Stop Making These Things!
Written: Oct 01 '00 (Updated Mar 27 '07)
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Product Rating:
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Pros: Small, Light, Cheap
Cons: Frustrating to Use, Poor Images, Lousy Mount
The Bottom Line: Buying nothing is a better choice in this case.
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| Pirich's Full Review: Celestron Tabletop 76 3 in. Newtonian Telescope |
I first saw this telescope around 1985 under a different manufacturer's name. Over it's life, I've seen this called a Jason, a Tasco, and I think it may have been sold as a Bushnell at some point. The exact same telescope can be found painted red, yellow, white, and now gloss black. This design showed up around the time Halley's comet was making its pass in 1986 as a telescope to sell to people who wanted to see it. This beginning would foreshadow its entire life as this instrument had nowhere near the light intensification power needed to make dim Halley's noticably brighter, and today still lacks the capability to do much of anything. As an aside, it is interesting to note that the telescope Celestron built back then for comet viewing, the cometcatcher, had a 140mm diameter and a 500mm focal length giving it 2.4 times the light gathering power of this telescope as well as a 17% wider field of view. Manufacturer honesty about this telescope's capabilities appears to have always been in the range of where it is for 60mm refractors- almost nonexistent. More general information on getting a telescope is in my article on Picking a Telescope.
This telescope has now appeared in Celestron's product line after the company was bought by Tasco in 1998. Amateur astronomers who had grown loyal to the Celestron brand's consistent quality have been holding their collective breath to see if this merger means an end to masterful telescopes such as the Celestron Schmidt Cassagrains in favor of cheap department store quality instruments which leave everyone who uses them feeling disappointed. Some have even joked, "What's next, is Meade going to be bought by Wham-O?" I recently got a chance to play with one of the newer versions of this telescope and see what it was like.
It's true, this is an inexpensive telescope, and almost any telescope I'd recommend would be twice as expensive and would be much larger when it was on a mount. However, in this price range, I feel the best advice I could give someone would be to get a pair of binoculars instead. They will be more useful, more portable, and will show you things not visible to the eye easily. To address this telescopes characteristics, I am putting this review in sections on description, performance, summary, and recommendations.
Description
The overall telescope looks like a miniature Newtonian reflector with a strangely oversized focuser. The mirror in the back appears to be a simple spherical mirror with a 600mm focal length. There is a glass plate in the front end without anti-glare coatings which serves to support the secondary mirror. At different times, some of the manufacturers claim this is corrector plate, such as one found in a Schmidt-Newtonian telescope (but they have never claimed this was a Schmidt-Newtonian). However, given the focal ratio of f/7.9 for this telescope, it would be unusual for it to require a specially ground corrector plate since the mirror is so small that any spherical aberration should be minor for a newtonian layout. Schmidt-Newtonians usually operate below f/4 where a corrector has large benefits for image quality.
The central obstruction for this telescope is quite large- about 25mm in diameter, or about a third of the total diameter. This takes the effective resolution of the system down to approximately that of a 50mm telescope or a pair of 50mm binoculars. The reason for this is the diffraction pattern from the central obstruction degrades the telescope's image by an amount roughly equivalent to subtracting the diameter of the secondary mirror cell from the diameter of the telescope. As a result, higher end compound telescopes have never gone below a diameter of around 90mm because of the rapid performance drop-off below this size. Newtonians with what is generally agreed to be acceptable performance start at diameters of about 114mm. The reason this telescope has such a large central obstruction is in order to keep the focuser from protruding into the interior with such a short tube, which puts the focuser ususually close to the back end of the telescope. As a result, this telescope has an optical design which will have mediocre performance, no matter how well the components were manufactured.
The mount and tripod for this telescope are made from stamped sheet metal held together with bolts with three tubes serving as legs. The reason this is called a tabletop telescope is there is no way to use it otherwise unless it were used on the ground. The mount has no slow motion controls for tracking or adjustment. The viewer loosens the set screws which hold the telescope in place and pushes it manually to each observing target. The mount is quite weak and flimsy and must be supported by a very firm surface. The best surface a user could hope to use for this telescope would be a concrete picnic table (and it must be one solidly mounted so it doesn't rock). This constraint takes much of the mobility which seems apparent at first out of this design since a typical table will move enough to push the telescope off target or start it bobbing if touched. In the case where I had a chance to use one of these, I didn't happen to have a concrete table handy and this caused some problems. The mount itself could be expected to be prone to vibration given the thin and springy arm and spindly legs it is mounted with.
Performance
I was expecting to get in to looking at some obvious objects such as the moon since I expected this telescope could at least do something useful with them, and was surprised (and annoyed) to discover just how difficult it is to use. The table we had was a heavy wood picnic table, but this would shift slightly when anyone touched it and move the telescope out of alignment so it had to be pointed again. The set-screw loosening and retightening needed to point the telescope made it practically impossible to track an object (since the rotation of the earth causes all astronomical objects to appear to move across the sky, all telescopes must be able to move to track them or they quickly move out of the field of view). The primary difficulty was getting the telescope pointed in the first place. To get the telescope pointing in the right direction so the finder scope can be used to do fine pointing, it is easiest to take the barrel and swing it until it is pointed at the object. In the case of this telescope, the table was often in the way so the telescope would have to be moved precariously close to the edge to make it possible to move it without nudging the table. If a second person was ready to take over and do fine tuning, then this was just possible.
