0
William Optics Zenithstar 66mm ED
Jan 05 2006 02:24 AM |
matt
in 60mm - 78mm Refractors
Discuss this article in our forums
William Optics Zenithstar 66mm ED Apo triplet
The little scope that really could
Kicking the tires
The OTA came with a beautiful (read: overbuilt) gold dustcap and an SCT-thread 1 º” visual back. There has been discussion on why they chose an SCT thread rather than the 2” which has become standard for high-end refractors, but, well, here it is. The visual back is a compression-ring type, so it can come in handy to upgrade your SCT’s visual back as well!
The scope weighs 1650g (57 oz) on my kitchen scale “naked”, and 1900g (4 lbs) with diagonal and eyepiece in place – heavier than your run-of-the-mill short tube 80, but lighter than other small high end scopes which I think are way overbuilt. The tube is short, about 12 inches “folded” and extends to about 19” in “operating” mode, so it can ride piggyback on any scope.
In the Appendix you will find a chart showing the various dimensions you might need to know to fit your scope on your current rig or attach accessories to it.
The “main tube” is 5.4” long. That length is important - it means that, for example, your standard Vixen male dovetail bar is going to be too long to put rings that will attach the scope. You will need to customize something, or get a clamshell-type bracket to put it on your regular mount. It's the same kind of little headache as the finderscope thing; this is not the kind of scope you use right out of the box, unless you planned a few things in advance. And 72mm is not really a standard tube size, so rings will have to come from Parallax or another manufacturer of custom rings.
Uh, accessories anyone?
There is no provision to mount a finder scope of any kind, which is a pity. Some might think that a 460mm FL refractor does not need a finderscope, but I am of those who think that any scope needs one, all the more because I am unable to aim with a right-angle finderscope. When you have a beautiful OTA like that, the last thing you want to do is profane it with double-sided tape to attach a red-dot finder. Maybe you can attach a finderscope to tube rings if you use the thing attached with tube rings, not the Kodak-thread bracket.
Focuser
Optical Performance
First light, first scope
The first evening after receiving the scope was clear, so I knew something wrong was brewing. The scope was totally out of collimation. At 50x, Arcturus was showing a fan-shape. Mars was terrible. After a few utterly frustrating minutes, I decided to send back the scope to the store. I will never know if it was a bad sample or if it was damaged during shipment. I will pass on the details; a month later I had a new one. I believe that the packing was insufficient (the soft carry case put in a cardboard box with no extra padding) to protect the lens’s collimation when the French postmen played soccer with it. I should have ordered it from theBordeaux France
Optical testing
Star testing - first light, second scope
My first tests included the double-double in Lyra, always a favourite for casual double star observers. At 115x with the 2-4 Nagler zoom, the split was easy. At 92x with a 5mm Celestron Ultima, the split was still positive. At 61x with the 7.5 Ultima, the “dash – pipe” “shape” of the system was still evident, with the “dash” components kinda split, but not the “pipe” components (At 61x, my FS102 still gets a positive split). Comparing with the FS102 is not fair game, but you might be interested in knowing it was about a tie with my father’s 100mm Synta achromat – the achromat showing smudgier stars, but compensating by the aperture “oomph”.
When I get some really stable seeing, I’ll post a few start test images to settle the case. Stay tuned.
While we’re at it, I looked at Vega for signs of chromatic aberration. Maybe due to seeing conditions, the Airy rings were slightly fringed, and circles not really concentric, but the spurious disk (the luminous part of the Airy disk, which we often think of as the Airy disk) was pure white at the reasonable limit of 50x per inch of aperture (130x). Some purists will point out that I don’t know what chromatic aberration is because I once wrote a review stating that the Takahashi was an apochromat, but the idea is, to me chromatic aberration was almost undetectable, so unless your hobby is to spend nights looking at Capella and Vega at high power looking for traces of fringing, you can consider this scope colour-free. It’s better corrected, for example, than an Orion / SW 80mm ED (which shows signs of CA but on which you can consider the CA does not affect resolution or contrast). It sends the venerable Pronto (not long ago the small scope against which all other small scopes are measured, and which still appears on the used market for the price of a new Z66ED) straight to the Chromatic Aberration Historical Society Hale of Fame. OK, we had said no names, but at least these are fairly common telescopes so they might serve you as comparison points.
