Takahashi
FOA-60 Review
What is the most perfectly corrected
refractor? It’s an interesting question. Previously the answer would likely
have been, ‘Takahashi’s TOA-130’. The acronym ‘TOA’ stands for ‘Triplet Ortho
Apochromat’ indicating that the TOAs have aberration levels below most catadioptrics and a hundred times lower than many
apochromats. They achieve this by using two ED elements, rather than the usual
one, along with big air gaps that can be used by designers as ‘virtual
elements’ to further control aberrations.
Takahashi recently extended the TOA
concept into smaller apertures to produce the FOA-60. In this case, they have
achieved a similar level of correction using a fluorite doublet. But this is
not any old fluorite doublet. It is a fairly long focal length at F8.8, but it
also employs a special mating element and a big air space as well.
Given that such perfection was never
going to be cheap, you might ask, ‘why bother?’ One clue is in the timing: the
FOA-60 was launched in time for the best Mars opposition in the current cycle
(2018). A perfect, long-focal-length scope with a small aperture stands the
best chance of cutting through the poor seeing inevitable when viewing Mars at
low altitude, as it will be at northern latitudes.
Of course, a really perfect and
portable tiny refractor has other uses – other solar system targets, eclipses
and high-power terrestrial viewing too. And whilst Takahashi have produced two
well-corrected 60mm scopes before (the old FC-60 and recent FS-60Q), neither
come close to the theoretical perfection of the FOA-60. Now let’s discover if
that putative perfection translates to the real world.
Note: I bought this as the complete
FOA-60Q with its quadruplet red nameplate; you could buy the blue-plated basic
FOA-60 and then add the ‘Q’ module later: the end result is optically
identical. I will also review the FOA-60Q separately, as it’s a very different
telescope with its own characteristics.
At
A Glance
|
Telescope |
Takahashi FOA-60 |
|
Aperture |
60mm |
|
Focal Length |
530mm |
|
Focal Ratio |
F8.8 |
|
Length |
510mm (dewshield
retracted) |
|
Weight |
1.8 Kg |
Data from Takahashi.
What’s
in the Box?
Few things in
life are better than unboxing a brand new Takahashi.
Design
and Build
The FOA-60 is
classic Takahashi and has styling cues – like the short focuser, super-long
draw-tube and slim OTA – from earlier days. This makes the FOA look more like
the descendant of an FC-60 than an FS-60, despite the new-style
silver lens ring. Build quality is gorgeously high and it has a luxury feel. I
would imagine the FOA-60 will be a collectors’ item one day.
FOA-60 with other Takahashi 60s – with FS-60C (top), with FC-60, FS-60Q
(bottom)
Lens cell and
sliding dew-shield detail
Optics
Tak’s
original planetary 60mm, the old FC-60 (see above), had a Steinheil
fluorite doublet with a regular flint element and a small air space. The FOA-60
is quite different. Not only is it a slightly longer focal length at 530mm (F8.8),
it employs a flint element ‘never used before’ (a special dispersion glass of
some type). It also reverts to the front-surface fluorite design of the
FS-series and has a very large air gap, like the old Sky-90, with a suitably
large, collimatable cell.
Takahashi’s
published centre spot image and crossings diagram suggest the FOA-60 achieves
tighter control than any other Takahashi refractor, even including the
outstanding TSA-102, a now discontinued F8 triplet. It significantly
out-performs their two best current 4” doublets, the FC-100DL and DZ.
The FOA-60
should perform very much better than an F6 doublet like the FS-60C (TV-60 etc),
especially at the far ends (red and violet) of the visible spectrum. In theory
at least, the FOA really does extend the ortho-apochromat concept into a small
doublet.
Quality of
figure from Optron is extreme: bench tests have
measured the FOA-60 objective’s real-world Strehl
at 99%, literally almost perfect (note that when Tak’
talk Strehl, they are referring to something different
- the theoretical spherical aberration due to spherochromatism).
