Two Tiny Apos from
The 66 SD Doublet and 66 ED Triplet
Trusock – 2/06
Left - Triplet, Right -
Optics 66 SD Doublet - $398
Dual Speed Focuser
correction not quite the same level as the Triplet
Optics 66 ED Triplet - $498/$548
not as flat as I’d hoped
Dual speed focuser is $50 extra (if purchased with scope)
telescopes - seems like I've seen a ton of them this past year. From
the WO 66 petzval, to the Tak FS60c, the TV60 and a ton of
different 80mm telescopes from various vendors – and I’m getting the
feeling that I’ve seen a pretty good sample of the different offerings
Right up front I’d point out that these tiny telescopes aren't for
everyone. When we’re talking about the apos - for their size,
they can be very expensive. Even the least pricey often costs as
much as an inexpensive 6 or 8 inch dob which should show you far more-
at least that's the traditional thinking, right?
And let's be honest – a 60 or 66mm telescope is a small scope. Very
small. In fact, their size has had some of the forum members
asking “What good’s a 66mm telescope anyway?” There are a lot of
comments to the effect of: “I always think 80mm is the bare minimum.”
I guess it all depends on your perspective. You could always extend
that to ask; “What good’s a 3.1 inch telescope scope anyway?” I
mean I’m not going to be pulling out the Hicksons with it, right? For
that matter – what good’s an 8” or a 12” if those are your intended
targets? I tend to think of telescopes like fishing
gear. You’ve got your lightweight tackle for small lakes and
streams, and deep sea setups for those who prefer to go
deep. While I’ll grant that I wouldn’t want one of these
for an only or first telescope I can have as much fun with a small
telescope as I can with a big one. Personally, I think there’s a
place for all apertures.
As a matter of fact, as I write this, I just got in from an impromptu
session with one of the two new scopes WO shipped me directly - their
66mm SD doublet. I'd not been feeling well all day, and although
I watch the weather on a habitual basis, I'd seen nothing that would
even think I'd spend any time at all outside. Both Weather
Underground and the Clear Sky Clock had predicted cloudy skies for the
entire day, and it looked like that was going to be the case. So
I spent the evening with the family and put in a little time on
CN. As I sat down to watch a little TV, I noticed the moon
peeking in and out of clouds through one of the windows, but didn't
give it much thought. An hour or so later I took the garbage out,
and was startled to look up into a crystal clear sky.
This was where the ultra light, ultra portable scope came in
handy. My FS102 and 18" Obsession were both in the garage, but
both mounts require power and are - well - not exactly lightweight tiny
things (particularly when you consider the mounts). The 66mm SD
doublet OTOH - that I can simply leave setup on a lightweight camera
tripod, grab two eyepieces and be out observing in a matter of minutes.
So I did just that.
In quick succession, I hit M31, the double cluster, M103, several of
the NGC's in Cass, M45, M1 and more. It was a 20 minute quick fix
that I wouldn't have had otherwise.
And people still ask what good tiny scopes are.
In any case, this article is really about two different scopes: The
William Optics 66mm ED triplet, and their newer SD doublet.
Triplet (front), is about 2 inches longer than the Doublet (rear)
The standard 66mm ED triplet comes with a single speed focuser, and the
doublet with a dual speed – (more on that later). Both came
with the standard black anodized ZenithStar finish, L bracket for
mounting, rotateable Crayford 1.6” focuser, retractable lens shade,
press on lens cap and 1.25" visual back. The doublet's drawtube
was calibrated, and it comes standard with the dual speed
focuser. The visual back on the 66mm WO scopes is a little
different in that it's threaded for SCT accessories. If you want
to use a 2" diagonal with the scope, all you need to do is unscrew the
1.25" visual back, and screw on a 2" SCT adapter - be warned though,
many users experience focus travel issues when using non-Williams SCT
diagonals so if you are going to go this route, I'd recommend that you
check on which diagonals will come to focus and which ones
won’t. I own one of their Quartz Pyrex SCT Dielectrics (an
excellent diagonal), and that was what I used on the refractors for
the test period.
