Takahashi FC-100 Classic (‘F’ Lens Version)
I
recently reviewed Takahashi’s latest 100mm apochromat, the FC-100DZ that brings
back an F8 Steinheil with superlative correction, including for high-power
visual use. It got me wondering about its illustrious forebear, the classic
FC-100 from the 1980s, a scope that’s loved by many in-the-know Takophiles, including Ed Ting.
Then,
as luck would have it, a rare late example came up for sale and I grabbed it
with a view to this review, but also to compare it with the new version and see
what thirty years of optical technology (and a ban on flint glass containing
heavy metals) have done for a famous design.
At A Glance
|
Telescope |
Takahashi
FC-100 |
|
Lens
Design |
Steinheil
fluorite doublet |
|
Aperture |
100mm |
|
Focal
Length |
800mm |
|
Focal
Ratio |
F8 |
|
Tube
Diameter |
114mm |
|
Length |
800mm
(31.5”) w/o visual back |
|
Weight |
4.2Kg (w/o
ring and finder) |
Data from Me.
Design and Build
This
scope, Takahashi’s original and classic FC-100, was introduced back in 1981,
long before the digital imaging revolution that led to the rebooted FC-100D.
Even so, its appearance and features have similarities with Takahashis from
every decade since.
At the
time, the FC-100 was part of a range of F8 fluorite doublets, from the
diminutive FC-50, through the FC-60, FC-76 and culminating with the FC-125. The
FS-range that superceded it changed the line-up slightly, swapping the F8 FC-60
with the hugely popular F6 FS-60 and adding a top-of-the-range 6” F8 fluorite
doublet, the FS-152 (I almost bought the last new one in the U.S., but that’s a
story for another time).
Note
that an FC-150 doublet was never offered. Instead, Tak’
made an FCT-150 – an F7 triplet that was fabulously expensive back at a time
when a 6” fluorite blank for the centre element cost $$$Big. In fact, that
FCT-150 was the top of a parallel range of rare and desirable triplet imaging
refractors that included an FCT-100 introduced in 1984. The FCT-100 looks much
like the FC-100, but has a bigger focuser and a focal length of just 640mm.
The
FC-range were all designed for excellent visual performance (especially for the
Moon, planets and double stars), but for 35mm emulsion imaging with a flattener
too.
The
FC-100 has developed a reputation for being one of the finest Takahashis for
contrast and high-power sharpness and some (perhaps unfairly) regard it as
superior to the FS-102 that superceded it.
This
particular FC-100 dates from the early 1990s – the last few years of
production.
Various
different versions were available over the years, including one that replaced
the standard
2.7” focuser with a heavy-duty item for imaging. However, unlike the FS-102, I
can’t find evidence of a sliding dew-shield version of the FC-100 (but as
always, reach out if you know better!)
1980s
FC-100 catalogue entry (image credit Takashashi).
The FC-100 and FC-50 were once part of
a whole range of Takahashi F8 Steinheil doublets.
Decals are classic 1980s Takahashi,
but early examples would have had grey detailing, like the FC-50 above.
Early 1990s FC-100 reviewed here, alongside
2020 FC-100DZ – both are 100mm F8 Steinheil fluorite doublets.
Optics
Both
the original FC-100 and the FS-102 that followed it from the early 1990s were
~F8 air-spaced fluorite doublets (made by Optron in
Japan as always). However, though the FS-102 has its fluorite crown element at
the front, making it a Fraunhofer type doublet (like most refractors), the FC-100
is a Steinheil doublet with the fluorite positive convex element at
the back. Takahashi have reverted to this lens type for their recent FC-100D
and FC-76D models.
Takahashi
adopted the Steinheil design because fluorite couldn’t be coated at the time
and was vulnerable (fluorite is soft and may deteriorate), so putting it at the
back, out of the way of lens wipes and dew, made sense.
That
fluorite crown was partnered with a flint containing heavy metals that wouldn’t
be used for environmental reasons today, but allowed excellent correction for a
doublet – one of the reasons the original FC-100 has such a strong reputation.
A
key point here is that most FC-100 Classics have an uncoated fluorite element
at the back, which means they transmit a bit less light than later models. However,
the FC-100 pictured dates from the last years of production, when some lenses
with fully coated fluorite were fitted. These later lenses have a red capital
‘F’ engraved in the lens ring.
