ScopeViews

Three-Inch APO Buyers’ Guide

An aperture of 70-80mm (3”) is the minimum for a general-purpose small APO in my view: significantly more capable than a 60mm, refractors in three-inch size range will appeal to beginners, wide-field imagers and those wanting a second scope for quick deployment and/or travel.

This guide is not intended to be exhaustive and reflects my penchant for the rare and unusual, but I’ll add to it whenever another scope crosses my path. Please note that I have tried many, but not all, of the scopes listed here. Also, some of the photos are old and not great quality, whilst others a generic marketing pics.

Please note: I do my research carefully, but to err is human and if you find one please get in touch!

Skywatcher Equinox 80

Skywatcher Evostar 80 ED DS Pro

Askar FRA400

Lens Design	Quintuplet (ED triplet + ED Petzval doublet)
Aperture	72mm
Focal Length	400mm
Focal Ratio	F5.6 (F3.9 w/Reducer)
Length	295mm min.
Tube diameter	90mm
Weight	3.2Kg

Askar is a Chinese brand that markets a bewildering array of scopes of all colours, sorts and sizes. This one is a variant of the Petzval optical design that’s proliferated since Tele Vue’s Al Nagler re-discovered it with the original Genesis and often encountered in Takahashi, Vixen (and once Pentax) premium imaging scopes.

The FRA400 is a bit different optically from most Petzvals, though. For one thing, it’s a quintuplet. For another, it has an ED triplet objective rather than a doublet like most of the rest. At the other end, the Petzval corrector is just a simple doublet with a small air space (the others typically have big air spaces to help with correction).

In any case, the FRA400 is a tiny (even for a 72mm aperture), if rather heavy scope, that performs very well for both visual use (surprisingly) and imaging. False colour is very low. A touch of astigmatism in the outer field – typical of Petzvals – is a minor downside. But Askar market a very nice 0.7x reducer-flattener to remove the remaining aberrations. Coverage at full-frame is good both natively and with the reducer.

Mechanically, the FRA400 is nicely made with a hefty imaging-friendly focuser. It comes with CNC rings and a Vixen-compatible dovetail plate. My only gripes were Allen-key tension adjusters on the rings, rather ineffectual locks on the rotator and drawtube and a slightly coarser focusing action than the best. Oh and the dew-shield is too short for urban environments where flare from streetlights can be a problem.

The only other minor drawback is all the glass and trapped air make for slow cooldown compared with a simple doublet (it’s not an ideal quick-look scope for that reason).

Overall, though, I was very impressed with the FRA400. It’s a much cheaper option for imaging than either Vixen’s VSD70SS or Tak’s FSQ-85EDP, at least in Europe. Alternatively, it could make a very nice do-it-all scope for travel.

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Borg 77ED

Stock image.

Lens Design	ED doublet
Aperture	77mm
Focal Length	510mm
Focal Ratio	F6.6
Length	Varies
Tube diameter	60mm or 80mm
Weight	N/A (varies)

The 77ED was one of Borg’s best selling objectives. With a focal length of 510mm giving F6.6, it’s a less radical objective than the 71FL that replaced it and uses an ED as opposed to fluorite crown. A second version of the lens was produced later, but I’ve no idea what the differences were.

I suspect that these earlier ED lenses weren’t made by Canon, unlike like the later 67FL, 71FL and 90FL et al. The 77ED certainly had a lower price point (a list price about 30% lower than the 71FL at the time).

I’ve seen some great images taken through the 77ED, but some of the early Borg ED lenses weren’t that good, so I’ll reserve judgement until I’ve tried one.

The 77ED is mostly found in a white Series 80 tube with a helical focuser (part no. 7835 – why do I remember that?). The 80mm OD OTA is compact and very light, has the advantage that various tube rings fit (including Takahashi 80mm clamshells for easy mounting on any of Tak’s smaller equatorial mounts).

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Borg 71FL/72FL

Stock image.

Lens Design	Fluorite doublet
Aperture	71mm
Focal Length	400mm
Focal Ratio	F5.6
Length	Varies
Tube diameter	60mm or 80mm
Weight	N/A (varies)

The 71FL is the smaller companion objective to the 90FL, in that it has the slower focal ratio (F5.6) of that lens, compared with the faster 67FL and 55FL (F4.5), doubtless because the good correction offered by the 67FL couldn’t be stretched any further (false colour increases with aperture for a given design).

I haven’t tried a 72FL, but if the 90FL is anything to go by (I’m on my second, both were outstanding), it should be a great lens.

