Takahashi FS-60Q Review
I had always wanted a Takahashi FC-60, a classic now out of production for many years. I advertised
for one on numerous occasions, but kept getting pipped at the post on Astromart. So I was close to
ecstatic when Takahashi announced the FS-60Q. But why exactly?
A 60mm APO is highly portable, but it also has surprising
potential as a quick-look/travel scope for the Moon, planets and eclipses,
easily rivalling a Questar. A perfect 60mm aperture will resolve detail down to
below 2” of arc, which is enough to show you a lot. Now given that even Mars gets up to 20”+
on a good opposition, a 60mm APO should easily show the polar caps and major
albedo features … if it’s a good ‘un. And therein lies the problem.
Most small doublet APOs (the FS-60C included) are ~F6 and suffer
from a number of limitations:
·
Significant
chromatic aberration
·
A
very steep light cone and a tiny focusing ‘sweet-spot’
·
Severe
field curvature and off-axis coma
·
Steep
lens curves which make it harder to achieve a really good optical figure
·
Spherochromatism
- their spherical aberration (and so effectively optical quality) changes with
wavelength: often good at shorter wavelengths for imagers, they are poor in the
orange and red (and so for Mars).
Just adding two F-stops changes all that, so a good small F8
doublet – like the original FC-60 - can be excellent for high powers on the
Moon and planets, Mars included, which is why I had long wanted one.
The FS-60Q achieves similar results in a different way - by
converting an FS-60C (an F6 doublet) with a thread-in module that extends the
focal length from 355mm to 600mm (F10). In theory this improves the optical quality, kills the
spherochromatism and flattens the field for imaging too.
That at least is the theory, but does it work in practice?
Let’s find out...
(Note that the scope with the blue serial plate has the older
green powder coat, the red-plated FS-60Q has the more recent blue)
The FS-60Q with Takahashi’s original long-focal-length
fluorite 60 – the FC-60.
At
A Glance
|
Telescope |
Takahashi
FS-60Q |
|
Aperture |
60mm |
|
Focal
Length |
600mm |
|
Focal
Ratio |
F10 |
|
Length |
45 cm w/o
visual back |
|
Weight |
~1.8 Kg
(without finder and ring) |
Data from Me/Tak.
What’s
in the Box?
The complete scope comes double boxed within a logoed
shipping carton:
FS-60C with CQ module bought as an accessory: note the blue
serial number plate for a doublet.
Red quadruplet serial-plate if you buy the package.
Design and Build
You can buy the FS-60Q as complete scope, in which case you
get the privilege of a red serial-number plate, just like other Takahashi quadruplets
(the FSQ-106 and FSQ-85). Alternatively, you can buy a screw-in accessory called
the ‘CQ Module’ that converts an existing FS-60 (in either C or CB variants) into
an FS-60Q (which is I suspect how most will do it). In either case, you can
always remove the module to convert it to a fast imaging
scope; and to me that flexibility really appeals.
Optics
FS-60C Objective
Laser test reveals front-surface fluorite as claimed: laser
disappears in fluorite crown element, but not in glass flint at rear.
We’ll begin with a quick review of the FS-60C optics, since
the FS-60Q is based on them: it’s an F5.9 doublet that has the fluorite element
(yes, it’s actually fluorite, not a high-fluoride glass – see above) at the
front. Technically this makes it a Fraunhofer design, compared with the FC-60’s
(and recent FC-76’s and FC-100’s) fluorite-at-the-back Steinheil.
That fluorite FS-60C lens sits in a slim fixed-collimation
cell. Unlike the FC-60 it replaced, the FS-60C suffers some chromatic
aberration and performs poorly in the red.
The Strehl (which amounts to optical quality) graph for the FS-60C shows
this effect and explains why both it and many other F6 doublet APOs struggle to
focus crisply on Mars, but work fine on other objects:
The Strehl (a measure of optical quality) of the FS-60 drops
off dramatically in the red.
The CQ Module
You can turn any FS-60C into an FS-60Q by unscrewing the lens
assembly and threading in the Q module behind it in one of two configurations,
depending on whether you have an FS-60C or an FS-60CB (they differ only in the
length of their tube). This ensures the module lens is at the optimum distance
from the objective.
The Q module screws in behind the objective to become an
integral part of the OTA. The Q-module is a doublet, so with it in place you
have a quadruplet (hence the ‘Q’) APO operating at F10 (600mm F.L.):
The module configuration varies, depending on whether it’s an
FS-60C or a shorter-tubed FS-60CB.
The CQ module acts as a 1.7x extender, increasing image scale
for those wanting to photograph an eclipse, for example; but it changes the
optics in other ways too. The CQ module flattens the field and reduces residual
spherical and chromatic aberration. According to Japanese websites, Strehl goes
up by 10% and the FS-60Q will supposedly cover a 35mm sensor sharp to the edge.
