Uncle Rod's Astro Blog

There’s no doubt there’s a slew of used SCTs available; unfortunately all too many amateurs find themselves in financial straits ranging from “concerning” to “dire” and decide they must sell a beloved scope. Shame, but when it comes down to feeding the kids and paying the mortgage, there is really no decision.

What follows is my advice on the used gear game, adapted and expanded from the short checklist at the end of my (free) Used CAT Buyer’s Guide. Like the checklist in the Guide, this is aimed at catadioptric buyers, but most of it is general enough in nature to be a help to prospective purchasers of used scopes of any design.

Before we get started, let me address a concern I’ve heard expressed more than once of late, the morality of buying used right now. Isn’t it wrong to take advantage of someone’s misfortune by buying their telescope for a song? As above, it’s a shame when someone has to part with their gear to make ends meet. And certainly I would hope these folks will get a fair price for their stuff. I don’t think there is anything inherently wrong with buying used telescopes in economic hard times. If your purchase of that LX200 means the person in question has another month’s grace with their mortgage, I’d say both y’all benefit. As for fair price? I don’t see many out and out steals. Prices are down, but telescopes ain’t being given away. Anyhoo, it’s up to the seller to set a price she/he thinks is fair or to accept an offer made by a buyer—or not.

The first question, of course, is where do you buy used? The best answer is always “locally” and especially “from a fellow club member.” By purchasing locally, you will get to examine the telescope in person, which is almost always a Good Thing. Most people are not gonna set out to cheat you, but it ain’t unheard of in this ol’ boy’s experience for somebody’s idea of “near mint” to be closer to his idea of “fair.” Even better than buying locally is buying locally from a fellow amateur.

The scope being sold by a deceased amateur’s relative or by the person who thought they wanted a telescope but really didn’t may be fine, but don’t expect these people to be able to tell you much about it. They may remember when that Super C8 was bought, but forget things like, “Does this NexStar have the user-upgradable motor control board?” Best is a fellow club member. Not only should this person be able to tell you anything about the scope in question, you may have used it yourself on more than one occasion at club star parties and be very familiar with its pluses and minuses. Also, a fellow club member knows they will be seeing you every month at meetings and star parties, so it’s unlikely they will intentionally rook you.

One other big plus for buying locally is the telescope will not have to be shipped. That means you won't have to pay today's astronomical shipping prices or worry that the seller has packed the scope sufficiently to survive the tender mercies of the Brown Truck Guys.

What if your city doesn't have a club, you don’t know any fellow amateurs in town, or none of them or anybody else has the C8 of your dreams for sale? The alternative is the online astronomy classifieds. Astro-classfieds have been a popular feature of the amateur astronomy landscape for at least three decades, starting with a little paper called The Starry Messenger. This monthly pulp magazine was nothing but amateur astronomy want-ads. Oh, how we loved The Messenger back in the 80s! Oh, how we waited for it every month so we could jump on them hot deals. Problem was, seemed like everybody in the dadgummed U.S. of A. got their copy before us here in Possum Swamp. Every time I responded to an ad for a “mint Cave 12-inch, $750.00” the response was the same: “Sorry, sold yesterday.”

The Internet astronomy explosion changed all that. By the mid-90s there were online astro-fieds that I could see as soon as somebody on the left coast could. The death knell for The Starry Messenger was sounded by Astromart, which cracked the code for what amateur astronomy online buying and selling should be.

Today, Astromart is not alone; there are, for example, classifieds on Cloudy Nights and Astronomy Mall (a site that is a real old timer in online amateur astronomy; happy to see it still survives). Still, when most folks think of used astronomy gear, they think of Herb York’s Astromart. There are a number of reasons for that. The website URL is easy to remember, “Astromart.com;” it’s simple to get to the ads; and, most of all, Astromart is safe, or as safe as any service of this kind can be. Can you get cheated on The Mart? You can, but it is far less likely than it could be thanks to the tireless efforts of Herb, his colleagues, and more than a few volunteer monitors. This is not to say other astronomy ad services are not necessarily “safe;” just that I know how much (day to day) effort that goes into keeping Astromart a good place for buyers and sellers both.

How about eBay? There is good and bad. With Paypal you do gain some protection, and some of our amateur astronomy vendors sell there. B-U-T…in my opinion, when you come right down to it, eBay can be a crapshoot. Fraud aside, you will likely be dealing with someone who knows absolutely nothing about astronomy and telescopes—witness all the images of 4.5-inch Newtonians with their mirror cells pointed at the sky. I’ve bought more than a few small astronomy-related items on the ‘Bay, and I have never been cheated. Not completely. I’ve always received my item, anyway. It ain’t always been in exactly the condition indicated by the ad, though. A time or two it’s not even been the exact item I’ve bid on.