Below you can
compare Takahashi’s own crossing diagram for their new best 4” fluorite
doublet, the FC-100DZ, with the FOA-60. I’ve also compiled spot diagrams for a
range of Tak’s best refractors for comparison. On a
purely theoretical basis, the FOA-60 reigns supreme!
Laser test
confirms the FOA-60 has a front-surface fluorite doublet lens with a large
air-gap. Compare the FC-60 with its fluorite at the back.
Note: I should mention that I have seen
an FOA-60 with minor mis-collimation, just like the old Sky-90 often had (the
lens and cell design are similar). So the FOA-60 may
not be a particularly robust travel scope and make sure you test it thoroughly
or can return it if there’s a problem.
Tube
The FOA-60
has the usual Tak’ white enamelled tube, but for the
FOA-60 it is a slim 68mm in diameter, the style of the old FC-60.
Unlike the both
the FC-60 and FS-60C, the FOA-60 has a sliding dew shield that sports the (in
more recent models) signature silver ring and a big lock-screw. It has a
perfectly fluid action and hits the stop with a satisfying clunk. The lens cap
is a black plastic clip-in affair on this one, but I have also seen a silver
pressed tin example like you get with an FC-76.
The slim tube
and beautifully executed sliding shield, together with the diminutive focuser,
do give the FOA-60 a more premium look and feel than the FS-60C/Q if that
matters to you. That makes sense – this is a very expensive 60mm refractor.
Focuser tube
is narrow, but still ends in a 2“ visual back, has
loads of travel.
Focuser
The biggest problem with the FS-60 (and
Q) is a serious lack of focus travel at just 25mm. It mostly work
for the FS-60C, but isn’t really enough with the Q module in place.
By comparison, the focuser
on the FOA-60 has no such trouble. Its drawtube is slightly narrower at a bare 45mm,
but has a whopping 85mm of travel to accommodate any eyepiece you could think
of. And the supplied extension is all you need for straight through viewing
Japanese style or imaging.
At first the focuser seemed frankly a
bit stiff. But after a few months of light use it freed to give an oily smooth
and superbly precise action, virtually free of image shift and up to the task
of minute adjustments at high power. Full marks.
Again, in line with the FOA-60’s
premium price tag, the focuser has the proper metal silver wheels in place of
the plastic imitations some entry level Takahashis (FS-60
and FC-60 included) get.
Mounting
Unlike the
longer and heavier FOA-60Q, the basic FOA-60 has a short light tube that works
on the lightest mount. But given the high magnifications the FOA-60 can take,
it benefits from a slightly beefier mount, though it does work just fine on the
Teegul SP and PM-SP.
The FOA-60Q
meanwhile really needs a mid-sized mount for use at high power.
FOA-60 on Teegul SP3 mount: pushed forward in its clamshell for
balance and clearance.
Accessories
A note on colour. Think Takahashi think
lime green. But that hasn’t always been the case. Takahashi has changed the
colour of its focuser and accessories a few times, to include black and bluish grey.
It’s recently done it again. Now the lime has a bluish tinge. I like it.
Trouble is, it doesn’t match the old colour – take care when buying accessories
if a perfect match matters to you.
The FOA-60
comes with one of Tak’s beautiful-but-heavy extension
tubes for straight through viewing or imaging. A 2” visual back with twin
lock-screws is supplied (again, the draw-tube is narrower than the FS-60C’s, so
its visual back won’t fit), along with a nice 1.25” adapter that ends in Tak’s characteristic silver twist-grip. Unlike previous Tak 1.25” VBs, you don’t have to unthread it to fit the 2”.
The obvious
finder is Takahashi’s peerless 6x30 unit shown, but you could fit a 7x50 with
an illuminated reticle, or indeed the tiny 5x25 if
you can find one.
The finder-ring
mount on the focuser is standard across recent Takahashi’s, but the older FC-60
and FC-50 need a different finder mount with a slimmer base and smaller screws.
