First Light: William Optics ZenithStar 66 SD

[Stratis]

Ok, I have to admit to a bit of uncertainty posting this initial review (and the follow-ups to come), on the grounds of relevance. William Optics have gone through a strange phase lately of pushing out numerous but ever-so-slightly distinct small refractors and then abruptly discontinuing the lines, only to release something yet again similar but different.

 

I am pressing ahead with this then, despite the fact that the entire ZS66 line is out of production, there don't seem to be suppliers holding any stock, and it has been superseded by a number of (technically) superior models. There is no reliable way of getting ahold of one, and finding this example was a total accident....

 

Thing is though, I love this tiny scope. Let me tell you why.

 

Background

I found myself looking for a scope this size out of a hatred of single-use parts. Some imagers I've met have a special little thing that is only used with this special other thing for this particular task and only on warm Tuesdays after Pentecost. Myself, I hate having 80% of my kit idle at any given time, instead I like to repurpose and re-use as much as possible. Sure I can buy a miniguider or an ST80 for a guidescope, but they're not really useful in any other role and that annoys me. 

 

Thus began my quest for a small, light, full-featured scope that could ride on the C8, guide the APO, and triple as a fully-fledged travel scope AND be useful for astroimaging on the road. A tall order indeed with a budget of low triple figures. Discarding the apparently awful TS Quadruplet, the definitely overpriced Borg Collective and the beautiful but just too damn heavy 80ED scopes from various sources, only the WO baby refractors remained.

 

 

When one came up on ABS, I had to have it; the William Optics ZS66 SD.

 

The Scope

The ZS66 was shipped in three versions; the 66 Petzval, the 66 ED Triplet, and the 66 SD Doublet. The Petzval variant was poorly received due to some serious CA issues unresolved by the Petzval elements, the Triplet is reported optically solid with a lack of contrast due to older coating technology and was too discontinued. The SD ('Special Dispersion') doublet hung in the longest, and after a few days with it I can see why. The coatings disparity is surprising, the ED version showing a bright purple reflection while the SD seems more neutral yet less visible. The 66 comes in lighter and almost two inches shorter than the other two designs.

 

 

First impressions, superb craftsmanship and a sense of style. This black-and-gold version has been dubbed "The Bling One" by my girlfriend and honestly looks more like something Iron Man should be using to defend freedom and justice. I know these scopes are marketed under many brands, but they must acquit each one with honour; the tube is light but substantial and heavy-feeling, the parts are smooth but solid metal, and not a single bit of anything moves unless you apply reasonable force. I would have preferred the option to mount a standard finder or RDS, but honestly this is not necessary.

 

 

The ZS66 has attracted some mixed reviews elsewhere, generally attracting terms like "Cracking little scope" but also mechanical complaints like "Loose focuser", "Rubbish focuser", and "Awful focuser". Naturally, upon getting the black-and-gold tube out of the case, the first thing I did was check this out. The scope comes with an SCT-threaded drawtube which is a lot more helpful than it may first sound; did I mention my love of dual-purpose? Well now I can re-use all my SCT-threaded accessories (which is nearly everything) to get a sound fixture without collimation trouble or slippage. Nice.

 

 

The focuser was absolutely fine, I attached a Canon 6D DSLR weighing nearly 1kg and pointed the scope skyward; not even 1mm of slip resulted. Perhaps I have just been extraordinarily lucky, but this one is solid as a rock and I wouldn't change it for anything. The axial rotation is perhaps a little over-stiff and requires a fair bit of muscle to turn, but I'd sooner have it that way around than too loose. The focus travel was butter-smooth both on coarse and fine, no grinding or sinusoidal characteristics. Attachment of some heavy accessories (see below) similarly revealed zero slippage despite over 1kg riding on an extended drawtube.

