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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

2020-09-22


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.


In the desert: Hubble Optics 14 inch f/4.6 Premium Ultra Light Dobsonian Telescope


About Me

  • 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.


Hubble Optics Sandwich Mirror


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).


Mirror support


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

cell-points

6

9

18

36

P-V

.000807

.000769

.000255

.000140

RMS

.000141

.000157

.00004198

.00001823


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.

Mirror cover from OfficeMax

Mirror cover from OfficeMax


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.


Azimuth Bearing

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).


Azimuth bearing with dust cover and ‘sticktion’ wheels


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.


Azimuth bearing dust cover


Altitude Bearings

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 importance of aligning the two parts of the altitude bearings


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.


Altitude encoder and tangent arm


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.


Moonlite focuser with 35mm Panoptic and Paracorr coma corrector


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.


Counterweights


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.


Ankle weights


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!


Counter-counterweights hung on the cross-member


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.


Upper cage


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.


Baffle


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.


Sky Safari connected to SkyHub-B


Set up and use of this system is straightforward, after a bit of fiddling with the attachment of the encoders to the tangent arm.


Red-green reticle pistol sight


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.


Laser pointer pistol sight on upper cage


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.


Original Hubble Optics 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.


Moonlite focuser with 35mm Panoptic and Paracorr coma corrector


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.


Modified HO 14 inch f/4.6


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.


Eyepieces, shroud and emergency hardware


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.


Hubble Optics 14" f/4.6: Observing in the desert (night vision)


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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38 Comments

Thank you for adding to the 'shallow pool' of information on Hubble Optics.

Any chance you could clarify your experience with the order time frame - 3 months or 6 months? - their web site clearly states ~60 days, however members of the now defunct Hubble yahoo group were saying 6 months+ to a year wait. (The group devolved to a email only thread where we have been exchanging experiences and question) Also there were records of wrong items, replacement parts needed etc. Also any experience you had with communication with Hubble - from the same group we were determining that communication was sporadic at best. One of my biggest concerns with pulling the trigger on a Hubble have still been these two issues. Thanks.

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Chris Westland
Sep 29 2020 05:31 PM

Any chance you could clarify your experience with the order time frame - 3 months or 6 months? - their web site clearly states ~60 days, however members of the now defunct Hubble yahoo group were saying 6 months+ to a year wait. (The group devolved to a email only thread where we have been exchanging experiences and question) Also there were records of wrong items, replacement parts needed etc. Also any experience you had with communication with Hubble - from the same group we were determining that communication was sporadic at best. One of my biggest concerns with pulling the trigger on a Hubble have still been these two issues. Thanks.

Six months to a year right now is about right, and communication with Tong is sporadic; the information you have from the group is in my experience correct.   I believe business is pretty good, and I think they are focusing on mirrors.  I also suspect that sales inside China are picking up, as there is more and more interest in astronomy there, though I can't seem to find a Chinese language site for HO.

Good Morning. Thank you for a very useful review. I would like to know if you have any information regarding the long term stability of the Hubble mirror. Are there any temperature or humidity storage requirements? If needed, can the mirror be re coated or re figured by standard means?

Thanks.

Ellis.

"I ordered my 18" on Jan 28th. Received it Late July. They did ship the wrong feet but a reshipment of the correct size feet was very quick. I found Tong's response to emails after I received the scope very adequate, within 8 hours even on a Sunday. prior to receiving the scope though it was hit or miss. My main dislike was that the downloadable manual was has not kept up with the changes made to the scope design. That was somewhat problematic. Haven’t taken it out yet but should be able to very soon."

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Chris Westland
Sep 30 2020 11:11 AM

Good Morning. Thank you for a very useful review. I would like to know if you have any information regarding the long term stability of the Hubble mirror. Are there any temperature or humidity storage requirements? If needed, can the mirror be re coated or re figured by standard means?

Thanks.

Ellis.

It's no different than any other mirror.  Mine is made of plate glass (you can also get, for more $, ones made of borosilicate glass).  It's just a bit lighter, and much faster to thermally stabilize because it has an air-gap in between the top and bottom plate.

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Chris Westland
Sep 30 2020 11:12 AM

"I ordered my 18" on Jan 28th. Received it Late July. They did ship the wrong feet but a reshipment of the correct size feet was very quick. I found Tong's response to emails after I received the scope very adequate, within 8 hours even on a Sunday. prior to receiving the scope though it was hit or miss. My main dislike was that the downloadable manual was has not kept up with the changes made to the scope design. That was somewhat problematic. Haven’t taken it out yet but should be able to very soon."

Thanks for sharing your experience Bill.