Both use the now standard cone baffle system. While both list 10
baffles, that’s not completely accurate – there are 10 ridges on the
cone, and the edge of the cone itself serves as a true baffle. In any
case both scopes are acceptably well baffled.
Mechanics (on both scopes) are top notch. The new two speed
focuser is a joy to use (particularly on their faster telescopes) and
previously noted is standard on the doublet, and is available as a
retrofit for the triplet at around $150 or at initial purchase for an
additional $50. Like many on the market,
it replaces a focus knob. If you install it yourself, you can
install it on either side of the OTA, but if it comes fitted it seems
to come on the right side as standard. It provides an inner knob
with standard or coarse focus, and an outer knob that provides 10-1
reduction. Tension needed to move the outer knob is extremely
light - simply a fingertip's pressure is needed.
Some users have complained about a sinusoidal feeling in the coarse
focus. After looking at several of these focusers, I’ve typically
found this is caused when the fine focus is not adjusted
correctly. Timm Bottoni goes into this in a bit more
detail in his article about the “William
Optics 2-Speed Microfocuser”.
The doublet is a TMB design that is 2 inches shorter than the triplet,
and slightly lighter. William Optics lists the focal length of the
doublet at 388mm and 460mm for the
triplet. Please note that I did not verify this experimentally.
Left - Doublet, Right -
The coatings on the doublet were unquestionably better than those on
the triplet. I've seen a few WO scopes at this point, and
frankly, these coatings looked better than anything else I've
seen. Close inspection revealed a lens cell touting STM
coatings - since I'd not heard of these, I contacted WO directly and
was told this was a new type of coating designed to provide better
transmission than other coatings used in the past. STM
stands for Super Transmission Coatings - whatever they call it, it
certainly works. The lens virtually disappears on the 66 doublet
- note the photo above. I'd be very surprised if WO does
not make these their standard coatings from here on out. Indeed,
it looks like the new ZenithStar 80 Fluorite Doublet (anniversary
edition) has also shipped with these coatings, and hopefully this is
their new standard.
The coatings on the triplet, on the other hand, are the more common
purple coatings one has come to expect.
While the doublet came in black and gold, Mr. Yang shipped me two
different versions of the triplet – the first with standard black
anodizing, while the second came tricked out in a deep red with black
and gold trim. With its gold lens cap, this has to be one of the
prettiest telescopes I think I've seen. While the the red version
of the 66 triplet is not yet on the shelves, I've been told it should
be shipping shortly.
triplet w/ dew shield retracted
The red triplet came standard with the dual speed focuser, while the
black triplet arrived with a single speed crayford. The the
triplet is offered with the dual speed focuer for an extra $50.
Users who have previously purchased the triplet can also purchase an
upgrade to the dual speed focuser for $148.
Optical Evaluations (Visual)
The triplet is noticeably longer and heavier than the doublet and takes
a bit more time to cool down. It’s winter here in the eastern
mid-west (we have four seasons: pre-winter, nearly winter, winter and
post winter) so I've had several opportunities to see how well (or
poorly) these scopes handle significant temperature changes.
not uncommon to see signs of pinched optics or spherical aberration in
a refractor during cool down, even in far more expensive telescopes,
these have surprised me. I've yet to see any serious issue with
either. To me, that marks a well designed lens cell, and is an
important consideration for northern users.
The field visually appeared slightly flatter on the triplet (however,
interestingly enough, preliminary photographic results don’t appear to
be bearing out a very flat field for the triplet – more on that later),
and the color correction is definitely a step better. While in
focus false color is virtually non-existent, the doublet revealed what
I would consider to be typical of a good ED/SD
doublet. Out of focus color on bright targets was green/yellow on
one side of focus, and purple on the other. The triplet - well,
there was pretty much no false color. Zip, Zero, Zilch - or to
use one of my young daughter's favorite words – Nada. No signs of
color either in focus or out.
