The Zhumell Z130: this remarkably inexpensive tabletop Dob is an outstanding performer.
U.S. Price: $199
Available at telescopesplus.com
What We Like: Good optics Rotatable tube Tube rings attach directly to most commercial mounts
What We Don't Like:
Requires tools for collimation Base unusually large and heavy
TO MY MIND, the perfect beginner's telescope should be inexpensive and easy to use, yet sufficiently capable to remain a prized possession even after one acquires a great deal of experience and possibly additional telescopes. One design that meets these criteria is the Dobsonian reflector. But full-sized Dobs are heavy, bulky, and clumsy-looking, which is a psychological deterrent for many beginners and a practical problem for people who can't lift much or have limited storage space.
A new alternative has become available in recent years: the 130-mm (5.1-inch) f/5, single-arm, tabletop Dobsonian. These gather almost as much light as traditional 6-inch f/8 Dobs, but in a much lighter, more compact package. And with prices around $200, they offer unparalleled bang for your buck. We have reviewed two of these scopes in the past: the Astronomers Without Borders OneSky (in February 2014 and December 2015) and the Meade LightBridge Mini 130 in December 2016. The latest entry in this field is the Z130 Portable Altazimuth Reflector from Zhumell.
I've been looking for a portable telescope to complement my 12 1/2-inch Dobsonian, so I decided to purchase a Z130 in July 2016 and put it through its paces. The first thing that I realized, even before unpacking it, is that the Z130 is very big for its class. At 18 pounds (8.2 kg), it's about 30% heavier than the other two 130-mm tabletop Dobs I've used, and it also has a much wider footprint.
The other striking difference is that the tube is held by rings that attach to the mount using a standard Vixen-style dovetail bar. That gives the telescope unparalleled versatility. When the tube is on its native mount, you can loosen the rings and rotate it to put the eyepiece at the perfect height. Or you can pop the rings and tube assembly off the tabletop base and put them on most commercial telescope mounts without purchasing any additional hardware.
Reflecting telescopes, especially ones like the Z130 that have relatively short f/ratios, only deliver sharp images when properly collimated. Some designs hold collimation better than others, but all reflectors need to be collimated sooner or later. It's helpful to beginners if a telescope arrives reasonably well collimated right out of the box.
Collimation requires some kind of tool, which can be as simple as a reflective cap with a hole in the center or as high-tech as a laser. It also requires the center of the primary mirror to be marked in some way, preferably with a white donut.
The Zhumell Z130, like the other 130-mm tabletop Dobs I've looked at in recent years, is shipped with a center-spotted mirror. That's a great convenience for experienced astronomers and a huge benefit for beginners. While it's not really very hard to remove a mirror, center-spot it, and re-install it, the process is intimidating for beginners. However, the Z130 does not include a simple collimation tool. That's a non-issue for an experienced astronomer, who is likely to own at least one collimation tool already, but purchasing a collimation tool is an added inconvenience for a beginner who buys a Z130.
The primary mirror of my Z130 was fairly badly out of collimation when it arrived, and collimating it proved surprisingly complicated. Most reflectors have large thumbscrews to adjust the primary mirror's tilt. With the Z130, you first need to remove a thin metal plate from the back of the scope, which serves no obvious purpose besides blocking access to the collimation screws and preventing the mirror from cooling down as fast as it might. Once the plate was removed, I discovered two sets of screws were required for adjusting the primary mirror. An Allen wrench (not supplied with the scope) is needed to loosen the 3 locking screws, along with a Phillips-head screwdriver to turn the collimation screws. Fortunately, the telescope has remained in perfect collimation ever since the first time I adjusted it.
The telescope is shipped with two Kellner eyepieces, with focal lengths of 25 and 10 mm, yielding 26x and 65x respectively. Those are excellent magnifications for deep-sky observing, and the 10-mm eyepiece together with a 2x Barlow lens shows fine planetary images at 130x. But the telescope is capable of much more. A 32-mm Plossl or 24-mm wide-field eyepiece yields low-power images that are significantly wider and somewhat sharper at the edges than the 2 5-mm Kellner. And I found 162x using my own 4-mm eyepiece just about ideal for planetary observing.
