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- FIELD TEST: CARL ZEISS APOCHROMATIC & SHARPEST (CZAS) BINOVIEWER
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- My experience with the Starizona Landing Pad
CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.
Celestron’s CG-5 (aka “clone”) compared to Vixen’s Super/Great Polaris Line (with a few comments about Losmandy)
Author’s 1989 Super Polaris mount combined with a 1999 C8 OTA
When I was a kid my mother gave me a 4.25” Optical Craftman telescope on a rock solid equatorial mount with a cast-iron pedestal. It was hard to move around but it was smooth and tracked well. I was very lucky: at the age of 10, after struggling with a very flimsy Edmund Scientific for two years (the legs kept falling off), my mother, a science teacher, decided I had an interest worth taking seriously. My early teen years with the Optical Craftsman (which is still in the family) scope conditioned me, as it were, to a fairly high standard of performance.
So, when I re-entered astronomy as a hobby after a thirty-year absence, I had buried expectations for high quality.
The CG5 and the Great Polaris are the most common mounts in use among people who have
a) gone beyond department store telescopes and
not gone into Dobs or
c) opted for expensive refractors on alt-azimuth mounts--though many refractors end up on CG5s and SP/GP’s.
Mounts are a critical part of the amateur astronomer’s viewing experience, regardless of whether or not he or
she is into photography. Equatorial mounts offer a particular kind of experience and quality not found on other
kinds of mounts. Since today’s amateurs always have the opportunity to sink money into more aperture by buying
a Dob, the merits of the equatorial system of viewing need to be considered in relation to their opportunity cost.
Selecting a good-performing equatorial system will always translate into an inch or more of lost aperture on a
Dobson. As an SCT user I like to urge people to get SCTs, but when they start talking about limited budgets and
putting an SCT on the CG-5, I tend to say that a good dob mount is better than a poor equatorial.
Basically, you should get an equatorial mount if you
a)Like the idea of digital or manual setting circles;
b)Might get into photography;
c)Like accurate tracking and electronic controlled centering of objects in the field of view
d)Like the superior stability and wind-resistance that machined metal mounts offer vis-à-vis other kinds of construction.
e)Like the relative portability that an equatorial mount usually offers vis-à-vis its alt-azimuth cousin, the fork mount.
f)Like the potential durability that well machined metal equipment offers over alternative systems. (See Appendix #1 on why durability might not matter.)
Dobs, incidentally, can be made to track and can be endowed with digital setting circles, but you won’t see them with manual setting circles. The accuracy of dob-type tracking and setting circle systems is usually less than that of a good equatorial, but the wide field of view offered by the typical dob makes accuracy less important than on an f/10 SCT or refractor. And for the complete novice, a well-reputed go-to system that hits the “sweet spot” on aperture, like the Nexstar C8, might be a better deal than most potential equatorial systems or dob systems. (See Appendix #1 on considering scope values.)
For my part, I value the equatorial mount because a good one is integral to finding and enjoying celestial objects.
That is not so if you are a “star hopper,” but I find that both manual and (more recently) digital setting circles
greatly enhance my enjoyment of the hobby. I also greatly value good tracking and electronic (rather than grab
and point) manipulation of the tube to center objects. Some people think that digital setting circle use encourages
flitting from object to object. What I like, by contrast, is to find an object, take a detailed description (such
as can be found in Luginbuhl and Skiff’s Observing Handbook and Catalog of Deep Sky Objects, which I have reviewed
on www.amazon.com), and carefully scrutinize the object for details mentioned in the description. Good tracking
is a great plus in this style of viewing, even though I don’t do photography. Not only can I read in the field
but I can also walk around, see what other people are seeing, and come back to my original object. This is sometimes
useful because some dob owners like to have a scope that’s already pointed at the object they’re looking for while
they home in. It’s sort of a hunting dog function. The SCT on the equatorial maintains the point while the 25”
Dob owners bring in the heavy artillery; while that is going on, I walk around. I also like electronic manipulation
(using a “paddle” or hand-held control box) of the optical tube because it allows me to “scout around” objects
for additional details with a great deal of precision, and helps maintain precise control at high magnification.
