Takahashi FC-100DZ Review
Takahashi
pioneered the fluorite doublet apochromat. It’s been making them for fifty
years. For decades the sweet spot was a four-inch F8 – a great all-rounder. But
then when Takahashi replaced the FS-102 with the FC-100DC and FC-100DF they
changed the design to appeal to a more modern astronomer.
How
so? Well, the new models re-introduced the Steinheil
lens configuration of the original FC-100 (succeeded by the FS-102 in the early
1990s), but with a faster focal ratio of F7.4, a design optimised for digital
imaging (hence the ‘D’), an eco-glass flint element and a lightweight tube. It
felt like quite a radical change, because there was a downside - the new
FC-100D slightly underperformed the original FC-100 for the critical planetary
viewing Tak’ doublets were famed for.
Later,
the limited-edition FC-100DL rectified that. But at F9 and with the same fixed dewshield as the DC and DF, it was even less portable than
the chunky old FS-102, even more of a specialist planetary scope.
The
latest and fourth variant, the FC-100DZ on test here, offers yet another take
on the theme of a light and compact 4” fluorite doublet. It splits the
difference between the other FC-100D models with a ‘classic’ focal ratio of F8 (same
as the original FC-100), but uses a sliding dewshield
to retain the portability of the F7.4 models.
So what does the DZ bring to a crowded model
line up? After all, the FC-100DC and DF are compact and usefully fast at F7.4, whilst
the F9 FC-100DL is optimised for high power lunar and planetary viewing, if
that’s your thing. The answer is that the DZ promises similar planetary
performance to the DL, but with the compactness of the DC and DF. Does it
succeed? Read on to find out ...
At A Glance
|
Telescope |
Takahashi
FC-100DZ |
|
Aperture |
100mm |
|
Focal
Length |
800mm |
|
Focal
Ratio |
F8 |
|
Length |
650mm with 2” visual back (595mm without) |
|
Diameter |
95mm |
|
Weight |
3.5Kg tube (4.6Kg w/ ring and finder) |
Data
from Me.
What’s in the Box?
Takahashis typically
come beautifully packed in a logoed carton closed with heavy staples, the
accessories separately packaged for extra security. Unboxing is a real event:
Design and Build
Even
as far back as the early 1970s – when I was a boy and men were walking on the
Moon – Takahashi refractors had a look they retain to this day, a high-end
version of the classic Japanese refractor. Back then, others – Nikon, Pentax,
Swift - were doing much the same thing. Only Takahashi still are.
That
signature Tak’ design - a high quality sand-cast
focuser with cast silver wheels, an oversized tube with knife edge baffles and
a cast lens ring, all threaded together - carries on to this their latest
model. It has a slightly retro vibe now, a kind of artisanal chic in the face
of mass produced scopes from China.
Both
the original FC-100 (see below) and the later FS-102 had a hefty, fully baffled
tube with a big focuser. But that changed when they replaced the old FS-102
with new FC-100D with its narrower tube and lighter, more compact focusers
borrowed from the FS-60C and the old Sky 90. The result is that all the FC-100D
models are lighter, more transportable and easier to mount than those older
models and this new FC-100DZ carries on that philosophy.
The
new DZ looks much like the older DF and DL models, with which it shares a
focuser. Compared with the FC-100DL which it effectively replaces, the DZ
version is much shorter but not that much lighter due to its sliding dewshield. The DZ looks similar to the FS-102S, but is
actually a smaller scope:
Fc-100DZ
(dewshield extended) alongside a classic FC-100 from
thirty years before.
The
rare FS-102S looks similar to the DZ, but has wider tube, heftier focuser.
FC-100DL:
the first ‘planetary’ FC-100D, it’s much longer than the DZ at F9 and has a
fixed dewshield.
Optics
Many will choose the DZ on the basis of its
new and special optics, so I’m going to go into some detail here. Skip it if
you’re not interested.
The original FC series (including the FC-100) introduced
an unusual lens design called a Steinheil that puts
the positive low-dispersion crown (in this case fluorite) element at the back,
where most doublet refractors put it at the front in the Fraunhofer design.
Takahashi originally did this because fluorite is fragile and hygroscopic (it
absorbs water and degrades) and they couldn’t protect it with a coating back
then, so they put it out of harm’s (and dew’s) way at the back.
