Takahashi
FS-128 Review
The FS-128 was my first Takahashi and
my first big refractor. It was a revelation. After a C8 and a basic achromat, I
just couldn’t believe a telescope could be that good. I eventually sold the
FS-128 to a friend and have regretted it ever since. I have a (different)
friend who sold his FS-128 and regrets it too. So what
was it about the FS-128 that makes it special even today and a great used buy
if you can find one?
At
A Glance
|
Telescope |
Takahashi
FS-128 |
|
Aperture |
128mm |
|
Focal
Length |
1040mm |
|
Focal
Ratio |
F8.1 |
|
Length |
1176mm |
|
Weight |
7.5Kg |
Data from FS Series Manual.
What’s
in the Box?
My FS-128 came in the top-quality Scopeguard case that I’d ordered for it.
Design
and Build
The FS range of refractors included
78mm, 102mm, 128mm (reviewed here) and 152mm models, all with F8 fluorite
doublets. The odd one out is the FS-60 which is an F6 and the only one still in
production.
As well as a shared optical design, the
F8 models all had a similar tube and focuser and family ‘look’. Most had fixed
dew-shields, all were bulky for their aperture. All had a strange but classy
cast ‘manhole cover’ dew cap that slid into the dewshield
with a perfect fit on a felt shim.
The FS-128 is the ‘big’ FS Series
refractor that most people could afford. At the time, it was half the price of
the FS-152 in Europe; what’s more it was light and so relatively easy to mount.
So quite a few were sold and most sold on like mine. Little did we know that
fifteen years later neither Takahashi, nor anyone else, would really have made
anything similar. An FC-125 perhaps? We’re still waiting …
Optics
The FS-128 objective
is 128mm aperture (!) and 1040mm FL (F8.1 to be exact). It has superb coatings
and a high quality, collimatable, temperature
compensating cell. The lenses for the FS series were made by Canon-Optron to Takahashi spec’s, like other Takahashi
objectives.
The FS-128 shares the
same lens design and cell with its larger and smaller siblings, all of which
are ~F8 fluorite doublets with the positive fluorite element on the front
(hence the ‘FS’ – Front Surface – moniker). This means the lens is a
conventional ‘Fraunhofer’ doublet, like a basic achromat, but with fluorite as
the crown.
Does fluorite offer a
genuine advantage over high-fluoride glass like Ohara’s FPL53 or OK4 (the stuff
LZOS make and use)? Possibly. Fluorite is not a glass, it’s a crystalline
mineral and it has optical properties that no glass can quite match, including very high transmissivity and low scatter.
The FS manual has this to say:
“… the use of
multi-coatings further increases light transmission over any ED glass. This
makes any fluorite objective brighter than any comparable glass objective …”
Does putting the
fluorite at the front make for a worse optic, as some have claimed? I believe
not. Check-out the excerpt from the FS manual below.
Meanwhile, independent
tests have found the FS-128 to be a true apochromat, at least as well corrected
as, say, a TEC-140 ED triplet. Despite being a relatively large doublet of
moderate focal length, the FS-128 manages to be a proper full-on apochromat,
something lots of ED doublets are not.
But the goodness doesn’t
stop there, because like all FS Series objectives, the FS-128 was very well
corrected for off-axis astigmatism and coma as well. What’s more they are
robust – the friend who bought mine rested it on its end and his son knocked it
over. CRASH! It was fine.
Overall,
don’t think of the FS-Series as inferior to a triplet. Instead think of them as
being optimised for visual use, offering razor-sharpness and maximum contrast
in a quick-cool, lightweight package.
Tube
Apart
from the objective design, the rest of the OTA is conventional, if large
(1176mm long by 145mm diameter, according to the manual). One advantage of the
doublet design is the deceptively (it looks massive) light weight of the OTA at
just 7.5 Kg. To get a sense of its size, see the title photo with the FS-128
mounted on an EQ6 with a Sky-90.
Takahashi
are famous for good finish and the FS-128 doesn’t disappoint. The finish is
different from, say, a Tele Vue though. The whole
thing has a spare and workmanlike feel – no mag-wheel focuser knobs or fancy
anodising here. The tube is simple, high gloss white enamel with a blue lens
cell ring and the focuser in textured pale lime green. It may not be fancy, but
this is a beautifully made OTA nonetheless, with flawless paint,
blacker-than-black baffling. Lens cell and focuser are threaded on and then
secured with inset screws so tiny you struggle to make them out at first
glance.
The
dew shield is very large and fixed by (very) fine threads – it’s difficult to fit
without cross-threading and you wouldn’t want to have to remove it for packing
every time you put the scope away.
The
cast aluminium, felt-lined “manhole cover” is a feature of the FS series. In
practice it is very easy to use, sliding easily in and out, but not falling if
you accidentally tilt the tube downwards. It has a central stop-down port of
50mm diameter (intended for use with Solar projection?)