Coatings
are an older type with a reddish-purple hue, but transparency is very good even
by modern standards – see comparison with a 2020 FC-100DZ below. It’s
interesting to note that my AP 130 EDT, made around the same time, has only
single coatings.
The
FS-102 that replaced the original FC-100 has a focal length of 820mm (F8.1),
making it slightly slower than the FC-100 which has a focal length of exactly
800mm, same as the recently introduced FC-100DZ (confusingly, of the other
recent FC-100s, the DC and DF are both F7.4, whilst the DL is F9).
Unlike
the rebooted FC-100D, this original FC-100 has a ‘proper’ lens cell, attached
with three pairs of push-pull screws to allow collimation. Whether this is
‘better’ than the integrated, non-collimatable cell in the FC-100D I can’t say,
but it does cool down very rapidly and benignly. Oddly, only the FC-60 had a
non-collimatable objective, the rest of the range (FC-50 included) had a
‘proper’ lens cell like this FC-100.
Original
cast dew-cap with solar port.
That
red ‘F’ denotes a coated fluorite element and modern performance.
Takahashi
FC-100 classic (right) with FMC ‘F’ lens compared with latest FC-100DZ (left).
Tube
(Note: I’ll go into some detail on finishes as they vary and
can be confusing when searching for a used example. You can read more about
Takahashi colours and finishes here.)
The OTA has a large (for a 4” refractor), fully baffled tube,
114mm in diameter, with a fixed dew-shield. As usual, both focuser and lens
ring thread on, held tight with tiny Allen grub screws.
In this case, the tube is finished in the usual off-white
enamel, the focuser and lens ring in the knobbly lime green powder coating that
has only recently been superceded by a bluer shade. Earlier FC-100s may have a
glossier grey enamel finish to the focuser and lens ring, seen on the FC-50
above.
The tube looks very similar to the later (only by a
few years in this case) FS-102, apart from the different dew-shield stickers.
Later FS-102s were distinguishable by a gloss blue lens ring, but earlier ones
had the same lime green lens ring as the FC-100.
However, the FC-100 is actually significantly
shorter than the FS-102 and a little lighter too – the FC-100 seems like a
smaller and more handy scope than its replacement model.
Internally, the tube features Takahashi’s usual
multiple knife-edge baffles for minimum stray light and maximum contrast.
The large dewshield is closed by a cast cap that
looks a bit like a small green manhole cover. It slides into the dewshield on
felt and has a 50mm threaded solar viewing port. It’s a heavy thing, but
functionally the best I’ve ever used. Modern Takahashis have press-over tin dew
caps that are harder to get on and off and much less classy and distinctive.
FC-100
(top), FS-102 (bottom) share tube sizes and focuser, but FC-100 is shorter.
Focuser
The FC-100 uses the 2.7” focuser that featured on
many Takahashis of the era, up to and including the FS-128. Despite being only
single speed, it has loads of travel, is smooth and stable and copes well with
heavy loads like CCD cameras and binoviewers. Astro Physics’ competing 2.7”
focuser from the same era boasts CNC construction, but is functionally no better
in my opinion, if anything slightly less smooth.
The silver knob on top is the lock screw and has an
excellent action. Again, it’s progressive and effective but avoids much image
shift. When new (and then if looked after), these focusers have very little
image shift in general, but if abused or tampered with image shift can be a
problem – caveat emptor when buying used.
The large drawtube was designed to avoid vignetting
on a medium-format emulsion camera and so works well with CCDs that have larger
sensors and full-frame DSLRs.
The focuser has Takahashi’s signature cast and
silver-anodised focuser wheels. On cheaper models, such as the FC-60 of this
era, those knobs could be plastic imitations, but on the FC-100 they should
always be the real thing.
The standard visual back in those days was a 1.25”
that has Takahashi’s signature silver-ringed twist-lock and threaded into a
heavy cast and green-coated adapter to the M72 draw-tube thread. The FC-100
would originally have shipped with several short, threaded extension tubes for
straight-through viewing.
A 2” visual back was originally available as an
optional extra and M72 adapter rings can still be obtained today to fit a
generic 2” visual back (often called an ‘eyepiece holder’). For example, Borg
currently make an M72-M57 adapter and several sizes of M57 eyepiece holder to
fit.
Takahashi
2.7” cast focuser was fitted to many of their scopes: it is smooth, stable and
has lots of travel.