So most original FC-100s had an uncoated
fluorite element. But not all. In fact, for a year or two before they
discontinued it in the early 1990s, Takahashi built a version of the FC-100
with a multi-coated fluorite element. The lens cell of those FC-100s is
inscribed with a red ‘F’ (see image below).
I’ll say again here that I don’t believe the Steinheil design is optically better per se. In fact, once Tak’ could coat the fluorite they soon put it back into the
‘normal’ front position for the later FS series. Below is a note from the old
FS series manual that discusses this.
So you might ask why Tak’
went back to the Steinheil format for the FC-100D,
especially since that old FS manual suggests the Steinheil
is more costly? One possibility remains durability. Some Takahashi lenses with
ED glass or fluorite at the front have suffered from heavy exposure to dew. Four inch refractors
typically get used a lot in my experience – in and out every clear night,
regularly dewing and fogging. So perhaps it’s a wisely rugged approach.
For whatever reason, the original Steinheil FC-100D lens found in the DC and DF models does slightly
underperform the original FC-100 for high power viewing, as I’ve noted already.
One likely reason is the faster F ratio. Another is that the old flint glasses performed
better, but were doped with heavy metals, especially lead.
Those leaded flints are no longer used for
environmental reasons, so Takahashi have taken a more innovative route with the
DZ (one pioneered by the FOA-60) - a special exotic glass – presumably one
with extra high dispersion - for the flint mating element is claimed to give
better correction than the DL, despite a shorter focal length.
The spot diagrams and crossings published by Tak’ (see below) suggest that the DZ does outperform the
DL, whilst coming close to the ED triplet TSA-102. For the FS-102 the situation
seems less clear. From what I can see, the multi-purpose DZ is better at the
blue end for digital imaging (it’s still an FC-100D, remember).
However, The FS-102 appears unbeatable in the red. This makes sense for Mars given
that the FS-series manual stated, “The FS refractors are particularly suited
for planetary observation”.
In any case, Tak’
claims the Strehl stays above 90% across almost the
whole visible spectrum, so that spherical aberration remains diffraction limited
from blue to red, only dipping a bit in the far violet. What does that mean in
practice? The lens is able to focus properly for all colours of light, avoiding
the problem of many doublets which can behave as if poorly figured in the blue
and/or red and so give blurry views of Mars and bloat white and blue stars in
images. Tak’ suggest that blue bloat on images is
reduced by about half compared to the F7.4 FC-100D.
So, on paper at least, its special flint
element gives the FC-100DZ very high performance for a doublet. No, it’s not
quite as theoretically perfect as the FOA-60, but it avoids the very large air
gap between the elements (and so heavy cell sensitive to collimation) used in
that scope: the DZ lens (still made by Canon/Optron
as always) has a foil spaced air gap and a regular cell with no collimation
adjustment.
Needless to say, coating quality is of the
very highest, though it doesn’t look much more transmissive than the FMC FC-100’s
(see below).
FC-100DZ
objective has premium coatings, reveals knife edge baffles behind.
2020
FC-100DZ on the left, c. 1992 FC-100 on the right. Note the FC-100 is an ‘F’
lens, so both are fully multi-coated 100m F8 Steinheil
fluorite doublets.
FC-100DZ Strehl stays
diffraction limited from blue to deep red.
The FC-100DZ improves slightly on the older F9 DL,
esp. for the g-line.
Some Takahashi spot diagrams for comparison.
Excerpt from the FS-series manual regarding front
vs rear fluorite: the FS was Front Surface fluorite.
Tube
The tube is basically the same as the other models
in the new ‘D’ series, but with a sliding dewshield
for extra compactness (a feature not seen on a Takahashi 4” since the demise of
the triplet TSA-102S). So it’s the usual 95mm O.D.
aluminium tube, carefully baffled and blacked within and enamelled in a
fetching creamy white without. Overall fit and finish is of the highest
quality.
The long dewshield
threads onto a sliding silver ring and locks with a thumbscrew. Internally, the
dewshield has machined-in ridge baffles and is
painted flat black to help prevent contrast-reducing stray light. The
lens cap is a pressed tin item like most Takahashis
nowadays, in this case finished in silver to match the lens ring. Owners of
older models will miss the cast ‘manhole cover’ (but not its weight), because
it was just so easy to fit and remove, whilst the tin cap can be a tight fit.