Confusing directional changes (east vs. west using a prism diagonal, vs. mirror diagonal, vs. straight through,
combined with everything changing when you point the scope somewhere else) often occur while observing. I find
an equatorial mount helps me to follow directions like 3” East when I can double-check field of view orientation
against gross movements of the scope on the mount. On a good mount, swinging back exactly to where you started
is easy, so you don’t have to worry about “losing” an object that took a long time to find. As a final point, sturdy
equatorial mounts seem to do better in the wind than the dobs.
In the following review I find the SP/GP mounts preferable to the CG5 clone, but I also provide a list of what might be called faults of design in the Vixen line and make a few points about the Losmandies. Though some CG-5 enthusiasts may take umbrage at my assessment, even die-hard CG5 advocates will find useful information herein. This review also discusses Celestron’s damping pads and, in the appendices, other practical tips. These include how to make Vixen/CG5 style battery packs work in cold weather (Appendix #2) and a few types of failure (and their remedies) when using JMI encoders (Appendix #3). Appendix #4 addresses defective setting circles on some CG5s and Appendix #5 explains, not how to polar align, but the specific order of tightening knobs and levers that minimizes the difficulty of the process. Appendix #6 is a short cut way for positioning the “little circle” for Polaris in the SP/GP/CG5 finders.
I have been at pains to make these appendices available because I have sold my SP+C8 combination and am moving into the world of Losmandy G11 viewing. I am very fortunate to be able to do this, but I think much of the information below will be useful to the many people who will continue using the SP/GP/CG5 equatorial mounts.
I was very keen on setting up my CG-5 with a C8 OTA. It was my first scope in decades, and I had kindled a warm
enthusiasm in advance by looking at the cool publicity pictures for the scope.
For better or for worse, however, the habits and expectations of that 1965 Optical Craftsman mount conditioned my response to the CG-5. I noticed within minutes that even though the 8” Celestron SCT OTA was great, the mount was god-awful. (I also had, incredibly, a defective set of setting circles, and if you have a CG5 and for love nor money can’t understand how setting circles work, see Appendix #4 below.)
The mount was not only unsteady, it had a poor “feel” in turning, like it had arthritis and needed a shot of cortisone. I got on the Internet and did research, and found Jeff Detray’s www.astronomyboy.com , which I now know is a widely-known source of CG5 information.
There I learned that I would have to take my mount apart and re-grease it and sand rough arts, etc. I was told about burrs and pieces of metal left inside the scope (confirmed!) and cheap grease that had a glue-like consistency (confirmed!). I did all the procedures, and the mount improved. But it could only improve so much. Because of poor machining, I had to choose between operating it too tight or too loose.
Too tight made it difficult to use. Too loose meant that if I centered an object and released the OTA, the scope would swerve somewhere else in spite of my best efforts. Mr. Detray’s web site, at the time I consulted it, also confirmed that some CG5s seemed “intrinsically tight” or “intrinsically loose.”
Because I wanted to use the RA and Dec setting circles, I bought the optional polar scope for $50. This turned out to be a gigantic pain. It is a piece of plastic with lenses. You stick it in the RA axis and then have to align it like you would a cheap finder.
The process is much more difficult than sighting a finder, however. Special instructions accompany the polar scope. Basically you have to sight the polar scope from two positions (each side of the equatorial mount), trying to find the midpoint between what you see on each side. It’s hard to do, the angle can be bad (you do this with a terrestrial object, and getting the polar scope to point to the horizon or even at the top of a distant tree is not easy). The polar scope’s function is to make your viewing easier by allowing fast polar alignment. Instead, it can become the source of serious new frustrations. And once you have it all lined up properly, the poorly designed adjusting screws will fail to hold the alignment at the slightest shock while packing up. Bumping the protruding end while observing also will knock it out of alignment.
I also spent $50 and got Celestron’s damping pads to assist the flimsy aluminum tripod in damping down. They work! But beware, if you like to polar align and use the setting circles or track well, the damping pads worsen your scope’s stability from the point of view of torque. As you swing the scope around from object to object, the tripod legs move on the pads and you lose your polar alignment. The pads themselves are also slippery on most surfaces. Some people try to drill holes in the pads to get them to adhere better to the tripod. But compared to a pointed tripod leg tip stuck in the grass or stuck in the small dimples typically found in asphalt, the pads don’t provide much grip. Moreover, drilling holes in the pads adversely affects their resale value, their resistance to moisture, and, perhaps, their performance.