Planetary observing
Mars was gibbous and about 13”: the WO66 showed it with its phase and a hint of surface markings. The image was sharp all the way to max magnification, but with no improvement over 120x. Here the views were better than on the 100mm achromat which has so-so contrast. On Saturn, the Cassini division was well seen at the “ears” and an equatorial band was visible. Here the 100mm does noticeably better – the contrast is not as much a problem on Saturn as on Mars. On Venus, a fine crescent was visible (ok, no real surprise) with some red-blue colouring probably due to atmospheric refraction, while the 100mm was showing plenty chromatic aberration.
I had only a few glimpses at the Moon; the detail was very good all the way to the magnification limit, with no image degrading. I tried to detect chromatic aberration by looking at the limb, but only saw an orangish tint at the South tip probably due to atmospheric refraction or the eyepiece used.
Conclusion
Note: there are as many cons as pros, but the pros far outweigh the cons. The cons are either the limitations inherent to this type of scope, or signs of a product which just came to market and will probably be followed by accessories.
Note 2: in my draft, I had written as a “con” the old cliché “66mm is only 66mm”. After a few outings with the scope I knew better.
Appendices
Matt’s world famous size chart!
The little scope that really could
|
Those of you familiar with Cloudynights and online-astrostuff-ad websites know that I own a lot of telescopes (4 or 5 at any given time) and have owned even more (I kinda lost track around 20; I must have owned 30 of these things). I have owned scopes in 60mm, 80mm (3.1"), 90mm, 100mm, 102mm, 127mm, 150mm, 203mm, 235mm, 280mm, 304mm and 406mm (16") apertures. Those of you will notice the absence of scopes in 10" and 13.5" diameters, but I hope you will not dismiss my review because of that flaw. On one hand, I had a “gift certificate” for an astro-purchase; on the other, I had a discussion with our own Tom Trusock about small apochromats after his own experience with this scope, the FS60 and the TV60, and at my umpteenth question, Tom said “Matt, Just buy one!”. Aaaaaaargh! So I obeyed him. And obviously I am not the only one; small William Optics refractors are the buzz in astronomy circles these days, as they seem to have made-in-China-level prices with an optical quality and a fit and finish which used to be the hallmark of much pricier Japanese and American scopes (we said no names!). As I type these words, WO offers 66mm in four (4) different designs (fluorite doublet, SD doublet, ED triplet, Petzval quad) , which makes following industry news exciting but also slightly confusing. Mine is a 66mm, f/7 triplet with an ED element. The mid-range f/ratio, small aperture, number of elements and use of ED glass are all indicators that this should be a true apochromatic telescope. |
Kicking the tires
|
The scope came in a soft-sided carry case, itself in a small carboard box. My first thought was: when will they learn to make a carry case where you can keep the diagonal, and perhaps an eyepiece, in place? If it is really a grab-and-go instrument, should you not be allowed to keep it in its bag ready to observe? Not to mention the fact that keeping the diagonal in place when you observe away from home is one fewer occasion to have dust entering the tube and accessories falling to the ground. Other than that it’s very convenient. You can throw in your “vital” eyepieces, diagonal, and the occasional astronomy magazine. It’s a little strange the “magazine” side of the case is not padded (I had some º” foam so I stuffed a sheet in the magazine pocket). It is more than airline portable – it could fit in the glovebox of a large car. The padding is certainly enough to protect the scope against the little hits it could take while you carry it around. Actually I discovered that driving back home. I picked up the package in |
|
The OTA came with a beautiful (read: overbuilt) gold dustcap and an SCT-thread 1 º” visual back. There has been discussion on why they chose an SCT thread rather than the 2” which has become standard for high-end refractors, but, well, here it is. The visual back is a compression-ring type, so it can come in handy to upgrade your SCT’s visual back as well!