The FOA-60’s
tube is 68mm diameter: the same as
the FC-60 and FC-50, but unlike the 80mm tube of the FS-60C. That means the
clamshell for FS-60C definitely won’t fit, but the FC-60’s fits fine.
The
elephant-in-the-room accessory for the FOA-60 is of course the ‘Q’ module, that
screws into the OTA in front of the focuser. The Q module increases the focal
length by 1.7x to make the FOA-60 into a 900mm/F15, flattens the field and
takes out the remaining aberrations. You can either buy the module as part of a
complete scope – which is how I bought the scope reviewed here - or as a
separate item.
The ‘Q’
module changes the scope so utterly, both physically (it’s much longer and
heavier) and optically, that it gets a separate review. Suffice to say it only
improves things visually at very high magnifications, because the FOA-60 is
already very well corrected (unlike the FS-60C which really benefits from its
dedicated Q module). But
don’t dismiss the FOA-60Q, because it does deliver very impressive results photographically.
The FOA-60Q seems
much longer and heavier.
This APS-C daytime
image through the base FOA-60 (no Q) is sharp to the edge and free of false
colour.
In
Use – Daytime
The basic
FOA-60 makes an excellent daytime spotting and birding scope because it remains
sharp and false-colour free at powers (100x plus) at which ordinary birding
scopes just don’t work. Daytime photos are excellent too, but the quality falls
off in the corners, especially at full-frame.
Terrestrial
photography is perhaps where the Q module makes most sense, as a 900mm
telephoto lens which is sharp and bright across a full frame sensor and free of
false colour in the most demanding situations. Want to image a rocket launch
against a bright sky? Or raptors nesting a hundred metres away? Here you go.
In
Use – Astrophotography
The FOA-60
delivered excellent lunar images, but again this is where the FOA-60Q with its extender
module fitted shows its advantage: more image scale of course, but absolutely
sharp across the whole frame. If you want a compact scope for lunar imaging
(collecting phases, for example), the FOA-60Q is the one. Similarly, the FOA-60Q
might be the best portable eclipse imager available.
The base
FOA-60 shows substantial off-axis curvature on a full-frame sensor and this is
where the Q module again shows what it’s for. Sure, it’s slow at F15, but the pay off is an extremely wide and flat field. Apart from a
touch of vignetting in the very corners (that might be due to my cheap T-ring;
a Takahashi wide-mount would be better), the ‘Q’ is flat and perfect
edge-to-edge.
Full frame
(EOS 5D) image of M42 with FOA-60 shows lots of curvature towards the edges
With the ‘Q’
1.7x extender module in place, the same full frame image is flat to the edges
Cropped image
of the Moon with the FOA-60 – sharp and detailed
With the ‘Q’
1.7x extender module, the FOA-60Q produces superb images of the Moon, showing
stunning detail for a 60mm
In
Use – The Night Sky
General
Observing Notes
The FOA-60,
mounted on Takahashi’s sadly-discontinued PM-SP mount, was particularly easy
and relaxing to use. The short tube vibes much less than the longer, heavier
FOA-60Q and the balance point near the focuser means the eyepiece doesn’t
change height much, always giving an easy viewing position, from horizon to
zenith.
The focuser
is easy to use and smooth, with minimal focus shift even at high power. The
focusing sweet spot is long enough to make finding it easy and the low vibes
help too. There’s enough travel for every eyepiece I tried.
High powers
with flat-field eyepieces deliver a completely flat FOV, but low powers with Plossls show just a bit of curvature.
The perfect
(really) optics give wonderfully sharp and bright stars with saturated colours
and no flare at all, making the FOA-60 an unexpected pleasure on the deep sky.
Cool
Down
Cool down seems instant, with a perfect
image minutes from a warm house.
Star
Test
The star test
is effectively perfect, with identical crisp diffraction rings either side of
focus, even illumination and tight in-focus diffraction pattern.
Since this is
an expensive, but small-aperture scope aimed at Lunar and Planetary observers,
I will expend a bit more digital ink than usual on the next section to
see what it’s really capable of.
