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Celestron 80ED Refractor

Posted by Gary Hansen   04/14/2005 12:00AM

Celestron 80ED Refractor
[ARTICLEIMGR="1"]Telescopes are subject to fads and fashion, just like clothing, only more expensive. I had owned ordinary achromatic refractors for years, and considered them “good enough”. High-end “apo” designs, are undoubtedly excellent, but unconscionably expensive – until now. Skeptical, I sold my old 4” achromat and purchased a Celestron 80ED refractor. To get to the point right away, it has superb optics and much better than average mechanics, all for $409. I am delighted with this is a great bargain.

Tradeoffs

I was looking for a small scope with “apo” or “semi-apo” performance for typical grab-and-go usage. I just finished building a nice 12.5” Dobsonian with Swayze optics, but there is something satisfying about stargazing with a minimum of heavy equipment between you and the firmament. Also, I wanted to be able to fit the scope, tripod, and accessories into an ordinary carry-on bag. This meant that the OTA had to break down to less than 20” and fill minimal volume. Aside from this, the usual expectations apply: it had to look nice and cost as little as possible. I enjoy doing a mix of observing, including lunar, planetary, and what deep sky objects I can see through the suburban murk in my back yard.

The three contenders were the Celestron 80ED, the Orion 80ED, and William Optics Zenithstar 80. While each of these is undoubtedly a fine scope in its own way, there were subtle differences that influenced my selection. The Orion scope had a bulky 100mm tube and was reported to have quality problems with mechanical components. In particular, I was put off by reports of focuser assembly being attached by screws that easily come loose, affecting collimation. It did have a Crayford focuser, but this was not a great concern for me. The Zenithstar looked beautiful, but it was still an achromat, though a high-quality one. The focal length was short, which makes it compact, but also makes higher powers hard to achieve with normal eyepieces. After much consideration – half the fun of buying a telescope – I sent for the Celestron. It supposedly has the same optics as the Orion, but in a smaller OTA with better mechanics. I was not disappointed.

First Impressions

The scope arrived triple boxed with no apparent shipping damage. (Of course it almost immediately began to rain, with risk of flash flooding. Really.) The main impression is that of quality: most parts are metal except for the lens cover and focuser knobs. It has a very solid feel, and workmanship is a notch above the Meade 500ACHR I had just sold. The finish is not up to the standards of Takihashi or Televue, but I did not expect it to be. Be fair, after all – the extra money does buy something! The metal parts are painted rather than anodized, resulting in a slightly bumpy finish. Not too bad unless you are in an irritable mood.

One thing that did make me irritable was that the OTA was shipped with the tube ring attached and some thin tissue paper stuffed between them. This marred the paint finish - not what you want to see in a brand new $400 item. Also, the tube ring is way too tight. It uses hasps similar to a toolbox, and they really squeeze the tube. There is no way to adjust it the tension, short of filing away a bit mechanism. I haven’t yet tried this yet.

The optics were clean and lovely. The objective is smoothly coated with a greenish antireflective coating, and bright light shows that all four surfaces are covered. The inside of the tube is darkly painted and well baffled. Optical performance on bright objects shows that off-axis reflections are well-controlled.

The focuser is smooth and backlash free. It’s perhaps not as “buttery” as a Crayford, but certainly serviceable. It came covered in the familiar glue-like grease from Synta. Why do they use that stuff? I replaced it with lithium grease and it works very nicely.

Features of the Scope

The Celestron 80 ED has an 80mm objective with high-dispersion ED glass that provides a high degree of color correction. It has a 600mm focal length (f7.5). The focuser is 2” diameter with a rack and pinion mechanism. Included with the scope is a clam-shell style tube ring, lens cover, 6x30 finder, 45 degree erect image diagonal, 25mm Plossl eyepiece, and a 1.25” eyepiece adapter.

The tube ring mounts on a Vixen dovetail mount, and also a standard photo tripod. The OTA weighs 4.5 pounds; so don’t expect a lightweight mount to be sufficient. I mounted the scope on a Meade LXD5000 tripod my means of a homemade adapter plate. This configuration was quite solid. There is an issue with balance with the heaviest eyepieces. It is possible to push the OTA upward in tube ring to compensate for a heavy diagonal and eyepiece, but eventually additional travel is blocked by the focuser. At this point, the scope is tail-heavy. I fixed this by adding slots to the adapter plate. This way, the entire tube ring and OTA assembly can slide farther upward until the scope is balanced. Alternately, an additional counterweight could be added to the top end of the tube. (In practice, only the RPD was heavy enough to cause problems.) Despite the heavy hardware on the end of the tube, the focuser was stiff enough not to require using the set screw.

That pesky tube ring was obviously meant to enhance the scope’s aesthetic appeal. It is all-metal, with a modern sleek design, but is still rather crudely made. I may keep it for travel, but I’m keeping my eye out for a nice set of rings for the equatorial mount. I tried the 6x30 finder but prefer a zero-power Mars Eye. This is easily attached to the finder’s dovetail mounting. The erect image diagonal works fine, but I did not use it extensively at night.

