The Z8 Optical Tube Overview
The Z8 is fairly standard among all of the 8” Dobsonians out there (which is unsurprising, since there are only two different OEMs for them). The optics in the one I had been quite good, and it went head-to-head with a premium 8” and came out surprisingly well in that contest.
The primary mirror in the Z8 is made of Pyrex for the minimal cool-down time.
The Z8’s mirror cell is collimatable and uses springs, but there are also 3 “mirror lock” bolts on the back. Supposedly these are to compensate for any weakness in the springs, but the springs can handle the mirror just fine and they could always be replaced if not. All the mirror locks serve as is a great way to get confused while collimating, or break your mirror if you drop the scope (since the locking bolts directly contact the glass). Just remove them.
The mirror cell also has a DC-powered cooling fan which runs off a small battery pack supplied with the scope. I am not exactly sure as to where one actually is meant to put said battery pack, but I Velcroed it to the back of the scope.
The Z8’s front cap is a bit of a weak point with this scope. It is not very tight-fitting and there is nowhere to grab it from the middle. However, this is a minor inconvenience at most.
The tube of the Z8 is longer than that of the Synta-made Dobsonians. It will not fit in the trunk/boot of most cars and must lay across the backseat.
The Dual-Speed Crayford Focuser
The Z8 comes with an extremely high quality dual-speed Crayford focuser. This focuser (like all Crayfords) rolls the focuser drawtube against 4 rollers for precision, smooth motion. The dual-speed part comes from the fact that it has a 1:10 fine adjustment knob for precision focusing at high magnifications. It also uses a brass compression ring so as to not mar your eyepiece barrels (as does the included 1.25” adapter). The GSO Crayford like the one on the Zhumell is often considered a decent one for astrophotography telescopes, which have more stringent standards than a visual-only telescope like the Z8.
About the Z8 Dobsonian Mount
The Zhumell/GSO Dobsonians are a bit different from your typical Dob, but the changes are mostly for the better.
For one, the altitude bearings are far different from pretty much any other Dob. Instead of using plastic on Teflon with tension adjustment via springs or the knob/washer system Sky-Watcher uses, the Z8’s bearings are ball bearings which can be adjusted for tension, and can slide along the tube for balancing. I was able to achieve balance even with a 14mm Explore Scientific 100-degree eyepiece and a Tele-Vue Paracorr, the combination of which weighs about 3.5 pounds.
Then there’s the azimuth bearing. Rather than Teflon on laminate it’s a roller bearing. This takes some getting used to but works pretty well and provides surprisingly smooth motions, especially since the laminate and Teflon most manufacturers are using is utter garbage that falls far from “buttery smooth”.
Like most mass-manufactured Dobs, the Z8’s mount assembles with just an Allen key and a handful of screws, a task which takes mere minutes to accomplish. It is, however, made of particle board which is quite heavy and easily prone to moisture damage if the laminate covering peels off it.
How Good are the Accessories
The Z8 comes with a 50mm right-angle, correct-image finderscope, a laser collimator, a Moon filter, and two eyepieces: a 30mm “SuperView” and 9mm Plossl.
The 9×50 RACI is decent, though RACIs are kind of difficult to use on their own. It would definitely be worth supplementing or outright replacing with a Telrad or Rigel Quikfinder, the latter of which I put on my Z8.
The included laser collimator is really well-made. However, the laser itself is frequently shipped misaligned with the barrel, making it useless. This can be solved by making a makeshift V-block and adjusting the tiny Allen screws in the collimator – tricky, but worth it.
The included 30mm SuperView is a decent low-power eyepiece, based on the Erfle design. While there is some edge-of-field astigmatism, the 70-degree apparent field of view and the 40x magnification it provides with the Z8 makes it great for low-power viewing of deep-sky objects.
The included 9mm Plossl works okay, but you have to press your eyeball right up to it to see the entire field. The field of view is also narrow for a Plossl at 45 degrees – as a result, you have to nudge the scope along quite frequently to keep your target in the field of view. I would recommend replacing it with a 9mm gold-line eyepiece, as well as getting something in the 15mm range for medium magnification.
The “Moon filter” is little more than a piece of cheap green-tinted glass, not a true polarizing filter. It will dim the Moon but you probably don’t need it, and if you must have a Moon filter there are much higher quality ones available.
The Zhumell Z8 is an absolutely fantastic telescope for beginners and experienced astronomers, and I highly recommend it to almost anyone starting out. You simply can’t go wrong for the price with the value the Z8 provides!