Takahashi’s
FS-Series all came with a lens cap like a manhole cover!
Focuser
The
focuser is typical Takahashi – a large (2.7”), long-travel rack and pinion with
a big tensioner knob on top and those signature silver wheels.
The
focuser isn’t quite as precise as a Feathertouch, but
is very smooth and completely stable, without any free play or backlash and
comfortably takes several kg of load if required. Unlike the shorter Tak’ focusers I have seen (FS-60, Sky-90), but just like
the TSA-102, there is little or no image shift or tilt. You can completely lock
the focuser using the knob on top which works very smoothly and progressively
and again creates minimal image shift.
The
visual back threads on and can easily be swopped for others, or for an endless
array of accessories from reducers and extenders to rotators. I had an electric
focuser attached to it for use with the webcam, but I never needed to use it
visually. People complain about Takahashi’s endless threads, but they have one
huge advantage over push-fit: perfect optical alignment and freedom from play.
FS-128 Standard 1.25” visual back.
FS-128 2.7” focuser with JMI electric
focuser in place of visual back.
Mounting
The
FS-128 has an elegant clamshell with a massive chunky clamp knob and a
double-hinged mechanism that makes it very easy to use, even with cold hands
(attention to details like these are what, in part, make Taks
special).
The
clamshell has two M8 bolt-holes spaced at 35mm apart which fit any Takahashi
mount. If you want to attach it to a dovetail a specialist item may be required
– Astro-Physics (for example) make beautifully engineered Losmandy
D dovetail plates with one or more circular indents for Takahashi clamshells.
You
need a good sized mount for the FS-128, not because it
is heavy, but because it is so large and long. It is too heavy for a Vixen GP
and a GPDX struggles; the more recent Sphinx and derivates would probably take
it. An EM-10 or EM-11 might just about work. I used the FS-128 with Takahashi’s
own EM-200 on the optional long pier, which was a simply perfect and very
stable match (see below).
If you don’t want to splash out for the rather over-priced EM200, or want
something with proper GOTO and fast slewing, an EQ6 Pro would be a fine choice
for mounting the FS-128 (see title photo above). One of Takahashi’s own
dovetail bars works a treat for this purpose and fits directly to the bottom of
the clamshell.
Takahashi
FS-128 on EM200 mount – the perfect combination.
Accessories
Most FS-128s would have been bought with the
7x50 finder. The 7x50 is a good finder and can be fitted with an illuminator,
but it is very expensive, has less eye relief and a smaller field than the
6x30. The latter is one of the very best finders available, with loads of eye
relief and a wide sharp field.
Takahashi made both a 1.6x extender and
a 0.74x reducer for the FS Series refractors. The FS reducer was a premium
product that delivered a 770mm focal length and large image circle, but it was
an expensive option.
Takahashi’s 7x50 finder.
In
Use – Daytime
One of the stiffest tests of chromatic
aberration does not involve the night sky at all: dark objects, such as distant
tree branches, viewed at high magnification against a bright daylight sky, show
up chromatic aberration in all but the most perfect APOs. The FS-128 showed no
in-focus chromatic aberration at 100x plus, but defocusing did show a trace of
violet one side, apple-green the other.
In
Use – Astrophotography
The FS-128 is slow for an astrograph,
but blue bloat is minimal and off-axis aberrations well controlled even without
a flattener. See the attached single frame of Comet Holmes imaged with the
FS-128 more than a decade ago. Not that the vignetting evident was probably the
result of a small-aperture T-Adapter and doesn’t reflect the FS-128’s potential
coverage with modern gear.
Like other razor-sharp apochromats, the
FS-128 takes great pictures of the Moon – sharp and detailed.
I did quite a bit of planetary imaging
with the FS-128, back when a webcam was the best tool for the job and got some
decent results despite its natively small image scale. See the single frame of
Mars and another of the Lunar crater Clavius (a
modern planetary camera would doubtless do much better).
Single frame of Comet Holmes, Nikon D40
91s at ISO 200.
Single webcam frame of Mars through
FS-128.
Single webcam frame of Clavius crater through FS-128.
In
Use – The Night Sky
General
Observing Notes
The FS-128 is
so good that generally it just gets out of the way. I end up out of review mode
and into observing mode, which is a good thing. Focus snap is perfect, stars
brilliant and sharp. There is no false colour, no flare or fuzziness. The 2.7”
focuser may not have dual speed, but it doesn’t really need it for visual use –
it is accurate, smooth and stable even with big 2” eyepieces.
Cool
Down
The
first thing you notice is how quickly the FS-128 cools: much faster than the
smaller TMB 100/8 triplet, for example. After 20 minutes it is usually usable
and is completely cooled after less than an hour from a warm house.