Like other premium Borg objectives made by Canon, the 71FL is a fluorite doublet with a wide air space, made by Canon/Optron. Like all Borg objectives, it can be purchased separately and retrofitted to an existing tube assembly. But unlike the 90FL, you can fit it to a Series 60 tube assembly with a flared adapter. This produces an OTA that looks like you might want to play it rather than observe with it (above), but that’s seriously light for its aperture.

The 71FL keeps the family look, with a satin black lens hood and (in this case and unlike the 90FL, fixed) dew-shield. Borg is increasingly focused (sorry) on photography/imaging and the 71FL was designed specifically for this purpose.

The 71FL was apparently Borg’s biggest ever seller, so obviously they discontinued it! Don’t worry, because the 72FL is more of the same, but supposedly with better correction and tuned more to the characteristics of modern sensors. It’s also still an expensive objective for its aperture, like other Canon/Borg objectives.

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LOMO 80/480, 80/600

LOMO 80/480 in A&M carbon tube. Image credit: Richard, with thanks.

Lens Design	ED triplet
Aperture	80mm
Focal Length	480mm or 600mm
Focal Ratio	F6 or 7.5
Length	N/A (varies)
Tube diameter	N/A (varies)
Weight	N/A (varies)

These twin objectives by the Russian company LOMO were to be found in tubes by William Optics, APM and Stellarvue around twenty years ago. Both were triplets with ED centre elements and were known for outstanding correction and very high optical quality. After a few years, LOMO discontinued them, so they’re quite rare. At the time both were expensive.

The objectives made it into at least four distinct tubes:

· William Optics in their old ‘Megrez’ style, with fairly basic Chinese hardware

· APM/TMB in a segmented (for ease of transport) lightweight tube with a Feather Touch focuser

· Officina Stellare (A&M) carbon tube, again with a 2” Feather Touch focuser

· Stellarvue in their typical style with a long dew-shield, yet again with a small Feather Touch Crayford focuser

The triplet lenses and rugged cells made all variants quite heavy for the class (although the A&M carbon tubed versions are a bit lighter).

At F7.5 the 80/600 had a reputation for planetary prowess and I would expect extremely low chromatic aberrations from such a relatively small and slow ED triplet, but this is a very rare beast. Indeed, it’s unlikely that a 3” APO of this quality will ever be made again. Why? It’s just not economically viable, especially with Russian products off-limits for the forseeable.

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Skywatcher Equinox 80

Lens Design	ED doublet
Aperture	80mm
Focal Length	500mm
Focal Ratio	F6.2
Length	370mm
Tube diameter	80mm
Weight	2.9Kg

SW once made a premium range of scopes from 66mm to 120mm aperture under the Equinox sub-brand. All shared a shiny black CNC tube with sliding dew-shields, a rotating CNC dual-speed focuser and a lot of shiny chrome that sometimes flaked off.

Like the other Equinox models, the 80 was a bit heavy for its aperture and I was never a fan of the piano-black-n-chrome aesthetic, but they were very well made mechanically.

Most Equinoxes shared optics with the utilitarian ED-Pro. The Equinox 80 was inexplicably different, with an F6 rather than an F7.5 objective. It’s supposed to use a crown element of premium FPL-53 in its air-spaced doublet, but I was surprised to find rather more false colour even than a TV-76.

Still, despite a bit too much false colour, the Equinox 80 was a decent and very well made small APO. It came with a hard case and CNC rings with a Vixen plate as usual, but no other accessories (unlike the generously-spec’d ED-Pro).

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Skywatcher Evostar 80 ED DS Pro

Stock image.

Lens Design	ED doublet
Aperture	80mm
Focal Length	600mm
Focal Ratio	F7.5
Length	~600mm
Tube diameter	80mm
Weight	4.1Kg incl. rings

The Evostar ED DS Pro range have been around forever. Perhaps the reason is that they’re really good: relatively inexpensive, with quality Vixen-clone hardware. The 80mm model sports a metallic-black tube with white powder-coated dual-speed focuser, rings and dew-shield, same as the 100mm and 120mm models.

In this case, the ED doublet is 80/600 (F7.5) with an FPL-53 crown like the rest. I haven’t tried the 80mm DS Pro, but was impressed by both larger models (the 100mm is a best buy).

For imaging it’s a well-corrected objective, if the others are anything to go by. SW sell a dedicated 0.79x reducer/flattener to speed things up to F6.37 (475mm F.L.)

The only negative thing about the ED DS-Pro range is its Crayford focuser. It has plenty of travel, precise and smooth fine adjustment, but is prone to slip with a heavy load. It could do with a drawtube lock for heavier eyepieces, cameras, filter wheels etc.

