Beautiful Scope, Ugly Tripod
Written: Apr 13 '03 (Updated Mar 28 '07)
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Product Rating:
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Pros: Fantastic optics, beautiful fit and finish, cleanest scope seen up to now
Cons: Clumsy tripod, no leg adjustments, too low, bad vibration
The Bottom Line: The telescope optics are perfect. The mount works and the drive is quiet and smooth. However, the "Wedgepod" tripod is a serious handicap.
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| Pirich's Full Review: Celestron Celestar 8 Telescope |
The Celestron C8 8" diameter telescope is a legend in its own time. The reason is quite simple: it changed everything for amateur astronomy. I first saw one in 1983 and have always wanted one since. In a strange sort of way, owning a C8 has been a sort of "Holy Grail" for me- it has represented the "Real" telescope I assumed I would eventually get to. I finally broke down and bought one, and learned some new things in the process. More general information on getting a telescope is in my article on Picking a Telescope. I am going to discuss the following topics on this scope:
Background
Description
Performance
Observations and Recommendations
Background
This review is for a recent version of this classic telescope called the Celestar 8. Back in the 1960s, a company called Celestron Pacific began building Schmidt Cassegrain Telescopes (SCTs) as an alternative to the Newtonian telescopes common for amateur astronomy at that time.
The goal was to build a better telescope. Newtonians are the simplest telescopes with their entire optical train consisting of a single parabolic mirror and a small secondary mirror up forward to bounce the image to an eyepiece in the side. These telescopes tend to be large since the tube is approximately the same length as the focal length for the mirror (typically over three feet for a 6" diameter telescope). They also have optical defects such as inherent distortion at the edge of their images called "Coma." A star which looks like a pinpoint in the center of the field of view will look like a little comet when it nears the edge due to this effect.
The only other alternative readily available to amateurs at that time were long focal length refractors. These telescoped need to bend light, which is dependent on the color of the light being bent. So, the red light in an image will reach focus in a different location from yellow light, as will blue light. So, refractors will put blue-purple colored fringes around bright objects and tend to show false color otherwise. Apochromatic refractors, designed to circumvent this problem were decades away, and when they appeared, showed up at about eight times the cost of a similarly sized newtonian.
The Schmidt design came from an observatory camera designed by Otto Schmidt to give flat fields of view across the image plane. This design uses a sharply curved spherical primary mirror with a strongly curved secondary mirror to make a long focal length telescope more compact. Unlike a Newtonian which will have a barrel close to the same length as its focal length, the SCT is inherently short. To correct for the curvature of the mirrors, the SCT has a thin corrector lens which covers the front of the telescope with mild curvature.
This hybrid telescope therefore is designed to avoid the worst problems of refracting telescopes by doing its light bending with mirrors and avoids the worst of the coma problems a Newtonian has by using a special lens to correct the light path. The other trick this telescope has going for it is its length is about 1/4 of its focal length, so it is much more compact than either refractors or Newtonians.
The early offerings from Celestron Pacific included an 8" SCT and larger scopes, including a 22" diameter behemoth. To a large extent, these telescopes were an experimental period as Celestron Pacific learned about how people used the telescopes and what the best designs were.
The apparent sweet spot between capability, size, cost, and flexibility was apparently reached in 1970 when Celestron introduced the C8. This was an 8" diameter SCT with a 2000mm focal length, or an f/10 scope. This put it firmly in the middle of the road between f/15 refractors and f/5 Newtonians. This telescope came mounted on a fork mount and tripod which made it a miniature observatory.
The SCT is very much a general purpose design. The focal length for these converged to f/10 for the system, smack in the middle between the f/15 for a dedicated planetary telescope and the f/5 of a wide field Newtonian. The resulting telescope has an intermediate field of view for its size and can be bumped up in focal length by a barlow or have its focal length cut down by a reducing lens assembly. The characteristic phrase for this design is "It won't give the best performance on either planets at one end or large Nebulas at the other as dedicated designs will, but it will do a fair job on both with one scope."