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jim molinari
Sep 30 2020 04:17 PM

"I ordered my 18" on Jan 28th. Received it Late July. They did ship the wrong feet but a reshipment of the correct size feet was very quick. I found Tong's response to emails after I received the scope very adequate, within 8 hours even on a Sunday. prior to receiving the scope though it was hit or miss. My main dislike was that the downloadable manual was has not kept up with the changes made to the scope design. That was somewhat problematic. Haven’t taken it out yet but should be able to very soon."

Thanks for your input Bill. Did you have your telescope shipped surface or air? I just ordered one late July and specified air shipment. I am at 60 days and waiting.

Great review, thank you so much.  It is indeed an interesting scope, and I really like the way you explain your modifications.

 

Regarding your extra counterweights to balance the large EPs you use, consider the hunk-O-chain method,  I like to flip between the big 2" EPs and dinky (by comparison) 5mm and 3mm 1.25" EPs, which always throws off the balance of my Dob.

After seeing a post on CN I went to ACE and got a 2', 8(?) lb. length of steel chain that is plastic coated,  This isn't screen door thickness, I'd trust it as a trailer safety chain.  I attached it to one of the bottom mirror retainer (not collimation) screws and it just sits on the ground when not in use.  What it like is that it is never overweight because any unneeded weight just coils on the ground.  As I add a larger EP a little more chain is lifted off until it is in equilibrium.  Not sure if it would work as well with a a go-to so you might need to keep an eye on it,

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Chris Westland
Sep 30 2020 09:41 PM

The hunk-O-chain method sounds interesting, and actually might work for my scope in place of the counter and counter-counter weights.  I may experiment with this.  Thank you for the idea.

    • BinoGuy likes this

Created an account to comment here after 18 months of reading the site as anonymous, as one other commenters has said thankyou for the additional information on Hubble's products. I too have just received one of their scopes (UL16 f4.5) but this only took 13 weeks to my door and a week of that was due to a misunderstanding on my part, which is quite different to other commenters wait times.

 

Clear skies

 

Edit; spelling

    • Chris Westland likes this
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Andrew Brown
Oct 03 2020 05:47 AM

Glad you're enjoying it but "twisted copper wire" really!

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Chris Westland
Oct 03 2020 12:56 PM

Created an account to comment here after 18 months of reading the site as anonymous, as one other commenters has said thankyou for the additional information on Hubble's products. I too have just received one of their scopes (UL16 f4.5) but this only took 13 weeks to my door and a week of that was due to a misunderstanding on my part, which is quite different to other commenters wait times.

 

 

Thank you for the kind words, and congratulations on your new scope.  I'm glad to see that the delivery time was reasonable.  I was considering the 16", but opted for slightly more portability.   I hope you post pictures once you've gotten it together with any modifications you might add.

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Chris Westland
Oct 03 2020 12:57 PM

Glad you're enjoying it but "twisted copper wire" really!

I know.  It works, but it's just not very elegant.

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alwayslookingup
Oct 03 2020 06:43 PM

Excellent review. I have ordered one myself the date was 6/14, however it was 11 days before they even acknowledged my purchase. Every email unanswered. Until finally after 90 days i decided to register a complaint with paypal, stating I never received product their response was go through the seller. Then all of a sudden Bam! next day get this reply from Tong your order is ready, will be shipped in 14 days, imagine that. Scope and options paid in full, now just waiting and trying to figure out how to overcome the problems you mentioned. Anyhow thanks for the info.

Excellent review! I tried to get someone at HO to answer emails (I was looking at a 16") but after several attempts (last year and then again in Feb), I gave up. No way I was going to just order one without a first contact of some sort (Hello? Anyone home?). I couldn't tell if the website was active or not and I've had two minor skirmishes with the relatives of dead web-store owners already.

 

I like the design of the scope itself and the engineering behind the mirror.

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Chris Westland
Oct 04 2020 03:32 PM

Excellent review. I have ordered one myself the date was 6/14, however it was 11 days before they even acknowledged my purchase. Every email unanswered. Until finally after 90 days i decided to register a complaint with paypal, stating I never received product their response was go through the seller. Then all of a sudden Bam! next day get this reply from Tong your order is ready, will be shipped in 14 days, imagine that. Scope and options paid in full, now just waiting and trying to figure out how to overcome the problems you mentioned. Anyhow thanks for the info.

Thank you for the kind words.  The ordering and communications are definitely a hit or miss process, but Tong has a good product.  I've never met him, but may try to look him up next time I get to Dallas.   I suspect this may not be his main job, or he may just have a pretty active business.  I do know he is the whole business more or less.  Everything HO sells is designed and managed by Tong, but it's all made in South China (I'm not sure exactly where, but I recall he is from Hong Kong, so it's probably in Shenzhen or Dongguan, Pearl River Delta area).  I've actually got another HO scope on order, and plan to buy the GoTo system whenever it's ready.