The plastic focuser included with the Z130 is rather coarse, so focusing at such high magnifications requires a little fiddling. Fortunately, the heavy-duty mount is very stable, so vibrations from twisting the focuser knob die away rapidly. The optical tube works even better at high power when placed on a sturdy equatorial mount, but that loses the benefit of portability; the combination is as heavy as a standard 8-inch Dobsonian and considerably less capable.
When used with its tabletop mount, the scope needs--or at least deserves --a custom-built support to raise it to an appropriate height. If you place it on a conventional table, the eyepiece is too high for use while sitting in a conventional chair and a bit low for a standing adult. Also, few portable tables are sturdy enough to permit the scope to be used at high power. Unlike many tabletop scopes, the Z130's base is too big to fit on a chair or stool.
If you're handy with tools and have a saw that can make accurate angled cuts, a support with splayed legs like the one under "DIY Improvements" at eyesonthesky.com is ideal. Having only hand tools, I built a small table with vertical legs from a scrap of 3/4-inch plywood, a length of 2x2 lumber, and six angle irons to keep the structure rigid. It works very well indeed when I'm sitting in a conventional chair, and when I turn the table upside down, the scope nests inside it for storage. But the combination of table and scope, while much lighter than a 6-inch Dob, is right at the limit of what I consider to be easily portable in a single trip.
Once it's set up, this telescope is a joy to use. When I set the eyepiece angle appropriately, I can view all the way from the horizon to the zenith in perfect comfort. My head is above the eyepiece when it's at its lowest and level with the eyepiece when it's highest, and the two effects cancel out almost perfectly. My only complaint is that it's a little hard to rotate the tube in azimuth when it's pointing near the zenith. This is an issue with all Dobs, but the short tube exacerbates the problem. I found that the best solution was to get more leverage by grabbing hold of the turntable base rather than the tube.
Star-testing indicates that my Z130's mirror has a slight turned-down edge. That's probably responsible for the fact that Jupiter appears somewhat soft. Although the Z130 provides good views of the Great Red Spot at 130x during moments of excellent seeing, these moments are rarer and less sharp than in my premium-quality 7-inch Dob when I set the two up side by side. Still, the scope shows Cassini's Division in Saturn's rings with ease, and at 162x on one night of unusually steady seeing, I got a good view of Mare Erythraeum on Mars when the planet was just 11 arcseconds across. That's impressive for a mass-produced mirror of this aperture!
As for deep-sky observing, the scope shows all the Messier objects with ease under dark skies, and it has enough aperture to resolve dozens of stars in the brightest globular clusters. The improvement over a 114-mm scope is bigger than you might guess from the numbers alone. The Zhumell 130 is an outstanding performer for its amazingly low price.
S&T Contributing Editor TONY FLANDERS is a long-time fan of simple, inexpensive telescopes.
Caption: The Z130 is very solidly built, which makes it considerably bigger and heavier than other one-arm 130-mm Dobsonians.
Caption: Collimating the main mirror requires removing a metal plate, then loosening three locking screws with an Allen wrench and turning the collimation screws with a Phillips-head screwdriver.
Caption: The optical tube is held in rings that attach to the mount with a Vixen-style dovetail plate. That makes it easy to attach to most commercial telescope mounts.
Caption: The red-dot finder is simple but effective. The plastic focuser, however, is only marginally adequate at high magnifications.
Caption: The center of the primary mirror is marked by a white circle. But users must supply their own collimation eyepieces or lasers.
Caption: The author built a low table to support the telescope out of scraps of wood. When the table is turned upside down, the telescope nests inside it during transport.
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|Title Annotation:||S&T Test Report|
|Publication:||Sky & Telescope|
|Article Type:||Product/service evaluation|
|Date:||Aug 1, 2017|
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