At
~3.5 Kg bare, the DZ is about a kilo heavier than the lightest of the new
range, the FC-100DC. But compared with the original FC-100, it’s ~1 Kg lighter
and more compact at 95mm vs 114mm diameter and just 650mm long including the
(now standard) 2” visual back (see comparison photo above). Unthread the visual
back and you get down to 595mm, but you’ll need to unthread the focuser to
make the FC-100DZ carry-on portable at just 540mm.
Note that Takahashi’s own quoted length of 770mm
likely includes the extension tube and/or 1.25” adapter. For visual use with a
2” diagonal neither are required.
FC-100DZ OTA details.
Focuser
Like the older FC-100DF and DL, the DZ uses the
compact focuser from the old Sky 90, avoiding the very small FS-60C derived
unit found on the entry-level FC-100DC. It’s a shorter and lighter unit than
the focuser fitted to the FS-102, but otherwise it’s just like any other Tak’s focuser: cast and powder coated (with the newer blue
shade), with tension adjustment via the big silver knob on top.
The focuser has a reasonable ~63mm of travel and
will accommodate most diagonals/eyepieces without the extension. The extension
is needed for straight-through viewing or imaging.
The drawtube is 70mm in diameter and the standard
2” visual back unscrews to allow other accessories to thread onto an M67
internal thread.
The big advantage with this focuser compared to the
older units is that it’s much shorter (and lighter), but the downside is a
short bearing surface for the drawtube. Perhaps that’s why I’ve seen some of
these focusers (though only on used scopes) with too much slop and image shift,
perhaps caused by lots of use with heavy CCDs or binoviewers. At high powers
you should expect a small shift when changing focus direction, but large jerky
movements mean a worn focuser. This
example, bought new, is free of image shift.
Like all Takahashi focusers, the action is oily
smooth and precise. For a relaxed F8 light-cone, no microfocuser
is needed to get perfect focus.
Note that the silver cast focuser wheels are just
that on the DZ. The entry-level FC-100DC makes do with plastic imitations,
perhaps to save cost but also to save a bit of weight (they really are heavy).
Focuser has 63mm travel, 70mm diameter drawtube.
Left: FC-100DC plastic wheel, Right:
FC-100DZ cast wheel.
Mounting
The OTA is mounted in the Tak’
standard cast clamshell which directly bolts onto Takahashi mounts via a
standard pair of M8 holes, although you can fit a dovetail bar – Takahashi make
a slim silver one that works with a Vixen/CG5 shoe. It’s not widely available,
but Takahashi do in fact make a dovetail to fit their mounts to make swapping
scopes easy.
The light weight and short tube of the DZ mean it will work
on just about any small equatorial such as an EQ5, or an alt-az mount like a Vixen Porta. This is a big advantage over
Takahashi’s older 4” models, which really need a medium sized mount.
FC-100DZ mounted on a Vixen SX2 using Takahashi’s
own dovetail rail.
Accessories
The FC-100DZ includes a 2” visual back as standard,
along with a
slot-in 2” extension tube for imaging or straight-through viewing and a 1.25”
adapter that also just slots in and features the classic Takahashi twist-lock
and silver end cap.
For
a finder you have the choice of the excellent 6x30, which has a sharp view and
lots of eye relief, or the much bulkier and more costly 7x50 which has less
E.R. but can be fitted with a reticle illuminator.
Takahashi
sell a microfocuser knob as an accessory, but it’s
expensive, fiddly to fit and you run the risk of losing a shim and getting a
sloppy focuser. If you must have a microfocuser for
imaging, I’d suggest replacing the whole unit or adding an electric one in
place of the visual back.
The
FC-35 0.66x reducer fits the FC-100DZ and shortens the focal length to 528mm
(F5.3).
Takahashi 6x30 finder and daytime view through it –
not your average finder!
In Use – Daytime
The FC-100DZ is obviously too large for spotting,
but I find viewing silhouetted branches at 100x plus (114x in this case) a very
good way of judging visible false colour. In this case there is effectively
none, either in focus or outside. Only the very best, usually triplet, 4”
apochromats achieve this, confirming that the new lens design with its exotic
mating element achieves outstanding performance for a doublet.
Prime focus daytime images at full frame show
vignetting only in the very corners. Zooming right in to silhouetted branches
reveals a trace of false colour similar to a fine 4” triplet like the TSA-102.