Well the next thing to do is build wooden legs. CG-5 owners repeatedly talk about how great their mounts are after they rebuild the legs and do an interior tear down and relube. Here, though, I gave up. I had already spent $100 on pads and a poor polar scope. I had invested $10 in a bicycle spanner to adjust the tension in the mount’s axes. In spite of these efforts, the mount was still either too tight or too loose, and didn’t have that “Optical Craftsman feel” that I had learned when I was a kid. Life was too short, I thought. So I marked the CG5 down below most of the prices I saw it going for on Astromart and sold it off.
On the mount’s behalf, I will say that when I parted with it, it was better than I found it. It had the right (northern) RA setting circle, it was smoother, and I did find several of the brighter Messiers, like M27, using the setting circle system. I had installed the cheap Celestron drives and the mount would hold an image at 200x for an hour. That is excellent performance, but I got no particular thrill out of it. To my mind, it was like getting a Yugo in shape to drive across the country at 75 miles an hour. The thing can be done, but is the game worth the candle? I was very difficult to get the mount into this level of performance and it was difficult to keep it operating at that level. Poor design characteristics kept getting in the way, like the tendency of the polar scope to lose alignment every time the scope is packed up.
Many CG5 owners say that the “new CG5s” with the ball bearings in the RA housing are “better.” They still do tear downs and remove burrs and build wooden legs. And they seem to do this cheerfully and are happy with their results.
I personally think the CG-5 is fundamentally flawed and does not provide what a good German equatorial mount should provide: stability, smoothness, good tracking, solid alignment polar alignment for manual or digital setting circles. I shudder at the thought of Celestron’s magnificent 9.25” SCT being sold with this mount.
Anyhow, in my view, if stability, smoothness, good tracking, solid polar alignment and good manual or digital setting circle performance don’t matter to you, you should get a nice dob.
CG5 supporters argue that once the mount is rebuilt and fitted with wooden legs you have a good German equatorial mount for not much money. My response is that people seem willing to accept a good deal less quality control in their telescope mounts than they do in their household appliances and cars. Few people would be willing to take a car, even a used car, off the dealer’s lot and sand down the engine cylinders and re-lube the bearings. Yet many CG5 owners cheerfully do just that.
And it’s not just the effort to do the rehab: you have to wonder, if these are the out-of-the-box problems,
what other flaws might be inherent in this product?
After the first draft of this review was initially posted, a number of comments from readers made me consider why there could be such discrepant opinions about the CG-5. I conclude there are two main factors:
a)Difference of philosophy. Some people get real pleasure out of “making their mount perform” and are proud of their accomplishment.
b)Difference in actual experience. In manufacturing, high quality is the result of a rigorous attitude to statistical variance in production (one can read about this in James Womack’s Machine that Changed the World, a study of international practices in automobile manufacturing). Statistical variance around a mean in manufacturing is exactly that. Some units may be excellent and others may be lemons. The problem with the CG-5 is that the average level is low, and the variance is wide. In English, “wide variance” means that the bad units are very bad, and that there are, by international manufacturing standards, a lot of them. The Internet furnishes a number of specialized web sites on how to tear down the CG5’s interior, and different ways to rebuild the legs. The very existence of this prolific how-to-fix information is indicative of a severe manufacturing problem. There simply is no analog in the Vixen line of scopes, and one won’t find abundant details about it in discussion groups, and no displays of rehab jobs on the Internet. The only possible explanation for this discrepancy in “Internet culture” between the CG5 and Vixen SP/GP scopes is that there are no analogous in-use difficulties with the Vixens. People just use them, rather than trade information and share techniques about what they did to them to make them usable. When I bought my Super Polaris and told its owner of ten years what I had done to make the CG5 usable and asked if I would need to do that to the Super Polaris, he looked at me like was I was from Mars. He had never heard of such a thing. In other words, the reason there are radically discrepant opinions about CG-5 performance is due to excessive variance in the quality of the product as it comes off the production line. In most other kinds of manufacturing, this degree of variance between the highest and lowest performance level of the product would be unacceptable.