 

The Optics

This was my main concern when looking for a baby scope. I absolutely did not want an achro, I had an ST80 in the stable and honestly hated using it. I've also looked through some awkwardly-named 'semi-Apo' examples and hated each and every one. I'm very sensitive to CA and colour in general, blazing blue and green halos everywhere ruin the experience for me entirely. This scope is described simultaneously as 'Special Dispersion' and 'Apochromatic' by William Optics despite the doublet configuration and non-specified glass... I honestly expected the dreaded 'semi-Apo' performance, but was pleasantly surprised.

 

 

All of these tests were performed with a Revelation Quartz 99% Dielectric mirror diagonal and a TeleVue Ethos 8mm. The 8mm is a perfect match for this scope, pushing magnification to only 49x and serving a sharp and flat field. I'd have liked to push to 100x, but sadly I lack an appropriate EP and my only Barlow lens introduces colour into whatever it touches.

 

Strapping the oddly-proportioned WO L-bracket to a Vixen Mini Porta is a superb little combo that can be lifted with one hand easily; I learned that with most EPs, this scope doesn't need a finder, you should be able to eyeball anything. With typical refractor 'focus snap', I got a beautiful view of The Pleiades only slightly behind the Ostara 102 APO I image with, and honestly I feel that's a difference more in focal length. Limiting magnitude was an issue, the cluster looked distinctly empty compared to the same view in the large SCT, but the visible members were bright and hard pinpoints with minimal bloom and zero flare.

 

 

Swinging to Orion, the main stars showed their colours faithfully, Betelgeuse particularly a bronze-orange point demonstrating good CA control in the red spectrum. The view of the Nebula was rewarding, lack of light grasp rendered the core stars slightly dimmer but perhaps sharper than I am used to, with easily discerned nebulosity and colour despite poor seeing. I prefer the view through the 4" APO, but this entire setup weighs less than that OTA by itself. Compared to an ST80, it is obvious that WO have focused on coatings and careful spacing to make the most of the 66mm of aperture; I'd stand this scope toe-to-toe with an 80mm any day.

 

The standard CA torture test is Jupiter, so off we went, and here we see the inevitab.... oh wait, no, we don't. The giant which slew my ST80 and the SLT102 is himself brought low by this baby refractor, with beautifully resolved cloud bands and tiny little moons with only the very-barest-hint (did I mention I hate CA?) of faint far-violet. Once in focus, CA disappeared entirely, dominated many times over by atmospheric refraction. This view stood up to the 4" on sharpness and even made me glance sideways at the C8 for a moment, I honestly did not expect such a superb view from a scope I could fit in a camera bag and take hiking. It also reinforced my long-held impression that refractors rule the solar system, the much larger 1145P Newtonian cannot match the sharpness and contrast on display from the ZS66.

 

 

A series of star-tests revealed appalling atmospheric currents but crispy-black diffraction rings of even white colouration, perhaps a shade warm, with about half a rings-worth of glimmering violet outside of focus. This performance is inferior to the 4" Apo in only the strictest sense, it definitely belongs in the class of 'near-perfect doublets' and stands a breed apart from even fine, slow achromats. I tend to characterise CA by jibbing in and out of focus quickly by tiny amounts rather than examining diffraction rings; this revealed a slight tendency towards violet and none at all towards green, but nothing even remotely objectionable. Get your focus locked in and it's white little diamonds all the way.

 

The Verdict

As should be obvious, this scope is a keeper. Huge leaps forward in optical design notwithstanding, I can see no reason to ever deprive myself of this little gem. It is light enough to mount anywhere as a guidescope or super-finder, bright enough to view the better DSOs, sharp enough to image without vignetting a full-frame DSLR and small enough to lose in a large suitcase.

 

William Optics have a number of designs since this one, the ZS70 and Megrez 72 being the closest in aperture. These scopes have more furnishings, digital readouts and temperature gauges, as well as the bonus of better focusers and sturdier construction. All this however comes at a price of increased package weight, the 66 stays well under the competition here, although obviously can't compete with ultralights like the Borg.

 

 

Assuming I am not offered some remarkable Tak or TV mini-Apo at a superb price, I shall be making use of this scope for a good long while. I'd heartily recommend it to anyone as a travelscope, guidescope or light imager. It mounts on damn near anything and serves gorgeous views that belie its humble optical recipe.

