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Coming Full Circle: The Zhumell 8" Dobsonian

Posted by david elosser   09/24/2006 00:00:AM

Coming Full Circle: The Zhumell 8" Dobsonian

Author’s note: Zhumell has announced changes and upgrades to this line of telescopes that may have now hit the market, including a two-speed Crayford focuser and RACI finder scope. The model I reviewed is an earlier version.

I have come full circle now. I started out about 6 years ago with a Chinese import 8” Newtonian goto system. My first “real” telescope purchase came years later, with the Televue Ranger. I was instantly hooked on refractornomics; wide field, tight pinpoint stars, excellent contrast, and simple alt-az navigation made this telescope easy to use even from my light polluted suburban front yard. I eventually ended up with four quality refractors ranging from 70mm to my 102mm doublet apochromat. I am in refractor heaven now, but sooner or later I knew the aperture bug would bite me again. So I started looking for another large Newtonian system. With my aging back, 8 inches was as large as I wanted to handle, but would I get another equatorial goto system? The advantages of the equatorial goto, tracking and automatic object location, can be quite attractive but I decided against this, and to purchase a Dobsonian for a number of reasons. First, is set-up time. The Dob can be carried or hand-trucked outside in one piece (or two for the larger ones) and set up in minutes, ready to observe anywhere in the yard, without the hassles of aligning the mount. This is important to me as I often have no more than 15 or 20 minutes of observing time, and an equatorial system would eat up too much precious time. Second, the Dob system is less expensive, as little as one-third the cost of a premium equatorial/goto Newtonian system. Third, it’s much lighter in weight, that issue being the reason I gave up the first 8” telescope to begin with. Now I have decided on the 8” Dob, but which one? For those of you new to the Dobsonian principle, it is basically any Newtonian telescope mounted into a simple but ingenious pressboard or hardwood base, balanced and tensioned to give smooth motions in both altitude and azimuth. There are many fine brands with systems under $500 out there; all priced rather close to each other, with exact specs and accessories varying from company to company. Some of the price leaders often “sweeten the pot” with sales or added accessories to attract your wallet. So I flipped a four sided coin and ended up with the Zhumell. My circle is now closed!

Arrival Day:
When you accept delivery of your new Zhumell Dobsonian, inspect the large box! After I opened it I discovered that the optical tube is not well protected from miss-handling. Carefully inspect the large box before you sign for it. If you see any outside damage carefully open it at that point to inspect for product damage. If you see or suspect anything, return both boxes and call your dealer. This will save you some hassle in the long run. Fortunately, mine arrived without damage. The smaller box is well packed with accessories and is not likely to have any damaged contents unless seriously miss-handled.

First Sight:
Good news and bad news. There are no assembly directions in the box. Well, there is, but I found them only after I had the telescope fully assembled: it is just a piece of folded paper not much bigger than a postcard. It’s so small that even with my near-sightedness I needed a magnifying glass to see the print! The good news: you can download a full sized multi-page instruction manual from Zhumell’s website in pdf format. It’s very nice and comprehensive, fully illustrated, and you can either print it out or have it on your computer when you assemble the telescope. I think this is a good idea actually, as it cuts down on the costs of the telescope. Unfortunately, there is no mention of it anywhere in the contents that I could find. It would have been better for Zhumell to have written in big letters on that piece of paper “download your free pdf instruction manual from our website!” I was lucky and stumbled across this web-manual before ordering the telescope, so I could be prepared. The next bad news is the dust cover. The type that came with my telescope is like a paint can lid, that is, it fits inside the rim of the optical tube. It is so tight I have to hammer it down with my fist, and it knocks paint chips from the rim onto the primary. The paint chips are not that big a concern, it’s an insignificant amount compared to the area of an 8” mirror, but it’s an issue that I hope Zhumell will address in the future.

Assembly was straight forward and easy with the supplied hardware. I only had two “misunderstandings” requiring me to back up, loosing about 10 minutes of assembly time. Everything fitted together without forcing or “modifying,” with total assembly time about 30 minutes. The kit comes with lots of accessories too: two plossl eyepieces, eyepiece tray, an 8x50 finder scope, laser collimator, cooling fan (on some models), and moon filter. I’ll briefly describe all of these in my next section…

Thumbs Up Thumbs Down:
Here is a list of the features and how I rate them, with a simple good or bad.

