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- Review of the Hubble Optics 14 inch, f/4.6 Premium Ultra Light Dobsonian Tele...
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Review of the Hubble Optics 14 inch, f/4.6 Premium Ultra Light Dobsonian Telescope
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Review of the Hubble Optics 14 inch, f/4.6
Premium Ultra Light Dobsonian Telescope
J. Christopher Westland
Hubble Optics 14" f/4.6 Premium Ultra Light Dobsonian Telescope
Hubble Optics (HO) produces some of the most elegant and innovative looking large Dobsonian telescopes on the market today. Yet, they seem to be quite rare, and even though they have been in production for a decade, I have found very few reviews for them on the Internet. Additionally, where Hubble Optics telescopes have been reviewed in the past, they seem to have generated a certain degree of controversy. Thus, I thought there might be interest in my sharing my owner’s experience with a 14" HO telescope.
I looked at HO telescopes for some time before purchasing mine. On paper, the design is elegant, and takes advantage of the 6063-T6 aluminum alloy used in all of the telescope’s components. The sandwich mirror is innovative. The upper cage looks more rigid than a flat ring, but without being too heavy. In general the HO telescopes are unique and affordable. I am a previous owner of an Obsession Classic 20", and Dave Kriege’s scope set a standard for what I was expecting from a Dobsonian telescope.
Out of the box, the HO 14" falls short of the Obsession standard, in my opinion because of design concessions made to reduce weight and cost, and to accommodate the GoTo system. Minimalism and affordability come with certain compromises – ones that I wasn’t prepared to live with longer run. Thus much of this review will cover modifications that I have made to improve the utility of the HO design for use as a manually guided Dobsonian.
- Location: Currently in Phoenix AZ for the semester, but permanent home is Chicago, IL
- Experience: 30 years, give or take
- Telescopes: Meade SCT 10" and 8“, Obsession Classic 20”, Televue Pronto
- Biases: Maximum aperture, maximum portability, minimum set-up; otherwise I consider myself to be rational and prudent.
Particulars about my Hubble Optics purchase
- Price & order time: $1,995 scope & mirror + $495 shipping (half down on order, and 3-6 month wait in my experience)
- Extras: Hubble SkyHub-B Wireless & USB Digital Setting Circle System ($199) + Shroud ($85) + Hubble Optics Artificial Star for Collimating and Testing Telescopes ($25)
Out-of-the-box: Design & build quality, and some comments about the company
The HO 14" Dobsonian comes well-packaged, and all components showed quality welds, good machining, and professional finish. Rocker and mirror box are pre-assembled, and along with truss tubes and upper structure are black anodized aluminum. All components are incredibly light, and the entire scope breaks down into an small package that could be loaded into even the smallest compact car. The mirror box is easily carried by hand, which is what I want in a portable telescope.
Tong Liu, the Dallas based owner of Hubble Optics, is a Tsinghua University engineering graduate (Tsinghua is the top engineering school in China). He claims that all the designs – mirrors and structures – have been through finite element analysis (this seems reasonable both given their design with a single material, and his background). His choice of material (6063-T6 Aluminum Alloy) is optimal for a lightweight bent and welded manufacture. Tong tends not to be particularly responsive to inquiries about the scope, and not as engaged with customers as, e.g., Dave Kriege or Ron Newman. This adds to some of the mystery around these scopes, as well as their construction overseas. His price points are 30%-50% of competitor scopes at a particular aperture, which also generates interest in his product lines. The HO product line-up has been relatively stable for a decade. It emphasizes portability, which is reflected in the extreme in their UC 12" scope, which packages up into a standard suitcase.
Optical sub-systems: sandwich primary mirror
The heart of HO’s telescopes is their sandwich mirror technology. This appears to be HO’s core business, and the major cost component of their complete telescopes. They manufacture research-grade optical mirrors for the amateur community and (according to their website) institutions like NASA, Cal Poly and the US Army. HO claims their open core and closed back design reach thermal equilibrium up to 10 times faster than a solid mirror without sacrificing stiffness and optical stability.
HO uses a pretty crude 6-point support for their 14" mirror (HO goes from 6 to 18 points between the 14" and 16" and larger mirrors).
The supports are held in place by bent copper wire, though some have replaced these with small springs. The stock setup seems fine to me, but I was curious whether more supports would help with the mirror wavefront. I used David Lewis’ PLOP (http://www.davidlewistoronto.com/plop/) to compute:
- Peak-to-Valley wavefront deviation given as an absolute (positive) number, and
- RMS value: statistical deviation from perfect reference sphere, averaged over the entire wavefront.
Here are the figures computed by PLOP for a 14" mirror
The 6-point support appears not to give up that much. It is no better than a 9-point support; an 18-point support is about 4-times improved, which might or might not be marginal. I’m not really motivated to upgrade the mirror support at this point.