The
Moon
On a night of
ordinary seeing, the Moon looks much like it does through any small
apochromatic refractor. But on a really steady night, with slight haze
dampening convection, I got stunning views of a 6-day Moon at 151x with a 3.5mm
Type 6 Nagler. Masses of detail was visible for a
60mm scope - the shadow of Albategnius’s pyramidal
central peak and its knotted rim on the terminator; small craters and rays in
Mare Serenitatis. I don’t generally reckon on finding rilles
with scopes this small, but Rima Hyginus and Rima Ariadaeus
were sharply defined with changes in width clearly visible, maybe Rima Triesnecker in deep shadow too.
A three-day crescent
Moon in good seeing showed surprising detail. This is a difficult phase of a
lunation: often low down in the twilit sky and lacking contrast. But the FOA-60
revealed the embayments around Mare Criseum in enough detail to really explore, all picked out
in icy whites and hard greys. The low sun highlighted crater Yerkes with its ‘winged’
shape; Swift, Peirce and Picard too. The rille in Petavius
was clear and distinct. Taruntius right on the
terminator was broodingly full of shadow, showing its inner ring of hills,
central peak and crater Cameron (astronomer, not the execrable British Brexit politician)
on the rim. Meanwhile nearby Mare Fecunditatis was
full of subtle shading and shadowed wrinkle ridges.
One
particular feature of the FOA-60 is lack of light bleed-over from the Lunar
limb. Even at 151x with a 3.5mm eyepiece, the transition to black space is
stark and it was possible to see a mag 7.5 star right close in
The Moon is
of course delivered with perfect sharpness and absolutely no false colour or
flare, as you might expect given the FOA-60’s optical quality and correction.
Venus
On a warm
spring evening, with bats flitting the air and a crescent Moon nearby, Venus is
bright and lovely in the western dusk sky. Also, it’s my wedding anniversary
(cue the strings). How romantic.
The Goddess
of Love thing fails with most refractors, even ‘apochromats’, because Venus’
natural platinum gets ringed with false-colour: amethyst or emerald. With the
FOA-60 there is none of that – Venus presents as a perfect brilliant gibbous
planet with <almost > no false colour, even out of focus. I say almost,
because at 180x the focused image is still perfectly sharp and clean, but there
is the merest hint of amber in the out-of-focus blur.
I labour this
to make a point about the FOA-60Q: that last faintest hint of CA outside focus
at ultra-high power on the brightest subjects is what its superlative
correction removes. Normally though, for visual astronomy at least, the base
FOA-60 is false-colour free in any situation.
The summary here is that for visual at sensible
magnifications you just don’t need to further correct the FOA-60 with the Q
module.
Mars
Mars just
after the 2018 opposition (i.e. large at 24.2” but very low in the sky) showed
a bright full disc with no false colour. I could make out Syrtis
Major and a hint of polar cap at 108x with a 5mm Nagler.
Later in the
year, with Mars much smaller (9”) but higher in the sky, 180x with the 3mm
setting on a Nagler zoom gave an excellent view with the
dark equatorial band of Tyrrhena, Hesperia and Cimmeria running out from the centre of the gibbous limb.
I revisited Mars with the FOA-60 two days after the 2020
opposition, with Mars still at 22” and in excellent seeing. A Nagler Zoom at 4mm giving 132.5x showed the tiny southern
polar cap, featureless (to a 60mm!) deserts of Tharsis
in the north and significant albedo detail in south including the ’Eye of Mars’,
the Solis Lacus region. Upping to maximum 3mm setting
and 177x showed no extra detail, but stayed perfectly sharp and crisp with no
loss of contrast or softening, no false colour in focus and just the merest
trace of a red rim one side out of focus.
Jupiter
The FOA-60 gave a perfect view of
Jupiter at 132x with the 4mm setting on a Nagler
zoom, but the best view was at just 108x with a 5mm Monocentric. In excellent
seeing, I could make out fine bands in the polar hood, the delicate-pink GRS
just coming around the limb and thickening and swirls in the NEB and SEB. I also
watched a shadow transit of Europa.