The scope weighs 1650g (57 oz) on my kitchen scale “naked”, and 1900g (4 lbs) with diagonal and eyepiece in place – heavier than your run-of-the-mill short tube 80, but lighter than other small high end scopes which I think are way overbuilt. The tube is short, about 12 inches “folded” and extends to about 19” in “operating” mode, so it can ride piggyback on any scope.
In the Appendix you will find a chart showing the various dimensions you might need to know to fit your scope on your current rig or attach accessories to it.
The “main tube” is 5.4” long. That length is important - it means that, for example, your standard Vixen male dovetail bar is going to be too long to put rings that will attach the scope. You will need to customize something, or get a clamshell-type bracket to put it on your regular mount. It's the same kind of little headache as the finderscope thing; this is not the kind of scope you use right out of the box, unless you planned a few things in advance. And 72mm is not really a standard tube size, so rings will have to come from Parallax or another manufacturer of custom rings.
Uh, accessories anyone?
There is no provision to mount a finder scope of any kind, which is a pity. Some might think that a 460mm FL refractor does not need a finderscope, but I am of those who think that any scope needs one, all the more because I am unable to aim with a right-angle finderscope. When you have a beautiful OTA like that, the last thing you want to do is profane it with double-sided tape to attach a red-dot finder. Maybe you can attach a finderscope to tube rings if you use the thing attached with tube rings, not the Kodak-thread bracket.
Focuser
|
The focuser is a Crayford unit. It is very, very smooth; smoother than the Nexstar5 unit which I considered best of all cat focusers, smoother than the FS102’s which is also considered excellent. The only complaint is that mine came totally loose, meaning that it was slipping all the way down quite abruptly everytime I pointed the scope upwards (which happens when you are an astronomer). I would have liked a manual at that point, because I was not really sure of what screws had to be tightened to adjust the focuser’s tension and I did not want something to come apart or get damaged. I have used a ton of telescopes so I found out rather quickly, but it might be an unpleasant experience for a beginner observer or one who has never used a Crayford. Testament to the focuser’s quality, it’s very easy to find a “just right” setting – you don’t spend your time fidgeting between a “too tight” and “too loose” settings, even when changing eyepieces. I was about to forget the focuser is rotatable, a feature useful for astrophotographers to adjust camera angle, or to have the (beautiful btw) focus knobs in a convenient position when using the scope on an equatorial mount. I think the feature is a luxury, but hey, I will take it. I just checked one thing – the optics, ota and focuser are perfectly aligned, as rotating the focuser did not affect collimation. |
|
|
Business end The OTA has a sliding dew shield (without a tightening screw) which works well. The lens appears coated with a pale purple colour, brighter than on the Takahashi, about as bright as on the Nighthawk. In good light, one sees that the interior is baffled with ridges, not knife-edge baffles. The documentation states 10 ridges, my picture appears to show 11 – maybe it shows something which does not qualify as a ridge! |
Optical Performance
First light, first scope
The first evening after receiving the scope was clear, so I knew something wrong was brewing. The scope was totally out of collimation. At 50x, Arcturus was showing a fan-shape. Mars was terrible. After a few utterly frustrating minutes, I decided to send back the scope to the store. I will never know if it was a bad sample or if it was damaged during shipment. I will pass on the details; a month later I had a new one. I believe that the packing was insufficient (the soft carry case put in a cardboard box with no extra padding) to protect the lens’s collimation when the French postmen played soccer with it. I should have ordered it from the
Optical testing
Star testing - first light, second scope
My first tests included the double-double in Lyra, always a favourite for casual double star observers. At 115x with the 2-4 Nagler zoom, the split was easy. At 92x with a 5mm Celestron Ultima, the split was still positive. At 61x with the 7.5 Ultima, the “dash – pipe” “shape” of the system was still evident, with the “dash” components kinda split, but not the “pipe” components (At 61x, my FS102 still gets a positive split). Comparing with the FS102 is not fair game, but you might be interested in knowing it was about a tie with my father’s 100mm Synta achromat – the achromat showing smudgier stars, but compensating by the aperture “oomph”.