Further eBay advice? Save yourself some money. Decide in advance what you want to pay for the telescope in question. Place a bid for that amount and do not place a new bid no matter what happens. If you lose the item, you lose it. I guarantee, there will be another one soon, and you will eventually get what you want. Get caught up in the bidding race and you will wind up paying way too much, defeating the purpose of buying used.

Before you even dream of shopping for a new CAT anywhere, the first thing to do is educate yourself. What kind of drive did the Meade 2080 LX3 have? Which finder shipped with the LX6? Did a hand control come standard with the Celestron Powerstar IV? Identify the models you think you might potentially be interested in and learn everything you can about ‘em. That’s easy in the Internet era. One place to start is my aforementioned Used Guide. Another is the Telescope Bluebook web site. I refer to it frequently and it has saved my bacon more than once. Yahoogroups are another good source of info. Almost every popular old scope has had a Yahoogroup established for it, and even if a given group is not very active, the archives will likely be mucho informative. Finding out all you can about a scope is doubly important if the person you are buying from—the Widder Jones down the street or some Goober on eBay—doesn't know much about SCTs.

Whether you’re bidding on the ‘Bay or buying from Elmer down to the club, what do you look for and out for in a used CAT? Naturally, you will not be able to check these things if you are buying off Astromart, but you will be able to use the following to at least formulate a set of questions for the seller.

Indoor/Daytime Checks

Overall Condition

First off, a general assessment. Is Miss Telescope in reasonable physical condition? Is the paint on the OTA and mount more-or-less intact? Is any rust minimal? When you loosen the locks on dec/RA does the mount move smoothly? Physical condition will, of course, be related to the age of the scope. You can’t (always) expect an Orange Tube C8 to look as good as a two year old ETX 125. If you’re buying a Meade with one of their chrome-plated tripods, expect some rust on the legs. The only way that (initially) pretty tripod will be free of orange spots is if it was rarely outside. And that’s the thing. A scope that has been used frequently and shows some normal wear may be a better prospect than the poor Super C8 Plus that was bought for Halley, used once or twice, and has been in a closet ever since. The scope that got outside likely has a knowledgeable owner who has kept the scope in good shape where it counts. I’d much rather have a Super C8 with a few paint nicks but a good optics set than I would one with spots of fungus on the primary from being stored in a damp utility room for years.

Mechanics

Unless the maybe-scope-of-your-dreams is a recent Celestron, it will have slow motion controls on both axes. Exercise these to ensure they operate smoothly. Remember, in the case of fork mount telescopes, you will have to have the declination lock at least partially engaged and the RA lock as least partially disengaged before you can move the mount with the slowmos. Never turn a powered-up LX200's slow motion controls; that can cause damage. A non-go-to GEM will often have manual clutches that will need to be engaged before using the slow motions (I’m not talking about the main RA and declination locks; those should be locked).

Carefully and thoroughly check the OTA/mount’s other mechanical functions. Does the focus knob turn easily and smoothly (if this is a Meade LX200 GPS or other recent Meade scope, make sure the mirror lock is disengaged before you start twiddlin’ the focus control)? Exercise any other mechanical fittings on the OTA and mount as well. If there is a wedge, does it have fine altitude and azimuth adjusters? Do they work right? If a wedge isn’t included with a non-go-to fork mount scope, by the way, insist on a hefty discount. The scope will not track without a wedge. Are the tripod fittings OK? All screws and bolts and nuts there and tight? Accessory tray present if there is supposed to be one? Leg extension locks operational and leg extensions un-dented (if they are, the locks were tightened down too tightly at some point, possibly compromising firm locking)?

Electronics

Whether the CAT in question is a computer heavy NexStar or LX200 or just an old warhorse with an AC synchro drive, power it up to make as sure as possible the drive functions as per normal. If this is a go-to scope, I urge you (or the owner) to do a “fake alignment” indoors. Run through the alignment process just as you would under the stars. Does the scope slew normally? No pauses or other hiccups (expect some scopes and mounts to be surprisingly noisy, especially the Meade go-to forks and LXD55/75 and the Celestron CG5 GEMs)? When doing the fake alignment, just accept the alignment stars the scope requests. When alignment is complete, do a fake go-to to an object which you know is above the horizon and for which you know the current location, roughly. If the telescope points in generally the correct part of the “sky,” it passes.