This scope was very popular, and its direct descendants are still in production today. If you go to any astronomy club gathering, you will see SCTs. The most common size will be the 8.
Description
These are very capable instruments, and have been popular as "Do it all" telescopes for many years. The focal ratio is between a deep sky wide field scope and a narrow field planetary scope. In many ways, they have earned a reputation for being "The one scope to have if you only have one scope" They aren't cheap compared to a Newtonian, but they are inexpensive compared to high quality refractors. They let an amateur use one telescope to observe just about any type of object and photograph them.
Many different combinations of mounts and optical tubes have appeared during the C8's production run. Currently, there are five fundamentally different variants in production. They all share the same optics with Celestron's StarBright high transmission coatings. Unlike Meade's offerings, Celestron does not sell a version with inferior coatings as a secondary pricing break.
The entry level version of the C8 available now is the G-8, which is a C8 optical tube mounted to a Chinese made German Equatorial Mount (these are the mounts with the telescope on one side of a rotating assembly with an arm carrying counterweights to balance it).
The second variant is the Celestar series of C8 telescopes. These telescopes are all mounted on fork arms on a tilted plate called a wedge to allow them to be equatorially aligned. These are the verion most similar to the original C8 from 1970. Unlike versions from the 1970s, the new variants have drive motors powered by 9 volt batteries able to run for about 50 hours. The version reviewed here will track on a spot in the sky once the user puts it there, but the user has to do the work to get it pointed to find everything.
The fork mount is very compact and causes less movement of the optical tube than the German equatorial mount while traversing the sky, so in many cases it is easier to move and use since the assembly is more compact and minimizes the need for counterweights. The downside of the fork mounted telescope is it is permanently mounted to the fork so the telescope and drive base are always moved together. The other result is you don't have the option of taking one telescope off and putting another on the mount in its place without doing some serious assembly and fabricating new custom brackets for the new scope.
Other versions of the C8 currently in production are single and twin fork arm mounted "GOTO" telescopes with integrated computerized robotic tracking systems. The fifth version is a brand new German equatorial mount with a GOTO drive system, which offers the flexibility of the German Eequatorial mount for changing the scope setup. When using a GOTO mount, one takes a computerized handset, selects an object, and the telescope slews to it by itself. As a dyed-in-the-wool purist, I have avoided these because I have wanted to learn the night sky. However, these mounts are the best telescope rigs Celestron makes, and they appear to be the way of the future since every manufacturer has included these functions in their high-end mounts.
When I was looking at making this purchase, I looked at what my experience was in day-to-day use with my other telescopes. When I had learned to get perfect collimation on the C5 telescope I have been using, the results have been incredibly good, and I decided to take the plunge and get the bigger telescope. Woodland Hills Camera (www.telescopes.net) had a special where a Celestar 8 cost less than the equivalent one did in 1982 ($999) with a simple fixed height tripod and equatorial wedge combination unit.
The telescope arrived by UPS in two boxes; one tall and thin, the other wide and squat. I reasoned the tall one was the tripod, so I opened it first since I would want to put the telescope on it to safely hold on to it. The tripod turned out to be a set of three 2" diameter steel legs with simple rubber caps on the tips mounted to the bottom of a plate with a wedge plate on it. Two of the legs were stiff and difficult to open while the third swung freely. I discovered the leg brackets didn't allow for the tension to be adjusted so I could even out the force needed to open and close the legs. The floor of the wedge was 30" off the ground when set up. This tripod had no provision for changing height, so this was where it would be. A plastic bag with other hardware had been taped to the mounting ring. Inside I found three hex-head bolts with washers and a small allen wrench. I used the allen wrench to set the wedge to the local latitude: 30 degrees north. There were no instructions, but given the way the C5 mount worked, I suspected the three bolts were intended to attach the scope to the wedge, but the C5 has hand knobs- this thing would need a wrench.
I opened the large box and found a second box inside. I pulled this one out and opened it to discover the bagged foam packing. I lifted off the upper foam block to find the telesope surrounded by an eyepiece, the diagonal, the finder scope, and the finder mounting bracket neatly arrayed in the bagged packing foam. Celestron packs all of their telescopes this way these days and it appears to guarrantee they will arrive intact as long as UPS doesn't actually run over the box.