A major bonus with the whole DS Pro range is all the freebies you get with one: an 9x50 finder, split tube rings, a Vixen-fit dovetail, a dielectric 2” diagonal and a surprisingly nice 28mm 2” eyepiece. If that lot wasn’t enough, they throw it all in a very decent hard case too.

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Takahashi FS-78

Lens Design	Fluorite doublet (Fraunhofer)
Aperture	78mm
Focal Length	630mm
Focal Ratio	F8.1
Length	740mm
Tube diameter	95mm
Weight	2.6Kg

By their own admission, when the technology enabled Takahashi to start hard coating their fluorite elements they retired the old FC-series with its fluorite-at-the-back Steinheil objectives and introduced the FS-series with the fluorite at the front.

The range originally included the FS-78, FS-102, FS-128 and FS-152. All had highly corrected F8 optics optimised for planetary and lunar viewing. Even the largest, the FS-152, suffers only minor chromatic aberration, so you can imagine that the FS-78 is virtually free from visual-wavelength false colour and spherochromatism, and it is.

The FS-78 was originally the smallest of the FS-series: there was no FS-50 and for some years no FS-60 either. The old Steinheil FC-60 continued in production alongside it, with the FS-60 only introduced later as a budget F6 imaging scope (not the family norm F8).

It may be the smallest FS model, but the FS-78 is not a small scope. All the FS series had oversized tubes fitted with knife-edge baffles and big dew shields to provide maximum protection from stray light. So it’s both bulky and quite heavy – much the same size and weight as a modern FC-100D. Its clamshell may have a ¼-20” thread but you won’t be mounting an FS-78 on a photo tripod.

The FS-78 is typical FS series, with its blue lens ring and cast manhole dew cap. But whilst the FS-78 has the classic buttery-smooth single-speed cast focuser with a 2” drawtube, it was an entry level scope so got the cheapo plastic focuser wheels, not the heavy anodised units the bigger ones got.

Nonetheless, if visual is your thing, the FS-78 remains one of the best corrected small APOs ever and unlike the LOMO 80/480 it’s quick to cool so great for quick looks. Is it as good as the earlier FC-76? Legend say no, me say yes and then some.

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Takahashi FC-76

Stock image.

Lens Design	Fluorite doublet (Steinheil)
Aperture	76mm
Focal Length	600mm
Focal Ratio	F7.9
Length	~650mm
Tube diameter	95mm
Weight	~2.5Kg

Not to be confused with the current FC-76D (below), the FC-76 was Takahashi’s original 3” fluorite apochromat, introduced in the 1980s and with the family look of all the FC range from the FC-50 to the FC-125. (Note: I believe the FC-76ES designation in the brochure pic above indicates the EM-1 mount it was sold on as a package.)

Optically, this was a little different from the current FC-76D. The objective is a Steinheil (fluorite behind) doublet of outstanding quality, made by Optron, but the modern scope has a shorter focal length of 570mm (vs 600mm for the FC-76) and other improvements for digital imaging, such as recessed foil spacers for better star images.

The smaller aperture and shorter focal length of the FC-76 mean it’s just a little more compact than the later FS-78 that replaced it, but bigger and heavier than the current FC-76DCU. Early FC-76s have blue-grey enamel on the their beautifully cast focuser and rings, later ones classic lime green. That focuser, whilst not the full-fat imaging model on the FCT-76, had a 2” drawtube and was heavier duty than the one on the FC-60 and FC-65; I’ve seen it retro-fitted to a recent FC-100DC.

Lore would have it that the FC-76 is better than the FS-78, but I doubt it. For one thing, Tak’s own blurb suggests otherwise. For another, whilst the contemporary FC-100 (that I have reviewed) is an excellent scope, I didn’t find it better than the FS-102 that replaced it. Apart from the Steinheil vs Fraunhofer debate, the fluorite element was uncoated, reducing transmissivity.

Old it may be, but mounting an FC-76 should be no trouble as all the sizes and fittings are standard Tak’.

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Takahashi FCT-76

Stock image.

Lens Design	Air-spaced triplet with fluorite centre element
Aperture	76mm
Focal Length	487mm
Focal Ratio	F6.4
Length	580mm
Tube diameter	95mm
Weight	~3.5Kg

Back in the mid-80s, Tak’ started to produce a range of high-end APOs above their bread-and-butter FC series. All featured fast fluorite triplets, from the tiny-but-fast (F4! In 1986!) FCT-65 to the ultra-rare but hyper-desirable FCT-150.