How about a non-go-to scope? Exercise whatever features and functions it has. You’ll have an idea of what these are if you took my advice and educated yourself about the model(s) you are considering before beginning to shop. If the scope offers faster-than-sidereal slewing speeds, for example, test them all. What if the telescope, an Orange Tube C8 for example, does not have any slewing speeds at all, only sidereal tracking? Make sure it tracks.

Keep in mind, of course, why they call it a “clock drive.” At sidereal rate, the scope will move very slowly; it will take 23-hours, 56-minutes, 4-seconds to revolve completely on its RA axis. So how do you know if the motor is workin’? Fasten the RA lock and power up. In half an hour, tube movement may be obvious. Better, some kind of marks on fork assembly and drivebase (maybe made with masking tape) will show-up movement sooner. Don’t use the RA circle as a reference; in most scopes it is driven to keep the current Right Ascension under the pointer as the telescope tracks. If you stick your ear up to the base, you may be able to hear the motor running, but don’t depend on that—nor on idiot lights. Make sure.

Optics

Aye, and there’s the rub: a used scope may have been meticulously cared for, but if it’s got punk optics, so what? What’s the most important thing a used CAT buyer can do to avoid buying a pig in a poke optics-wise? Refuse to buy any SCT made between about 1986 and 1990 without testing the optics thoroughly. We refer to these poor kitties as “Halleyscopes;” they were built during the huge Comet Halley Craze and its aftermath in the 1980s.

Celestron and Meade wore out their tools and workforces trying to ship as many telescopes as they could when Mom and Pop America was clamoring for SCTs to view the spectacular visitor (ahem). QA fell by the wayside and many (but not all) these scopes are optically sub-par. It took at least till the beginning of the 90s for the two companies to get their optical houses back in order. This is very important for the used consumer; by eliminating the Halleyscopes, you eliminate at least 90% of the optical dogs. Will viewing terrestrial objects tell you much about optical quality of a scope? Unless the CAT's optics (or collimation) are truly putrid, viewing terrestrial objects, especially given daytime "seeing" over the heated earth, ain't gonna be too informative. Looking at the Sun through a Solar filter? Maybe minimally more revealing.

As for the physical condition of a candidate’s optics, let us review what not to do first: the dadgummed flashlight test. What I mean is looking at the optics of the scope in a strong oblique light—sunlight, a flashlight shone down the aperture, whatever. Any telescope’s optics will look horrid if you do that. Even the smoothest and best coated mirrors and lenses will scatter some light across their surfaces and every tiny dust mote and imperfection will stand out in stark relief.

What should you do? View the optics in normal light. The coatings should be in good shape, no fungus or other suspicious spots on corrector or secondary or primary, and reasonably clean. What’s reasonably clean? The internal surfaces should be clear of everything but a small amount of dust. What if there’s more than a little dust on the corrector’s inside surface? Quite a few Meades from the 80s have an icky film on the corrector inside from some kind of outgassing, apparently.

If you’re confident around a CAT you shouldn’t turn down a scope because the inside of the corrector needs cleaning. You can do that job in 15 minutes. The surfaces of the mirrors? That’s another story. Sure, you can clean ‘em, but you always run the risk of damaging the coating when you clean a first surface mirror. The real show-stopper? What caused a primary or secondary to get so dirty? Usually only bad things like the scope being stored for long periods with the rear port open or the corrector plate being removed and left that way for a long time. I’d turn down a CAT with a grungy primary or secondary unless it was almost bein’ given away.

One last optical caveat is the secondary on the Meade LX3. For a little while, Meade offered “MCSOG” optics as an option on these 80s scopes. That stood for “Multi-coated SILVERED optics group.” The secondary mirrors on the telescopes so equipped are not aluminized but silvered. Alas, as I coulda told ‘em would happen, those silver-coated secondaries, while wonderfully reflective, deteriorated in a relatively short time. Meade was replacing the secondaries on these scopes for free under their Lifetime Warranty for quite a while. Now? And for someone not the original owner (though I doubt Meade knows pea-turkey about who the original owners of cotton pickin’ LX3s were this far down the road)? Don’t count on it. How do you get a good look at the secondary, by the way? If the reflection of it in the primary is not overly informative, just pop off the rear port cover and take a peek up the baffle tube.