When I get some really stable seeing, I’ll post a few start test images to settle the case. Stay tuned.
While we’re at it, I looked at Vega for signs of chromatic aberration. Maybe due to seeing conditions, the Airy rings were slightly fringed, and circles not really concentric, but the spurious disk (the luminous part of the Airy disk, which we often think of as the Airy disk) was pure white at the reasonable limit of 50x per inch of aperture (130x). Some purists will point out that I don’t know what chromatic aberration is because I once wrote a review stating that the Takahashi was an apochromat, but the idea is, to me chromatic aberration was almost undetectable, so unless your hobby is to spend nights looking at Capella and Vega at high power looking for traces of fringing, you can consider this scope colour-free. It’s better corrected, for example, than an Orion / SW 80mm ED (which shows signs of CA but on which you can consider the CA does not affect resolution or contrast). It sends the venerable Pronto (not long ago the small scope against which all other small scopes are measured, and which still appears on the used market for the price of a new Z66ED) straight to the Chromatic Aberration Historical Society Hale of Fame. OK, we had said no names, but at least these are fairly common telescopes so they might serve you as comparison points.
Planetary observing
Mars was gibbous and about 13”: the WO66 showed it with its phase and a hint of surface markings. The image was sharp all the way to max magnification, but with no improvement over 120x. Here the views were better than on the 100mm achromat which has so-so contrast. On Saturn, the Cassini division was well seen at the “ears” and an equatorial band was visible. Here the 100mm does noticeably better – the contrast is not as much a problem on Saturn as on Mars. On Venus, a fine crescent was visible (ok, no real surprise) with some red-blue colouring probably due to atmospheric refraction, while the 100mm was showing plenty chromatic aberration.
I had only a few glimpses at the Moon; the detail was very good all the way to the magnification limit, with no image degrading. I tried to detect chromatic aberration by looking at the limb, but only saw an orangish tint at the South tip probably due to atmospheric refraction or the eyepiece used.
Another pic, just for the pleasure… |
Deep sky observing You will see down there that my conclusion that 66mm is still 66mm, but hey… This scope is a surprise. On M42, the views under a good sky are better than in a “suburban” 8”. It does not show a very large extent, but the little mottling at the centre which makes M42 so exciting, as well as M43 and the Running Man nebula nearby. The trapezium shows 4 stars (I was hoping for 5!), but the 4th component seems dim and I think it cannot show the E component because it is too faint, not because of a resolution problem. Still in Orion, M78 was visible (less bright than in the 100mm of course, with comparable detail – or lack thereof), as well as the Flame Nebula near Zeta. I did not see the Horsehead; anyway, you would not have believed me  . The view of M31- NGC205 – M32 was a breathtaking
panorama with the 24mm panoptic (19x) thanks to a contrast you will not find
in binoculars; M33 did not show spiral arms of course, but the
“feeling” that you are seeing a rotating disk is there (a little like when
you look at M51 through a 6”: you don’t see the arms but you see this is not
just an oval blob).
