cord (through the fork from the rear to the front) to interfere with either my access to the RA knobs or the ability to swing the OTA to 90 degrees dec. This was easily solved by running the cord up from the front of the scope. It seems to be a matter of preference, and ample cord has been provided to be routed either way.

As the MSII+ was being designed, the Scopetronix website was updated on a regular basis. At one point, the website showed a pulley-driven focuser which allowed the focuser to be used even when the OTA was set to 90 degrees declination. Fairly close to the release date the design for the focuser was changed. (The manual explains that the original design was difficult to build, required a bit more skill to install, and was more expensive to make than the current model.)

Unfortunately, it is now impossible to get the OTA to go beyond 60 degrees declination with the focuser motor's power cord in place. A lower profile plug is important here. Unfortunately, a 2.5mm right-angle plug is not a standard item at Radio Shack or any other electronic stores I visited. I decided to bite the bullet and use a regular plug and bend the lugs at right angles. A little shrinkwrap and I had a usable plug with a much lower profile. I am now able to swing the scope easily to 80 degrees declination, and can get 85 degrees by making sure the cord's set just right.

I've discussed this issue with Jordan Blessing, who agrees that a 90 degree power cord would greatly reduce or remove this problem. He is looking into this for the next production run of the MSII+. I'd like to point out that it's easy to simply unplug the power cord to achieve polar alignment or to get the scope to the 85-90 degree area. This is a relatively small and (I believe) relatively featureless area of the sky, so losing the focuser in that area is not a major disaster. It should be noted that the JMI focuser can't get to this region of the sky without removing the focuser motor entirely, so this problem is not unique to the MicroStar II+ - it's an inherent problem in the design of the ETX, with virtually no clearance when the scope is set to declinations approaching 90 degrees.

The hand controller is a nice little unit that's simple to use, and has only a single ribbon cable connecting it to the ETX. It sits conveniently on the shelf created by the Bogen offset plate created by Steven Stanford when I'm not using it, it has an LED to indicate that it's on (which will also help finding it in the dark), and good quality microswitches. Once it was set up, I had no trouble panning around the backyard and focusing back and forth.

In terms of its operation, the MicroStar II+ works well. The preset speed for the Declination slew seems fine. The RA slew, preset to 8x with no variation, took me a little time to get used to. It is slower than I thought it would be, especially compared to the dec slew rate, but 8x is a reasonable speed. The JMI Commando unit goes up to 10x by using a different motor, and that's not a big difference. (The Commando also will _only_ work when you use the JMI tripod, Wedgepod and Wedge or standard legs! Since I already had a very nice tripod and head, I wasn't going to consider replacing them in order to use the Commando.) It's important to note that the MicroStar II+ is not going to turn the classic ETX into a goto scope, or even provide fast slewing to any point in the sky. The Declination motor is limited by the slow-motion declination range of the ETX mount, and 8x RA slew is pretty good performance from the little ETX motor.

What it _will_ do is let you get near an object and pan around the general area without having to fumble with the slow-motion knobs on the ETX. That's something that will be nice on the cold evenings still to come!

I can't go without mentioning the manual. It's well-written, clear and informative, giving not only the basics on setting up the unit, but also why some things have been designed the way they were, and what to do when things go wrong. Items like fixing a binding Declination control or what to do if the focuser rod goes too far and falls into the OTA are covered, which I feel is above and beyond what's required in the manual.

All in all, I'm reasonably happy with the installation. It took me about 2 hours, including a fix to a a bent Declination control screw. It functions exactly as advertised, and is much less expensive than the equivalent products I've seen advertised for the ETX. I also had the opportunity to call Scopetronix a few times to check on the order, which sat at my local post office for almost a week(!). At all times the folks at Scopetronix were reachable and helpful. I'd be happy to do business with them again, and can recommend the MicroStar II+ as a nice package to add versatility to the ETX.

Part II

I finally had skies clear long enough to try out the Scopetronix MicroStarII+ that I installed earlier in the week.

I had a very limited amount of time at dusk last night to use the scope, so I went for the obvious target, the moon. I jumped right up to 256x using the 9.7mm eyepiece and the Barlow. What a joy to be able to pan around the moon's face without using the slow-motion knobs! It was great being able to follow the terminator just by pushing a few buttons, but it was not without a problem - a binding declination knob. I had previously gone in and straightened the long screw that connects the two slow motion knobs, and I had pretty smooth motion, but when I used the motor, it was very jerky. It would move, then stop, then move, then stop.

This was NOT a problem with the MSII+!!! The manual clearly states that any problems with the RA or Dec mechanisms will be magnified by the MSII+. This is most certainly true. I ended up having to disassemble the whole declination mechanism to loosen up the fork the dec drive nut rides in. I also put a tiny smidgen of liquid graphite on the plastic. The declination motor now rides very smoothly to both ends of its travel.

I must say that I was underwhelmed the first time I opened up the ETX. The declination mechanism is pretty darn flimsy, if you ask me! I cannot over- emphasize the need to have your declination mechanism as close to perfect as possible to get the most out of the MSII+.

A side note: I took the opportunity of having the dec assembly apart to put a white line down the center of the dec arm. Since there's a little cutout in the inside fork cover, I can now tell at a glance how far the arm has traveled to one side or the other.