A very few Celestron scopes in the early 80s were equipped with StarBright primaries that were silvered. These scopes are not common (Celestron soon changed the StarBright formula) and their silver seems to have held up better than that on the LX3 secondary. Bottom line? Any pitting on any scope mirror means “no way.”

Outdoor/night-time Checks

Unless the SCT in question belongs to a fellow amateur, it probably ain’t gonna be possible to give it a test run under the stars, but if that is possible, that is the best way of guaranteeing you get a scope to your liking…

Mount Operation

If we’re dealing with an old-fashion non-go-to scope, all you need to know is that it tracks accurately when decently polar aligned. If you’re new to this stuff, though, please remember that if the mount is not precisely polar aligned, which it likely won’t be, not unless you do a drift alignment, objects will drift in the field in a north/south direction. If the RA axis is at least pointed at Polaris, though, that should be slow enough to show the thing is tracking. Not sure? Center an object at high power and shut the drive off. NGC Umptysquat will dash out of the field quick enough to make your head swim.

If the mount offers faster than sidereal slewing speeds, try them. (Did you know many old Celestrons offer a higher “centering” speed? Hold down an east or west button on the hand control and mash its opposite number.) For motorized slow motions to work, both RA and declination locks must be locked, of course. What else? Check anything that couldn’t be vetted by daylight—polar scope and finder illuminators, for example.

If the scope under test is a go-to model, check it thoroughly in every part of the sky for acceptable accuracy. What’s “acceptable”? A modern scope like a CG5, an LX200 GPS, or a CPC should put anything you request in or very close to the field of a low power eyepiece at f/10. An older scope like an Ultima 2000? At least close on deep sky objects (see the Guide for some words about the Solar System and these old scopes).

What if the scope does not seem sufficiently accurate? What if it’s missing targets by large amounts? Don’t be too quick to condemn it. Was the go-to alignment done correctly and carefully? If the owner did it for you, did he seem to know what he was doing? If the scope hasn’t been used for a while, he/she may have missed a step; that’s why it pays to educate yourself about your candidate scopes and their operation. Sometimes the quality of a battery or AC power supply is the culprit. Or a failure to set backlash characteristics (Drive Training for Meades, use of up and right keys for final alignment star centering for Celestrons). Anyhoo, I’d be suspicious at least of a recent go-to that can’t be made to land on targets.

Optical Performance

Determining how optically good a telescope is is often difficult and sometimes nearly impossible. Yeah, you can try the consarned star test, but you will need good seeing for that and you will need to be able to interpret the results, something that’s not always easy if you are new to scopes in general or, especially, CATs. As I’ve often said, the best optical test for an SCT is probably the way a planet looks at high magnification under good seeing. The problem is that you need good seeing and a planet above the horizon (Jupiter, Mars, or Saturn). If the telescope’s images don’t look quite right given acceptably steady seeing conditions, check the SCT’s collimation. If it is “off,” request the owner either adjust it or allow you to do so. I wouldn’t buy a telescope that exhibited poor images even if I were 99.9% sure collimation was the problem.

Other than image quality, what to look for? Mainly focus shift. Due to the telescopes’ moving mirror focusing system, SCT images move a small amount in the field when the focus control is adjusted. A little shift should be expected. How much is “a little”? For a modern scope, maybe 45-arc seconds to 1-arc minute. About the width of Jupiter in other words. Some older scopes may have more, but sometimes that can be improved upon. If Miss CAT has not been used in a while, racking focus to both ends of its travel to redistribute grease on the baffle tube may help a lot. Sometimes the focus shift can be further improved by adding a little (and I do mean “a little”) grease to the baffle tube in a very thin coat if the scope is old and dry. Sometimes fiddling with the focus shaft after loosening the screws on the focuser assembly can help as well (I can send you the procedure if you are interested), but if redistributing the grease by moving the mirror to both ends of focus a few times didn’t help, expect to have to live with whatever amount of shift remains. Can you?

Other Stuff

That good ol’ SCT checks out fine, you reckon? There are a few miscellaneous considerations to ruminate upon before you whip out the checkbook. First is age. For some telescopes “newer” equals better. That is surprisingly not the case with the earliest CATs. I have a 1973 Orange Tube that works just as well as it ever did. The same is true with early Meade 2080s. They are simple telescopes with little to go wrong. If they’ve been stored indoors and/or cared for by somebody with a modicum of sense, there’s not much to deteriorate. Their “electronics” consist of an AC power cord and a synchro motor (“motors” in the case of early Celestrons). When you get to mid 80s scopes, though, scopes like Powerstars and LX5s, circuit boards enter the picture. Even if they are simple, the electronics are there and their failure will disable the clock drive. When you start talking older comput-o-scopes, the Compustar, the LX200, and the Ultima 2000, “used” is often spelled t-r-o-u-b-l-e.