To me, the popularity of the CG5 is a mystery. But it has many defenders on Internet discussion groups such
as sci.astro.amateur. Most of my objections to the CG5 would be moot if it were marketed disassembled, as a kit,
complete with sandpaper for de-burring and recommendations about what grease to use and where to buy or how to
make wooden legs. Most of the users who are happy with their CG5s basically treat the out-of-the-box product as
a kit, and their pride and satisfaction are similar to those of anyone who has successfully put together a kit
assembly and found it to be useful. But it’s not advertised or sold as a kit, and there are bound to be many users
who never get the word and will end up leaving the mount, the scope, and the hobby in the closet.
After all, not everyone is a suburban homeowner. If you’re an urban apartment dweller without space or inclination to have a table saw and other typical garage equipment, even the simple recommended do-it-yourself upgrade will cause problems. There are vendors of wooden legs for the upgrade, but this will bring you $50-$100 closer to the Vixen Great Polaris price, raising the question of paying nearly as much for not as much performance. Doing the degreasing and de-burring in an apartment is feasible, but you will be using solvents in a closed space or else venturing out onto the sidewalk with bushings, rings, and washers. Home owning amateur astronomers with garages and a few power tools may enjoy the challenge of making the CG5 work better. Urban apartment dwellers who think the CG5 is a mount they can take, as-is, out of the box and throw in the car for vacations at dark sites, may find themselves confronted with a series of practical difficulties.
With wide variance in production standards, a high number of out-of-the-box CG5s will be lemons, even though wide variance also means, by definition, that some will perform well.
The Super Polaris
After struggling to get the CG5 to a performing level, the Super Polaris (made, like the Great Polaris, by Vixen in Japan) seemed nothing short of miraculous in its differences. Large manual setting circles provided very accurate star finding capability. Amazingly, I had acquired it with a digital setting circle system (JMI NGC Max with encoders) free! About these I will simply say, watch out, once you go digital, you’ll never go back.
I took my modern C8 OTA and put it on the Super Polaris: the 1999 OTA has holes that allow the differently designed
SP mounting bracket to be securely fastened. The main design features that make the Super Polaris so wonderful
in comparison to the CG5 as currently sold are as follows:
1. Wooden legs are already on as standard feature, you don’t need to be a shop guy/gal to get the mount up to speed. The damping time was reasonable, at about 1.5 to 2 seconds, compared to about 4+ seconds on the CG5/aluminum tripod. (The Celestron damping pads reduce the aluminum tripod’s damping time to a marvelous 1+ seconds, but you as mentioned above, the pads decrease torque performance.) Curiously, the Celestron pads did not improve damping performance on the wooden SP tripod. Since the digital setting circles showed me clearly how the pads exacerbated torque problems, I sold them, and never felt I was missing anything. The pads however are essential on the CG5’s aluminum tripod. The Super Polaris + C8 combination is fundamentally stable and I was never tempted to build my own tripod legs, even though when I put the different parts together I expected the C8+SP combination to be my only scope for two or three years. Nonetheless, damping performance could probably be improved with heavier, more solid wood, or alternatively, a good pier.
2. The SP (and GPs) features a machined in place polar scope. I can’t say enough about how fantastic this is. It’s accurate, dead on every time, and doesn’t move when you pack up the scope.
3. The illuminated polar scope is a standard accessory, and this is worth mentioning as a separate feature. If your impression of what a polar scope can do is based on the CG5’s optional accessory, you are in for a big surprise. Illumination makes polar alignment much less confusing. The red light floods the polar scope’s field of view and washes out all stars dimmer than Polaris. When you see a star, you know it is Polaris (or at least, you should). You don’t have to dangle a red light in front of the polar scope to see the positional markings. This may sound small, but if you are on asphalt or wet grass, anything that reduces time on your knees is welcome.
4. The Vixen drives are like Ferraris compared to Celestron’s Chinese drives: the Super Polaris offered 16x sidereal compared to 8x sidereal top speed for the Chinese Celestron drives. Today’s Vixen drives offer 32x sidereal (which is why they use 8 batteries rather than the Super Polaris’ six). The Vixen’s drives are speedy and accurate, and backlash is more easily controlled on these good quality drives than on poor ones.
5. The machining is superb. You don’t need to open this mount up and pull out burrs and shrapnel. It’s smooth as silk, built right and built to last. You can feel the difference just holding it and letting gravity twist it around in your hands. This translates into much greater ease of pointing and holding objects and makes a huge difference at high magnification.
6. The polar alignment adjustment knobs are more accurate and work more easily. You have three such knobs, compared to two on the CG5 (the Polaris line has a lock knob on the side whereas the CG5 just has the azimuth adjustment in front and the knob in the back for altitude).