I mentioned in my earlier post about the 8x RA slew speed and how it seemed slow to me. This speed seemed just about perfect when looking at the moon. So now I've learned not to rely on terresrial viewing to make judgements!

It is also worth mentioning that overcoming the initial inertia is more difficult the slower the focuser is set to. Increasing the focuser speed on the hand controller can sometimes, but not always, overcome this problem. The real solution is to spend as much time as necessary getting the coupler aligned as well as possible. It seems pretty good now, but again I had only terrestrial objects to focus on. We'll see how the clouds hold out for tonight!

One point I'd make is that with the dec motor installed, using the slow-motion control manually doesn't seem to be a good idea. There's a lot of resistance from the belt, and I'd be afraid of stretching the belt or stripping gears (or most likely breaking something in the ETX's cheesy dec linkage!). If you want to use the slow-motion knob manually rather than with the MSII, slipping the belt off first might be a good idea.

I'm really happy with this unit, and with Scopetronix. Jordan Blessing's been very accessible through email, and very informative. He's given me the straight dope on everything, warts and all, when I've asked questions.

Part III

I've had the opportunity to use Scopetronix's Microstar II+ for a couple of weeks now. While I am generally pleased with the unit, I have found a shortcoming in using the electric focuser: after sitting out in the cold for a while, the focuser stops working.

This is due to the lubricants in the ETX focus mechanism and the focuser motor thickening in below-freezing temperatures. With this thickening, more torque is needed to turn the focus mechanism, but because of the low current fed to the motor in order to turn the focuser rod at a slow speed, it is not able to overcome this "stiction," and the focuser controls stop responding.

I have found that the problem exhibits itself even in milder temperatures, though still below freezing. Last night the temperature was about 28F but I still had the problem after the scope had been outside for about an hour.

Jordan Blessing, when asked about this, confirmed than a couple of people have reported this condition, which he says is one of operating the unit outside of its design limits. Given the number of units shipped so far, this problem is likely to have more to do with the type and amount of lubricant in the ETX focus mechanism than in the MSII+ focuser motor.

Jordan has offered a number of different options to the people who have run into this, which is consistent with the excellent service I've gotten from Scopetronix so far. His commitment to keeping me a satisfied customer is quite evident, even when it is not his unit at fault.

Unfortunately, this is a case where I need to lower my expectations! In responses to a query I posted in the Usenet group sci.astro.amateur brought a number of responses from folks who have problems with telescopes in temperatures both below and even above freezing. It seems to be a fact of owning a telescope that operating in less-than-balmy temperatures is not of great importance to the scope manufacturers.

The reason that telescopes with moving primary mirrors tend to have focus problems in the cold is that since the cored mirror must slide back and forth on the central tube it must be cored slightly larger than the tube. ANY sideways movement of the mirror results in miscollimation and annoying focus image shift. So a VERY thick grease is used between the mirror and central tube, and this thick grease by its very nature thickens even more in cold temps. This thickening is what keeps the MSII+ focuser from moving the mechanism.

The focuser motor is easily removed and the original focus knob replaced, so before a night's viewing, I will check the temperature and determine whether I should use the MSII+ focuser or the manual knob.

The RA and Dec controls have not been affected by this problem, most likely because those motors have more power fed to them, providing more torque. In fact, in my last viewing session, I spent quite a bit of time on the moon (because its glare made other observing difficult!) and found that I was truly enjoying the use if the panning controls. Jumping from crater to crater along the terminator at 258x was a snap! What a difference from the manual slow-motion controls!

This wraps up my account of installing and using the MSII+. I can honestly say that everyone with a Classic ETX should get a MicroStarII! The panning controls make the ETX experience a joy. I also recommend, with a caveat, the MSII+. When the focuser works, it's wonderful, but on my ETX, the unit is highly sensitive to lower temperatures. Other scopes in similar climates may be better able to handle the cold, or you may live in a climate a little more hospitable to motorized focusers. Your mileage may vary. If you're considering buying the MSII+, I suggest calling Scopetronix and finding out the options available to you. Jordan is a straightforward person who will be honest about which unit best suits your needs."

Part IV

Much has happened at Scopetronix since I bought the MSII+. They are no longer providing focuser motors for the MSII+. The controller for the MSII+ will control the motors for other focuser motors.

In the course of writing the 3 parts above, I had the opportunity to exchange quite a bit of e-mail with Jordan Blessing. During this discourse, in which I got an education not only on the ETX's internal focusing mechanism but on the importance of clarity in language, Jordan offered to exchange my MSII+ focuser motor for one of his original design, which does not attach directly to the focuser shaft, but instead sits above the focuser and uses a toothed belt to connect the focuser shaft and a pulley on the motor. This design was both harder to install and more expensive to produce, so it was not released. I accepted the offer, and installed the "old" version. What a difference!

The pulley design must provide more torque, since I have never had a problem with focuser stiction while using it. The lower profile also means that I can now bring the scope all the way to a 90 degree declination without removing the focuser. Another advantage to this design is that the original focuser knob is left in place. If (when!) the batteries die during an observing session, I can simply remove the belt and operate the focuser manually. No screwdriver is required for this operation, as a thumbscrew adjusts the belt tension. It's too bad that this final design never made it to market. It works very well! I'm extremely happy with this unit.

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