Only a true ortho-apochromat like the FOA-60Q (or a reflector!) does better.
Full frame telephoto with FC-100DZ/Canon EOS 6D Mk2,
incl. inset at full resolution.
In Use – Astrophotography
For photography with a DLSR you will need to use the
extension tube. The DZ makes for an excellent astrograph out of the box, with a
flat field for a doublet, good coverage at full frame and low levels of violet
bloat, as you can see from the unprocessed full frame sub below.
The focuser has in I.D. of 67mm to avoid vignetting
with larger sensors. A reducer/flattener is available (see accessories
section).
I found the focuser accurate enough and free of
image shift for imaging with a DSLR, the lock likewise very progressive and
free of image shift.
Typical of fluorite doublets, the FC-100DZ produces
excellent whole Moon images (much better than say an 8” SCT in my view).
M38: single frame with FC-100DZ/Canon EOS 6D Mk2,
30s at ISO 3200.
Crop of top right corner at full resolution.
Single frame of Comet Neowise,
taken in a hurry, with tracking errors due rough polar alignment: Canon EOS 6D
Mk2, 20s at ISO 3200.
Crop of Moon with FC-100DZ/Canon EOS 6D Mk2.
In Use – The Night Sky
General Observing Notes
Overall, the FC-100DZ reminds how much I love 4”
apochromats and particularly fluorite doublets which give perfect views of
everything you set them onto. However, the FC-100DZ will most likely be bought
by connoisseurs of the finest lunar and planetary views, so I will spend some
extra time here discussing solar system performance.
Cool Down
After a heavy LZOS triplet and a Mewlon reflector, I had forgotten how fast a Takahashi
doublet cools – it’s usable more or less straight from a warm room into a
frosty night, but gives its best after 20-30 minutes. This is a huge factor for
usability as a quick-look scope.
Star Test
Unusually for modern lenses, which typically show
some under-correction, this one has a virtually identical diffraction pattern
either side of focus. There is almost no false colour in the star test, even on
Sirius.
The Moon
A good 4” apochromat makes a wonderful scope for
fans of the Moon. Focusing through the bright lunar limb with this example at
160x there is no false colour that I can see and the contrast is intense.
Masses of detail is available in good seeing.
Early one frosty January morning, a 24-day Moon
hung low in the south, with Copernicus right on the terminator and clear even
with 7x bino’s. The DZ quickly started to give wonderful views at 160x – of
Montes Carpatus near Copernicus, Sinus Iridium and
the Gruithuisen domes. Gassendi
south of the plains of Oceanus Procellarum
with Kepler and its rays, bright Aristarchus and ghostly Reiner Gamma. Then I
turned to another refractor alongside and it was a yellowish mush of
turbulence. The DZ gives amazing views in poor seeing.
By contrast, literally, a night of really stable
seeing on a waxing gibbous ‘Apollo’ Moon gives views that are breathtakingly
good. Detail in the rough dome fields near Copernicus (itself still in the
darkness) is extraordinary.
I start finding rilles
everywhere. Snaking Rima Hadley near the Apollo 15 landing site is traceable
for its whole length, likewise Rima Birt near Rupes Recta; I spot more rilles
in Fra Mauro, running down into Bonplan. Rima Hippalus looks like the Grand Canyon.
Then there is the contrast. I see subtle variation
in the Maria that I don’t think I’ve noticed before: Mare Nectaris
is a filigree of ghostly rays. There are those dark spots in Ptolomaeus and a strange, tiny white spot north of the Rupes Recta that is really a minute crater – Lassell C. Finally, there is the contrast between the limb
and black space. It’s perfectly delineated at 160x in the DZ, with white hills
jutting into black space and no colour fringe or stray light in between.
The difference between the FC-100DZ and
an equally fine smaller refractor is that it’s not just about quick lunar looks
because there is so much detail at any given lunation you can spend happy hours
with an atlas exploring it and discovering new things.
Venus
Venus at 114x with a 5mm
Monocentric showed a perfect gibbous phase with no false colour or much stray
light from the objective at all in focus and just the slightest, faintest hint
of yellowy green tinging the platinum outside. I am convinced I could see
curving streaks, variations in the brightness of the clouds. Few refractors
give views of Venus to equal this.