I carefully lifted out the telescope and unwrapped it. It was beautiful. The mount assembly and fork arms were in a flat black finish and the lift handle was polished aluminum. the Optical tube wasn't the gloss black I had expected; it was a beautiful gloss metallic gray. Unfortunately, there were no knob-type mounting bolts I had been hoping for, so I needed to use the hex head bolts to mount the telescope. I installed the top bolt part way into the drive base's top fitting then hooked it on the mount ring as it is designed to. However, turning it with my fingers to get a good purchase while supporting the telescope proved to be extremely diffiult. So, I had to hope I had it well started and let go so I could get a wrench. This was a moment of aprehension. Getting the other bolts started also proved difficult since there was little to hold on to to thread them. Finally it was installed, and I decided to look up www.mcmaster.com to buy some knob-handled bolts to make this easier. I noticed the back end was close to the ground, but I decided it was probably sized to be used while seated, which could be nice.
I assembled the finder scope and installed the diagonal. I moved the boxes out of the way and prepared to move the telescope away from the center of my living room. And that was when I discovered this was more easily said than done. I turned the fork so the handle was on top and locked it in position. Now, I am a fairly large guy (football player type of build, I do 50 push-ups every morning in one set), so I thought this thing should be movable as one piece since it isn't really all that heavy.
I was wrong. The two stiffer legs held out where they were and the loose tripod leg swung in to hang straight down. The optical tube and drive base both swung as the tripod leg moved and the two stiff legs fell towards me as the center of balance changed. The three legs in a row leaning against me made it impossible to move except by side stepping, which I did to get out of the center of the living room. Then I was faced with a real problem: How do I get it resting on the legs again? I eventually succeeded in getting the tip of the free swinging leg to stay put on the floor while I gently nudged the tripod to drop onto the other legs. I was very happy when I could safely let go if it again. However, the fact I was now facing a two piece move and installing those bolts in the dark with a wrench had dropped the reading on the coolometer by at least 20%.
Looking in to the front of the telescope, I saw something I had not seen before in an SCT- no trace of dust of any kind. None. Zero. Not one speck. This scope had been assembled in a clean room. Apparently getting the company private again after the Tasco ownership period had come with some improvements.
Performance
Strangely enough, the new scope curse did not set in and that night it was clear. I took the tube off of the tripod and set it on the living room table on the flat bottom of the drive base and set the tripod up outside. This time I had a wrench in my back pocket and though a lot of fumbling was involved, Assembly wasn't as difficult as it had been earlier. I took a small chair out and set up a small table with a selection of eyepieces to try out. Then I made the worst discovery- the scope was way too low even to view from a chair. I had to kneel on the ground to look at objects near the zenith.
I put the scope on to Aldebaran and centered the finder. I pushed the magnification to get ready for collimating the telescope after shipment, and discovered the perfect bulls-eye pattern of a perfectly aligned set of optics. I went ahead to my first observing target- M42, the Orion nebula. It was a jaw dropping view. I pushed up the magnification and the details and shadows in the nebula popped out into high contrast. The four stars of the trapezium were very clear, and were joined by the fifth star- an acid test for an 8" SCT performing as it should.
I moved on to Saturn and was rewarded with one of the most beautiful images I have ever seen through any telescope. The Cassini division was razor sharp and clear all the way around, and the outer ring showed gradations. The planet had the white cummerbund showing and the darker stripe next to it showed some of the swirl in its clouds. Titan and three of the tiny moons were visible. This was a treat indeed. The thought I kept having was "No one thinks SCTs can be this good- things have changed."
Jupiter was still low in the sky, but I gave it a try. Here the atmosphere interfered with the scope getting to its full potential. I was able to see the usual two large stripes and some of the swirling, but the image wiggled and blured from the air closer to the horizon. With that said, this was still an outstanding image. The only real problem was waiting another two hours for it to get to the clearest air in the sky.
