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Takahashi FC-76DC / FC-76DCU Review

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When Takahashi discontinued the FS series, they replaced the four-inch FS-102 model with two slightly different variations on an older theme. Both were still fluorite doublets – Tak’s stock-in-trade – with the same optical design as the original FC-100, but a different emphasis and no nasty heavy metals in the mating element. Then a couple of years ago, they introduced a pair of three inch apochromats, replacing the old FS-78: two new FC-76 models that updated an older model to the digital age.

The FS series refractors were F8 fluorite doublets of Fraunhofer design (fluorite at the front) in oversized tubes. They were aimed squarely at the solar system observer, with old-style film imaging as a sideline. In contrast, the new FC-76 models are Steinheil fluorite doublets (fluorite at the back) in slim, lightweight tubes with a slightly faster F ratio of 7.5 and designed with the digital imager in mind (though still excellent for visual work).

There were initially two FC-76 variants. The FC-76DC has a fixed dew-shield in an 80mm tube and with the small 2” focuser from the FS-60C; it’s lighter and ideal for viewing and casual imaging. The imaging-oriented FC-76DS version has a sliding dew-shield, a larger (2.7”) focuser to handle bigger cameras and a 95mm tube like the old FS-78; but it’s much heavier at 3 Kg vs 1.8 Kg for the FC-76DC.

This being Takahashi, they love to add some complex and interesting options, so the telescope on review here is a third (newer) variant: it’s an FC-76DC that screws in half for easy transport (airline carry-on included). At one time, you had to do this yourself by buying the FC-76 objective unit and swapping it onto an existing FS-60C, but from late 2016, Takahashi released it as a complete and separate model – in Japan at least - the FC-76DCU on review here. (This also allowed them to release a fourth variant – the catchily named ‘FC-76DCU+EX-CQ’ - as a limited edition, but more on that later.)

At A Glance

Telescope

FC-76DCU

Aperture

76 mm

Focal Length

570 mm

Focal Ratio

7.5

Length

329 mm + 335 mm

Weight

1.8 Kg

 

What’s in the Box?

I don’t usually photo telescope unboxings – just a big brown cardboard box after all. But Takahashi’s cartons are unlike any I’ve seen: The FC-76 came triple boxed, each Russian-doll layer cleverly separated by fold out spacers – box origami!

Design and Build

The basic FC-76DC is the smaller and lighter (but longer) of the two main FC-76 variants. To recap, it has the 80mm diameter tube from the FS-60 and the short, lightweight 2” FS-60 focuser too. With a thread-on (i.e. fixed) dew-shield and a thin tin dew cap (gone is the old FS-series ‘manhole cover’) it still weighs just 1.8 Kg – remarkably light for a 3” APO.

Otherwise, the FC-76DC is standard Takahashi – a beautifully finished white tube with love-it-or-loathe-it lime-green for the focuser and silver detailing where the FS series had blue enamel. Each one has an individual serial number plate on the focuser as always.

So how does this FC-76DCU version differ? It is identical to the FC-76DC in every way, except that it screws in half. This is a great idea because the FC-76DC is lightweight and slim, but quite long and wouldn’t fit in carry-on luggage. Putting a thread in the middle reminds me of those adventure-touring bike frames you can get in two halves with connectors – a simple idea that makes a big difference to practical transport. The two halves of the FC-76DCU would fit in my wife’s designer handbag.

Optics

The new FC-76 models have all reverted to a Steinheil configuration for their air-spaced doublet that puts the fluorite element at the back, like the original FC-76, helping protect it from dew (Fluorite is hygroscopic and could potentially degrade). Their forerunner, the FS-78, had a conventional Fraunhofer design that put the mineral up front. Unlike the older FC-76, though, all optical surfaces in the modern Steinheil lens are fully coated.

Another departure from previous Takahashi 3” doublets is a reduction of focal ratio to F7.5 from the FS-78’s F8, giving a focal length of 570mm. Half an F-stop may not sound a lot, but makes quite a difference to exposure times for imagers. The ‘D’ in the name indicated the optic has been optimised for imagers in other areas too, with excellent coverage and low field curvature/coma off axis. In addition, the spot sizes of the original FC-76 have been reduced and the optic pulls the violet G-line closer into the main crossing to reduce violet blur.

Like other Takahashi objectives, this one was made by Canon/Optron in Japan. It’s in a proper little cell and has superb coatings, but the cell screws onto the tube and doesn’t have collimation screws like the FS-78 did.

Canon fluorite doublet has some of the best coatings you’ll find anywhere. Tube has classic knife-edge baffles, despite compact dimensions.

D for Digital – the new FC-76 improves on spot sizes and violet blur.

Tube

The 80mm diameter tube splits along a central thread - the focuser section is 329mm long, the objective 335 mm. The thread seems robust and well-machined, but I would advise mating it with the tube held vertically to reduce the possibility of cross-threading.

