Takahashi
FC-100DC Review
Takahashi’s FC-100DC is the
lightest and cheapest of their range of 100mm fluorite doublets. Promising the
usual sharp and well-corrected views with better digital imaging
characteristics and a faster focal ratio than its predecessors, its price point
makes it something of a bargain in Tak’s range.
I originally posted a combined mini
review of both the FC-100DC and FC-100DL, having had the opportunity to view
through both with friends and at star parties. But I was recently able to
borrow an FC-100DC to complete this full review.
A big thanks to Richard and to Mike Hezzlewood and Paul Yates, for letting me play with their
toys and for allowing me to use their photos and sketches.
At
A Glance
|
Telescope |
Takahashi FC-100DC |
|
Aperture |
100mm |
|
Focal Length |
740mm |
|
Focal Ratio |
F 7.4 |
|
Length |
815mm |
|
Weight |
2.8 Kg |
Data from Takahashi.
What’s in the Box?
The FC-100DC comes in a thick logoed
cardboard crate (shown here the one for an FC-100DZ):
Design
and Build
Takahashi make (or have made) four
different FC-100D variants over the years.
The F7.4 FC-100D objective is found in
two different models, the FC-100DC on review here and the FC-100DF. The
FC-100DC has a fixed dew shield and a small focuser, but it’s a kilo
lighter and cheaper too.
Takahashi also made an FC-100DL in two
brief runs and the FC-100DZ (reviewed here). I discuss and compare these models
below.
FC-100DL and FC-100DC.
The F8 FC-100DZ with an original
FC-100. Note the FC-100DZ’s retracted dew-shield (other FC-100Ds’
are fixed).
FC-100DC (with FC-76 focuser) and AP
Stowaway.
FC-100DZ objective alongside (fully
coated) original FC-100 for comparison.
Laser test confirms that this is a
Steinheil doublet with the fluorite element at the back (fluorite doesn’t
scatter the laser, glass does).
Optics
The FC-100DC,
like most smaller Takahashi refractors, has a fluorite doublet objective with a
foil-spaced air gap, made by Canon/Optron, in a fixed thread-on cell. However,
Takahashi have carefully kept the spacers out of the light path to produce
cleaner star images (this matters).
Fluorite
doublets are found in some of my favourite scopes. Fluorite is a mineral and
scatters less light than any glass (which is why anti-reflection coatings are
made of fluorides). Fluorite allows for a very well corrected doublet at this
aperture, with the advantage of lighter weight and faster cooling than a
triplet.
Takahashi have produced a lot of
variations on the theme of the 4” fluorite doublet over the years. The
current FC-100D is quite different from the original FC-100 (reviewed here) and the FS-102 (reviewed here) that was produced between the two.
Just like the original, the current
FC-100D is a Steinheil design that put its fluorite in a protected position at
the back, compared with the FS-102 which was a Fraunhofer configuration with
its fluorite up front.
But whereas the original FC-100 was an
F8 primarily intended for visual use with some film photography thrown in, the
current version is squarely aimed at the digital (hence ‘D’)
imager, with a faster focal ratio of F7.4 (the difference doesn’t sound
much but reduces exposure times significantly) and a better corrected field.
As I mentioned above, there are two
other FC-100D variants that have different objectives again. The current FC-100DZ reverts to the classic F8
focal length and uses an exotic glass mating element to achieve correction
that’s up with most 100mm triplets for critical high-power viewing. The
FC-100DL was even slower at F9 and was also aimed at planetary viewing, but was
only produced in two small runs.
Given that
Takahashi made these two FC-100D variants specifically for high-power planetary
viewing, you might think that the basic FC-100DC on test is a bit compromised
in that department, but as we will see it really is not – differences
from the F8 and F9 versions are very small.
Tube
The FC-100DC
has a simple off-white-enamelled 95mm-diameter aluminium tube with a fixed
dew-shield and a silver lens ring, matching silver pressed-tin dew-cap (gone is
the cast manhole cover from the original FC-100). Finish is excellent as
always.
Internal
quality is flawless too: there are two knife-edge baffles and everything is
coated in the blackest camera paint.
The original
FC-100 (and the FS-102 too) had fatter tubes and larger dew-shields, so the
FC-100DC is substantially more compact than either. It’s much lighter
than its forebears too, at just 2.8 Kg – one of the lightest in its class
(no heavier than the AP Stowaway, even with its clamshell).
Thread-off
the focuser and dew-shield and the FC-100DC is carry-on portable at under
19” - see below where it’s fitted into the same Peli Air 1525 case
as my AP Stowaway. You might think this risks cross-threading, but the threads
are large enough that the risk is minimal if you’re careful (and always
mate the threads horizontally).
For
reference, note that the FC-100DL is 12.5cm longer and a kilo heavier than the
DC. Meanwhile, the FC-100DZ is the only current variant with a retracting
dew-shield (the previous FS-102 did come in a sliding dew-shield version too).