I can vouch that star tests (with the HO artificial star) are perfect for the 14" mirror right after it is set up and on into the evening. You don’t need a fan, and you don’t need to worry about thermal settling, at least with the smaller HO mirrors – all of this suits my desire for setup in minimum time with minimum fuss. The image quality is near perfect, and mirror surface “seeing” seems not to be a problem. Now that I have owned one, I would be inclined to purchase HO mirrors in the future for any other Dobsonian I might build. They weigh in at about 60% of a solid mirror, which is not a huge difference. But for my 14" scope, it is part of the reason that my mirror, rocker box and base can be picked up and carried as a unit (even with the counterweights).
I didn’t purchase the mirror cover from HO, rather went to OfficeMax and purchased black poster-board ($4) and cut it to size. I keep it over the mirror whenever I’m not using the telescope, to avoid dropping things into the mirror box.
Motion control sub-systems
Hubble Optics designed all of its scopes to be GoTo scopes using their $1500 Hubble SiTech GoTo System. They don’t inherently have the mass, ‘sticktion’ and smooth motion control of the Obsession Classics. The first modifications that I have made to improve the utility of the HO design were to the Altitude and Azimuth bearings to give them the smooth control I expected from manually guided Dobsonian.
I had read complaints about the HO ‘bump’ in the altitude bearing, and the lack of ‘sticktion’ on the azimuth bearing. The first problem arises from incorrect assembly of the telescope and is easily remedied. The second, though, requires a small modification.
The azimuth bearing is a lazy susan ring which ubiquitous in Chinese restaurant banquet tables. It’s a bit different system than the typical Dobsonian solid base with Formica and rotating Teflon pads. The traditional Dobsonian base makes it easy to mount encoders, and provides a smooth motion with ‘sticktion’. The lazy susan doesn’t provide either, and want’s to just keep spinning, which creates a problem with motion control at the eyepiece. Tong Liu designed the HO line to be ‘GoTo’ telescopes, with his affordable drive system. The lazy susan makes sense for his GoTo system, but is a poor choice for manual control (though it looks neat).
The ball bearings between the two concentric azimuth rings rotate too smoothly for manual control, offering little resistance to motion. Just bumping the eyepiece with your eye sends the scope spinning off target. I fixed the problem of runaway azimuth bearing with a couple of robotic wheels that are a light brake on the motion and make it ‘sticky’. It does lack the heft of my Classic Obsession 20, but that’s what you get with any of the ultra-light dobs (but more on that later, as I’ve fixed that problem as well).
The lazy susan ring also tends to pick up dirt in the bearings, which causes it to wear. I’ve placed a metal cover over the bearings to keep out dirt.
The altitude bearings are provided in two pieces, and can be disassembled for very compact storage and portability. Some attention needs to be given to reassembly, as the two parts need to line up with each other or the catch on the Teflon pads. The simple way to do this is to only tighten them to the rocker box while they are aligned on a Teflon pad.
The altitude bearings also have a tendency to wander off the Teflon pads; they are narrow and only held in the base by the two sides of the base. I’ve added Plexiglas guides on the front bearings to stabilize the two halves of the altitude bearings. I’ve put notches in these to allow an Allen wrench to tighten down the bolts on the rocker box, while the two parts are aligned on a Teflon pad. After this, the altitude motion is perfectly smooth.
I purchased the SkyHub-B tracking system from HO, which is a system a lot like the Nexus II. There is no dedicated position readout, rather you connect it to a planetarium program like the excellent Sky Safari. Again this fits with my goal of fast setup and portability. The original metal screw kept slipping on the encoder shaft, so I substituted a nylon screw, and tightened it down hard. The system is accurate across the whole sky to within a degree or less, which is enough for me to locate anything in my larger eyepieces.
As with most telescopes, wire management can be a problem. I purchased plastic wire guides from Amazon that have two-sided tape on their bases. I then made sure that the alt-az encoder wires were given enough play for the movement of the scope, but otherwise tightly held against the scope to avoid them getting tangled.
Balance and counterweights
HO’s ultra-compact 14" f/4.6 is on the edge of needing a coma corrector, and the scope in its original form is balanced for smaller eyepiece loads (a testament to the lightness of the sandwich mirror). I use 35mm Panoptic, 19mm Panoptic, and 8mm Ethos eyepieces which are heavy, and also need the coma correction because they have more ‘edge’ to suffer from coma. Thus I added a Paracorr to the stack, and that’s enough to make the telescope top heavy.
I needed a flexible system of counterweights, and initially thought of a spring system to keep weight down, but instead experimented with detachable weights bolted to the rear of the rocker box. These were cut and drilled from iron rods and sheets.
The largest of these weights perfectly balances the heaviest eyepiece assembly (35mm Panoptic and Paracorr coma corrector). Once it was attached, I was hesitant to unscrew it from the rocker box, so I experimented with soft weights (workout ankle weights) hung from the front altitude bearing cross-member or from the upper cage.
These in fact provide me a lot of flexibility with minimal effort to add and remove. Neither do they hamper portability. There was another significant benefit to adding these weights on front and back. They enable both altitude and azimuth motion to be much smoother, approaching the ‘sticktion’ and control of my Obsession Classic 20". Weight matters!