 

Cracking little scope 

 

Clear skies everyone!

~Paul

[Naemeth]

It does make a nice little wide-field scope, doesn't it . I've got a clone of it that I use as my cycle scope.

[Stratis]

I think what impressed me most was the clarity of the optics.... there's something beautifully sharp about the way the scope delivers the view.

It's often said that the best camera lenses are functionally invisible and just stay out of the way of the photography.... definitely true of this family of tubes.

[Alien 13]

I think what impressed me most was the clarity of the optics.... there's something beautifully sharp about the way the scope delivers the view.

It's often said that the best camera lenses are functionally invisible and just stay out of the way of the photography.... definitely true of this family of tubes.

I will 2nd that i love my WO

Alan

[RobertI]

Bit late on this one, just read your great review Stratis thanks for taking the time to post it. I was interested to hear you views as I also have the ZS66 SD - mine is the orange tube version (possibly even more blingy!) I 'lucked in' really as I bought it as a super finder for my C8, but soon got into astro photography and realised it made a perfect light weight imaging scope which would not tax my modest CG5 mount. I also got the WO Flattener 2 which works great and has the added advantage that the focusser is almost completely wound in when in focus, meaning no 'droop' occurs, which I have heard can be an issue, though not witnessed it myself. I agree with all your comments about build quality and optics, I love this scope. You mention stiff axial rotation - I assume you mean rotating the focusser tube? I too had this problem, but cured it by undoing the three grub screws holding the focuser, removing the focusser and lightly greasing the rotating joint. It now rotates very smoothly and easily. I also have the megrez 72, which has the advantage of taking 2" eyepieces and a wider focusser tube but is significantly heavier (at least a kilogram heavier). The ZS66 SD is an incredibly versatile scope which I will definitely be keeping.

[RobertI]

I also got the WO Flattener 2

Actually it's the WO Flattener 6.......just in case anyone cares.......

[Martin Meredith]

Thanks for taking the time to put this extensive and frank review together. I love the (foreshortened!) picture of the Ethos on the scope. I wonder what a 21mm would look like, barlowed and all?

I'm in the same market: something for getting started in imaging, later as an auto-guider and travel scope. I'd been looking at the 80s but seeing some of the shots taken by the likes of the WO71mm makes me reconsider, as does your review.

Martin

[Rossco72]

I realise this was some time ago, however I have to stick up for my 66ED.

The colour correction is better than a TV pronto I owned, I compared them side by side and sold the Televue.

My focuser was OK but as I use the scope for imaging I fitted a feathertouch and think its about the ideal 2.5" scope.

Cheers

Stuart

[Chris]

Sorry for dragging the thread back up.

Great review and bang on the money I'm excited to be getting a WO ED66 SD back next week hopefully. I sold one a couple of years ago and regretted it since. This time I'm getting a snazzy metalic blue one!

As above I'm going to use it on my C8 for widefield imaging/guiding/super finder, plus also grab and go on the porta II mount with my ES100's and Vixen SLV's

I'm not making the same mistake twice! once received its hear to stay!

Edited November 16, 2014 by starfox

[RobertI]

Welcome back to the 66 fold Chris! Congratulations on your purchase. My 66D still doing good service, in fact I have just bought a Horizon Tripod for some quick grab and go with either of the two WOs.

[ollypenrice]

I have one of these as well, and a Pronto. I prefer the Pronto, personally, but it is heavier. However, I don't find the 66 focuser to be capable of carrying much. It was fine with a small CCD and manual filterwheel but would have no hope of holding my present CCD gear. That said, it couldn't cover a large chip so nobody would ask it to do so. It does give a nice visual image and is incredibly competent as a narrowband imaging scope on chips which it can cover. To be honest it isn't far behind a Baby Q in narrowband and with a small chip. Imaging in broadband does show its limitations, though. Stars are far bigger and less controlled than with the premium stuff, but what do you expect? I think it does well.