7. The large mechanical setting circles on the Super Polaris are superior to those on the modern Great Polaris and the CG5. Even if you go digital, there may be nights when the battery fails on your computer, and it’s nice to know the manual setting circles are there.
In short, the C8 on the Super Polaris mount very much pleased the kid who once operated an Optical Craftsman. I had great aperture on a very solid, sweet mount. Compared to the CG5 it is usable out of the box. Getting it to find, track, and hold an object at 200x became routine rather than a hard-fought battle.
The Vixen Great Polaris
I have not owned one of these but I have briefly used scopes on them. Its main differences are:
1. They do not come with wooden legs. But the aluminum tripod is heavier and better than the CG5’s.
2. The setting circles are smaller and more difficult to use. I fear manual setting circles are becoming vestigial due to the creeping influence of go-to and digital setting circles, both of which are expensive options.
3. The machining, the illuminated polar scope, and other features remain very good and similar to the Super Polaris.
What would make you swap out of a Great Polaris or Super Polaris mount?
An unanticipated stroke of financial good fortune allowed me to move on from the SP mount to a Losmandy G11.
The SP with a modern C8 OTA is an unusual combination, but I put it together after considering various options,
and had the intention of keeping it a long while. Nonetheless, when opportunity struck, I decided to move fast.
If you don’t turn that extra cash into a Losmandy G11 you might well do something crazy with it. You might blow
it at Las Vegas, use it as a down payment on a new car, or save it for old age only to discover, too late, that
you’re the one who dies early. After all, an average life expectancy of 75 doesn’t mean YOU get to live to be 75,
so why are you waiting for that upgrade on your mount?
The GP/SP design, although it performs well in the field, has the following defects compared to higher end mounts like the Losmandy G11 (or G8). So, if you too should have a stroke of financial good fortune, perhaps you too will want to make the move for the reasons below. The CG5 shares all the deficiencies below (except for no. 3, because the CG5’s designers took the worse option of no lock knob at all), but coaxing a good performance out of it is much more difficult. The Losmandy G8 is almost exactly priced to compete against the Great Polaris with drives so these items are worth thinking about before buying.
1. The !#!%!@!! clutch levers. The Vixen, CG5, and CI700 mounts all have these levers that must be loosened to slew the scope and then re-tightened to permit tracking and operation with the control paddle. The Dec lever twists with the Dec and you’ll always be fumbling around for it. I didn’t have these levers on my equatorial mount thirty years ago and I hardly see the need for them today. Neither does Losmandy, by the way.
2. The perils of manual slow motion controls. You are best advised to remove these if you are using an electronic drive system with a hand paddle. The Vixen GP/SP and CG5 imitator have silver knobs (clutches) on the drives that must be tightened for the drives to work. They must be loosened if you wish to use your manual slow motion controls. If, as is common in observing, you want to adjust an object in your field of view and you happen to reach for the slow motion control while the drives are engaged, you could strip the gears and destroy the drives. You might be able to train yourself never to make this mistake (could you really?), but at star parties people reach right for those knobs.
3. The #!#$!# lock knob on the side of the mount. This is a great feature of the SP/GP line, especially relative to not having it at all, as on the CG-5. Once you’ve tightened it, your mount is considerably more stable than otherwise, and it eliminates even small amounts of altitude drift that tend to creep into a CG-5 when you’re not looking. Nonetheless this feature has its annoyances. Especially this: THE LOCK KNOB MOVES THE MOUNT OUT OF ALIGNMENT AS YOU TIGHTEN IT. This is frustrating. I have discovered that a very precise order must be followed to minimize cursing and swearing. I can do it in a few minutes now. But it is a pain, and I’m tired of it. The Losmandy design avoids this problem (Appendix No. 5 tells you how to live with it).
4. You should be wary of one major design flaw, common to all Vixen systems, particularly if, like me, you are ham-handed and tend to drop things. Vixen puts the electronic brains that make the drive system work into the paddle. Every time you drop the paddle, which does happen, you are jolting a lot of vital circuitry, and over time it will get damaged. On the Losmandy the “brains” of the electronics are secured to the mount in solid machined weatherproof aluminum and all you hold in your hand is a box with some simple switches.