The FCT-76 was the second model released (after the FCT-150) – in March 1985. Like the others, it offered astonishingly high levels of correction for its aperture and fast F-number at the time, but at a high price. Consequently, these are very rare, especially in Europe. I’ve never seen one or even seen one for sale.

The FCT-76 was very short, thanks to its native focal length of just 487mm (F6.4), but has an oversize 95mm tube, if a rather short dew-shield that some have swapped for the longer one from an FS-78 when working around ambient lights.

The standard focuser has a wider drawtube, better suited to heavy cameras with large sensors (up to medium format 645), than the FC-76’s. It also seems to have been available with a big Pentax-like helical focuser (see pic above) that was finished in fetching Takahashi silver.

Takahashi virtually pioneered reducers for astrophotography (with film back in the day) and they produced an F4.5 reducer for the FCT-76.

I can’t speak for the performance of the FCTs, but physically they were like other Tak’s of the time, with blue-grey enamel where later models would sport lime green.

The clamshell featured the usual pair of M6 bolts at 35mm spacing that fit just about any Tak’ mount.

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Takahashi FC-76D

Lens Design	Fluorite doublet
Aperture	76mm
Focal Length	570mm
Focal Ratio	F7.5
Length	N/A (varies)
Tube diameter	80mm or 95mm
Weight	~2.4Kg incl. rings

The current FC-76D is one of my all-time favourites and a Scope Views best buy, not to be confused with the original FC-76. There’s lots to unpack, so pay attention (or move swiftly on)!

On the face of it, the FC-76D is a simple foil-spaced fluorite Steinheil doublet like the old version from thirty years ago, but it’s a thoroughly modern lens. Designed for imaging (hence ‘D’) – with low violet bloat on hot stars and a well corrected field for a doublet – it nonetheless offers outstanding visual performance too. The icing on my Christmas cake is that it’s rugged, fast-cooling and comes in various tube options that are all notably lightweight for a 3” APO.

The basic FC-76DC used an 80mm tube and small focuser borrowed from the venerable FS-60, but it was replaced by a version that splits in two – the FC-76DCU. The headline benefit of this arrangement is carry-on portability, but hidden in the user manual was an option to thread in the CQ 1.7 extender module from the FS-60Q to create the Franken-scope FC-76Q.

The CQ extender transforms the FC-76 into one of the very finest small planetary and lunar scopes – super sharp and well corrected with a very flat field for imaging and weighing under 3Kg all-in. It’s a great portable solar system imaging machine.

If deep sky imaging is your thing, another variant - the FC-76DS - offered the larger focuser from the FC-100DF (and old Sky-90) in a 95mm tube. This has recently been replaced by the FC-76DP with an odd hybrid design of 95mm and 80mm tube sections, that nonetheless combines the light weight and split-tube of the DCU with the focuser from the DS. What’s more, Tak’ have produced a market-leading 0.65x fluorite reducer for the new version.

If you don’t want to splash for the new (‘FU’, yes really) reducer, you can deploy Takahashi’s cheap-but-excellent 1.04x multi-flattener - just buy the ‘Multi CA Ring 76’ adapter.

The older versions used the existing 80mm or 95mm cast clamshells, but the new FC-76DP has a set of handsome Tak-silver CNC rings for about the same price (you can use the old clam but Tak’ advise that it overlaps the 80mm tube section).

Did I mention there’s yet another way to get an FC-76D? You can buy just the objective unit to replace the business end of your old (or new) FS-60.

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Tele Vue Ranger

Lens Design	ED Doublet
Aperture	70mm
Focal Length	480mm
Focal Ratio	F6.86
Length	400mm
Tube diameter	3”
Weight	1.5Kg incl. mount rail

The Ranger had 70mm F6.8 (480mm FL) doublet optics with a positive crown element made of ED glass that was reportedly a cheap one delivering only modest benefits in false colour correction.

Externally, the Ranger had styling cues from other TVs – white or green pebble-finished tube with black-anodised dew shield and focuser. But here the dew-shield is fixed to reduce weight and has a plastic clip-in cap. The focuser isn’t Tele Vue’s usual rack-and-pinion, but a combination of drawtube for coarse focus and a helical for fine. The biggest downside is that it doesn’t allow for 2” eyepieces.

The Ranger was intended for terrestrial use as well as for astronomy. It was eventually replaced with the conceptually similar TV-60, that has completely different (proper ED) optics and a smaller CNC tube.

Most Tele Vues mount via a clamshell, but the Pronto has a built-on sliding bar arrangement that saves weight and makes it easy to balance. The bar has the usual ¼-20” threads on the base.