The original positioning became a minor concern when the problems with tracking showed up. Each time the set screws were tightened, they would shift the telescope as they distorted the flimsy mount and moved the telescope. If they were loosened to the "Friction point" the telescope mount had so much springiness that you had to push it past where you wanted to go so it would come back to that point when you let go. This, of course, would be after it stopped bouncing from being touched. I found this experience extremely frustrating, as if it had been designed to be an annoying and difficult piece of equipment. Besides the bouncing flimsy mount, the next worst problem was the ridiculous finderscope, which is mounted so close to the barrel and the focuser that is is practically impossible to move your eye to a position to look through it without hitting the telescope and moving it by accident. We ended up doing allignment by dead reckoning with a low-power eyepiece with the main telescope. All in all, I can't imagine someone enjoying this sort of experience.
The strange thing about this mount is though the telescope is advertised as being a beginner telescope, it is far more difficult to use than any of the "More advanced" telescope it is supposedly built to precede. The very people who the designers should be trying to help out by making the telescope simple and easy to use are instead confronted by tempermental, awkward, and clumsy mechanisms which attempt to thwart their every move. Even the optically excellent Questar Standard would have abysmal performance on this mount.
For viewing, the mount reared its ugly head once again as any touch to the telescope's focuser would start it bouncing on the mount for over ten seconds at a time. Lightly touching the telescope slowed it more quickly, but still caused it to move some. The views themselves through the telescope were actually a little better than I had expected after my original inspection. Unfortunatly, this isn't much of a compliment. About the only things which looked good were craters on the moon, which are visible with binoculars. Jupiter's moons did come out, though there was a bit of image fog and doubling which may be due to the uncoated glass plate in the front. However, after seeing what even telescopes only slightly larger such as 80mm refractors can do, this telescope left much to be desired. The pleiades came in fairly nicely, but I can't say it looked much better than what a pair of binoculars would have produced, but without the extreme frustration of trying to move the telescope to point at them. At higher magnifications, the movement of the telescope became such a problem I really had trouble tracking objects well enough to get more than short glimpses of them. The blurry, dim, and featureless image of Jupiter I saw at 150X made the claim of being able to see things at 150X seem perverse. I think I should point here that I generally don't even operate my C90, a far more capable telescope than this one with a 90mm aperture, over 133X.
Summary
I really don't understand why this telescope got into production in the first place, or why it has stayed around this long. I think it is apparent why every company who has had it show up under their brand name has forwarded it on to someone else. I am sickened to think of how many people must have given up on astronomy over the years after deciding telescopes are too difficult to deal with and the views on the brochures must only come from huge observatory telescopes. The mount this telescope is equipped with is one of the worst pieces of any sort of equipment I have ever encountered. How anyone ever thought this was acceptable to include with a product of this type is beyond me.
As for how it is being sold, I must say I am sad to see Celestron's name appearing on the side of this thing. The company which made the world of amateur astronomy a better place with master works such as the C5, C8, C11, and C14 hardly fits with this sort of instrument.
Recommendations
I do not recommend this telescope under any conditions. It is so frustrating and difficult to use, if one were given to me, I still would not use it. I would strongly suggest either getting something else or nothing at all.
If you are looking to buy a small telescope, I'd strongly recommend you only consider something 80mm or larger in diameter to get a good enough view to make it feel worth your time. With a telescope that size, you will find objects such as galaxies, nebulas, and planets all are visible with your own eye, and are quite beautiful in a way photographs can't quite capture. If your budget will not support a $250 80mm telescope on a real tripod mount, then I suggest you consider these three alternatives:
(1) Get a pair of binoculars. A pair of 7X35mm wide angle sports binoculars or 7X50mm birding binoculars or something in that neighborhood will brighten up the sky (lower magnification and larger diameters are preferable) and make many things visible to you for starting stargazing. Best of all, some fairly good binoculars are available for less than this telescope costs, and are guaranteed to be easier to use.
(2) Join a local astronomy club with an observing party/ site/ location. For example, here in New Orleans the local astronomy club, the Ponchartrain Astronomy Society, runs the local Kenner observatory. On weekends, club members can go see objects through the large C14 telescope, an instrument which starts at $5500, for free. Or, members of the general public can go in for viewing for a dollar. Other events such as star parties give people without telescopes a chance to get time behind the eyepiece.
(3) Just wait until you can get a more capable telescope. It really is better to go longer with no telescope than to get something which would leave you questioning your own competence because it is so difficult to use and produces such disappointing images. In short, this piece of equipment isn't really what it is being sold as. Look around, see some other instruments, and at that point you can find something you will enjoy. Consider a subscription to a magazine such as Sky and Telescope or Astronomy and getting a planisphere (a type of sky chart which will predict what stars are overhead at any given time throughout the year) and just doing some casual stargazing.
NOTE
If a representative of the manufacturer reads this, I would ask that you consider ceasing production of this item. Not only is it alienating scores of people who might otherwise be astronomers some day, it is also costing your company future sales; people who have a bad experience with this telescope and decide it must be impossible to get good views with a home telescope never place orders for other telescopes. I expect there is some sort of marketing scheme which shows beginners first get the little telescopes and then work their way up. I suggest this is deeply flawed. Practically every single person I mention astronomy to immediately will say, "I had a small telescope years ago, but you really couldn't see much with it, so I kind of dropped out of that." I think perhaps a model you should instead look at is Sony's walkman stereos. The most inexpensive walkman Sony sells has crystal clear sound and does exactly what they claim on the package. Other models may have more features, yes- but the base model has excellent quality. Telescopes like this one are self defeating, and ultimately producing them is a waste of natural resources.
Recommended:
No
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Epinions.com ID:
Pirich
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 in Electronics |
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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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