So, is the CQ module just an expensive barlow
lens? Yes and no. Optically it is a negative doublet like a barlow,
but because its position is fixed and it has been designed for a specific
objective, it can achieve a level of correction that a generic barlow plugged into the focuser could not: it works as an
integrated part of the objective lens.
These spot diagrams, published by Takahashi, show how much
the off-axis performance betters that of the standard FS-60:
The CQ module in
one of two configurations, depending on your model of FS-60: flip the lenses
assembly inwards for the other.
Enough theory, what does the CQ module look like? It is a
section of white OTA-tube that matches the FS-60C OTA perfectly, with a doublet
lens threaded into it. The threads match the existing FS-60 ones. It’s a
beautifully made unit and the 40mm diameter lens in the CQ module has just
about the best coatings I have ever seen: it’s almost invisible; no worries
about light loss at least. In fact, looking up the tube with the CQ module in
place it is quite impossible to see the module’s lens – the tube looks empty as
far as the objective! Internally, the module is painted a perfect flat black,
so adds no nasty reflections.
The CQ Module weighs 300g and is about 17.5cm long. Even with
the module in place, the OTA weighs just 1.8 Kg and will fit in a carry-on
case.
40mm CQ-Module Doublet lens.
‘Q’ modules for the FOA-60Q on the left, FS-60Q on the right.
Two Takahashi 60Qs: FS-60Q (top) and FOA-60Q.
The CQ module is no longer the only such integral extender
Takahashi make. Their newer FOA-60Q also uses a module (the 1.7XR, on the left
above) to extend the focal length of the basic FOA-60, in that case from F8.8
to F15. The two modules are not inter-compatible because their tube sizes are
different. Nor are they optically the same, though they both extend the focal
length by 1.7x. The 1.7XR is also a bit more expensive than the CQ1.7.
The 17XR is dedicated to the FOA-60Q, but the CQ1.7 as
described here can also be plugged in to the FC-76DCU (see separate review).
Tube
The lengthened OTA does look a bit strange and the Q module
is so lightweight that it gives you a balance point with most of the tube
beyond the clamshell and that leaves both joins exposed. Practically this has a
big advantage, though, because with an equatorial mount the eyepiece changes
height less and the OTA is still so light the Teegul
mount takes it with ease.
FS-60Q is carry-on portable without disassembly, at 45cm
long.
Focuser
The rack-and-pinion focuser is the same unit as the FS-60. It
has the familiar Takahashi lime green enamelled casting, the familiar silver
knobs and oversized tensioner. Unlike the larger FS models, the focuser on the
FS-60 has a very short body for compactness, a bit like the one on the Sky-90,
but with a smaller (~55mm) diameter drawtube. The short travel means you might
need an extension tube for some 2” eyepieces and diagonals or cameras.
This focuser is now used on the lightweight versions of the
FS-76 and FC-100 as well as the FS-60 and variants.
The visual back threads-on to the end of the focuser and
allows various configurations (you knew it), including attachment of a reducer,
extender or rotator. The most important variants are the standard 1.25” visual
back with the usual Takahashi twist-to-clamp mechanism, or the optional 2”
visual back. Both are shown below.
As I noted in the FS-60 review, I’ve had mixed experiences
with this focuser. My first one had too much image shift, a problem noted by
other reviewers. This example, however, is virtually perfect: smooth, solid,
precise and suffering from just a tiny amount of image shift at high powers and
worked very well with my DSLR.
I suspect the issue is that hanging heavy CCD cameras off
these little focusers causes wear in the bushings that leads to slop and image
shift. Check before you buy!
1.25” and 2” visual backs thread onto the focuser tube.
Spacing
One downside of the FS-60Q is the short focuser travel. That
means to get things to focus you need to get spacing right on the visual back.
Here are a couple of tips (these apply to the factory version with the shorter
FS-60CB tube. If you use the CQ module with an FS-60C it may be different):
1)
For
visual use with the camera rotator in place (you need it for imaging – see
next) a prism diagonal works best to get a range of eyepieces to focus
2)
For
prime focus DSLR imaging, use the rotator + supplied thread-on extension tube
(there won’t be enough out travel otherwise):
Mounting
It goes without saying that the FS-60Q will go on the
smallest mount.
It is ideal with Takahashi’s Teegul
SP, a miniature German equatorial mount which breaks down into palm-sized
chunks and weighs little more than the OTA, but which has sadly been
discontinued. Tak’ replaced the Teegul
briefly with the PM2, but that’s also been discontinued.
FS-60Q on Teegul mount/Berlebach tripod.
FS-60Q package in later blue powder coat on a rare PM2 mount.