5. Unreasonable difficulty in maintaining the equipment as it gets older. The control box I owned had all of its electronic id numbers on the interior parts removed, as in filed off. Neither Orion in the U.S., nor Vixen in Japan, will help you with a defective Super Polaris control box. They advise you to replace the box AND the drives (I have heard that the newer control box works on the older drives, but I haven’t confirmed this). One cannot help but feel a bit resentful at being advised to throw out a perfectly good set of drives because the paddle is damaged. The drives could last forever. By contrast Losmandy electronics have all identifying parts and they will either tell you how to fix them or fix them for you. But you won’t need it anyhow, because of #4, above. (Since the first draft of this was posted I have received email from one user indicating the parts numbers were not filed off his controller. I am uncertain as to what this means, whether Vixen started and then stopped doing it, or whether the company didn’t do it and then started to do so later.)
I consider the GP/SP Polaris line to be the king of the lower priced, truly functional equatorial mounts. If
you want to have the experience of using a German equatorial mount with minimal problems and frustrations, I think
the entry level to the “German equatorial experience” starts here. The CG5 has all of the defects and none of the
benefits of Vixen’s good engineering and production practices. As a matter of impression, it seems to me that Celestron
of the 1990s and early 00s has basically decided to abandon premium quality mounts in pursuit of lower retail sales
prices. The company abandoned the Losmandy G11 from its upper end SCTs and the GP/SP from its midrange SCTs. The
company’s substitute mounts, though cheaper, do not seem to offer the same performance capability.
By contrast, I consider the Losmandy line to be the beginning of the upper end mounts. The GP+drives is priced the same as the Losmandy GM8. I would choose the GM8 over the Vixen line because I’m tired of clutch levers, lock knobs, and what have you. Losmandy still takes manual setting circles seriously: they’re big and accurate and easy to use. There are people out there who can use RA and Dec but who may not be ready to plop out an additional $600 to digitize their setting circles. Vixen’s decision for small manual setting circles is practically pushing you to buy dscs or their $900 go-to system.
So, in a sense, the Losmandy, which gives you a manual setting circle option equivalent or superior to the good equatorial mounts of the 1960s and 1970s, offers a cheaper start-up for those who like to use stellar coordinates. (Not everyone does, and I am amazed at the number of star hopping owners of equatorial mounts.) Finally, by not filing off parts numbers from its internal electronics, Losmandy is giving its customers the chance to fix their equipment, by themselves, with the help of a technical friend, or with the company’s help. To me, this points to a fundamentally superior philosophy of customer support, and sets an example that Vixen might well wish to consider.
If you trade in your CG5 for either a Super or Great Polaris you will notice significant performance improvement. A friend in New Zealand did not believe me with regard to the demerits of the CG-5, but he believed me enough to do a side-by-side of the GP and the CG-5. He immediately put his CG5 onto the used market.
The CG5 has a fair number of advocates, and to many users is a good value relative to the outlay required. Nonetheless, many CG5s “Like New In Box” are available on Astromart for 30% to 40% less than well-used GP/SP mounts. I cannot help but think that this is a market judgment of significant differences in performance, design, and manufacturing quality. But I do not think the price differential conveys all that needs to be known. I believe that the CG5 “out of the box” has an outsized potential to discourage would-be amateur astronomers from the hobby. In spite of the many supporters of re-worked CG5s, I continue to believe that a good Dob offers a better value. I recommend that people interested in exploring the virtues of viewing with a good equatorial system should save the additional sums needed to move directly to a new or used Vixen mount. (See Appendix 7 on cost differentials)
Appendix No. 1. ON RECOVERING COSTS AND VALUE OF DEPRECIATING EQUIPMENT. Re-sale value and cost-of-admission
are values that everyone must consider in buying equipment. If you buy a scope for $1000 and sell it a year later
for $700, then for $300 you have had the use of a telescope for year. That’s a good deal, especially if the scope
gave you good value. People pay thousands to go to Europe or go skiing for a few weeks. For $300 net outlay you
can have access to the universe for a year. The C8 Nextstar go-to system offered by Celestron does not look particularly
durable to me, but I think it could be an excellent value for the money. Let us say that you bought one new for
$1700 and, after a hypothetical complete system failure after three years, sold only the optical tube assembly
for $500 three years later. That works out to a net outlay $400 a year for three years, which is not expensive
for a “guided tour” of the universe. Complete computerized go-to is the astronomical equivalent of a trip to Europe
with all hotels, meals, and guided tours arranged in advance. It is not for everyone but for many it beats staying
at home, and such a scope might offer better value to a beginner than an $800 refractor on a CG5 mount that required
a complete rehab and even so presented operational difficulties intrinsic to its design. Such a scope might sell
for $600 after three years and seem financially a much better deal, but many might be discouraged from the hobby
because of it.
