The Celestron C8 Schmidt-Cassegrain is one of the longest running continuously produced telescopes in history (perhaps only the Questar has been around longer.)  In 40+ years of production, while the mounts and accessories around the scope have changed and advanced (sometimes dramatically) the optical tube itself has changed remarkably little.  Celestron started out in the 1950s as a branch of Valor Electronics, a company selling electronics to the aerospace industry (Valor is still around today, and is now known as Pulse, Inc., which sells electronic components.)  Tom Johnson, who founded the company, built telescopes as a hobby.  A short time later, in 1964, he founded Celestron as a division of Valor.  Early SCTs ranged widely in aperture from 4" all the way up to 22".  These are extremely rare today.  Around 1970, Johnson teamed up with Alan Hale, a businessman, and the modern Celestron company we know today was formed..

Tom Johnson and an early C8

In 1970, Celestron introduced the C8, an 8" f/10 Schmidt-Cassegrain.  It sold for $795.  The scope was an immediate success, offering high quality optics in a compact package that was reasonably affordable.  This was during a time when almost all telescopes were handmade Newtonian reflectors.  It took the resources of a large company to mass produce Schmidt-Cassegrains, which were much more complicated to make.  Celestron telescopes became widely popular not only among amateur astronomers, but with institutions and the government.  The original line of Celestron telescopes contain what would be considered today an odd range of apertures: There was a C10, a C12, a C16, and a C22(!)  Through the years, Celestron settled into the range of apertures familiar to amateurs today - the 5" f/10, the 14" f/11, and later, in the late 1970s an 11" f/10 was added.  The smaller C90 Maksutov filled in the lower end of the range.  There were also 5.5 inch, 8 inch, and 14 inch Schmidt cameras in the line.

Original Celestron company logo

The C8 scopes at the time came in one compact 23 lb swing-through unit.  The drives were AC powered.  They were fork-mounted, with setting circles on the RA and Dec axes.  The tubes were painted a distinctive orange color, which is still being used today (newer tubes have a deeper iridescent shade of orange.)  Original C8 tubes used lead-based paint, so be careful around it if you own one.  Since the unit was technically Alt-Az as supplied, the entire assembly had to be mounted on a a wedge and a tripod to achieve proper polar alignment.  This generally didn't pose a problem for the lighter scopes like the C5 and C8, but the entire contraption got a little unwieldy as you got to the 11" and 14" models.  Polar alignment was accomplished by turning the tube 180 degrees and sighting Polaris through the finder.  This was awkward, and mechanically precarious on the larger models.  As the industry gradually switched over to DC, Tim Gieseler introduced the Accu-Trak drive corrector system.  Gieseler went on to found Orion Telescopes and Binoculars.  Eventually, setting circles disappeared from the scopes entirely.

What do you mean "The Real Universe?"  You mean Star Trek wasn't real??

Through the inflation-prone 1970s and early 1980s, the prices went up steadily.  In a May 1981 price list, the base price for the C8 assembly was $1050.  Unless you had a mount for it (which hardly anybody did back then) the scope was pretty much useless without the wedge and tripod.  The wedge was $60 and the tripod was $150, and if you wanted the enhanced coatings, you had to fork over another $100.  An interesting side note: The Consumer Price Index (CPI) from 1981 to 2009 rose by a factor of 2.33.  So your $1360 C8 package is $3168 in 2010 dollars!  Consider that right now you can get a NexStar 8 from most retailers for about $1100.  If you really wanted to go to town, a C14 with coatings, wedge and tripod sold for $6550 - a cool $15,261 today (computer controlled C14s sell for $9000 - $11000 today depending on what you get.)

Celestron Price List from May 15,1981

Neither Meade nor Celestron (nor Criterion/Dynamax for that matter) were exactly shy in their advertising during this period (late 1970s - early 1980s.)  I still have a collection of brochures from that era and I still get a chuckle out of reading them.  Check out this obviously biased example from a 1985 Celestron catalog.  It takes the reflector/refractor/catadioptric comparison chart to new heights:

The era featured the now-famous "Celestron girls."  These ads were not subtle.  At the same time, Meade was going in the opposite direction with their ads, often showing nerdy scientists in white lab coats.

This ad makes no pretense about what you might do with that 750 mm lens

I'm a C8 and I like long walks on the beach...

Come hither; there's a Celestron Newtonian in it for you!

In contrast, Meade was portraying their telescopes as serious scientific instruments

As a company Celestron went through major changes starting in the 1980s.  After the frenzy of the arrival Halley's Comet in 1986, sales languished.  Celestron had already been sold to a Swiss company back in 1980 and by 1985 or so, quality began to slip.  In 1998 Celestron was sold to the dreaded Tasco, which itself folded in 2002.  Then, after operating by itself for a few years, Celestron was acquired by the Chinese Synta company in 2005.  At first this raised some eyebrows, but overall, the alliance has been good.  Quality has come up, and there are plenty of new products from the new Celestron company (I'm very pleased, and pleasantly surprised, at the quality of my C6, and the new C90s are a steal.) 

Variations:

The C8 has been through so many incarnations that it's hard to enumerate them all.  The original C8 has remained in the lineup since the beginning, but there have been a slew of offshoots:

• The original C8.  These were made more or less continuously from 1970 to about 1982-1983.  $800 - $1000 new, depending on vintage.

  

• The Super C8 was an upgrade to the standard C8.  It was largely seen as a response to Meade's 2080 SCT, introduced in the early 1980s.  You could get one in orange or black.  One attractive selling point of the scopes was the Byers worm gear drive.  It was still fork and wedge mounted.  The Starbright coatings were an option, until Celestron introduced the Super C8 Plus a couple of years later, which had the coatings as standard.  These were made in the mid 1980s.  $1200 - $1500 new, depending on options.