Despite being so slim-line, the tube still manages to fit in four knife-edge baffles to control stray light. It’s has been carefully blacked with matte paint inside, like all Takahashis. Both Interior and exterior finish are first rate, plain and simple like all Taks.

Focuser

The 2” drawtube FS-60 focuser is a proven unit. There is no micro-focuser as standard, but Takahashi focusers are some of the smoothest around and have a unique feel that I love. This one has the old solid metal knobs, but newly bought examples may have hollow plastic knobs that look the much the same.

The focuser is equipped with a large lock-knob on top that is wonderfully progressive and free of image shift; it has the standard mounting holes for a Tak’ finder bracket.

The back of the focuser has an M50 thread and can be fitted with 1.25” or 2” visual backs and various other accessories.

The main downside with this very short focuser can be image shift, but I have come to suspect this mainly happens on units with the shims worn by lots of use with heavy CCD cameras. This (new) example is fine and is quite robust enough for a heavy DSLR like a Canon EOS5D, but it might struggle with really massive cameras or binoviewers.

The other downside is limited travel, which means extension tubes are often needed for long focus eyepieces or for imaging.

Takahashi’s tiny Teegul SP2 mount easily holds the FC-76.

Mounting

This is an area where the FC-76D really improves on the old FS-78, which was big and fairly heavy and needed an EQ5 sized mount. The FC-76D OTA is so light and compact that any mount will take it, including Takahashi’s own tiny Teegul mount, which is surprisingly stable and vibe free with the FC-76DC on a light Berlebach tripod.

The FC-76D/Teegul combination makes for a powerful and portable system to rival Questar and would be great for eclipse chasers.

Accessories

The first fifty FC-76DCUs will be sold with a rather fetching blue camera bag that just fits both parts of the split OTA.

Numerous other accessories are available, including a rotator for the focuser, various extensions and adapters and two flattener options:

If you want the full-on reducer/flattener, Takahashi make one for under £500 that reduces the focal length of the 76D to 417mm (F5.5) with an image circle of 36mm.

Alternatively, if you don’t want to spend big on the reducer, they make a basic flattener that extends the focal length slightly to 594mm (F7.8), but gives you a flat image circle of 40mm that should provide decent coverage on a full-frame sensor.

To extend the focal length, the split tube FC-76DCU also has another accessorized trick up its sleeve, buried in the user manual – slot in the CQ 1.7x extender module for the FS-60Q and you have the best planetary and Lunar 3” APO I have ever seen. But since the FC-76Q briefly became a product in its own right, that is a story for another review.

Finally, the lack of focus travel could be addressed with aftermarket focusers from Moonlite or Starlight Instruments; a 1.5”-2.5” long drawtube would probably be ideal, but check with the vendor. The Moonlite focuser can be fitted with a Takahashi-standard finder base too.

In Use – Daytime

The daytime field of view is flat and sharp and mostly false colour free, but this is largely academic because the FC-76 is too large to mount on a photo tripod and use as a spotter (unlike say a Borg 71FL).

In Use – Astrophotography

Off-axis aberrations are very modest for a doublet and coverage excellent – even on full frame. Violet bloat on bright O-A stars is well controlled. See image of M42 below.

You can really tell Takahashi designed the FC-76DC and DS for digital imaging (hence the ‘D’). For APS-C sensors you could get away without a flattener to get you started, a big advantage over most F6 doublets where a flattener is essential. My preferred option would be the cheap, basic flattener: with modern sensors and low noise electronics, F7.8 isn’t that slow and the image circle is larger too (see accessories section for more details).

The main real drawback of the FC-76DC for imaging is focus travel: you might need to be creative with extensions and/or judicious positioning of the camera nosepiece.

Imaging the Moon can tell you a lot about how a scope performs in terms of sharpness, resolution and contrast at high image scale and how it handles seeing, revealing flaws you miss visually. I managed to image the Moon with FC-76 at exactly the same phase and under similar seeing conditions to the FS-78 years back. Zoomed right in, the images are very similar, suggesting the FC-76 gives little away to the older scope in these areas.

Full-frame image of M42 with FC-76 and Canon EOS 5D – 45s at ISO 1600.

Moon at prime focus with FC076 – cropped and slightly enhanced contrast.

In Use – The Night Sky

General Observing Notes

Cooldown is benign and rapid – a godsend if you are used to waiting for triplets, Maks or SCTs (and waiting … and waiting …).

Despite the longish f-ratio, perfect focus is such an absolute point that finding it would be easier with a microfocuser; as it is you need to be practised to nudge in perfect focus with the tiniest movement of one of those silver Tak’ wheels.

As usual, the little Tak’ delivers hard, very white, very contrasty views. There is minimal stray light around Venus or the Lunar limb, so nasty halos around Jupiter or red blur around Mars. This really is what you are paying for compared to a cheaper optic of modest quality.