A simple semi-APO it may be, but I love the Ranger – it has a friendly, do-anything personality if visual is your thing and you can live with a bit of purple fringing at high power. Many apparently bought them for spotting and birding and TV even sold a stay-on field case at one time.

Tele Vue once sold a Ranger with a solid brass tube, which would look great in your study overlooking the sea, but actually give great views of the shipping and gulls too (unlike those brass nautical scopes on Amazon). They made a very rare walnut “executive” desk mount for it at one time (I always wanted one for some reason).

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Tele Vue Oracle

Stock image.

Lens Design	Cemented triplet (regular crown/flint glasses)
Aperture	76mm
Focal Length	560mm
Focal Ratio	F7.4
Length	(?)~450mm
Tube diameter	3”
Weight	Kg

The Oracle is an early Tele Vue, contemporary with their original Petzval, the ‘Genesis’ (why have their evocative names died out in favour of TV-76 and NP-101?), introduced in 1986 and sold through the early 90s.

Superficially, the Oracle looks a lot like a cross between a Genesis and a TV-76. It has the latter’s 76mm aperture, the same focuser (at least as an early TV-76) and a cream-pebble coated tube too. Early Oracles had the short fixed dew-shield and solid chromed wheels of the Genesis, later ones a slider like the TV-76 and TV-85.

Unlike the Genesis, the Oracle’s wasn’t a four-element Petzval, but a cemented triplet. Also different optically from the ED air-spaced doublet TV-76, the Oracle had a longer focal length too, at 560mm vs 480mm, which is why it was physically longer.

In terms of performance, the Oracle seems to have had much lower false colour than the (basically achromat) Pronto, but a little more than the TV-76. That’s likely because the slower (F7.4) triplet objective contained ordinary flint and crown glasses. Is that a thing? Yes indeed! Such triplets were the original apochromats, but are rarely seen now that ED glasses are cheap and ubiquitous.

If Oracle build style and quality seems much like later Tele Vues, the optical quality was too, i.e. uniformly excellent.

Details of the finish varied over time too, with some even having plastic focuser wheels, others those lovely ‘mag’ ones. Some also pioneered the satin black focuser and dew-shield that reappeared much later.

The clamshell and twin ¼-20 threads are the same as later TVs, so it should go on any of their mounts like the Telepod or Panoramic.

The Oracle seems rarer than the Genesis and for some reason. It’s one of those scopes I’ve always hankered after, if only because it comes from a time when triplets were rare and exotic.

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Tele Vue Pronto

Lens Design	ED Doublet
Aperture	70mm
Focal Length	480mm
Focal Ratio	F6.86
Length	360mm (14.5”)
Tube diameter	3”
Weight	Kg

The Pronto was a very popular scope twenty years ago – one of the first small ‘apochromats’ with quality optics and mechanicals not made by Takahashi or Vixen! The Pronto shared the 70mm ED doublet objective found in the Ranger, but in a larger and heavier astronomy-oriented OTA with an ordinary focuser.

Externally, the Pronto is almost identical to the original TV-76 that replaced it – a compact but surprisingly weighty OTA in cream or green pebble powder coat, gloss black anodised single speed focuser with ‘mag’ wheels, a matching sliding dewshield and a screw-on cap (screech, screech).

Internally, there are (as usual) no baffles just black sand (sorry, flocking) paper. The lens cell is fixed with blind screws and collimation is usually very robust.

Like other small TVs, the Pronto has an anodised clamshell with two ¼-20 threads to fit TV mounts and a third central one for camera tripods, but for which a Vixen dovetail adapter is readily available. The Pronto came in the usual grey TV semi-rigid case with cut foam.

The important things to understand is that the Pronto may look exactly like a TV-76, but it really isn’t one. The difference is the lens. The TV-76 is a 76mm (!) doublet with a front-surface crown element of ED glass (probably FPL-53) and so excellent correction. The Pronto’s 70mm ED doublet uses a barely-ED crown glass that gives it at-best semi-APO performance: at high power the Moon and Venus reveal plenty of dull-purple false colour.

So the Pronto is rubbish then? Absolutely not! Optical and mechanical quality is reliably top-notch. I did a side-by-side comparison with a TV-76 back in the day and in use the two are closer than you might think, visually at least.

The 2” visual back was good news for budding imagers too and Tele Vue’s generic TRF-2008 0.8x reducer/flattener was originally made for it (it even says Pronto on mine!) and cheaply available used. Results can be surprisingly good, especially if you steer clear of bright O-B stars (results on extended DSOs like M31 are great).