Saturn
On a cold evening in early October,
with a clear dusk sky but surprisingly good seeing, Saturn is at only 13
degrees altitude, just above the trees opposite my balcony: a long way from
opposition and just 16.8” in size. The circumstances are hardly ideal. Nonetheless,
the FOA-60 gives an excellent view.
The 5mm Monocentric giving 108X looks
good, but I sense the FOA-60 will take more and I’m right: the 4mm Zeiss Abbe
Ortho yields my favourite view, noticeably brighter than the 3-6mm Nagler zoom. This is where minimalist eyepieces like the
Mono and the Abbe Ortho come into their own. The FOA has superb optics and can
take high powers, but then gets quite dim and benefits from the very best light
throughput.
Saturn through the Zeiss Abbe at 132x
is that Cassini-in-miniature view that I love: perfectly crisp with all the
major stuff on show. Part Cassini division, planet obscured by the rings,
shadow of the planet on the rings and both a hint of a band and the polar hood.
Through a 60mm! Again, the only problem is that it’s easy to want more, forgetting
this isn’t an FS-128.
The
FOA-60 is, in very good seeing, a better planetary scope than a 60mm has any
right to be.
Deep
Sky
I hadn’t
really been looking forward to testing a 60mm F8.8 scope on deep sky, but on a
dark clear night of good seeing in February, I had great fun with it.
At 59x with a
9mm Nagler, M42 looked better than it had a right to,
with knots in the nebulosity, the extended arms and dark lane all clearly
visible, the Trapezium nestling within, bright stars like Nair Al Saif with not a trace of false colour or flare. A great
view which I lingered over.
Open clusters
– M35, M36-38 in Auriga and the Double Cluster – looked particularly beautiful
through the FOA-60, perhaps due to the super-tight PSF delivered by such
perfect optics. Stars are such pinpoints that the faintest ones are just the
tiniest pin-points of light in dense black. The shape of the Starfish Cluster,
its arms of stars, were easy with direct vision. The Pleiades had that misty
sparkle that only fine refractors give.
Fainter
Messier objects like M1, the Crab Nebula, were a bit dim but still easy to pick
out from perfectly black space.
Rigel and
Castor were both an easy split.
Later in the
season, I had a wonderful view of M3 – much more than just a fuzzy star, I had
fun trying to start to resolve it at 58x with a 9mm Nagler.
In case all
this deep sky goodness was a moment of madness, I repeated it. And again. No,
the FOA-60 really is a very nice small refractor for deep sky.
Summary
In no way could you call Takahashi’s
superb little FOA-60 good value. But if you like perfect small refractors then
you will probably want this one. Making negative comparisons with a similarly
priced Dob’ is a bit like pointing out that a Nissan GTR is faster than a
Morgan; so I won’t.
There’s not much else to say, because
this is as close to a perfect 60mm aperture as you will ever find. It has clearly
(and nowadays unusually) been designed with visual use in mind. As such, it
does a surprisingly good job on the Moon and planets, but you need good seeing
to realise why it really is better than any other 60mm apochromat. It also
exudes a certain gorgeous hand-built retro charm, a refractor-guy’s Questar,
maybe.
True, in most circumstances an FC-76 is
a better choice and will show you more. It also has to be said that an FS-60Q
is in many ways a more adaptable telescope and gives just a little away to the
FOA-60 at high powers.
But in the end, the FOA-60 has a magic
exoticism that neither the FC-76 or FS-60Q can match. Plug in the Q module and
it delivers aberration-free lunar and terrestrial photos at full-frame like
almost nothing else.
In the end, I’d be quite happy, stuck
on a desert island with clear skies and only the FOA-60 to explore them; and
you can’t say fairer than that.
As an irrational fan of tiny
refractors, I absolutely love the FOA-60. But for most practical purposes, I’d
have to recommend an FC-76 or FS-60Q instead. You want an FOA-60 anyway? Me too.