So 66mm is 66mm (or 2.6”), but it definitely overachieves on deep sky, and a lot of usual targets take a new and pleasant appearance here. |
|
Terrestrial observing I’m not a birder, just use the scope in the daytime casually, but a few words: - even on very contrasted objects (dark poles against bright sky, etc), I did not see any CA or image distortion. - The scope is definitely backpack portable, though you will want to put it in some extra protection to avoid scratches (I use a “widowed” rugby sock) - At 4lbs, it takes a pretty sturdy tripod to get good images, so when you hike, carrying a tripod will be more of a problem than carrying the scope. The tripod on the photo at left, for example, is only OK for casual viewing around 50x. |
Conclusion
|
What do I like in this scope? It delivered what I expected: You get a scope with excellent optics and excellent mechanics for a very little price. You can set it up in a matter of seconds – I can grab the eyepiece case in one hand, the scope on its photo tripod in the other, and just go out. Actually the eyepiece case is bigger. It’s also a scope that can really follow you anywhere. The downside is, for the same price you could have a mid-sized scope of decent mechanics and optics, which would deliver better views of pretty much everything. But if you are an aperture hog with a soft spot in your heart for exquisitely-made scopes, this can satisfy your craving without having to get a 4" apo. |
|
|
Pros - excellent optics (no noticeable CA, great contrast, magnifies well) - F/7 f/ratio makes both high- and low-power work easy. - excellent mechanical build (dewshield, focuser) - for $500, you too can have a heirloom apochromatic refractor! - cute |
Cons - few mounting options. Mr Yang, please make some 72mm I.D. rings! - no provision to mount a finderscope - focuser travel limits accessory options - you will want a 3-6mm Nagler zoom in a hurry with this scope! |
Note: there are as many cons as pros, but the pros far outweigh the cons. The cons are either the limitations inherent to this type of scope, or signs of a product which just came to market and will probably be followed by accessories.
Note 2: in my draft, I had written as a “con” the old cliché “66mm is only 66mm”. After a few outings with the scope I knew better.
|
who is it for? veterans who want a small or portable, yet excellent, telescope people who really want to have a quality, apochromatic refractor, but are not insane enough to shell out the $2,500 for your typical 4" Apo OTA. people who already own 4 scopes but really want another one. |
who is it not for? - beginners who might not appreciate fully the scope's qualities, and rather need a larger scope - definetely not a "one and only scope", more a second, if not third, scope. |
|
A homemade cradle for setting the scope on a Vixen-type mount |
Appendices
|
Various configurations tested: I had planned on testing the scope with a bunch of accessories, but actually, the 60mm of focuser travel prove insufficient for most of the cases I had planned on testing. Basically, this scope is made to use with a 1 º” diagonal and that’s it. WO writes in its literature that the scope can use its 2” SCT diagonal. On my side I used a 2” SCT visual back and a 2” mirror diagonal and could not reach focus with a 2” eyepiece. CAVEAT EMPTOR: I used a 2” SCT v.b. sold by Scopestuff.com, which works perfectly well on my C9.25 but here it wiggled on the thread: at first I thought it was too wide, but I realized the problem is that there is nothing between the focuser and V.B. to “stop” the screwing, which is actually what makes the screwing tight. Stock visual back and 1º” diagonal YES Stock visual back and 1º” diagonal, barlow after YES Stock visual back and 1º” diagonal, barlow before NO Stock visual back, SCT f/6.3 focal reducer, and 1º” diagonal NO Stock visual back, straight through NO Stock visual back, straight through, 2x Barlow NO Stock visual back, f/6.3 focal reducer straight through NO 2” visual back, straight through NO 2” visual back, 2” diagonal NO I’m did not go through testing both mirror and prism diagonals thoroughly, but I used a takahashi prism diagonal, a Synta mirror diagonal, and a Televue Everbrite 1 º” diagonal successfully, and feel pretty confident that a configuration working with one of them would work with the others. I will not dwell over the impossibility of using 2” stuff in my tests – in my opinion there is little point in getting a 3lb telescope, and then loading it with accessories heavier than the OTA. My primary widefield eyepieces on this scope are the 24mm panoptic (19x, 3,5° TFOV) and a 32mm plossl (14x, 3,5° TFOV). If I want 10x power, my binoculars are easier to use than a 35mm panoptic. |
Matt’s world famous size chart!