Still, for high-power use and more ‘serious’ imaging, the TV-76 is superior and should command a much higher price used (please note). Yet, oddly, the Pronto seems more expensive than the optically identical Ranger, perhaps because it is a very lovely thing with its mag’ wheels and has a gorgeously individual and retro vibe now.

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Tele Vue TV-76

Lens Design	ED Doublet
Aperture	76mm
Focal Length	480mm
Focal Ratio	F6.3
Length	360mm (14.5”)
Tube diameter	3”
Weight	2.8Kg

The TV-76 has been in production for some twenty years so it must be doing something right. It replaced the Pronto (above) and is outwardly almost identical, but substituted the Pronto’s 70mm semi-achromatic optics with a 76mm ED apochromat of 480mm focal length (F6.3).

All versions have the signature Tele Vue features: a compact but quite weighty (~2.8 Kg) tube coated in very durable pebble-finish gloss powder coat (either cream or green for birders), with a sliding dew shield and focuser in black – original versions were gloss anodised, more recent examples satin – and a heavy screw-on dew cap.

Early focusers were single speed with Tele Vue’s ‘mag’ wheels and a chrome drawtube. More recent examples have a dual-speed pinion, a less tapered body and a satin black drawtube. All versions have a 2” visual back as standard.

If you want to image, Tele Vue market the TRF-2008 0.8x reducer/flattener than screws straight into a T-ring camera adapter and slots into the 2” visual back.

Performance is generally excellent. The lens is sharp and well-corrected for both visual or imaging.

Like all Tele Vues, the TV-76 attaches to a mount via a heavy 3” ID clamshell with three ¼-20 threads on the base and has a mounting dovetail for TV’s own Starbeam red-dot finder. Tele Vue’s own smaller mounts, the Panoramic and TelePod are a good match for the TV-76, as are other light-medium alt-az mounts like Vixen’s Porta or Skywatcher’s AZ4 for visual, or smaller equatorials for imaging.

The TV-76 is super portable and comes in a nice soft case with cutouts for your eyepieces (Tele Vue of course). Tele Vue’s are exceptionally rugged in my experience, both in terms of finish and resistance to minor bumps and knocks, so ideal for travel.

Any downsides? The TV-76 shows some softness on Mars and minor false colour on Venus, like many fast ED doublets and a bit more violet bloat on O-A stars than the best. It’s heavier than some in this guide and you pay for its hand-built boutique style with a high price, especially new. Later versions with a more imaging-friendly dual speed focuser just don’t have the simple beauty of the original IMO (yes, yes, I know – it’s a telescope FFS, not a sculpture).

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Vixen SA-70S

Image credit w/thanks: C. Cammoranesi.

Lens Design	Regular crown/flint glasses
Aperture	70mm
Focal Length	600mm
Focal Ratio	F8.6
Length	N/A
Tube diameter	N/A
Weight	N/A

You want rare and exotic? I can’t provide parrots or dancing girls (this is 2025!), but let’s talk about the Vixen SA-70. The SA-70 is so rare I hadn’t even heard of it until a fellow connoisseur of small APOs contacted me about it. Consequently, I’m short of data on this one.

Unusually for Vixen, the SA-70 was a triplet. But why though?

Maybe Vixen dreamed it up as a response to Tak’s radical FCT-65? Nope! The little Tak’ is a fast apochromat designed for astrophotography. But the SA-70 has a semi-apochromat (i.e. no ED glass or fluorite) 70/600 F8.6 objective that’s actually slower than the FL70S doublet (see below).

It seems to have been positioned above their once very common small (but excellent) achromats, but below the later FL-series.

So I’m guessing the SA-70 was an early (unsuccessful?) foray into highly corrected small refractors that avoided the difficulties of fluorite before Vixen were ready or able to grind the mineral.

Mechanically, it looks much like any other Vixen refractor of the time, with Hammerite (grey not green) bits and a large white tube, split rings and a Vixen dovetail. How did it perform? Not very notably, I’m guessing from its rarity, so definitely one for the collector.

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Vixen FL-70

Lens Design	Fluorite doublet
Aperture	70mm
Focal Length	560mm
Focal Ratio	F8
Length	~560mm (510mm minimum)
Tube diameter	75mm
Weight	2.3Kg

Back in the dark ages at the end of last century, Vixen pioneered fluorite objectives alongside Takahashi. Like Tak’, they made a range of small, highly corrected APOs with F8 foil-spaced Steinheil (fluorite at the back) doublets. Unlike Tak’, I believe they were made in-house (correct me on this if you know better!) The early versions had collimatable lens cells and were of extremely high optical quality, but an uncoated fluorite element means transmissivity is well down by modern standards.