Quibbles and Complaints

For $400, one is not allowed to complain too much, but I will dare to petty anyway. It seems that many of my quibbles are for needless problems: things that could be easily fixed if the manufacturer was paying attention. My worst complaint is the marred paint finish; it really seems a shame in an otherwise beautiful scope. As mentioned above, the tube ring is too tight and is nonadjustable. Another quibble is that the eyepiece set screws are mounted too close to the end of the eyepiece holder. This hits the very edge of the machined groove found in most diagonals. The result is that it is hard to adequately secure the diagonal to focuser: it tends to come loose and rock. I added a small 1/8” spacer ring between the diagonal and scope; this moves the set screw to the center of the groove, solving the problem nicely. It is also possible replace this component with a compression ring part from Mercury Systems. Less importantly, the plastic lens cover is functional but seems cheap compared to the rest of the scope. However let me put this in perspective: the Celestron 80ED is still a nice scope and a good bargain.

Optical Quality

I tested the scope with the following eyepieces: 9mm Nagler T1, 12mm Nagler T2, 22mm Panoptic, 32mm 1rpd, and 11mm, 17mm, 20mm and 26mm Tele Vue Plossls. Lowest power was with the 1rpd (19x, 3 deg 44 min field). All of the above eyepieces came to focus with no problem. Highest power was the 9mm Nagler with a 3x Tele Vue Barlow (200x, 25 min field). The manufacturer recommends a useful maximum of 189x, and I agree that beyond this amount is pushing the limit. I also used a Tele Vue 2” standard diagonal. Testing was done both with and without the diagonal, and no obvious difference was seen.

The lens cell is not adjustable, but this was not an issue. The collimation was dead-on, and since both lens cell and focuser a threaded to the tube, this is not likely to change.

Star testing showed no obvious aberrations. Diffraction rings were round, uniform, and concentric on either side of focus. The rings closely resembled each other on either side of focus, perhaps with a faint tinge of color. The color correction is not perfect, but in-focus star images were pinpoint-tight with little, if any, purple halo. Since this is what people want to hear about, I will elaborate on this point. Yes, on the brightest stars it is possible to see a very faint purple fringe. However, you need to look for it, and on most nights forward scatter due to atmospheric haze overwhelms it. All things considered, this is a quantum leap better than what I was used to with achromats. I compare it to listening to a high fidelity sound system for the first time after owning cheap radios – you really can tell the difference, and that difference is exciting.

Unfortunately I don’t have other “apos” to compare to; this would make a fine review for someone else to write. Take it for what it’s worth: the Celestron 80ED is a definite upgrade to most conventional refractors on the market.

Under the Stars

So, all the details aside, how does the scope work under the stars? Very well. As I said, it is noticeably better than any achromat I have ever looked through. Stars are tiny pinpoints, and bright objects are sharply defined against a dark background.

On a night of moderately poor seeing, Saturn was clear and sharp at 106x but lost substantial detail at 164x. On a better night, 200x resulted in a beautiful view of the ringed planet, with just a bit of image degradation. And no purple that I could see. Cassini’s Division was visible most of the way around, and I thought I could glimpse several moons in addition to Titan. On that same night, Jupiter was an impressive sight. I just happened to catch a transit of Io, and gazed in fascination as the tiny moon merged with the planet. Once in front of Jupiter, I could no longer see Io with the small scope (but following it was easy with the 12.5” reflector). Multiple belts and zones were visible, but fine detail was lacking. This is to be expected for an 80mm scope pushed to its limits.

I found much pleasure in hunting down some of the brighter Messier objects. The globular cluster M3 was easily visible, but unresolved at any power. The more distant M53 is described by Stephan James O’Meara as a “bold glow”. I saw it as a “faint smudge”, perhaps because I live in Minnesota, not a mountain in Hawaii. Still, the bright galaxies M65 and M66 were brighter than expected. M65 was distinctly lenticular, and I could just barely catch the prominent dark lane in M66.

This scope really shines with open clusters. It was easy to fit the Double Cluster into one 67x field using the 9mm Nagler, and the Pleiades looked best at 27x using the 22mm Panoptic, my favorite eyepiece with this scope. The Beehive was also a fine sight at this magnification. For all of these objects, there was a strong sense of three dimensions: a scattering of small bright diamonds on black velvet – a very pretty sight.

Several nights later I viewed the five-day-old moon on a night of unusually good seeing. Despite being low in the sky, I was delighted with the fine detail visible on the lunar surface. The shadows were dark with the bright limb clearly defined against a fine black background. At 200x I looked hard for purple or yellow fringing but found none. Impressive! This was the highest magnification obtainable with my eyepiece set, but I didn’t feel it was too high.

Summary

To briefly summarize the pros: excellent f7.5 apochromatic objective, collimation close to perfect, solid all-metal mechanics, attractive design, no larger than it needs to be for this aperture. The cons: damaged paint due to poor packing, too-tight tube ring, and balance problems with heavy eyepieces.

For reasons best known to Celestron, this fine instrument is primarily pitched as a spotting scope. This is a shame, because it’s ideal as a high quality first scope for a beginner or a second scope for an experienced amateur. I really enjoy using the scope and appreciate its clean, pure images. I think I’ll keep it for a long time.

Note: I am not affiliated with Celestron or any of its dealers – just a humble amateur.

Click here for more about this subject. -Ed.