The Teegul and PM2 rigs shown are
very lightweight and super-portable, whether in and out of the house or on and
off a plane. I love the idea of a complete RA-driven mini-observatory system I
can carry about fully set-up and the FS-60Q/Teegul
fills that role better than anything I know. Even a Questar system ends up
being significantly heavier due to the weight of its tri-stand.
Because both the FS-60Q and the Teegul
break down into small sub-assemblies, it makes an obvious choice for
eclipse-chasers.
You can read a complete review of the Teegul
mount here.
For these tests, I also mounted the FS-60Q piggybacked atop
my AP 1200 mount for maximum stability.
FS-60Q Piggy-backed atop my TMB175/AP1200.
In Use – Daytime
Having first screwed-in the CQ 1.7, I turned the now
lengthened scope on the field across the way with a 25mm Plossl giving 24x. The
view is immediately impressive – sharp, bright, with snappy focus.
Next I pushed the power to 120x with a
5mm T6 Nagler, about the maximum I’d ever use in a 60mm scope and a power that
had the basic FS-60C turning slightly fuzzy. Expletive. Wow. Why? Because the
FS-60Q is a scope transformed. The high-power daytime views are extremely
sharp, even at high power. Even at 120x the FS-60Q remains sharp and free from
in-focus chromatic aberration, even focusing on tree branches silhouetted
against a bright sky, with just a trace of residual CA either side of focus.
With a 3.5mm Nagler, giving an extreme 171x and an
over-the-top 70x per inch, the daytime view remained completely crisp and free
of false colour: quite usable if a bit dim.
Overall, high-power daytime views are
among the best: the FS-60Q has great potential as a high-power daytime spotter
or birding scope.
In Use – The Night Sky
General
Observing Notes
The FS-60Q takes just a little longer to cool than the base
FS-60C, but is still delivering high-power views 10-15 minutes from a warm
room, which is what you need in a quick-look scope.
The focuser on this FS-60 is a good one in the first place:
smooth and with little image shift, as I said above. But with the basic FS-60
you really need a micro-focuser for high powers, because the sweet spot is so
small. The CQ module changes that. The extended sweet spot that the longer F10
light-cone gives makes focusing a doddle, even at 170x and that’s true for
imaging too. On this example, the focus lock works perfectly - i.e. with no image shift. For modest loads the lock isn’t
necessary to prevent rack-out and I only used it when slewing with a DLSR
attached.
The Moon
The FS-60Q makes an excellent small lunar scope, despite its
limited aperture. Lots of detail is available at 120x and the view is still
perfectly sharp and reasonably bright at 170x. Contrast is excellent for the aperture.
The whole Moon fits into the field of a 5mm T6 Nagler at 120x and the flat
field makes it a very enjoyable view.
On a low Gibbous Moon at 120x, I was able to study the
slumped walls of craters Tycho and Copernicus, their central peaks, the retreating
dawn shadow in Marius, the arcing crater chain in Clavius and the Apennine
mountains.
There is almost no chromatic aberration on a bright Moon,
even focusing through the limb at 170x. Flare around the limb of the Moon is
also very well controlled (something that might have been a problem with the
extra glass surfaces introduced by the module, but isn’t).
This means that the FS-60Q is one of those scopes that excels
when looking at Lunar mountains right on the limb highlighted against space. I
always like doing this because you see the mountains’ real form – rounded and
smooth – rather than the exaggeratedly jagged look they have on the terminator.
When I returned to my first draft of this review, I thought I
was over-egging the pudding a bit regarding the FS-60Q’s view of the Moon. So I went back and checked it out again with the same
result. Enjoying crisp and very detailed views at 120x, let alone 171x, just
isn’t what I expect from this aperture. Usually I
would stick at below 100x on the Moon in a 60mm scope, but with the FS-60Q I
always found myself using 120x and sometimes more.
Mars
The prospect of good performance on Mars was one of the main
things that got me interested in the FS-60Q. So how does it perform?
Near a fairly unfavourable
opposition, with Mars at just 15” apparent diameter, the FS-60Q was able to
reveal significant albedo detail at 120x and 171x. On one occasion, in good
seeing, Mare Acidalium was very obvious, as was
Syrtis Major on another. The polar caps were both just about visible, although
much diminished in the Martian summer.
Some other albedo detail was glimpsed as well, including the dark band
stretching from Syrtis Major towards Solis Lacus and I think I could make out a
patch of bright limb cloud too.
Chromatic aberration is not a problem on Mars in focus, but
just a touch was visible either side of focus at high power that the FOA-60Q
eliminates. Nonetheless, the FS-60Q gives a more satisfying view of Mars than
many small doublet APOs I have tested, the FS-60C and Sky-90 included.