The FL range included the FL-55 (not to be confused with the current FL55SS) and two larger models, the FL-80 and an F9 FL-102. The FL-70 is a compact scope – smaller and lighter than the FC-76. Still, it’s not going to work on a photo tripod the way a contemporary TV Ranger could.

The FL-70 has an old-fashioned mid-range look to the modern eye: Vixen ‘Hammerite’ green enamel on the hardware, a small focuser with black plastic wheels and an oversized tube with a big dew-shield. Typical of the era, it is clearly intended for visual use (huh, whassat?), given the 1.25”-only eyepiece holder.

Another distinctive feature was the finder on a long, swivelling stalk. This looks weird, but solves a real problem with finders on small scopes – it’s easy to move aside while observing!

Don’t be fooled by the old-skool style of the FL-70, though. It’s a high-performance optic. The first time I looked through one at Venus I was astonished: this is one of those rare refractors which is basically free of false colour, to the eye at least. It’s extremely sharp too and delivers really outstanding lunar and planetary views for the aperture.

Like most Vixens, it came with cast split rings and a Vixen dovetail plate, so it’s easy to mount and use today.

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Vixen FL-80S

Lens Design	Fluorite doublet
Aperture	80mm
Focal Length	640mm
Focal Ratio	F8
Length	650mm (600mm min)
Tube diameter	90mm
Weight	Kg

The FL-80 is IMO the sweet-spot in a very sweet range of small fluorite apochromats. Why? The FL-70 is great too, but not much smaller or lighter. Meanwhile the wonderful F9 FL-102 is UUUGE [sic] by comparison! For general info about the FL series, see the entry for the FL-70 above.

Like the FL-70, the 80 is an outstanding optic – an F8 Steinheil fluorite doublet with very low false colour and offering ultra-sharp and high-contrast solar system views. The version I reviewed is later than the FL-70 above, with a different tube style (much more compact) and a non-collimatable lens cell. I preferred the old-style, but this newer one has the advantage of a proper imaging-friendly focuser with a threaded 60mm drawtube and a 2” eyepiece holder and imaging extension as standard.

It’s not all about solar system views either. Despite the uncoated fluorite element, deep sky images are good and reveal minimal violet bloat on hot stars (though you’d need some kind of flattener or reducer – Tele Vue’s TRF-2008 should work ok at this focal length). Native snaps of the Moon are top-notch for this aperture – exceptionally sharp and detailed.

The OTA really is super small and exceptionally light. Performance is similar to its Tak’ contemporary - the FS-78, but this is a tiny OTA by comparison. Slide off the dew-shield and it would easily go in a carry-on bag too.

Mounting hardware is standard Vixen. Nuff said.

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Vixen VSD70SS

Stock image.

Lens Design	Five elements air spaced
Aperture	70mm
Focal Length	385mm
Focal Ratio	F5.5
Length	368mm (299mm dewshield retracted)
Tube diameter	90mm
Weight	3.5 Kg

The VSD70SS is crazy expensive for a 70mm scope, especially in Europe, and it doesn’t even ship with a finder! Still, the VSD70SS is very impressive and is probably the best small imaging APO in this guide, at least for now. Read on to find out why.

Basically a smaller clone of its larger brother, the VSD90SS, the VSD70SS has five-element Petzval optics, with two premium ED (called SD by Vixen, but probably FPL-53 or even FPL-55) crown elements, one ED flint (like a Tak’ FOA-60 for example) and another element of special Lanthanum glass!

All five elements feature very large air gaps for even better correction, despite which Vixen say this scope works for visual use on the planets too. This is unusual because most camera lenses built this way absolutely wouldn’t. That’s because big air gaps make it difficult to achieve the high overall optical quality needed for high powers – lots of camera lenses (and complex astrographic refractors too for that matter) suffer from decentring.

Still, high powers on planets are not the reason you’d pay this much for a 70mm APO. Rather, the aim is to produce near-perfect star images – minimal astigmatism, false colour and vignetting (i.e. brightness reduction in the outer field) across a wide image circle for big sensors. All these things are difficult with a Petzval and the 70SS has a large rear lens group to achieve it.

If their published specs are true, the VS70SS achieves an excellent 90% illumination across a 55mm image circle (i.e. medium format, never mind full frame which is 44mm), although this drops when using the 0.71x reducer (but do you really need a 275mm FL?).

Spot sizes are tiny too, even out beyond full-frame. The optics have also been cleverly designed to tolerate minor defocus and still produce decent axial images, so better for noob imagers.

Meanwhile, centre field it’s supposed to have a poly-chromatic Strehl of 96.7% - a very high value that promises minimal violet bloat (and those super-sharp planetary views too). Wow. I’m starting to understand why the 70SS is so expensive.