While both views were exceptionally good for refractors of this size, I
actually liked the doublet just a touch better – although it has
slightly greater chromatic aberration, it also seems to have a bit more
contrast. I don't know if it was the improved coatings or
one less optical element, but I suspect they both had a little to do
While DSO views were quite good (the colors of individual stars in open
clusters just seemed to "pop" with both scopes), it was the moon that I
found most rewarding. There's SO much that a small refractor can
show you on Luna, it's not funny - even one as small as 2.4 inches.
TFOV on these scopes is around 7 degrees
These are extremely versatile telescopes – while they are fantastic low
field scanners yielding a maximum field size of around 7 degrees, they
also effectively provide magnifications that top out around
Image Credit SkyMap Pro
While 66mm is a very small amount of aperture it's amazing what you can
see with it - providing of course, you know what to look for. These
ultra small telescopes require almost more of a binocular mindset
(although granted it’s more of a binocular that can vary its
magnification from 7x to 140x). I’d recommend that owners
types of telescopes take a look at the book “Binocular Astronomy” by Crossen and Tirion –
think of it as a Burnhams Celestial Handbook for binoculars with a
copy of Tirion’s Bright Star Atlas included in the back.
In regards to their maximum magnification - while they could be pushed
higher, and it certainly was fun to do so at times, I never felt there
was any more detail revealed. In addition, on anything other than
the moon and bright planets, you tend to run out of light fairly
quickly. Let’s face it - 2.4" is not an overly large amount of
When viewing DSO's, I found I mainly used two different eyepieces - a
28 or 42mm 58 deg AFOV eyepiece from Olivon Optics (see the CN report
in the eyepieces section for details on this line) whose light
weight seemed to make them a perfect match for the 66's, and a 13mm t6
Nagler. These low power lightweight eyepieces made
excellent finders and I found that most of the time, I didn't even
bother with the WO RDF (red dot finder). The 13mm t6 presented a
image which added enough magnification to study the larger DSO's in
detail, while providing a nice, dark sky background and typically
framing the object quite well. For those high power planetary and
lunar views, I found I reached most often for my Nagler 3-6 zoom.
After given sufficient time to cool down, both scopes proved themselves
to be of decent quality optically. No, they (for the most part)
aren’t Tak FS60C killers, but they are ˝ the price – less if you
include the accessories.
Several of us did get a chance to side by side the Tak FS60C with the
WO 66ED triplet, and we felt that while the stars were a touch tighter
the Tak, we were quick to notice the WO’s 10% aperture advantage, and
all of us thought the views were quite comparable. While we all
liked the Tak just a tiny bit better, we all agreed that for the money,
the WO Triplet was a much better buy – at least for a visual observer.
While I didn’t get a chance to side by side the doublet with the Tak, I
feel it’s very comparable to the Triplet in most areas, and as far as
these particular samples go, may actually have slightly better optics
Both 66’s provided good views of the brighter deep sky objects, luna
and the planets. While there’d not be a lot of planetary detail
available in a 66mm telescope, you can expect to see Saturn’s rings, a
few bands on Jupiter, and during the opposition, some of the markings
on the surface of Mars.
Your mount consideration, ironically, may be one of the more important
sections of this article. Proponents of the “80mm as a minimum”
argument often forget one crucial component – you have to mount these
guys. A 66mm scope (especially the doublet) is typically lighter
than an 80mm – this means you can get by with a substantially smaller
and lighter tripod – not an unimportant concern if you are looking for
the ultimate in portability.
Triplet and Microstar take a business trip to Mexico
Courtesy Gary Gibbs
There were three mount setups that I used during the review period -
the first being the MicroStar Deluxe mounted on two Bogen tripods (3001
and 3036). In my opinion, this mount has several advantages to
other lightweight travel mounts on the market. First off, it's
fairly inexpensive; secondly, it's very lightweight and compact. The
dovetail plate that comes with the deluxe version not only allows
you to swap scopes quickly, it also allows you to balance the Optical
Tube by sliding it backwards and forwards in the mounting, and it’s
compatible with the GP/CG5/LXD standard. Its one disadvantage (at
least in use with the doublet) is that the
doublet was so short, I couldn't take advantage of the rotatable
focuser to put the knobs in their usual position, and wound up with the
focus knobs in a vertical position (this might be possible with a
shorter dovetail). While I wasn’t initially all that hot on this
arrangement (it’s funny what we get accustomed to), after a minor
adjustment, this proved to be much smaller an issue than I had
thought. The triplet, being two inches longer and with a
different weight distribution, did not have this problem.
