Shown below is some pictures of my Celestron G3 on its German equatorial field tripod. Shown with a 6x30 LER finderscope, the 1.25" visual back, and 17mm Plossl/Ultima Barlow on the 1.25" mirror diagonal. Also shown is an Orion "Flexishield" dewshield, which works great and doesn't seem too susceptable to low temperatures. Bear in mind I snapped off these shots fairly quickly with my wife's little Kodak [the pentax is in for cleaning!]. I hope these will be clear enough to get the idea...

Improvements on the G3 optical system:

    The G3 comes with a hybrid mirror diagonal of reasonable quality, but it is plastic, not very rugged, and is internally "stopped" to accomodate both 0.965" and 1.25" eyepiece barrels. This presents two main problems: insufficient loading and wide field eyepiece performance. This may be rectified using either a better 0.965"-1.25" adapter [Orion sells one for US$20], or a superior solution as shown above is to get a Large Accessory Ring [LAR] and 1.25" Visual back. One must then also purchase a 1.25" star diagonal. I avoided the use of a prism type, since two of the ones I tried on my G3 showed definite collimation problems, which resulted in quite poor images at higher magnifications. I opted for Orion's 1.25" Mirror star diagonal and it is simply great.

    I had the privelage of speaking with one of the heads of Celestron's Technical department. He told me about the G3 having been designed with a 1000mm focal length, this being measured at 50mm beyond the back of the scope [as is]. The G3, being a Maksutov-Cassegrain optical system, has its focus at a 200mm distance from the central mensicus mirror, again ending up 50mm behind the back of the scope. This corresponds to a 5:1 focal advantage in the G3's optical system [1000/200], or a 129mm change in the system's focal length per 1" change in the focal plane. As an example, say with the accessories listed above, the prime focus moves back to 70mm behind the exit port. That means that the scope has an additional 20mm beyond the 50mm prime focus. 20x5=100, so we've just added 100mm to the system's focal length, making it 1100mm instead of the 1000mm it was before!

    The helical focus of the G3 has several advantages over more standard telescope optical systems. The optics remain permanently collimated, and there is a tremendous freedom in the focal ranges this system will accept. Focal travel with the G3 is VERY large - great for all applications, with no fear of failure to achieve focus with almost any accessory package - BIG PLUS!! However, in order to achieve a good, crisp focus in an eyepiece, it is important to remember the above 5:1 focal advantage. VERY small changes in the focus make dramatic changes in the image quality, especially at higher powers. Also, the image brightness is highly affected by the focus - more so than say, a reflector, so once you know where your focus will be with the accessories on the scope, try to get it close before trying to see an object, or you may run into some problems seeing it. The unit usually needs at least 30 minutes to "cool down" to give optimal results, and I usually get the unit into "pre-focus" and make minor corrections as needed when viewing. I use the grip marks on the rubberized focus ring to adjust my focus - it takes VERY little to get a crisp image.

    The mount shown above is a nicely designed portable field tripod of the German equatorial design that comes with the G3 [and also the G5!]. Although not a rock-solid LX200 type of mount, It is highly adequate for the loads presented by the G3 and G5, provided that the counterbalance is positioned correctly. The mount should be capable [with caution!] to handle loads up to about 10 lbs or so. It is 17.5 lbs total weight, and portable enough to take virtually anywhere, for which it was primarily designed. The RA/Dec setting circles are easy to read, and are well located for easy readings. The RA ring can freely rotate, and has a locking screw to allow the unit to advance RA siderially during tracking. The manual slow motion controls are well located and my unit had no backlash detectable; if anything, it was a bit on the "stiff" side, but loosened up with use, maintaining very little backlash. The declination control has limited travel of about +/- 15 degrees either side of centre - to be used for minor corrections.

    The motorized version has a very useful hand control unit that's DC operated and operates the RA motor. The motor does not display any tracking delay, although I've observed a bit of inertia in the system if I go from, for example, the 4x rate back to the normal tracking rate, but then again continues tracking. Even at higher powers of 220x, the unit should not allow targets to drift much in the field of view before resuming the normal tracking rate [I have seen less than a 15% field drift rate typically when the unit is resuming tracking]. The motor engages with a small cam-style lever, which separates it from the main drive gear. This action should be smooth. On utilizing the "clutch", I have observed immediate tracking, with less than 10% drift in a 24' field of view [estimated].

    The key to this type of performance is to ensure proper polar alignment, counter balance, and proper adjustment of the motor tension control [more later on this]. The alignment can be done by using an eyepiece to give at least a 45' field of view. I first make sure that the mount is LEVEL. I then use my 17mm Plossl, and once I know my sidereal time [LST], I initially line up on Polaris, then adjust my latitude/azimuth [with the turret on the mount] to position Polaris near the edge of the visual field in the position it should be at my LST. Although not always dead on, it should be possible to get to within, say, about 6' of arc error with this technique. That's close enough to require minimal tracking corrections with the hand controller during visual observation. If done well once, only azimuthal adjustment of the turret is required [after levelling the mount] to align on the celestial pole.

    The motor/drive gear tension control is primarily handled by a spring. A secondary control is affected by using the set screw on the motor mount assembly, where it attaches to the base. If too tight, the motor will not engage properly in a consistent manner. I find that by loosening the set screw, then tightening until the onset of resistance [just getting snug] is the optimal position to yield reliable performance of the clutching/motor system, but periodic adjustments may be necessary over time. I know that this system isn't the best design, but it will work reliably when optimized, and will perform much better than some tracking systems I've used, such as that on the ETX's drive.

    The battery life for the drive system should be at least 18-20 hours of continuous use [alkaline cells] at nominal temperatures. I've gone well over 15 hours at below 28F and still had adequate power - I've yet to drain my initial set of 4 "D" cells. I'm going to use 2 4xAA battery packs in parallel to run the scope. Since I have rechargeable Alkaline cells, this should work very well, too.

    All in all, the motorized G3 is a nice, slick little portable telescope system that, with some smart improvements, can really perform at the intermediate to more advanced amateur astronomy level. I have not set this system up yet to do astrophotography, but I plan on giving it a whirl in the next few months, and I will post those pictures [hopefully not as fuzzy as these!] when I get them. Please feel free to drop me a note if you have any questions about this system. The total for what you see here, including the scope, mount, motor control, diagonal, dew shield, and Barlow came to just over US$800. Not a bad price for what it is and should be capable of doing!

Clear skies and Happy New Year!
Darren Hennig
Edmonton Canada