FC-100DC
broken down into a carry-on Peli 1525 Air case, with room to spare for a couple
of eyepieces.
Focuser
The
FC-100DC’s focuser is based on the focuser from the FS-60C: it’s very
compact, has a 2” diameter drawtube and limited travel. The focuser is
attached to the tube by a cast extension finished in the same Takahashi green
or blue powder coat as the focuser.
By
comparison, the other three FC-100D variants use a larger 2.7” drawtube focuser
derived from the old Sky-90, that has more travel and is better suited to
heavier cameras or binoviewers, but that adds to the
OTA weight.
Note that the
FC-100DC in some of the photos is not standard – it has had its focuser
replaced with one from an original FC-76 (not the
recent FC-76D) that has a 2.7” drawtube with more travel and a longer
body. This hack is an improvement in many ways, but does then need a downstream
extension to focus with some diagonals and eyepieces.
As standard,
the FC-100DC has the plastic focuser knobs found on the FS-60 and FC-76, in
place of the cast items found on the more expensive models (in this shot
they’ve been upgraded by the owner).
FC-100DC focuser, based on the FS-60C
unit.
FC-100DZ Focuser, based on the Sky-90’s.
FC-100DF is similar.
Mounting
The FC-100DC is
short and light enough for a smaller equatorial mount like an EQ5, or the Vixen
GP in some of the photos (or a more recent AP). I also mounted the FC-100DC on
a small Vixen APZ alt-az which proved very stable,
better than the basic AZ-4 you see in the photos.
For
Vixen-compatible mounts, Takahashi make a dovetail bar (intended for the
Mewlon-210) with two threaded M8 holes at 35mm spacing to match Takahashi
clamshells.
Accessories
Like most
Takahashi refractors, the FC-100DC comes with a clamshell-type ring that has
two M8 holes at 35mm spacing. The standard finder is Takahashi’s 6x30 unit
that goes in a Tak’s own proprietary ring.
Fo imaging,
Tak’ expect you to buy the DF version with larger focuser, so the DC may
not support all the various reducers, flatteners and extenders are available
for imaging with the DF. However, the 1.04x multi-flattener that fits
various Tak’ doublets can be connected using the ‘Multi CA Ring
100’ adapter/spacer’ for the FC-100D.
FC-100DC mounted on a Vixen GP with the
Mewlon-210 dovetail bar.
Silhouetted branches are sharp and free
from false colour.
In
Use – Daytime
My standard
test for chromatic aberration – viewing silhouetted branches at 100x –
showed just the merest hint of false colour fringing out of focus. The
difference between this and the most perfectly corrected refractors in this
test is so small as to be academic.
In
Use – Astrophotography
As the
full-frame images straight from the camera below reveal, D-for-digital is no
idle claim. Violet bloating on the blue-white stars of the Pleiades is very
well controlled. Vignetting at full-frame is very modest and stars aren’t
too comatic except in the very corners. With some cropping you could start off
imaging without a flattener.
The absence of intruding foil spacers make for very clean star images. Compare the FC-100DC with the original Vixen SD103 with intrusive spacers on Pleiades
star Alcyone in the image below. In this harsh test, you can see that the
Takahashi generates a little less violet bloat too.
I’ve
lined up frames of the central Pleaides, taken with the FC-100DC and the F8
FC-100DZ, side by side to compare. The images are both straight from the same
camera with the same exposure and ISO. As you can see, the DZ version does have
slightly less violet bloat as expected, but the difference is modest.
The cropped
snap of the Moon shows excellent sharpness and detail, no false colour.
The Crab
Nebula (M1) region: 30s at ISO 3200, Canon EOS 6D MkII,
straight from the camera but reduced size (not cropped).
Crop of the
top right corner.
M38 and NGC
1907: 30s at ISO 3200, Canon EOS 6D MkII, straight
from the camera but reduced size (not cropped).
Pleiades
(M45) through FC-100DC left and FC-100DZ right: 30s at ISO 3200, Canon EOS 6D MkII, straight from the camera.
Alcyone: 30s
at ISO 3200, Canon EOS 6D MkII with Takahashi
FC-100DC (left) and Vixen SD103 (right) showing effect of foil spacers in light
path.
In
Use – The Night Sky
General
Observing Notes
I found the
FC-100DC very easy to use. Its light weight and compact size make it painless
to get mounted into the dovetail and the quick cool-down (see below) means
minimal waiting to get going. This may be the ‘basic’ version of
the FC-100D, but correction is outstanding, without the residual false colour
that most ED doublets suffer.
Cool
Down
The FC-100DC cools fast and benignly,
without the slight pinching some have noted with the FC-100DZ variant. This is
a major advantage over a triplet too, one that was very apparent on one viewing
night over the Mars opposition, when the temperature dropped over the session
and the larger triplets struggled to keep up.
Star
Test
The FC-100DC
I’ve viewed with more recently had a sensibly perfect star test.