In checking out an SCT, one of the big questions is always how much mirror shift the focuser has. These telescopes focus by turning a knob on the back which pushes a little screw jack to move the mirror forward and back The mirror did show a small amount of shift, but less than any I had seen in other C8 scopes. There was no discernable lag between moving the mirror forwards and back in focusing. This was quite intriguing. Either I was incredibly lucky with a superb optical tube assembly and optics, or the SCT isn't what it used to be.
However, by the time I had spent a couple hours outside with the scope, I was miserable. The optics were perfect. The drive tracked with earth's rotation perfectly. The eyepiece was so close to the ground that it was torture to keep climbing down there to look through it. The tripod also had one other shortcoing- excessive vibration. To put it shortly, it had an amazing amount of vibration. After touching the focuser, the assembly would bounce for 12-15 seconds. I had become used to the C5+ mount which damps out in about 2-3 seconds on concrete, and even faster on the ground. This tripod was a disaster.
Observations and Recommendations
The next day I called up the folks I bought the scope from at Woodland Hills (www.telescopes.net) to find out what was possible to get the tripod problem fixed. They said there is a heavy duty tripod and a separate wedge which are much sturdier, are adjustable for height, and are about $600. So, I was faced with a very strange problem. Here I had the best optical tube I have ever owned combined with the worst tripod imaginable.
I really didn't want to give up an optical tube that good. At the same time, I really didn't want to have to crawl around on the ground to use the scope. I noticed the cost for just this wedge and tripod was 60% of the price difference for getting the nicest version of the C8 Celestron has ever offered: the NexStar 8 GPS which comes with the big tripod, the version of the scope with the composite tube for low thermal expansion, and a computer drive capable of finding 40,000 objects on its own. This is combined with the ability to track at different rates automatically.
So, I talked to my wife, who observes with me. She pointed out a few things about being a purist. First, much of the reason for it is to learn the sky, but after that, it still takes a while to get pointed when you know precisely where you are going. Second, there are two ways of being a purist: (A) You go out, look up in the sky, and then look at the objects you see and then look them up on a map later to find out what they are. This mode is what we have both done, and having a GOTO scope just means you would drive it there and it would track for you, but otherwise it would not interfere since it can't tell you where you are pointing. Afterwards, you know where it is because you found it in the first place. (B) You read about an object and go out to find it. Usually you will do this by what is called "Star hopping" where you start with obvious visible guide stars you can see and then follow a progression of observations someone has put together for you to find it, or you look on a map and try to reason it out. Either way, you will need to use this method every time you want to revisit that object. For both of us, the second method has always been work more than fun, and it doesn't come with the joy of the "Eureka" when you see an object, look at it, and discover it for yourself. I suppose it is a little like the enjoyment of going exploring off the beaten path and finding a neat restaurant versus being told one is there and following the instructions to get there.
So, we ended up reasoning for the things you know are there, GOTO takes nothing from the experience, and for the things you would have followed a map to get to, what you are missing is tedious, anyway.
And so, I ended up taking the bizarre step of sending back the best optics I have ever owned. Woodland Hills did not hesitate to give me full credit towards a NexStar 8 GPS. That review has a very different ending.
conclusion
In summary, I would have to say the C8 is the best it has ever been. After having looked through a lot of scopes, I would have to say I now would have to say any serious observer should own one of these at some point. The wedgepod tripod, though, is a different matter. This piece of equipment needs to be redesigned or replaced.
The best thing I can say about this scope was the optics were good enough to encourage me to find one mounted so I could use it in the midst of the scope system being a failure. This scope made me reconsider all of my assumptions and beliefs about this hobby to do it. And don't worry- the story does have a happy ending- I have a lot to tell about the NexStar.
Recommended:
No
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Epinions.com ID:
Pirich
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 in Electronics |
 - Top 500 |
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Member: Rich W.
Location: Tucson, AZ
Reviews written: 137
Trusted by: 40 members
About Me:
Dad, Engineer, Scientist, Astronomer, Traveler; order may vary.
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