While it’s not the best way to mount these scopes, due to their
extremely small size and weight, you could also mount them on a small
photo tripod. I will note that due to it’s smaller size (2”
shorter) and slightly lighter weight, the doublet rode much better on
the standard photo tripod. I wouldn't want to use it at high
power in that arrangement, but up to about 50x or so with a fairly wide
field eyepiece it worked acceptably well.
- triplet, Right - doublet
The third option I used was the new WO EZ-Touch mount which can be seen
in several of the pictures accompanying the article. I recently
acquired this mount, and will be offering some comments on it in an
upcoming review of the William Optics 105 triplet. Let’s just say
that if you are looking for an alt/az mount in the $500 class range (w/
tripod) this is an excellent contender. About its only drawback
is in its apparent lack of ability to mount encoders for those desiring
computerized pointing. However, since you’ll mainly be using this
mount for scopes 4” and under, this really isn’t that big of an issue.
|Sidebar - A Word on SD
and ED glasses:
The terms ED and SD were (to the best of
my knowledge) invented by the
camera companies a couple of decades ago. Both describe a family
glasses with abbe numbers in the (approximately) 70 plus range. Both
were initially used as marketing terms to indicate to the consumer that
there were glasses contained in the lenses which had Extra Dispersion
or Special Dispersion properties to better control chromatic
aberration. Today, while the term in use is generally ED, SD is
as I am aware, perfectly acceptable – if a bit uncommon – at least in
the US. The most often used ED glasses in today’s scopes have
numbers generally on the level of FPL-51, FPL-52 or most commonly
FPL-53. You should note that these really aren’t the names of the
glasses – they are catalog numbers. They will vary depending on
supplier you get it from. While the glasses from different
may not be exactly the same, they are usually fairly close. If
interested in the different companies offerings, you may wish to check
out GlassBank – a very nice
resource for the amateur - http://glassbank.ifmo.ru/eng/
One final note – there’s been a lot of discussion comparing an FPL-53
type glass to fluorite, and it comes complete with a number of several
common misconceptions. The only statement I’m going to make on
topic (at least in this article) is that FPL-53 (or an analogue from a
different company) is nearly visually indistinguishable, and lastly
I’ll point out that the abbe number for fluorite is just over 95, while
that of FPL-53 is just slightly lower. For comparison, FPL-51 is around 81, and FPL-52 around 90. It should be noted that WO at this time has not stated definitively which glasses are used in their telescopes.
Visually, I tend to prefer doublets. But a triplet, in theory,
should be a better photographic performer. With this in mind, a
few friends and I undertook the task of trying to get a handle on the
photographic performance of the triplet.
There has been some debate about a finished photo’s ability to truly
represent the capability of the lens – some think that you can’t tell
much if anything about how the telescope performs from a final
image. Frankly, I disagree. I don’t care how much post
processing went into the shot, the pretty pictures that come out of
that telescope are representative of its final potential as a
photographic lens. You may have to perform a lot of manipulation
to get it to that point, but the images show what’s possible for a
However, after considerable discussion, I decided that it would be more
instructive to offer a raw, completely unprocessed photo – straight out
of the camera. Those seeking finished photos can find them in
various locations on the net. For this test, Joe Bruessow, a
good friend of mine - offered to take the following image.
Sample Image - Resized
We’re looking at an image of M35 and its companion NGC2158. This
is from an ST-2000XM, with a KAI-2020 sensor (1600x1200 pixels),
unbinned, with an exposure length of 1 minute. This image has had
nothing done to it in terms of processing - not even dark frame
Performance - 100%
I’ve resized it and converted it to a jpeg so it can be displayed in
the article, and have cropped a corner and the center of the image to
display at full size so the reader can see the effect of field
curvature at its worst points and best points.
