Vixen FL70S Review
Vixen made their classic 1990s apochromatic refractors - the
FL series - in a range of sizes, from 55mm to 102mm. All have fluorite doublets
at F8 or F9. All are light weight for their aperture.
The sweet spot in the FL range is arguably the FL80, a scope
I tested here and found to be excellent. But Vixen
made a couple of smaller models as well – the FL55 (not the rebooted imaging
scope) and this, the FL70.
The FL70 was the one that got me interested in the FL series.
I first saw one at a friend’s many years ago and one look was enough to tell me
it was something special. The views it gave of Venus were some of the best I’d ever had back then, with any scope.
But that was a long time ago and I was curious to see how the
FL70 stacks up today. This is a rare telescope now. People hang on to them. So to find out, I sourced a near-mint example from its
homeland for this review.
At A Glance
|
Telescope |
Vixen
FL70S |
|
Aperture |
70mm |
|
Focal
Length |
560mm |
|
Focal
Ratio |
F8 |
|
Length |
510mm
excl. visual back |
|
Weight |
2.3 Kg
incl. finder and rings/plate |
Data from Me.
Design
and Build
All FLs have the same workaday mid-range look as Vixen
achromats from that era, less premium than a Takahashi of the time.
The focuser knobs are black plastic, as is the focuser
lock-knob; whereas on a contemporary FC-series Takahashi they are anodised
metal, or at least a classy-looking plastic imitation. The Vixen rings are
formed rather than Takahashi cast. And the tube has too many stickers for my
taste. The cast parts don’t quite exude quality like a
Takahashi somehow, either.
Though this earlier FL looks the same as later examples, it
does have some subtle differences. Whilst later FLs seem to lack a serial
number, this FL70 has one, much like a Takahashi, even if here it’s punched into a sticker, rather than a screw-on metal
plate.
Note that some of Vixen’s FL models were re-badged with the
Orion brand (the US importer, not Orion Optics in the UK).
Note the six white dots – the lamp LEDs reflect white because
the fluorite element is uncoated.
Optics
This objective really does use the mineral, not some high-fluoride
glass like FPL-53. I confirmed this with a laser, which disappears completely
only in fluorite, not glass.
So, like a contemporary Takahashi FC60, the FL70 has a
premium F8 Japanese-made fluorite doublet lens. But note:
· Like the Takahashi FC-series (old and
new), the FL70 is a Steinheil configuration with its positive fluorite element
at the back, where it’s protected from dew and lens
cloths.
· In modern Steinheil doublets the
fluorite is coated, but the FL70’s rear fluorite element is uncoated as was the
FC-60’s. This results in lower transmissivity and a noticeably more reflective
lens (see above).
· This older FL70 has a colimatable (and probably temperature compensating) cell
like larger Takahashis of the time, complete with
engraving in yellow where a Tak’ would have had green.
But the closest contemporary Takahashi, the FC-60, has a fixed-collimation
screw-in cell, like the modern Takahashi FS-60 and the later FL80S I reviewed.
This FL70 was made back when flint glasses were doped with
lead and other heavy metals. Some leaded flints made excellent mating elements
for fluorite, but were deemed hazardous and were discontinued in favour of
‘eco’ glasses. In my experience, only a few recent high-end scopes - think Tak’s FOA-60 and FC-100DZ - have fluorite doublets with
‘eco’ (in these two cases, special dispersion) flints that match the
performance of these FL doublets.
I should mention that the FL series have legendary optical
quality. That little FL70 I saw years ago was sold to a chap who got it tested
on an interferometer; he was thrilled to find that it had a Strehl
above 99% (Tak’ fluorite doublets of the time were
made to a minimum of 95% Strehl – still excellent). Bench
tests indicate exceptionally low false colour, into super-APO territory.
Note: FLs were expensive scopes new and would be expensive to
make now – check out the prices of Optron fluorite
doublets in Taks and Borgs today.
Tube
The later
FL80S I reviewed reminded me of a big Tak’ FS-60C – a
compact tube with a short dew-shield and black-anodised fixed cell of the same
diameter. This older FL70 is classic Japanese refractor by comparison: a
large-for-the-aperture tube finished in off-white enamel, with oversized
dew-shield and a traditional lens ring in hammer-green to match the focuser. In
both cases, focuser and lens cell attach with threads. Personally, I prefer the
classic look.
The FL70S is
510mm long to the end of the focuser drawtube and 75mm diameter. Despite the
fixed dewshield, it is carry-on portable without disassembly. At just 2.3 Kg
including rings, plate and finder the FL70S is
lightweight too.
Internally, the FL70 has 3 knife edge baffles and is painted
flat black.
Focuser
The FL80S I
reviewed had a larger focuser with a 2” visual back and clever built-in rotator
suited to imaging. This one is more basic and aimed at visual use.