Since this review it might be worth noting that the little TS Quad has, it seems, had its pinched optics cured.

I'm not sure that I'd call my ZS66 a keeper but, then again, I've kept it and have no plans to sell it, so I guess maybe it is! I also started imaging with it so it has some sentimental value. I'll put one of my early attempts below. Atik 16HR, 13Nm Ha filter.

Olly

Edited November 18, 2014 by ollypenrice

[davidgr1976]

Welcome back to the 66 fold Chris! Congratulations on your purchase. My 66D still doing good service, in fact I have just bought a Horizon Tripod for some quick grab and go with either of the two WOs.

Hello,

I'm going to re-open this thread.

I've been testing my ZS66SD with SBIG STF8300M and the stars in the corners are very very elongated.

I don't if this is because large chip, flattener, weight of the ccd, miscollimation..... what is your opinion since i can see you have experience with this scope?

thank you!

[ronin]

Hello,

I'm going to re-open this thread.

I've been testing my ZS66SD with SBIG STF8300M and the stars in the corners are very very elongated.

I don't if this is because large chip, flattener, weight of the ccd, miscollimation..... what is your opinion since i can see you have experience with this scope?

thank you!

What flattener do you have on the ZS?

I assume that you have set the spacing correct for the flattener+camera.

I see the SBIG STF8300M has a big chip - 18x13.5mm. I wonder if the image circle produced is small then the sensor, so the corners lose out.

Edited May 29, 2015 by ronin

[RobertI]

Can you post the image so we can guage how elongated and the type of elongation? Is it the same in all four corners? I seem to recall my ZS66+WO Flattener 6+Canon EOS1100D was producing slight flaring in the corners, but nothing major.

[Chris]

From memory the WO 0.8 flattener reducer mk 2, 3, and 6 work reasonably well. 

Also I've found that the Altair 0.8 reducer works for a lot of scopes around f/6, and it's a snip at 75 pounds

[Chris]

Here is a pic of M31 taken with a WO66 and 1100D with APC size sensor (no flattener)

Does it look like this?

[davidgr1976]

Here is a pic of M31 taken with a WO66 and 1100D with APC size sensor (no flattener)

Does it look like this?

I think i have a skywatcher flattener ( ibought it second hand with the zs66sd and i doesn't appear nothing except "field flattener").

Here I pic of 600" in h-alfa:

thank you!

[Chris]

I think your corners are possibly a touch better than on my image without a flattener, but it's close.

Maybe try different spacing?

[davidgr1976]

If the flattener is an skywatcher one, it should be around 55mm.  I that sub is around 46mm. I tried with 55 and 60mm and the result is similar or worse....

[Chris]

Interesting. Can you try less than 46mm to see if it shows a trend? 

[davidgr1976]

Interesting. Can you try less than 46mm to see if it shows a trend? 

ok, I will try: 34 mm and 17. (I can't other spacings because I don't have rings for other distances). 

I will tell you. But this days are cloudy in Madrid....

thank you!!

[Chris]

I think it's cloudy everywhere by the sounds of it

[Stratis]

I am quietly thrilled this thread is still going... I'd taken a long break from AP as a new job ate all my waking hours, but I have that under control now and I've got a few new scopes in the stable.

The ZS66 of course, remains

I have just completed construction of a 50mm finderscope conversion into a guidescope for my Lodestar; if early tests are any indication it will guide up to 1500mm no problem so everything in my lineup is catered for, with a guide load of barely 250g. Seriously, if nobody's tried guiding with one of these setups they should, once the guidecam is screwed into the finderscope it is like an iron bar, no flex whatsoever and no possibility of focus slip. 

I have a field flattener yes, it's the Altair Astro cheapo one that reduces to 0.8x and flattens, I believe. I haven't tried it with the ZS66 yet but perhaps I ought to. Is anyone familiar with the proper spacing for those?

Edited June 27, 2015 by Stratis

[Thimitri]

Awesome thread.. glad I kept my ZS66SD..