The FC-76 in standard form isn’t great for binoviewing – there just isn’t enough in focus travel and many Eps won’t come to focus even with the refractor OCS in the nosepiece of my Denk’ Standards.

Star Test

The star test is all but perfect – very similar either side of focus. Even more impressive is the perfect, faint, in-focus diffraction ring around a bright star on a steady night at 163x.

The Moon

Takahashis of old have always been great Lunar scopes and the FC-76 is no exception: it gives one of the best views of the Moon I have had with a 3” refractor. With a 5mm Type 6 Nagler giving 114x, the whole Moon fits in the field and it is sharp and full of detail and contrast from limb to limb.

On a 13-day-old gibbous Moon, in steady seeing at 163x with a 3.5mm Nagler, I can explore a wealth of terminator detail: several bright craterlets on Plato’s dark floor; the strange and solitary black shadow from Promontorium Laplace; the Gruithuisen domes; stripes in the crater wall of Aristarchus; hints of rilles in Gassendi.

Venus

Venus showed a brilliant white crescent with no flare or stray light and virtually free of false colour (just a hint of gold out of focus), even at 143x with the Nagler zoom set on 4mm. This is where the longer focal length of the FC-76 shows – Borg’s F5.6 90FL shows quite a lot of proper purple-and-green false colour on Venus at the same magnification.

Mars

At just 5.7” in size, Mars was very sharp with no false colour at up to 190x with a 2-4mm Nagler zoom. I spotted hints of albedo markings on its minute ochre disk. Small F6 APOs often fail on Mars, giving a mushy soft view because their Strehl is poor in the red; not so the FC-76.

Jupiter

At 143x with a 4mm Nagler zoom, Jupiter showed a crisply-defined cream disk free of false colour or softness, with quite a lot finer detail – narrow belts north and south of the main NEB and SEB, shading in the polar hood and hints of dark storms.

Deep Sky

I confess that I don’t usually use the FC-76 (or other small scopes) now for deep sky, preferring to use my 15x56 binos for quick DSO sessions. But I thought I should try it out for this review and ended up having a lot of fun. For most of the easier stuff, I just swept using a 32mm Plossl and then upped the power with a 15m Panoptic as required; I never needed the finder.

Orion’s Great Nebula looked wonderful, with lots of nebulosity sweeping into space. Bode’s twin galaxies were much more interesting and distinctive than they have a right to be through such a small aperture. The Pleiades were classic diamonds-on-velvet embedded in faint wisps of nebulosity. The Starfish and Pinwheel Clusters showed their sweeping arms of stars and looked great. The Crab Nebula was easy to spot north of Zeta Tauri and its shape was readily discerned. The Andromeda Galaxy was bright and showed hints of dark lanes; the wide field easily encompassed most of it.

The FC-76 seems good at splitting doubles, too. Epsilon Lyrae was easy. On a night of fairly steady seeing I had one of my best ever views of Rigel, with Rigel B much more obvious than usual, perhaps due to the FC-76’s high Strehl objective that packs so much of the light into the Airy disk and less into the space around it.

Surprisingly (I thought) the FC-76 proved really good at visual deep sky – much better than any 60mm scope and better than some larger scopes I’ve seen; blame that high-contrast, high-Strehl lens.

Summary

The FC-76 reminds me how much nicer a longer focal length often is – less off-axis aberrations for imagers and a sharper high-power view for observers. This is a proper apochromat, just like it says on the dew-shield.

As with previous 3” Takahashi fluorite doublets, it offers quick cooldown and razor-sharp views of everything – the Moon, planets and deep sky - with minimal false colour. If its predecessor, the benchmark FS-78, gave a better view, it wasn’t by much. Ditching the lead and arsenic, speeding it up and returning to a Steinheil configuration hasn’t spoiled those essential Tak’ fluorite-doublet values.

Unlike the FS-78, though, the FC-76 is lightweight and highly portable for its aperture – especially in this split-tube FC-76DCU version. And that half F-stop extra speed is a bonus for imagers. Built-up, it is quite a long scope, though - Borg’s larger-aperture 90FL is much shorter.

The only real negative point is the focuser – perfectly smooth and accurate and largely free of image shift, it could just do with another few cm of travel. I can see quite a few FC-76s ending up with Feathertouch or Moonlite focusers.

No, the FC-76 is not cheap, but current prices are competitive with other small APOs in the premium class (including Borg’s, which also use Optron fluorite objectives). Build quality is usual Tak’ – simple but superb.

In the end, the only doubt about the FC-76 is whether you really need that supreme light-weight and portability. If not, then you might be better paying just a bit more for an FC-100, which will have better performance just due to its larger aperture (the difference between 3” and 4” is quite substantial) and is very light and compact too - about the same size and weight as the old FS-78 in fact!

If you need a really portable small APO that will do both imaging and high powers for the Moon and planets, one that cools fast too, you just found it – highly recommended.

 

 

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