  

• The SPC8 was the first equatorially-mounted C8, using a Vixen Polaris/Super Polaris mount.  They were popular from the mid 1980s to the early 1990s.  The retail prices ranged from $1000 - $1300 depending on options.  You still see some of these around.

  

   

• The Compustar was the first Goto C8, introduced in 1987.  It was ahead of its time.  Maybe a bit too ahead of its time.  There have been accuracy and reliability issues.  It's mostly a curiosity now, but the model does have some devotees.  About $3500 new.  If you get one, be sure yours has the Y2K compliant mod.

   

   

• The Powerstar C8 was the first DC powered C8, made in response to Meade's then-new LX3 models in 1987.  The big innovation here was the DC drive system.  There were many versions and this model was produced for nearly 10 years.

  

   

• The Ultima C8 (1988) had a number of incremental enhancements, including a rechargeable lead acid DC battery (later replaced by a simpler 9V battery) sturdier mount, and upgraded electronics.  Later versions have PEC.  Very desirable today if you don't want or need computers.  Expensive for its time at around $2400.

  

   

• The Ultima 2000 from the late 1990s was the first computer controlled C8.  The "U2K" was expensive at $2700.  Later versions were Fastar compatible.

  

• The Celestar 8 was a back-to-basics non-computerized C8.  Later versions were Fastar compatible.  Otherwise, it retained the traditional wedge and fork mount.  The tube was black and the secondary had an orange cover.  From about 1996 to about 1999.  The scopes sold for $1100 - $1300 new.

  

• The NexStar 8/se, first introduced around 2003, was the first of the single-sided swing arm ("one armed bandit") computerized scopes.  Later units have GPS.  These were given a facelift in the late 2000s (to "SE" status) and were given upgraded electronics.  The original 2003 version had a gray tube.  Newer "se" units have the orange tube.  The scopes initially sold for $1700, but prices have dropped to around $1100 in 2011.

  

• The CPC 800 was/is a GPS enabled C8.  The CPC 800 was fork mounted with a black tube.  These looked somewhat like the original C8s, but the forks were much thicker and bowed outwards.  As a result, they look unusually large for an 8" SCT.  These are still sold today.  About $2000 new.

  

• The Edge 8 models feature excellent correction at the edges of the field for astrophotographers.  The tubes are light gray.  Expensive ($2000 - $2500 list.)

What to look for in a used C8:

Because so many of them have been made, used C8s are not hard to find on the used market.  Most are quite usable today provided that they have not been abused.  When considering the purchase of a used C8, it always helps to see the scope in person.  Pictures help, but there is no substitute for seeing and touching the scope yourself.  In reviewing the comments below, you'll see that many of the problem areas have nothing to do with the optics, which are relatively robust.  It's the mount, drives, and accessories that you need to be concerned about.  In brief, here is a checklist.

• Check to see if there is any obvious physical damage.  If so, move on.  There are plenty of fish in the sea.

• If the scope was made between 1985 and 1990 (ie, the Halley's Comet era) be extra cautious.  These were not good years.  Powerstars seem to be especially suspect.

• Conduct a quick star test.  With an eyepiece in the diagonal and the telescope pointed at a star, go in and out of focus.  If it's daytime, catch a glint of light off something.  In a pinch, point a flashlight at the scope from far away.  Any optical aberrations should show up under this sensitive test.

• While you're doing the star test, see if the image shift is acceptable to you (there will almost certainly be some image shift.)  And while you're at it, see if the scope is collimated.

• Do the coatings look good?  Note that faded or dirty coatings are not by themselves a reason to reject the scope, if it looks good otherwise.

• Is the optical tube fork mounted or rail mounted?  These days, a rail mounted OTA is a definite plus.  Older fork mounted tubes can be drilled for Vixen-style dovetails, but this is not always a simple operation.  Are you sure you know what you're doing?  People have accidentally drilled into the primary.

• If it's one of the old fork mount units, do you plan on using the clock drive in it? If so, you need to check it out.  Clock drives sometimes sit unused for decades.  With the scope polar aligned, look at an object near the horizon.  Does it track?  If so, swing the scope to the other horizon.  If it still looks OK, stop and ask yourself again - Are you still sure you want to deal with a wedge mounted, fork mounted C8?

• Older controllers like the Accu-Trak (and even ca. 2000 Celestar hand controllers) are becoming very rare.  Be sure they work.  If the owner has an spare, that's a plus.  If you're looking at a Celestar with a missing or broken hand controller, check to see that the manual controls aren't too stiff for your taste (good luck with that one!)

• It's an unfortunate fact of life that fancy Goto electronics fail.  Don't pay too much extra (if any) for a computerized mount.  Some of the original Ultima 2000s are getting to be 15 years old already.  If you are buying a Goto mount with your scope, assume it will fail.  Now price it accordingly.

• In any paddle-controlled scope, there will be drive backlash.  Check to see that the amount is acceptable to you.

• How much is it worth?  This is a tricky question to answer.  Assuming you are not dealing with one of the new expensive Edge OTAs, used prices for optical tubes seem to be settling in the $250 - $500 range, depending on vintage, condition, and what accessories the owner is willing to throw in.  This is a rough guideline only!  Your exact situation may be different.

My own preference is to find a clean, used OTA with good optics and rail attached.  The rail gives me flexibility to use a variety of mounts.  The scope will likely outlast the mount, so you need the ability to remount it as needed.

-Ed