Appendix No. 2. MAKING YOUR BATTERIES WORK IN COLD WEATHER. The SP/GP/CG5 line all feature battery packs, usually of “C” or “D” batteries, that make the telescope’s drives work. These should give you about 20 hours of performance. In very cold weather, as in below freezing, you will notice that battery failure can occur much, much sooner, after even twenty minutes of viewing. In moderately cold weather, like 40-50 degrees F, the failure mode is more subtle. The RA drive will keep working because it is drawing current continuously. When you press the Dec switch, nothing may happen. You may erroneously conclude that your Dec switches are failing. What seems to be happening is that the extra draw of current, from adding the Dec to the RA, pushes the unit over the edge, as if the batteries were failing. You don’t notice the RA stopping when you push the Dec button because you only do so for short periods. In any case, here are several solutions: 1) Put the battery pack under your coat. This is “not recommended” because you may walk away from the scope and jerk the wire hard. 2) Take a wool sock, put the battery pack in it, and a chemical hand warmer in. These are sold, six for $1.80, at Wal Mart and are usually in the hunting goods or outdoors sections. They last for hours. 3) Move your entire system to a heavy duty Marine battery, which you’re likely to do if you’re using a Kendrick or other dew removal system. 4) If you’re using a Kendrick system but haven’t yet bothered to attach the drives to that large marine battery you’re already using, put one of your Kendrick warming strips on the teeny battery pack. It’s silly to use a big battery to warm small batteries, but it works.
Appendix No. 3. UNUSUAL FAILURE MODES OF THE JMI SP/GP/CG5 ENCODER SYSTEM. JMI is very good about discussing the most common failures, such as putting the RA wire in the Dec encoder. Here’s a couple they don’t usually mention. DEC failure mode: Is your counterweight shaft screwed in tight? If it’s wobbling, your Dec readings will be bizarre. RA failure mode: 1. On the GP/SP line, make sure the polar scope eyepiece is tight but not so tight you can’t loosen it later to focus. The rotation of that eyepiece is what turns the encoder. 2. In the encoder “RA butt cup” you will see a little wheel that spins around. That wheel has a set-screw on the side which can be accessed via a hole in the “RA butt cup.” If that silver aluminum wheel is loose on its shaft, you won’t get good readings. 3. Faulty wires. It can happen, the wires can fail in the field. It’s a good idea to have a backup set. You can make these 8-pin wires if you buy the equipment from Radio Shack, but the tool is a pricey $30.
Appendix No. 4. DEFECTIVE SETTING CIRCLES. The previous owner of my CG5/C8 had confessed that he “never understood” how setting circles work and couldn’t get anyone to help him at star parties peopled largely by star-hopping dob owners. I was initially extremely frustrated trying to use the setting circles: I couldn’t get them even approximately to work on major, easily identified stars. After several frustrating nights I decided to keep meticulous track of all RA and Dec measurements as I calibrated the setting circles and swung back from star to star. I then posted the results on sci.astro.amateur. Astute people noticed that my results were consistent with a southern RA setting circle! Celestron technical support quickly confessed: “Oh yeah, a few of those went out” and replaced it for free. I mailed the southern RA circle to an internet friend in New Zealand to get it south of the equator where it would do no more harm. There are four lessons here. One, Celestron technical support was quite competent and speedily rectified the problem. Two, Celestron’s quality control was below par, which seems to be systemic with the current level of manufacturing practiced in main land China. Three, the previous owner of my scope gave up on astronomy and used the money to buy a fancy bicycle. He may have done so anyhow, but it indicates that “at the margin” people are driven out of the hobby by equipment that does not perform out of the box. Four, I was able to remedy the problem because of my unabashed willingness to go public with my ignorance and my problem. This is a hobby in which people need to ask each other for help. (sci.astro.amateur is an excellent resource; there are also user groups on www.egroups.com)
Appendix No. 5. ORDER FOR TIGHTENING ALIGNMENT KNOBS ON SP/GP MOUNTS. 1. Put the mount on the scope, tighten the knob underneath the tripod head so that the mount can still move slightly. This makes it easier to do azimuth adjustment. 2. Find Polaris. Make approximate side-to-side (azimuth adjustments) up on the top using the two plastic knobs. Because you’ve left the knob loose on the bottom, this should not be too hard. 3. Get Polaris so it is BELOW the little circle you want to put it in. 4. Tighten the knob underneath the mount head, not as tight as you can, but snug. 5. Tighten the lock knob with Polaris still under your final objective, the little circle. It will move out of correct azimuth. 6. Fine-tune azimuth with the knobs in front. 7. Using the rear altitude adjuster, raise Polaris to the little circle. This sounds more complicated than it is; same with no. 6, below.