Upper cage & Truss tubes
HO’s design uses a traditional 8-tube truss structure, which is less subject to twisting forces than a 6-tube structure often found in ultra compacts. Each truss tube has four holes drilled at the upper cage end to accomodate different focal length primary mirrors. I’ve had no issues with rigidity of the entire structure, which is important when you are moving the telescope by grabbing the upper cage. The upper cage ring is made of angle aluminum welded into a dodecagon, with a trapezoid secondary mirror holder which seems quite rigid.
The upper cage design is inherently more rigid, for a given amount of weight, than the flat donut of metal used in some other ultra-compact dobs. It also provides both vertical and horizontal surfaces for mounting the focuser and guide scopes. When I keep track of the truss tubes, I can basically avoid re-collimating between setups. Although I purchased the shroud for this telescope, I don’t use it. The quality and fit of the shroud are great, but it doesn’t really add anything to observation, and it’s a bother to take on and off. I did mount (with Velcro) a light baffle opposite the focuser, as the scope does need one.
The upper cage is supported by eight truss tubes assembled with hand hardware, and joined at the top in a flattened end, tightened with a knob and wing-nut assembly. It is easy for a single person to attach the lower end of each pair of truss poles to the mirror box and install the secondary cage on top of the truss tubes I keep the truss tubes paired and attached at the upper end. This minimizes re-collimation, and makes attaching upper cage to truss tubes to rocker box a 5 minute, one-person chore.
The upper cage is a twelve-sided ring made up of angle aluminum, 1.5" in width. The narrowest inside dimension is 18 inches from side to side. The user is responsible for installing the spider vanes, hub, and focuser, as well as gluing the secondary to the hub. There are holes drilled for two focuser locations: one even with the side above the altitude bearing, and one at an angle about 30 degrees upward. I drilled added holes for my Picatinney rails.
The telescope can be setup without tools. The primary collimation adjustment knobs have large brass heads, and the “lock” screws are cap screws that can both be adjusted and tightened without tools. I do take along a small box of extra hardware, pliers and ratchet screwdriver with many insertable heads. Just in case.
Guidance and target acquisition subsystems
I wanted this telescope to be manually guided, with positioning primarily determined by the digital setting circles. My DSC system is the SkyHub-B with Bluetooth connection to a Samsung S4 tablet running Sky Safari Pro planetarium software.
The original metal screw kept slipping on the encoder shaft, so I substituted a nylon screw, and tightened it down hard. The system is accurate across the whole sky to within less that a degree, which is enough for me to locate anything in my larger eyepieces. I end up using my guide sights only for setup.
Set up and use of this system is straightforward, after a bit of fiddling with the attachment of the encoders to the tangent arm.
The initial two-star alignment needs a sight. I initially had a cheap red dot sight on the upper cage, but decided to install two Picatinny rails on the cage, and install a reticle sight for a gun, as well as a green laser sight. I love using the laser pointer for alignment, but am careful around airports, where I use the reticle sight. I think gun sights work much better than bespoke astronomy sights: the Picatinny rail keeps solid alignment, and internally, they are designed to take repeated shocks from gunfire. They also aren’t any more expensive.
Eyepieces, collimation and focuser subsystems
The original Hubble Optics focuser that came with my purchase is a servicable 1:1 and 10:1 reduction focuser.
Being used to the Starlight focuser, I found it rough, as well as being challenged by loads like a 35mm Panoptic + Paracorr. So I swapped this for one of Ron Newman’s MoonLite focusers (1:1 and 10:1 reduction). Almost all of your interaction with a telescope is at the focuser, so I wanted the best. The MoonLite focusers are a bit less expensive, and I feel their motion and comfort has a slight edge on the Starlight focusers, though both are incredibly nice. I had to realign the MoonLite focuser with the secondary – this took two copper washers, but after that was spot on.
I use an all-in-one laser collimation tool to collimate. Given the small size of the telescope, and the excellent alignment hardware for the primary mirror, this takes only 1-2 minutes max.
Final Assessment of the Hubble Optics UC14 package
The design of the rocker box is very elegant: it is light, but with weighting achieves motion control comparable to an Obsession Classic. The rectangular frame is constructed of black anodized aluminum, and measures approximately 18" x 22" x 4" high.
The azimuth ring is 18" in diameter, and very low profile, being only 1/2" in height. I can use the telescope without a ladder (I’m 5’7"), which to me is an important part of my objectives of convenience. It fits into my Honda Civic with minimal disassembly.
Now that I have taken it out into the Arizona desert and used it a few times under the stars, I am satisfied with its performance, smooth motion and rigidity.
The eyepiece image settles down a couple seconds after focusing, and I really don’t notice that the optics need time to reach thermal equilibrium (though this may be different in autumn or winter). It takes 5-minutes to setup and break down the telescope and the scope is incredibly compact. The heaviest component is the rocker + mirror box (which I keep together) which is about 30 pounds. I can reach the eyepiece for everything with my feet on the ground (I’m 5’7") though I do take along a foldable step-stool for convenience.
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