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Chris Westland
Oct 04 2020 03:36 PM

Excellent review! I tried to get someone at HO to answer emails (I was looking at a 16") but after several attempts (last year and then again in Feb), I gave up. No way I was going to just order one without a first contact of some sort (Hello? Anyone home?). I couldn't tell if the website was active or not and I've had two minor skirmishes with the relatives of dead web-store owners already.

 

I like the design of the scope itself and the engineering behind the mirror.

Thank you.  And I could certainly understand your hesitance.  But HO is legitimate, and committed to quality.  I just suspect that Tong has more business than he can handle (I'll give him the benefit of the doubt).  He lives in Richardson TX, so I perhaps you could find a phone number and just call.

Have you tested the edge support on these.  It appears to be a belt sling on a light thin split mirror.

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Chris Westland
Oct 06 2020 12:38 AM

ButterFly, on 05 Oct 2020 - 05:41 AM, said:

Have you tested the edge support on these.  It appears to be a belt sling on a light thin split mirror.

 

 

It is ... it seems to be a standard Dobsonian mirror mount (pictures below).   This should distribute weight well: it's a light, small mirror so the surface should be quite solid.  

 

Should I be looking for anything specifically?

 

 

 

b1.jpgb2.jpgb3.jpg

 

Thank you for a great review. Very interesting read, for someone dreaming of making such an instrument ATM.

Could you please explain what these metal rulers are doing? I didn't understand, is it your own mod or was already in the scope?

Thank you.  And I could certainly understand your hesitance.  But HO is legitimate, and committed to quality.  I just suspect that Tong has more business than he can handle (I'll give him the benefit of the doubt).  He lives in Richardson TX, so I perhaps you could find a phone number and just call.

I moved on and bought a used xx12i Orion this past August. If I had seen your article before that, I would certainly be giving Tong a call. Very happy with the xx12i though.

 

If I ever go DIY, their mirrors will be on the top of my list.

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Chris Westland
Oct 06 2020 01:52 PM

Thank you for a great review. Very interesting read, for someone dreaming of making such an instrument ATM.

Could you please explain what these metal rulers are doing? I didn't understand, is it your own mod or was already in the scope?

Thank you for the kind words.  All of the scopes come with the cut metal ruler struts that hold the encoder.  Since the Az bearing is a Chinese lazy susan ring(a 转盘)you don't have the  center stud for mounting.  I'm guessing the factory that makes these are getting metal school rulers from the local office supply store in bulk (I have a bunch of these rulers that I brought back when we returned from China).  They look nice, and the rulings help assure that the encoder mount is dead center.  You don't have the same issue with the Altitude encoder strut, because it isn't fastened at the bottom.

 

BTW Dave Kriege gave an interview about 10 years ago where he described the operations at Obsession.  He said that the original idea for the company came from John Hudak of Galaxy Optics, who liked Kriege's structure, and realized he would sell more mirrors if he didn't require buyers to DIY their own structure.  Dave keeps about 200 scopes in production / inventory at any time.  Since HO's scopes are cheaper than Obsessions and they have to be 'containered' from China to the US/Europe/Australia/etc., I'm guessing that number may be a lot larger at HO, with mirror making and structure manufacture occurring at two separate source companies.  Dave is pretty amazing as he spends a lot of time with customers; the customer outreach is not as organized at HO as it is at Obsession.

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Chris Westland
Oct 06 2020 02:02 PM

I moved on and bought a used xx12i Orion this past August. If I had seen your article before that, I would certainly be giving Tong a call. Very happy with the xx12i though.

 

If I ever go DIY, their mirrors will be on the top of my list.

Check HO's site and eBay, as they are always selling a range of HO mirrors.  Particularly if you want a non-standard size/focal length, you can find them at these sites.  Also sale priced mirrors.

 

It is ... it seems to be a standard Dobsonian mirror mount (pictures below).   This should distribute weight well: it's a light, small mirror so the surface should be quite solid.  

 

Should I be looking for anything specifically?

 

Edge support is absolutely critical for thin mirrors.  Sandwich mirrors are essentially two thin plates with supporting pegs between them.  The belt type sling can transfer some of the stresses from one plate to the other, which may not be cooling in the same way.  Here is TOMDEY's edge support for a much larger sandwich mirror.

 

If your seeing permits, do some star testing over many many nights.  Look out for astigmatism especially.  Here is an article by Mike Lockwood's to pin down sources of star defects: Why aren't my stars round?.  His general article A modern guide to mirror support is a must read.  If you can notice defects, swapping to another edge support may help out a lot.  Belt slings are rather ancient by now.

 

Sandwich mirrors are very responsive to temperature changes, which is a great thing, but that responsiveness can induce wavefront errors if not supported well.



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