Interestingly, the cell seems to do a great job of maintaining lens figure
during cool-down; the only symptom of ongoing cool-down is currents in the big
tube.
Star
Test
FS Series
lenses were supposedly spec’d to a minimum of 95% Strehl
and the star test confirms it, with perfect and virtually identical diffraction
rings either side of focus and a textbook PSF in-focus.
FS-128
diffraction patterns either side of focus.
The
Moon
The
Moon shows a wealth of detail in the FS-128, a real step-up from a four-inch
APO. The contrast is fabulous and for some reason my other APOs seem to give a
slightly yellowish tint and softness compared to the Takahashi. Rilles and craterlets and low-contrast ejecta blanket
details stand out in stark contrast where you hadn’t seen them before.
One
steady night, I could see detail inside the twin Messier craters and individual
mountains around the margins of Mare Criseum were
standing out in 3D on the terminator: no false colour and absolute crispness in
the details. It’s easy to waste time just cruising over the moon with this
level of detail on offer and the perfect tracking and easy hand controls of the
EM200 make it a breeze. Lunar observing feels more like exploring with this set
up. A wide-field eyepiece like a Nagler gives more of
a “Lunar Module window” feel than almost any other scope I’ve used this side of
my TMB-175.
Mars
The FS manual says,
“The FS refractors are particularly suited for planetary observation. Their ultra high contrast, sharp images will reveal a wealth of
detail.” True …
Mars
is a difficult object, but the very high optical quality and precise baffling
of the FS-128 help make it appear as a 3D planet with changing texture and
albedo in its surface features, rather than the bright blurry orange ball that
an imperfect scope shows.
Many
refractors make a mess of Mars because they are highly corrected in the blue
and green, but fall off a cliff in the red; not so the FS-128.
The
FS-128 shows significantly more than smaller apochromats and can be really
involving. Mars showed quite a lot of detail in the albedo features during the
2005 opposition and I was able to explore all the major highlights, including Syrtis Major, the polar caps, bright Hellas, Mare Acidalium.
I
tended to use a 5mm eyepiece with the FS-128 for planets (giving 208x) with the
little Pentax 5mm SMC ortho’ being my absolute favourite. I also really liked
the TV 3-6 zoom and used the 4mm setting (260x) on Mars as it shrunk after the
2005 opposition.
Jupiter
Jupiter
is always a difficult target visually, but the FS-128 gives a lot of cloud-belt
detail when the planet is high in the sky and with good seeing: lots of smaller
dark storms mottling the belts and shading in the polar hoods, as well as the Great
Red Spot and shadow transits sharply picked out on the clouds.
Saturn
Saturn
is wonderful through the FS-128, with the crepe ring on view and lots of subtle
shading in the cloud belts.
Deep
Sky
This
FS-128 is a nice compromise between useful aperture and a shortish focal length:
you still get a decent wide (and flat) field, but stars and nebulosity are
brighter than with smaller apochromats. It may have been designed for Lunar and
planetary, but the high contrast and brightness make this my absolutely
favourite scope for deep sky.
Open
clusters are stunning in the FS-128, with that jewels-on-velvet effect. A 26mm
Type 5 Nagler will fit the entire double cluster in
the FOV. Why do optically fine refractors like the FS-128 give a level of
brilliance to stars that others scopes can’t match? Simply this – they throw
more light into the tight inner airy disk and less into the diffraction rings;
the better the, optics the stronger the effect. Compared to smaller apertures,
the FS-128 delivers brighter (true) star colours too.
My
site may have poor seeing, but it is quite dark, so the Orion Nebula is a
stunning mass of whirls and tendrils, much more detailed than through smaller
apertures.
Summary
For
some years this was my favourite telescope and one of the few that I have owned with which I can find little to
criticise. The FS-128 just delivers wonderful views and images of anything
you choose to set it on.
Personally,
I preferred the light weight, quick cool-down time and perhaps slightly
superior transparency and contrast of the FS-128 to the complete lack of
chromatic aberration that the most perfect triplet, such as the newer Takahashi
5” - the TOA130 - would provide. In any case, as I’ve said, the FS-128 gives
very little away to other super-APOs in terms of CA (or anything else). And the
TOA-130 is much heavier (especially
once you add in the necessary counterweight).
In
common with the rest of the FS-series, the FS-128’s main drawback is its size:
this a light but large OTA and needs at least a medium-sized mount.
As
I said at the start, the FS-128 has few competitors, even now. Most larger
apochromats are now triplets, with their inherent extra weight and slow cool-down.
If Takahashi produce an FC-125 I will be in the queue.
The FS-128 still gets my very highest
recommendation if you can find a good one.
Updated by Roger Vine 2018