Note that
the fluorite scopes have thread-on focusers, whilst the similar-looking
achromats used basic set-screws.
The focuser doesn’t have the famously buttery feel of a Takahashi unit,
but it’s still a high-quality, all-metal (well apart from those knobs) item.
The feel is smooth and precise with minimal image shift.
The chromed
55mm diameter drawtube sports a thread-on visual back, three internal
knife-edge baffles and a cross-cut rack. The 80mm of travel is fine for most
eyepiece/diagonal combinations. Two internal bearings with adjustment screws
and side-mounted lock knob mean it’s stable and won’t
rack-out on its own with a heavy eyepiece.
The supplied
visual back is 1.25” only and has a set screw rather than a lock-ring. It’s the same item that came with the later FL80S. It screws
into the drawtube with an adapter on what looks like a thread about M52, so a
2” visual back might fit. A pair of thread-in extension tubes are provided for
straight-through viewing.
The 1.25”
visual back adapter has a standard thread and could be swapped out for a
different one, such as Takahashi’s twist-lock.
Mounting
This FL70 is
labelled ‘Super Polaris’ and this means it originally came on the small Vixen
equatorial of that name, a forerunner of the similar and more commonly
encountered GP mount (see below).
The FL70 is
too heavy and bulky for most photo heads (unlike, say, a smaller 70mm TV Ranger
from the same era), but works really well on a small
alt-az mount like a Vixen Porta (not the mini
version), where slightly heavier and longer scopes (even the TV-85 I was
testing at the time) struggle with excessive vibes.
If you want
a period-correct alt-az mount, then you could seek
out an old Vixen example with matching green enamel, but bear in mind that the
rings bolt-on to these mounts and don’t hinge open, so
you’ll be moving the whole setup as a unit.
For greater
flexibility I’d prefer the old ‘D’ (for dovetail)
version with (you guessed) a Vixen dovetail built-in but also weighted to
counterbalance large eyepieces.
The Vixen
Porta is later than the FL series, but works well.
Vixen FL80S on a GP mount – the later version of the SP mount
for the FL70S.
Accessories
This FL70
came with the original formed rings and Vixen dovetail plate. The rings have
the advantage of light weight, but aren’t a match for
the quality of a cast Takahashi clamshell and don’t hinge open which means
removing the focuser if you want to take the tube out!
The original
6x30 finder has quality optics (not stopped down like many cheap optical
finders) and though it has a plastic eyepiece with less eye relief than the
peerless Takahashi 6x30, field of view (8°) is the same.
The finder
mount is unusual: it allows the finder to rotate to either side, presumably to
clear the eyepiece area when used on an alt-az mount.
The
period-correct eyepieces would have been Vixen’s own Circle-V 0.965” Orthoscopics. These are of excellent quality (if not up to Tak’ or Pentax Ortho’s) and can still be had quite cheaply
if you want to assemble a full retro’ rig.
In
Use – Daytime
The size and
style of the FL70 means you probably wouldn’t use it
in a hide for nature viewing or birding, the way some do a small Tele Vue; but
daytime views are simply outstanding.
I tried using
the FL70 to view waders – Curlews and Oystercatchers - out on the bay sands
near my home. The view was almost hyper-real: sharp and vivid and completely
free of false colour in a way few spotting scopes manage. But I did get asked
by a local birder why I was using an astro’ scope!
At 100x,
silhouetted branches (my usual ‘test’) are basically free of false-colour
fringing: none in focus and the faintest (really) tint focusing through. This
is a rare result for a doublet. Sharpness meanwhile is perfect even at this
power.
It may be an astro’ scope, but the FL70 works outstandingly well for
nature viewing.
In
Use – Astrophotography
Lack of a 2”
visual back (and I couldn’t find one to buy as an
accessory) precluded deep-sky imaging, but I did take a snap of the Moon, which
is sharp and free from flare or false colour, detailed for the small image
scale.
In
Use – Observing the Night Sky
General
Observing Notes
The superb
optics are let down slightly by the focuser – it’s not
worn or sloppy or imprecise, but heavy at room temperature it gets pretty stiff
when cold and may need re-lubricating.
Cool
Down
A small
doublet in a proper cell cools fast and this is no exception – completely
usable within a few minutes and giving its best in ten to fifteen, with no
pinching or severe spherical aberration that I’ve seen
from simpler cells. This is such an important feature for a quick-look scope.
Star
Test
The star
test is effectively perfect with evenly illuminated, identical rings either
side of focus and no perceivable under or over correction. In focus at high
power yields a perfect Airy disk and dim single diffraction ring.
The
Moon
A low first quarter Moon in turbulent seeing across
the bay nonetheless shows all the major features you can see with a ~3”
refractor, including the dramatic crater grouping of Theophilus and Catharina
near the terminator.
Focusing through the bright limb at 112x reveals no
false colour fringing at all – this is a perfect Moon of only blacks, whites, greys and buffs.