Jupiter
Jupiter can be a difficult subject due to its low contrast,
but the FS-60Q gives one of the best views of it I’ve had in a small scope. On
a night of steady seeing, a lot of subtle detail was visible at 120x and even
more at 170x, including banding in the polar hoods, width variations in the
equatorial belts, the Great Red Spot (even in its current pale and diminished
state) and the thickened region downwind of it. I was also able to watch
Ganymede in shadow transit. On a really good night, the Galilean moons stand
out as four hard tiny balls of slightly different size and colour, the way they
do in much bigger instruments.
Deep Sky
With just 60mm aperture, the FS-60Q is not a deep sky scope,
but the flat field and tight stellar images produce some great views of
brighter DSOs. The Pleiades were particularly sparkly, as they tend to be in
scopes with low off-axis aberrations and a tight PSF. Clusters like those in
Auriga looked good through the FS-60Q too. Fainter, smaller Messier
objects – e.g. globular clusters M15 and M2 and the Ring and Crab Nebulae -
were a bit dim due to the small aperture.
It’s an irony that although low power views of extended DSOs
are harder to achieve given the longer focal length, they are more satisfying
than with the FS-60C due to that flat field.
Doubles
Rigel is challenging for a small scope because the faint
companion tends to get lost in the diffraction ring. Nonetheless, The FS-60Q
split it comfortably at 120x. In good seeing the twin dumbbells of the 2.3” ‘Double
Double’ just resolve into discrete Airy discs.
In Use -
Astrophotography
You’d think taking an F-ratio of 5.9 and bolting in a module
to extend that to F10 would kill the astrographic potential of the FS-60Q, but
that’s not really the way it works out. Sensitive CCDs and stacking techniques
can get around slow F-ratios to some extent. Meanwhile, the larger image scale
is more often a help than a hindrance, unless trying to image very extended
objects. The high optical quality, absolute focus snap and longish sweet-spot
make it easy to get perfect focus when using a DSLR with Live View. But the
main plus points are field flatness and coverage.
The following full-frame image of M42, straight from the camera,
together with a 100% crop of the top right corner, demonstrates excellent
flatness, coverage and low chromatic aberration (violet bloat), just as
promised.
Full-frame image of M42 region and 100% crop of corner below:
Canon EOS5D at 59s and ISO 1600 with no post-processing; minor tracking error.
As you can see below, allowing for its modest aperture and
resolution, the FS-60Q takes an exceptionally sharp and detailed image of The
Moon. In fact, the FS-60Q takes better
images of the Moon than any other ultra-portable telescope I’ve tested, Questar
included.
The FS-60Q would be perfect for taking art shots of Moon
rises, ideal for Lunar and Solar eclipses too (see below).
The Moon through FS-60Q: single, cropped but otherwise
unprocessed image with Nikon D5100
Lunar eclipse through the FS-60Q: cropped but unprocessed
frame with Fuji XM-1
In Use – Terrestrial
photography
The FS-60Q also works very well as a terrestrial telephoto
lens too, as you can see in the following Fuji APS-C image of autumn leaves.
Below it I’ve included a crop of the top right corner to show the fine edge
performance and limited chromatic aberration.
FS-60Q: This crop of the top right corner shows the flat
field and just a trace of chromatic aberration (much less than most camera
lenses)
As you can see from the image
below, coverage remains good and sharp into the corners at full frame with very
minor vignetting; with a wider T-ring coverage might be even better.
Full-frame image taken with
a Canon EOS 6D MkII DSLR.
Summary
The FS-60Q is honestly one of the most exciting scopes I’ve
tested for a while. It offers new buyers two excellent, but quite different,
refractors for the price of one. Alternatively, it gives FS-60C owners an
interesting (and for Takahashi inexpensive) way of expanding the capabilities
of their existing telescope.
The CQ module is both literally (because of those amazing
coatings) and metaphorically transparent – you never detect its presence as a
separate item, it just makes the FS-60C into a completely new telescope.
The FS-60Q is still only a 60mm refractor, so don’t expect
miracles, but performance is exceptional for the aperture, especially on the
solar system. For my money it beats a Questar in most areas and is actually
more portable when paired with the Teegul mount.
The FS-60Q’s portability, image scale, sharpness and flat
field make it absolutely ideal for imaging eclipses.
The CQ module enhances FS-60C performance in five key ways:
1)
The
FS-60Q takes high magnification far better
2)
The
longer focusing sweet spot means finding focus at high power is much easier
3)
The
FS-60Q has lower levels of chromatic aberration and spherochromatism than the
FS-60C and continues to perform into the red. It gives great views of Mars,
something the FS-60C can’t do
4)
The
FS-60Q has a much flatter field than the FS-60C, so extended objects look great
and image really well too
5)
Full-frame
coverage, flat field, high optical quality and low false colour make for a
great 600mm terrestrial telephoto
The FS-60Q is a specialist scope and you can get much more
sheer performance for the same cost in a larger aperture. But it still gets my
highest recommendation, if you’re looking for an ultra-portable refractor with
a huge range of capabilities.