Performance - 100%
The chip used is a medium sized sensor. Field curvature would
most likely be more severe if a larger chip was used.
Crop - 100%
In the NGC2158 crop above, note
the resolution and number of stars - IMO, it is pretty amazing what can
be done with such a short exposure and small telescope.
Another good friend, Jeff Thrush, provided some analysis of this image
and supplied the shown visualizations of field flatness by using
CCDInspector. I’m deliberately choosing not to include the
specific numbers here because of the fact that we were somewhat limited
in time due to weather constraints.
Visualization of the triplet's field flatness - Angle 1
We agreed that the actual numbers generated by CCDInspector were
somewhat suspect in this case; most likely due to several issues
including poor seeing as well as less than perfect guiding and
focusing. Time restrictions limited our ability to continue
Visualization of the triplet's field flatness - Angle 2
My thanks go out to both Jeff and Joe for their assistance in this
From what I understand there has been some experimentation with SCT
field flatteners / focal reducers – given the back of these scopes is
threaded for SCT accessories, this seems an obvious thing to try. For
more details on how these work with the scopes, as well as some samples
of fully processed astrophotos, try checking the
William Optics Yahoo Group or our own forums.
Although we concentrated mainly on the triplet for seemingly obvious
reasons (to us at the time anyway), I’d like to eventually amend this
article with similar data about the 66 SD Doublet. Assuming, of
course, that time and circumstances permit.
So – which would I pick?
Well, I’m a visual observer through and through and with these types of
scopes, I’m looking for the ultimate in portability. I want
something as small and as light as possible. Plus, as a visual
observer who has probably used more than his fair share of refractors,
I’ve found I tend to prefer doublets as a general rule. I often
find they have a tiny bit more pop/contrast/image sharpness than a
comparable triplet. They also tend to cool down a bit
quicker. True, the color correction usually isn’t quite as good
as in the triplet, but it’s good enough for (my) visual purposes.
Others may feel differently, depending on their own preferences.
Choosing between the WO66 Doublet and Triplet, given the smaller size
(although not by much), lighter weight (although not by much), the
standard 2-speed focuser, and lower cost - I’ll personally take the
doublet for visual use. If I wanted slightly improved color
correction, I'd opt for the Triplet.
While the optical quality is not quite
up to Tak or TV standards (it's close though), these scopes are
about ˝ the cost or even less, if you consider they come with
very nice cases as standard equipment, and the fit and finish is quite
If you're in love with small refractors, looking for an ultra portable
apo, or want a dual purpose birding / quick look astro scope, then for
these prices – they are nearly no brainers. Because of the very small
aperture, I wouldn't recommend this as an only or a beginner
telescope. For that I'd still recommend a 6 – 8 inch dob.
finish on both scopes is
typical of WO products.
Finally, a word about WO, their philosophy and their telescopes in
general might be appropriate.
With all the raving that's going on about WO scopes and equipment
lately, someone might get the wrong idea about where their products lie
in the market.
William told me at NEAF last year that his goal was to make good
quality optics available at reasonable prices to the average
astronomer. Apo's are expensive - he wants to make them affordable.
Don't pick one of these up expecting an optical Tak killer, or the
refined in-depth design elements of a Tele Vue or other top dollar
design. If you are the type of person who demands absolute perfection,
you'd probably be better off on the AP list. Don't get me wrong, the
WO's are great scopes, but I've talked with David (NA Rep) extensively
about this, and (with a few exceptions - the FLT-110 comes to mind), in
WO really isn't trying to hit that market. What they
are trying to do
is provide an excellent bang for the buck. They are
shooting for the middle market - in short, they're not going for
perfection, but for "good enough". And from what I've seen, they are
pretty much right on target.
The WO 66 Triplet and SD Doublet are a couple of very nice little
scopes at prices that won’t break the bank, and come recommended for
those seeking the ultimate finder, versatile travel scope or ultra
light grab and go.
And dealers worldwide.