Appendix No. 6. Short cut to putting the “little circle” in your finder scope in the correct position. Polaris is just off true north, as is well known. The SP/GP/CG5 polar scopes come with detailed instructions about how to use the dial on the RA axis to use date and time to move the little circle in the finder to the correct position. This is necessary because Polaris is “off” true north in a different direction (from the Earth) depending on where it has rotated relative to true polar north. Here is a shortcut that works. 1. Find Cassiopeia. Look at the star that is the left-most (when seen as a “W”) or the right-most (when seen as an “M”). 2. Draw a line from that star in Cassiopeia to the horizon. That line points to six o’clock; the left most star of the “W” is the center of the clock. 3. Find Polaris. What hour is Polaris indicating relative to your reference star in Cassiopeia? 4. If Polaris is at 10 o’clock, put your little Polaris circle at 4 o’clock. If Polaris is at 12 o’clock, put the little circle at 6 o’clock. If Polaris is at 4 o’clock, put the little circle at 10 o’clock. The pattern here is that the “little circle” should be set exactly six hours off the “Cassiopeia clock” you established in steps 1-3.
Appendix No. 7. PRICE DIFFERENTIAL FOR THE CG5 AND VIXEN MOUNTS. I have seen advertisements for a new CG5 mount and dual axis drives for $510, which breaks down to about $170 for the drives and $340 for the mount. To this you will add damping pads ($50) and the poor quality polar scope ($50) if you want approximate functionality comparisons to the Vixen. So call the “real effective price” of the CG5 $610 plus $20-$40 in rehabilitation stuff depending on what you have in the garage. (Figure $50 to $100 more if you are going to buy pre-made legs for the upgrade.) The Vixen GP goes new for about $750 and the dual axis drives with paddle are about $450, or about $1200. The superior polar scope and illuminator is included. So, exclusive of shipping charges, call the CG5 a $630 item (excluding your labor time) and the Vixen a $1200 item (your labor time not needed).
The CG5 can be bought complete with Chinese dual axis drives and a C8 OTA for about $1150. Since the C8 OTA only sells in the neighborhood of $750, the “package savings” is in the neighborhood of $100 to buying the mount separately.
In any event, we are talking about a price differential in the neighborhood of $600 between the CG5 and Great Polaris line. If you want to reduce that price differential, I would strongly recommend buying the GP with the Chinese Celestron drives. That move alone shaves $300 off the $600 differential in price. So we are now talking about $300 net difference, and I do think that for a $300 net difference it is worth delaying the purchase, saving the $300 over the next three to six months, and getting the better equipment. The Chinese drives can be sold in a year or so for $100 which can be put towards the $450 Vixen dual axis drives as a future upgrade. These humble drives will do much better with a Vixen worm gear than they do with the CG5 worm gear. Looked at another way, and not to encourage excessive debt, but the $300 difference could be financed on a credit card at 18% over a year with monthly payments under $30. (The net difference and Vixen system just described would be $200 if, not owning home power tools, you would be planning on buying wooden legs for the tripod upgrade.)
In the used market a CG5 with Chinese drives and polar scope will run in the neighborhood of $400 excluding shipping. The Great Polaris with Vixen dual axis drives and illuminated polar scope will run $750 to $900 depending on how much of a hurry the owner is in to sell. The Super Polaris range will typically be $100 less than for the more recent GPs. (New prices are from www.astronomics.com, www.poconoscopes.com, and www.khanscope.com . Used prices are from www.astromart.com ).