Optical tube: Well built, none of the flexing I can feel in my 6”/f8 Newtonian. The tube (and base as well) is painted black. I like that because it cuts down on reflections from the neighborhood lights. Thumbs up.

Focuser: The Zhumell comes with a Chinese made Crayford style 2” focuser with 1-1/4” adapter. While it is no JMI, (and certainly no Feathertouch!) it compares equally well with the R&P focuser on my Orion 6” Newtonian. There are two features I really like. First, as with all Crayfords, there is no image shift when focusing. Second, there is a thumbscrew to adjust the tension for the weight of the eyepiece you are using. This is a nice feature as it does not require a hex wrench and you can adjust the tension “on the fly.” My only real complaint is the coarseness of the focus, as it is rather hard to get a precise focus using powers over 200x. Still, I would give this focuser a thumbs up.

Mirror optics: My Meade 28mm 2” SWA makes a good wide field eyepiece, giving me nearly a 1.6º true field. Although there are a few issues that I will go into detail later, I give the overall image quality a definite thumbs up.

Base mount: very well constructed and easily assembled. No flexing or wobbling that I can detect. It uses nylon bearings throughout, which gives a firm feel with very little back lash. Another thumbs up.

Cooling Fan (installed on most models): A great idea! This cools the primary mirror down so that convection currents are brought to a minimum, which makes the image steadier. Thumbs up.

Eyepieces: You get two, a 25mm and a 9mm Zhumell brand plossls. These are well built eyepieces and are much better than the stuff you get with the Wal-Mart wonders. They may not give as pretty an image as, say, my Naglers or Pentax’s, but basically anything I can see in the premium eyepieces I can also see in the plossls. The 25mm has enough eye relief for eye glass wearers. Two thumbs up (one for each.)

8x50 finder scope: Also well built, with glass optics. Plenty of eye relief, crosshairs can easily be seen, and it focuses easily with a locking collar ring. It also fits securely in its holder and is easy to align. My only complaint is that it is a straight through, rather than right angle, finder. Thumbs up!

Moon filter: A little disappointing. It works well with the 25mm Zhumell plossl, but puts an ugly green cast to the lunar surface, and there is some loss of resolution. With the 9mm plossl I can easily see some image degradation. At higher powers, this degradation becomes more apparent. My polarizer and neutral density filters work much better. Thumbs down.

Laser collimator: a nice accessory to have, if it would work. But when I used it and compared the collimation with another Cheshire eyepiece and eyeballing down the focus tube, it clearly did not put the scope in alignment. The laser tool might be able to be adjusted, but without any directions on checking or collimating your laser, I would imagine the average beginner could end up with miss-collimated optics and not know it.
It’s a great idea but at this point I have no idea if my problem is typical or a rare example, so I have to give it at least a tentative thumbs down.

Sights To Behold:
My overall impressions with the image quality are very good. I am no expert in star testing, so I’ll relate what I see through the eyepiece. I spent a few minutes collimating my telescope. (It is not “perfect,” but very, very close.) I’ll break this down into categories. Keep in mind that I am observing from my light polluted suburban front yard, were the average visual dark sky magnitude is 4-1/2, sometimes better, usually worse.

Emission/reflection nebulae: Very good but a bit low in contrast. M27, the Dumbbell Nebula, shows a dimmer image in my 102mm doublet apo, but the image has better contrast and it is easier to pick out the details. Likewise with many of the brighter Messier nebulae in Sagittarius. The scope has excellent image quality at high powers though. I ran the power up to 240x on the Ring Nebula in Lyra (with the 5mm Nagler) and the bright outer edge was distinguishable along with the 13th magnitude star nearby. There are certainly many deep space objects, like the Trifid Nebula, that I can see well with the Zhumell that I cannot see with my smaller refractors (at least without the aid of filters.)