CNC 2.7”
Astro Physics focuser from the same era is no better than the cast-bodied Tak’.
Mounting
Like other Takahashis up to this size, the FC-100
has a cast clamshell-style ring with a dual hinge, a heavy chromed clamp knob
and thick (green) protective felt. The clamshell is equipped with a pair of
holes for M8 bolts at 35mm spacing for direct fitment to Takahashi mounts.
3rd party dovetail plates are available
to fit this hole spacing, but for fitment to a Vixen-style dovetail (also
Sky-Watcher etc), Takahashi make a slim silver dovetail (intended for the Mewlon 210) that has the same chamfer.
The FC-100 is quite large for a 4” refractor, but
it’s notably lighter and shorter than the FS-102 that followed it and so a bit
easier to mount. Small to medium German equatorial mounts should support it
fine; my Vixen SX2 needs only its lightest counterweight and is very stable
with the FC-100.
For quick looks with an altaz mount (something the
FC-100 works well for, due its rapid cooldown), you would potentially need
something larger than a Vixen Porta or SW AZ-4 for stability at high powers.
FC-100 OTA
with clamshell ring and 1.25” visual back.
Accessories
The complete package would have shipped with the
clamshell ring and 7x50 finder as standard, but you could have bought a bare
OTA and then a smaller finder – 5x25 or 6x30. All three finder types are excellent;
but with the optional illuminator, the 7x50 makes finding things a doddle: it
boasts an illuminated reticle with a central gap for
the target, good eye relief, super-sharp optics and a wide flat field.
Other accessories would have included a camera
rotator and reducer/flattener that shortened the FC-100’s focal length to an
ambitious F5.9.
Illuminated
7x50 finder was standard.
6.3° FOV of
the 7x50 Takahashi finder – flat and sharp.
In Use – Daytime
Viewing silhouetted branches at 100x gave a very
sharp view with only the faintest traces of false colour either side of focus
and very little in focus. For comparison, the latest FC-100DZ showed no false
colour at all, whereas a TV-85 generated a light wash of green and purple
either side of focus at the same power and with the same type of eyepiece (a
Tele Vue Nagler Type 6).
One big difference compared with a modern doublet is
evenness of illumination and you can see this on telephoto images taken with
the FC-100 during the day. Centre field sharpness and false colour correction
are excellent, but brightness varies off-axis in a way you don’t get with an
FC-100D. I’ve seen this effect in other older Optron
lenses, such as the Vixen FL80’s.
Prime focus daytime
shots are sharp but illumination is uneven, typical of older doublets.
100% crop
shows low level of false colour.
In Use – Astrophotography
Daytime telephoto images are noticeably inferior to
a modern FC-100D in terms of even illumination, but for imaging (at least on
smaller sensors) the FC-100 Classic produces serviceable subs even without a
reducer.
Like most quality apochromats, the FC-100 produces
excellent prime-focus images of the Moon that are sharp from limb to limb.
Flatness
across APS-C sized crop is quite good.
In Use – Observing the Night Sky
General Observing Notes
The cast manhole cover dewcap
remains the best ever. It slides in and out with perfect friction – easy to
remove and put back (in the dark, when you’re cold and tired) - but never just
falls out. I much prefer it to the press-over tin on modern Tak’s,
honestly to Tele Vue’s screechy screw-caps too.
The FC-100 is just a pleasure to use: it’s ready to
use after a few minutes, shows brilliant, pinpoint star images across the
field.
The focuser just works, even with heavy diagonals
and eyepieces, even after thirty years of regular use. It has little image
shift and no tendency to rack out on its own. The lock knob on top is
progressive, effective and again free from image shift.
I appreciate the Steinheil lens for a scope that
gets used a lot, just because I worry less about the lens getting dewed up
(it’s fronted by hard flint glass, not a fragile fluorite or ED crown).
Cool Down
In keeping with its thin lens elements and proper
cell, the FC-100 is fast-cooling for a 4” refractor, ready within 15-20
minutes.
Star Test
The star test appears excellent with evenly illuminated
similar diffraction rings either side of focus and a very tight and dim
diffraction ring and dazzlingly small Airy disk in focus.
The Moon
The FC-100 gives outstanding lunar views. Think
Tele Vue, think the deep sky; but think classic Tak’,
think Moon and planets. Minimal false colour means that terminator shadows are
intense black against brilliant white, ditto the bright limb against dark
space, with minimal scattered light and no violet wash of false colour to
reduce contrast.