I managed to see a two-day-old Moon from the top of
the fell – only a few degrees above the horizon, it’s
a difficult phase. The FL70’s peerless contrast revealed more features than I’ve ever seen in this thinnest of crescents, including Mare
Marginis and Smythii on the
very limb, dark-floored Mare Humboldtianum and spectacular
crater Gauss.
Venus
Perhaps the ultimate visual test for any refractor, a
razor-sharp crescent Venus was my first taste of the FL70’s capabilities all
those years ago.
Now, a dazzling magnitude -4.7 crescent at just 20
degrees altitude and 112x with a 5mm Nagler shows only a hint of gold on the
limb that might be atmospheric, no significant false colour focusing through
and no flare either.
Mars
The Red
Planet troubles F6 ED doublets like the TV-85 with red blur and softness. Not
the FL70. There was no blur of deep red false colour, in or out of focus; no
light bleed or flare from the limb into black space.
I
was able to view Mars near the 2022 opposition at 16.9”, near transit at 57° Altitude in fine seeing. At 140x with the 4mm setting of a Nagler Zoom, and 187x
with the 3mm in steady moments, Mars
revealed its most famous face - Syrtis Major just off centre extending into the lighter equatorial regions of Arabia to the
north. A hint of bright Hellas, with its clearly
defined arc of northern boundary, lay to the south-west. To the west, I noted the connecting strip of dark albedo – Sabaeus Sinus according to my atlas – leading to the
prominent dark area of Meridiani Sinus on the limb.
This level of detail is impressive from a 70mm.
Jupiter
A large and bright Jupiter shows its creamy hue to
perfection, with no false colour and perfect sharpness. All the main details
are on show, including the equatorial belts, polar hoods, a hint of storms and
of course the tiny disks of the Galilean moons. The maximum power I could get -
187x with the 3mm setting on a Nagler zoom - was still perfectly sharp and
contrasty.
Saturn
Again, Saturn has that buff, almost pink hue unsullied
by false colour or flare. The Cassini division is visible in the ring ‘handles’, along with the polar hood and a hint of cloud-belt banding.
It’s a perfect view at this aperture and noticeably
more feature-rich than through a 60mm apochromat of similar quality.
Deep
Sky
The superb
contrast and very tight stellar images from the high-strehl
objective make the FL70 a surprisingly good tool for visual deep sky. I had a
most enjoyable evening with it just after New Year, viewing out over the bay
from a secluded and dark spot on the Prom’.
The Great
Nebula in Orion revealed significant structure at 112x – as good as I’ve seen in a small scope. I easily picked the strange oval
misty patch of the Crab Nebula out of the darkness above Zeta Tauri too.
Open
clusters seem to be a particular strength. The Pleiades were the glitteringly
brilliant blue I’m used to in a quality refractor, but
I was surprised at the amount of nebulosity I could see, including a hint of
structure around Merope. Similarly, the Starfish in Auriga showed its sweeping
arms of stars more clearly than I recall in a scope of this aperture.
The Owl
Cluster in Cassiopea is one of my favourites, one of
the few objects that really looks its name, with ‘spooky’ (according to my
daughter) eyes and outstretched wings. The FL70 gave a wonderful view of it,
ditto the nearby Double Cluster.
Epsilon Lyrae was a perfect split in both components at 112x, but
upping the power to 187x with the 3mm setting of a Nagler zoom revealed four
perfect Airy disks with overlapping first diffraction rings and black space
between – startlingly good for a 70mm optic. I split Rigel from its dim
companion easily at 112x, even when low in the sky.
Summary
The FL70S
offers almost perfect correction in a light and compact OTA with a wonderful
classic vibe. A proper lens cell means it’s super
quick to cool – the perfect quick look scope for the Moon and planets.
Planetary and lunar views are outstanding. Terrestrial views at high power are
sharper than any spotting scope.
The only
downside is its focuser, which lacks the fluidity and absolute precision of a
Takahashi (or a modern dual-speed unit).
Most small
apochromats these days are optimised for imaging. The Vixen FL series (like Takahashis of the time) were mainly intended for visual
use, especially on the Moon and planets. What does this mean in practice?
An F8
fluorite doublet like the FL70 gives better sharpness at high magnifications
and lower in-focus false colour and spherochromatism
than a modern ED doublet built for imaging.
This was
brought home to me again when viewing Mars near opposition recently. A TV-85
gave a slightly softer view, with more unfocussed red light
bleeding into the seeing.
Finally, the
FL70’s in-between-sized aperture is unusual, but I really like it: noticeably
more capable than a 60mm, it’s still smaller than the
only modern equivalent, the Takahashi FC-76D.
Vixen fluorites like the FL70S are
getting rarer, but still make a superb alternative to a small Takahashi,
especially if lunar/planetary observing is your thing.