The
Moon
I got an
extended viewing session on a 6-day-old Moon between crescent and first quarter
with lots of interesting craters and formations on the terminator. Most of the
viewing was done with bino’d ~17mm Plossls giving between 150x-200x and critical high-power
views with a 5mm Super Monocentric giving 148x.
The FC-100DC
revealed reveal stunning lunar detail at a level highly comparable with the F8
and F9 models.
Theophillus,
Cyrillus and Catherina are a triplet of large craters and a favourite since
childhood. To the north of Theophilus lies Sinus Asperitatis
and an area of extraordinarily rough terrain – hummocks and craterlets
and blocks – presumably ejecta from Theophilus.
Nearby lie rilles
Hypatia and Gutenberg and the Crater Mädler (a German
astronomer who with Beer compiled the first proper Mars map), source of a
bright ray that sweeps out across Mare Nectaris and seems to have deposited a
bright patch in lava-flooded Daguerre.
Other
highlights included Posidonius, its rille system clearly picked with details
smaller scopes miss; strange keyhole-shaped Torricelli, floor in inky darkness,
walls of the surrounding ghost crater picked out in the low sun; Plinius (after
Pliny the Elder, who died in the eruption of Vesuvius that destroyed Pompeii)
and its unusual cratered central peak.
Mars
On a recent session comparing various
scopes on Mars at the 2022 opposition, the FC-100DC gave excellent views with no
false colour, softness or the red blur often found with ED doublets, just
excellent contrast and albedo-marking detail.
Of all the scopes we used during the
comparison session, the FC-100DC gave the best views. We speculated this was
because the temperature was dropping fast and the larger telescopes with their
larger glass masses and cells – A Tak’ FSQ-106 and Mewlon 210 alongside an LZOS 123/780 – couldn’t
keep up. I mention this because smaller doublets often make the best of tough
conditions.
On that night, Mars was 17.1” in
size and well placed at an altitude of 20°; seeing was good. At 160x with the 4mm
setting of a Nagler Zoom, the dark stripe comprising Mare Sirenum and Mare Erythraeum was clearly visible, with the paler Solis Lacus
region betwixt (Solis Lacus isn’t really visible in its true ‘Eye
of Mars’ form at this aperture) and the dark square of Mare Acidalium reaching down in the north east.
The owner of
the FC-100DC in my original test, Mike Hezzlewood,
specialises in the Moon and planets and like me is particularly interested in
Mars. Unlike me, though, Mike is a very accomplished sketcher and has made the
following outstanding map of Mars by transferring his eyepiece sketches onto a
cylindrical projection. This map says much more about the FC-100’s
ability to reveal fine planetary contrast than I can convey in words, so
I’ll shut up and let Mike’s drawing skills speak for it.
Jupiter
During a recent session comparing
various scopes, an FC-100DC gave the best Jovian views of the night, with
perfect sharpness and loads of cloud belt detail on Jupiter at 160x with the
4mm setting of a Nagler Zoom.
Deep
Sky
The
outstanding contrast of the fluorite doublet makes for a better visual deep sky
scope than you might expect, given its modest aperture. With a well-corrected
eyepiece, the FC-100DC shows pinpoint stars all the way across the field,
helped by high optical quality that throws all the starlight into the Airy disk
and first diffraction ring.
I had superb
views of open clusters M37, M38 and NGC1907, with both fully resolved into
masses of fainter stars. At 39x with a 19mm Tele Vue Panoptic, the Pleiades
glittered icily brilliant, embedded in faintly blue nebulosity – the way
only a fine small refractor shows them.
The Crab
Nebula supernova remnant was easy to pick out of the background and revealed
more of its shape than smaller apertures or ones that transmit less contrast.
The FC-100DC
gave a perfect split of the Double Double at 160x,
with bright and sharply defined Airy disks, black space between.
Summary
The FC-100DC is that rare thing –
a high performance 4” apochromat that is also very portable (even
carry-on sized, if you unthread the dewshield and focuser). It is super-sharp,
delivers outstanding contrast and is very well corrected for both imaging and
visual use. It gave stunning views of everything I pointed it at. Its light
weight and fast cool-down make it very user-friendly and great for quick looks.
For digital imaging, the
‘D’ design brief has produced a doublet that’s well corrected
for violet bloat and delivers surprisingly pin-point stars across a wide field.
Compared with the ‘better corrected’ FC-100DL and FC-100DZ,
differences are truly tiny. The FC-100DC doesn’t have the weak spots in
its correction that most ED doublets do.
However, serious imagers might prefer
the same lens with the bigger focuser that is the DF version.
So, by the standards of high-end
telescopes, with its Canon Fluorite objective, the FC-100DC seems almost cheap.
Equipped with a few good eyepieces and the multi-flattener for imaging, it
could be a satisfying only scope.
The FC-100DC is a user-friendly, do-anything
bargain and one of my very favourite four-inch APOs. It’s a Scope Views
Best Buy.