Why? It’s not because these SCTs are inherently failure prone. Some folks will tell you early LX200s, for example, are better built than their GPS descendents. The problem is two-fold. First, their circuitry is more complex than that of later telescopes. As time went on, Meade (and Celestron) was able to accomplish the same tasks with greatly simplified circuitry. “Simpler” almost always equals “more reliable.” More importantly, just a few years after the end of production both companies typically stop supporting their old SCTs with parts and service. To their credit, Meade kept going with the LX200 for well over five years after the GPS came out. Alas, it appears support for the LX200 from Meade has finally dried up.

You might not be able to fix a malfunctioning go-to scope or someone else might be able to fix it for you, but that is not assured, especially if critical and custom parts like some IC chips are no longer available. These telescopes (Meades and Celestrons) will eventually have problems. That might not happen for a long time—quite a few early LX200s are still cooking—but it will happen. If the electronics survive the first 12-hours of powered up condition, yes, they will likely last a right long spell, but not forever, muchachos, not forever.

There’s one obsolete scope to always avoid, and it ain’t got no electronics: The Criterion Dynamax. These SCTs, made in apertures of 4, 6, and 8-inches initially, competed with the Celestron Orange Tube in the 1970s, and, when the company was sold to Bausch and Lomb, were an alternative to Meade and Celestron SCTs through the mid-80s. What do most of the Criterions and B&Ls have in common? Very poor optics. You can read the whole sordid story in the Used Guide, but, suffice to say, if you are confronted by any of these scopes (other than the fairly nice B&L 8001 Pro), RUN LIKE THE WIND!

If you are considering an obsolete scope, you must also take the accessories into consideration. If they are not present, you may not be able to replace them. That can be particularly debilitating in the case of a hand control, and almost as bad with something like the non-standard visual backs a few of the very earliest scopes sported. One common problem is drive correctors. If you have a desire to take pictures with the “new” 2080 or Orange tube, you will need a “drive corrector,” a variable frequency inverter, to guide it during long exposures by adjusting the speed of the AC motor. If one is not furnished with the scope, well, good luck finding one today.

OK, OK. You’ve considered the ramifications of buying an orphaned CAT, have avoided Halleyscopes and Dynamaxes like the plague—or at least star tested them—and are ready to buy. How much should you pay? Negotiating a fair price is between you and the seller, but there are a few guidelines. Firstly, don’t pay more for that old SCT than it’s really worth. For example, zillions of C8 Orange Tubes were made. It’s a classic, sure, but with a small C. Given their numbers and the prices of modern go-to scopes, an Orange Tube shouldn’t sell for more than about 500 bucks in good condition. Mint with some sweet accessories? Maybe a little more.

Usually the prices asked by working amateurs are pretty reasonable. Overinflated prices tend to come from folks who’ve inherited the scopes (“This is my Granpa’s EXPENSIVE SCIENTIFIC INSTRUMENT!”) or who bought the scope, put it away shortly thereafter, and have an exaggerated memory of its worth (“I am sure I paid three thousand dollars for this Super Polaris C8, even if it don’t got no clock drive.”). The best you can do in these situations? Pass ‘em by. There are plenty more where they came from. If you are in need of a baseline idea of what a particular scope should cost, a survey of old and new Astromart ads will help.

Don’t get the idea I am trying to scare you away from buying used with my tales of Halleyscopes and cautions about obsolete and too expensive used CATs. I just want you-all to be aware of the possible pitfalls and aggravations inherent in pursuing an old(er) SCT. Me? I’m not afraid to hack into an LX6 OTA or drivebase, but even I would be wary of an old LX200 or Ultima 2000. Which doesn’t mean one might not be a good scope for you as long as you are aware of the possible perils and are prepared to deal with ‘em. On the other hand, I would not have the slightest hesitation in buying a (non-Halley) non-go-to scope. In fact, as the years pass, I seem to have an ever greater desire to replace my foolishly sold Orange Tube C8 or to acquire one of the legendary Blue and White Celestrons I stared at in the Sky and Telescope ads of the 60s, but, of course, couldn’t dream of affording in the days of my misspent youth.