Mars
Just before the 2020 opposition, with Mars at 30
degrees altitude and in good seeing, I popped in a 4mm Zeiss ortho with a Tele
Vue Mars bandmate filter. At 200x magnification, the FC-100DZ delivered perfect
sharpness and excellent detail for a 4”: a tiny southern polar cap opposite a dark
region (Mare Acidalia) with white limb cloud at the
north pole. I could easily make out a dark central band with lobes descending
towards Mare Acidalia, resolvable in steady moments to
the strange ‘eye’ shape of Sabaeus Sinus and Meridiani Sinus with their surrounding lighter areas. I
could detect no false colour, in or out of focus: the DZ is just a little
better than the FC-100DC in this respect and every bit as good as the F9 DL.
Jupiter
Albeit low in the sky for 2020, Jupiter still showed
plenty of detail at 160x with the 5mm setting on a Nagler
zoom, revealing variations in the NEB and NEB, in width, colour and tone. Towards
the poles, the dark polar hoods hinted at multiple thin belts within them. At
200x, the Galilean moons clearly resolved into tiny discs.
Saturn
Just left of Jupiter, Saturn also gave a great view
despite its low altitude: excellent colour and perfect sharpness at 160x with a
5mm monocentric eyepiece (my absolute planetary favourite). Details included
the Cassini Division, shadow on the rings, the grey polar hood with hints of
belts within and one dark equatorial belt. I could just make out the body of
the planet through the rings in places.
Deep Sky
Late one dark and clear January night, with wife
and neighbours asleep, I had a great deep sky session with the DZ. The Orion
Nebula looked stunning with a 15mm Tele Vue Panoptic, sweeping from the central
bright region out into the curving arms; hints of colour too. I easily found
nebulosity in other sword areas as well – NGC 1975 above M42 and around the
star Nair Al Saif below.
Clusters look really special in a good 4”
apochromat like this one, with dazzlingly pin-point stars sparkling across a
wide flat field. True to that norm, the DZ gave a magnificent view of the
Pleiades at 40x with a 20mm T5 Nagler - lots of
blue-misty nebulosity and icily brilliant stars with plenty of spare field
width to frame the cluster. The Double Cluster in Perseus looked lingeringly
beautiful, with its central twin red stars and the star chain that arcs across
to another cluster, Stock 2. The main Beehive stars were all brilliant icy
diamonds too, with its three yellowish outer stars in a triangle.
The DZ set on comet Neowise,
summer 2020.
Summary
The FC-100DZ reimagines Takahashi’s classic F8
fluorite doublets of yesteryear, the FS-102 and the original FC-100. Like those
older models, it makes for a near perfect all-rounder, but in a lighter and
more compact package even than the rare FS-102S. Optically, though, it’s every
bit the equal of the FS-102 and slightly superior to the old FC-100. So, this
is probably the current FC-100D model you would choose: it combines most of the
best features of the DC, DS and (now defunct) DL.
As anticipated, the FC-100DZ is among the very best
refractors for solar system viewing, offering razor-sharp and high contrast,
low flare views of the Moon and planets, with no compromises on Mars or Venus
(both of which can challenge lesser apochromats). You just don’t need a
triplet for visual use now: the DZ is lighter and cools faster, yet performs
every bit as well (and perhaps delivers just a tiny bit more contrast).
You might think of the DZ as a planetary specialist;
it really isn’t. Field flatness is excellent and views of the deep sky
stunning. Meanwhile, F8 is often fast enough for sensitive modern cameras and
(unlike an F6 doublet) offers a fairly flat field as standard. With a reducer
flattener you’d have an excellent imaging machine.
If someone were to ask me to recommend an only
scope, this would currently be it. It shows you so much more than a 3”, but
isn’t that much larger or slower to cool.
In truth, the FC-100DZ is approaching the limits of
optical technology – it’s a near perfect 4” apochromat, but in a doublet and
without the fragility of front surface fluorite. For me the only real downside
remains the usual one – portability. It may be lighter than an F6 triplet and
more compact than any of its FC-100D peers, but it still needs the focuser
removed to be carry-on portable.
The
FC-100DZ gets my very highest recommendation. It’s light, compact,
fast-cooling, beautifully made and optically near perfect; great for visual or
imaging. It’s not quite carry-on portable, but you can’t have it all.