Open Clusters: Excellent! This 8” scope easily reaches at least magnitude 13 with stars in my light polluted sky. The Zhumell 25mm plossl scores well on open clusters. M11, the Wild Duck Cluster, was absolutely stunning with my 5mm Nagler (240x). The star field was fractured into small groups of stars, separated by dark voids, giving me the impression of an unassembled jigsaw puzzle. This scope also pulls in Czernik 43 quite well. This is a very dim but tightly packed open cluster right next to M52, and I have never spotted it in my 102mm telescope from my suburban yard.

Globular Clusters: Again excellent. Using the supplied eyepieces, brighter globs like M13 or M22 resolve easily into stars. Even many dimmer ones like M10 and 12 in Ophiuchus will show some dusting.

Double and Multiple Stars: Rather poor. No matter how well I collimated the optics, I still could not match the resolution of even my 80mm Nighthawk achromat. Izar was much easier to split with the Nighthawk using my 5mm Nagler (96x). My 10mm Televue Radian in the Zhumell (120x) showed little of a split. I had to bump the power up to 150x to begin to see a comfortable separation. If your primary interest is in splitting stars, I think there are better telescope options out there. Still, with continued tweaking of the collimation, I believe the user can enjoy many of these jewels of the night sky.

Planets and Moon: Very good but with low contrast issues. My Nighthawk does not have the fine-line detail of the much larger aperture of the Zhumell. On Jupiter, for example, the Zhumell with a 10mm Radian for 120x, showed better detail inside the Equatorial Zone, but the better contrast of the little refractor made some features like the South Temperate Belt and barges on the North Equatorial Belt easier to see when I used the same power with a 4mm BO/TMB Planetary eyepiece. I had similar results with the Moon. The Zhumell showed the hair-line Triesnecker Rilles with little effort, but the Kies Pi dome was easier to see with the Nighthawk when used side by side on the same night with similar magnifications. But as with double stars, continued tweaking of the collimation would give the user some very satisfying views of the Moon and planets. Even though my collimation was not 100% centered, The Zhumell readily shows the tiny Stadium craterlets, a target much more difficult with my 80mm or 70mm telescopes. If your primary interest is in these targets, I think the Zhumell Dobsonian should be on your short list.

Okay, so which do I like better- my 8” Zhumell Dobsonian or my Stellarvue Nighthawk? Well, it’s apples and oranges really. Both have strengths and weaknesses. The 80mm Nighthawk has better optics, is much lighter weight, sets up instantly and cools down quicker. It also has a much wider field of view for better views of open clusters or scanning large swaths of the Milky Way. But any 80mm telescope won’t yank the dim fuzzies out of my light pollution like a large Dobsonian, and the aperture can in some instances make up for the optical deficiencies. I like them both, and in fact frequently pull out both to work in tandem. I guess sometimes I really can have my cake and eat it too.

Although the scope balances well with the Zhumell
Plossl eyepieces, I use hardware magnets lined with
Adhesive backed felt to balance my heavier eyepieces.

I purchased and installed a red dot finder to make my
Star hopping easier.

The eyepiece tray holds three 1-1/4” eyepieces and
One 2” eyepiece, but you might want to drill holes
And mount it lower so you don’t bang the eyepieces
On the tension spring!

Conclusion: in my humble opinion the Zhumell 8” Dobsonian package is an excellent buy, for both the beginner and the more advanced observer. Some of you may be thinking if it is really worth buying a $290 Nagler eyepiece for a telescope that costs only a little more. I believe, yes, the optics of this telescope is good enough to justify such a purchase. Consider this: you can buy a comparable quality Newtonian on an equatorial mount, with or without GOTO, for over $1000. That same $1000 will buy you the 8” Zhumell package, AND a 13mm Nagler AND a 5mm Nagler AND a pocket atlas AND the book “Turn Left At Orion.” Now you are ready to begin a journey to hundreds of destinations for years to come. If you only have three or four hundred dollars to spend, I consider this package to be remarkably complete for the money spent. You need only add some inexpensive observing aids, like a book or pocket atlas, a 2x Barlow or a few filters. I give the Zhumell 8” Dobsonian a big, well deserved Thumbs Up!

David Elosser
Kernersville NC

Click here for info about a similar scope to the one reviewed. -Ed.