Mechanically, it looks good too. The VSD70SS has big focuser designed for heavy loads with a lever lock and is compatible with 3^rd party motor focusers (though a micro-focus wheel remains an accessory, as for other Vixens).

The VS70SS is very small and fairly light, so should be easy to track and guide accurately on a medium mount. The dew-shield slides down over the tube for easy storage and transport. Unlike its larger sibling, the 70SS has a dovetail shoe which means no ring required.

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Vixen SD81S

Stock image.

Lens Design
Aperture
Focal Length
Focal Ratio
Length
Tube diameter
Weight	Kg

The SD81S is the latest in a long line of 80mm Vixens and is basically a smaller version of the SD103S. That means a rather workaday-looking OTA with what appears to be an old SkyWatcher focuser. Looks can be deceiving though (or so I ‘ve long hoped).

In fact the SD81 is a modern imaging machine that features:

1) An F7.7 ED doublet with an FPL-53 crown and excellent correction, including in the violet ‘g’ band that can lead to bloating on O-A stars

2) A heavy duty focuser with a 60mm-aperture drawtube

3) An annular spacer in the objective (instead of the little foil tabs) for cleaner star images

4) Optional but inexpensive 1.02x flattener with full-frame coverage, optionally combinable with a 0.79x reducer for a superbly corrected and well-illuminated F6 field

The SD81 is quite light, though not as compact as a Takahashi FC-76D. Unlike the Tak’, the SD81 comes with a full set of accessories: rings, plate, handle, flip-mirror diagonal and a nice red-dot finder. Viewed as a package like that, it’s much cheaper than the imaging-centric FC-76DP, but is still a quality Japan-made scope, likely with strong long-term support.

The SD81 has a reputation (in Japan at least) for taking excellent images. I was quite impressed with the similar SD103S, but the SD81S should be even better corrected.

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William Optics GT81

Stock image.

Lens Design	ED Triplet
Aperture	81mm
Focal Length	478mm
Focal Ratio	F5.9
Length	390mm (dew-shield retracted)
Tube diameter	90mm
Weight	3.95Kg (4.5Kgs WIFD)

The GT81 is designed primarily for imaging. It is a triplet with an ED (premium FPL-53) centre element that operates at a fairly fast F5.9, but is otherwise conventional.

The GT81 sports a dual-speed CNC focuser with a scale, a micrometer in one of the wheels and a rotator. It only has a lock on the pinion, though, not on the drawtube which I prefer for heavier cameras if properly implemented.

You either love WO’s coloured anodising … or not. I have a friend who sold a wonderful scope because he didn’t. His was gold accented, but the GT81 is available in the red we see everywhere now and a restrained grey too. I think I like the red best.

There is also a version acronym’d WIFD (too WIFE adjacent for my taste) that uses an internal focuser like an old Zeiss Telementor. Back then it was probably to stop school kids busting it. Now it should mean less vignetting and no chance of droop (always embarrassing) or image shift. It also means better weight distribution, but odd centrally-placed wheels and an increase in weight to a fairly substantial 4.5Kgs.

Either version should be well corrected for false colour and a great imaging tool, but you’ll need a reducer. William optics do a very decent and inexpensive 0.8x one to take the F ratio down to a fast F4.72.

The GT81 is excellent value, but I notice that a major UK retailer is offering these ‘Checked and Tuned’ so I’m guessing there have been quality problems (and I’ve seen reports of such) – check carefully if buying used.

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Summary

So which one is best? As usual, no single answer. There are many fine scopes in this guide (and more I haven’t covered, yet)!

· The basic FC-76DCU is a best buy for visual, with an outstanding optic and flexible configuration. It’s expensive in Europe, but not in Japan (wink)

· For imaging, the Vixen VSD70SS is likely the cost-no-object choice here

· For an inexpensive Japanese-made alternative to either, I’ve heard great things about Vixen’s SD81S, but it’s not as flexible or portable as the Takahashi

· The lightest and most flexible travel scope is surely the Borg 72FL and likely to be excellent optically too

· For the very best corrected 3” APO of all, the 80mm LOMO has a formidable reputation

· As a low-cost (esp. used), fast imaging machine with excellent optics and mechanics that’s super-small to travel to dark skies with, the Askar FRA400 is a no-brainer

For visual, Takahashi’s fine FC-76DCU is the obvious choice. For imaging, the VSD70SS looks amazing if you’re spending big. For low-hassle imaging straight out of the box, the Askar FRA400 is unbeatable value.