I’ve mentioned this before, but one test of a good
lunar scope is viewing lunar mountains etched against black space on the Moon’s
very edge and Tak’ doublets do this especially well,
with minimal scatter and false colour fringe to interfere.
Highlights of a ten-day gibbous Moon included the
rugged hills of the Montes Carpatus north of crater
Copernicus, picked out in long-shadowed dawn relief. Near the southern limb,
prominent craters Clavius, Longomontanus and deep Moretus with its tall central peak near the very edge of
the Moon, really caught my attention. Further north, I found multiple
craterlets in Plato (students at his Athenian academy, perhaps) and followed
wrinkled ridges around mathematicians Euler and Lambert in Mare Imbrium.
Mars
Takahashi F8 fluorite doublets
always seem to work well on Mars because they are well corrected into the red
(whereas some ED doublets just aren’t) and the FC-100 is no exception.
At 13” in size, well
after the 2020 October opposition, Mars at 267x with the 3mm setting of a
Nagler Zoom was clear and sharp, though in some ways I preferred the view with
a 4mm Zeiss Abbe Ortho giving 200x.
In both cases, Syrtis Major was clearly visible and the gibbous disk
rendered crisp and with no false colour in or out of focus. Overall, the view was
indistinguishable from the FC-100DZ alongside, with both scopes delivering a
sharp view, snappy focus at 267x and complete freedom from chromatic
aberration.
Both fluorite scopes gave
better views that the two ED glass doublets I had to hand (Sky-Watcher’s 120ED
and Tele Vue’s TV-85), both of which sloughed off red flare into the seeing and
gave a slightly mushy view with lower contrast and less snappy focus.
Deep Sky
Views of deep sky objects with a Panoptic 19mm (an
excellent deep sky eyepiece giving a moderate magnification of 42x and a nicely
wide, flat field of view) were outstanding with dazzlingly brilliant and
strongly (natural) coloured brighter stars, peerless contrast and a very flat
field.
I had spectacular views of all my favourite
early-winter DSOs: diamonds-in-mist Pleaides; the string of open clusters large
and small in Auriga; smaller planetary nebulae like the Dumbbell, Ring and
Crab; globular clusters - M15 in Pegasus, M13 in Hercules - that start to
resolve nicely at this aperture.
The outstanding contrast makes low-power surfing of
the Milky way especially pleasurable – a feast of star dust and clusters. The
FC-100’s compact size and light weight mean it’s safe to loosen the mount
clamps and just pan it by hand.
Overall deep sky performance was very similar to a
modern 100mm (such as the FC-100DZ I tested alongside) thanks to that fully
coated ‘F’ lens. Older models with an uncoated fluorite element are likely to
perform less well for deep sky.
Takahashi doublets have a reputation for resolving
double stars, due again to their high contrast and pinpoint stars. The Double Double in Lyra showed an excellent split, one of the best
I’ve seen in a 4” scope: initially at 114x with a 7mm Tak’
Ortho, then at 200x with the 4mm setting on a Nagler Zoom yielding a big dark
gap between the components of both stars. Likewise, Rigel was a very easy split
with the fainter companion floating free of the dazzling main star.
Summary
A classic Takahashi fluorite doublet notable for its
beautiful-but-simple build quality, ease of use and all-round excellence. The
FC-100 gave just wonderful views of everything I set it on, from Mars, to the
Moon and deep sky too. Light, fast cooling and trouble free, it’s a mid-sized refractor
that works really well for quick looks as well as longer observing sessions.
Whilst I didn’t have an FS-102 for comparison, I
suspect performance of this fully-coated ‘F’ lens version of the FC-100 is very
similar, whilst it is usefully shorter, lighter weight and likely to stand up
better to regular dewing thanks to having its flint element up front.
Meanwhile, the FC-100 gives very little away to the
new FC-100DZ for visual use – just that very last trace of chromatic
aberration.
The FC-100’s older lens design does, however, give a
less evenly illuminated field for imaging and you might be better off with an
FC-100D if imaging is your main use (unless you can find one of the premium
0.7x reducers originally sold as an accessory).
The classic FC-100 deserves its
reputation for excellence, especially in this late version with a coated
fluorite element. It’s a classic that makes few compromises. Highly
recommended.
