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Takahashi FS-60Q Review

The FC-60 was a classic small Takahashi refractor that has been out of production for many years, but still I wanted one. I advertised for one on numerous occasions, kept getting pipped at the post on Astromart in the US. So I was close to ecstatic when Takahashi announced the FS-60Q. But why exactly?

A 60mm APO is highly portable, but it also has surprising potential as a quick-look/travel scope for the Moon, planets and eclipses, easily rivalling a Questar. Titter ye not! A perfect 60mm aperture will resolve detail down to below 2” of arc, which is enough to show you a lot. Now given that even Mars gets up to 20”+ on a good opposition, a 60mm APO should easily show the polar caps and major albedo features … if it’s a good ‘un. And therein lies the problem.

Most small doublet APOs (the FS-60C included) are ~F6 and suffer from a number of limitations:

·        Significant chromatic aberration

·        A very steep light cone and a tiny focusing ‘sweet-spot’

·        Severe field curvature and off-axis coma

·        Steep lens curves which make it harder to achieve a really good optical figure

·        Spherochromatism - their spherical aberration (and so effectively optical quality) changes with wavelength: typically fine in the green and blue for imagers, they are poor in the red (and for Mars).

Perhaps surprisingly, just adding two F-stops changes all that, so a good small F8 doublet APO – like the original FC-60 - can be excellent for high powers on the Moon and planets, Mars included, which is why I had long wanted one.

The FS-60Q effectively fills the gap left by the FC-60. It is an F10 quadruplet optimised for high-power use, but based on the FS-60C, which you can convert with a plug-in module. In theory this improves the optical quality, kills the spherochromatism and flattens the field for imaging too.

At A Glance

Telescope

Takahashi FS-60Q

Aperture

60mm

Focal Length

600mm

Focal Ratio

F10

Length

45 cm w/o visual back

Weight

~1.8 Kg (without finder and ring)

 

Design and Build

You can ether buy the FS-60Q as complete scope, in which case you get the privilege of a red serial-number plate, just like other Takahashi quadruplets (the FSQ-106 and FSQ-85).

Alternatively, you can buy a screw-in accessory called the ‘CQ Module’ that converts an existing FS-60 (in either C or CB variants) into an FS-60Q (which is I suspect how most will do it). In either case, you can always remove the module to return to a fast imaging scope; and to me that flexibility really appeals.

Optics

DSC_0003

FS-60C Objective

Laser test for fluorite: laser disappears in fluorite crown element, but not in glass flint at rear.

We’ll begin with a quick review of the FS-60C optics, since the FS-60Q is based on them: it’s an F5.9 doublet that has the fluorite element (yes, it’s actually fluorite, not a high-fluoride glass – see above) at the front. Technically this makes it a Fraunhofer design, compared with the FC-60’s (and recent FC-76’s and FC-100’s) fluorite-at-the-back Steinheil.

That fluorite FS-60C lens sits in a slim fixed-collimation cell. Unlike the FC-60 it replaced, the FS-60C suffers some chromatic aberration and performs poorly in the red.  The Strehl (which amounts to optical quality) graph for the FS-60C shows this effect and explains why both it and many other F6 doublet APOs struggle to focus crisply on Mars, but work fine on other objects:

The Strehl (a measure of optical quality) of the FS-60 drops off dramatically in the red.

The CQ Module

You can turn any FS-60C into an FS-60Q by unscrewing the lens assembly and threading in the Q module behind it in one of two configurations, depending on whether you have an FS-60C or an FS-60CB (they differ only in the length of their tube).

The Q module screws in behind the objective to become an integral part of the OTA. The Q-module is a doublet, so with it in place you have a quadruplet (hence the ‘Q’) APO operating at F10 (600mm F.L.):

takahashi-fs60q01

The CQ module acts as a 1.7x extender, increasing image scale for those wanting to photograph an eclipse, for example; but it changes the optics in other ways too. The CQ module flattens the field and reduces residual spherical and chromatic aberration. According to Japanese websites, Strehl goes up by 10% and the FS-60Q will supposedly cover a 35mm sensor sharp to the edge.

So, is the CQ module just an expensive barlow lens? Yes and no. Optically it is a negative doublet like a barlow, but because its position is fixed and it has been designed for a specific objective, it can achieve a level of correction that a generic barlow plugged into the focuser could not.

These spot diagrams, published by Takahashi, show how much the off-axis performance betters that of the standard FS-60:

takahashi-fs60q02

takahashi-excq17x-03

The CQ module in one of two configurations, depending on your model of FS-60: flip the lenses assembly inwards for the other.

Takahashi CQ 1.7x Module

Enough theory, what does the CQ module look like? It is a section of white OTA-tube that matches the FS-60C OTA perfectly, with a doublet lens threaded into it. The threads match the existing FS-60 ones. It’s a beautifully made unit and the 40mm diameter lens in the CQ module has just about the best coatings I have ever seen: it’s almost invisible; no worries about light loss at least. In fact, looking up the tube with the CQ module in place it is quite impossible to see the module’s lens – the tube looks empty as far as the objective! Internally, the module is painted a perfect flat black, so adds no nasty reflections.

The CQ Module weighs 300g and is about 17.5cm long. Even with the module in place, the OTA weighs just 1.8 Kg and will fit in a carry-on case.

CQ-Module Doublet lens

Module2

Tube

The lengthened OTA does look a bit strange and the Q module is so lightweight that it gives you a balance point with most of the tube beyond the clamshell and that leaves both joins exposed. Practically this has a big advantage, though, because with an equatorial mount the eyepiece changes height less and the OTA is still so light the Teegul mount takes it with ease.

FS-60Q is carry-on portable without disassembly, at 45cm long.

Focuser

The rack-and-pinion focuser is obviously the same unit as the FS-60. It has the familiar Takahashi lime green enamelled casting, the familiar silver knobs and oversized tensioner. Unlike the larger FS models, the focuser on the FS-60 has a very short body for compactness, a bit like the one on the Sky-90, but with a smaller (~55mm) diameter drawtube. This focuser is now used on the lightweight versions of the FS-76 and FC-100 as well as the FS-60 and variants. The short travel means you might need an extension tube for some 2” eyepieces and diagonals or cameras.

The visual back threads-on to the end of the focuser and allows various configurations (you knew it), including attachment of a reducer, extender or rotator. The most important variants are the standard 1.25” visual back with the usual Takahashi twist-to-clamp mechanism, or the optional 2” visual back. Both are shown below.

As I noted in the FS-60 review, this focuser is a puzzle. My first one had too much image shift, a problem noted by other reviewers. This example, however, is virtually perfect: smooth, solid, precise and suffering from just a tiny amount of image shift at high powers. As I said before, I think the issue is wear and tear: this example worked very well with my DSLR; even the lock caused no change in focus, ideal for imaging. But I think that people are routinely hanging big CCD cameras off these little focusers, causing wear in the bushings that leads to slop and image shift.

Mounting

It goes without saying that the FS-60Q will go on the smallest mount. Specifically, it is ideal with Takahashi’s Teegul, a miniature German equatorial mount which breaks down into palm-sized chunks and weighs little more than the OTA.

FS-60Teegul

FS-60Q on Teegul mount/Berlebach tripod

The Teegul is cleverly designed to use the RA motor as a counter-balance, so the tiny 0.6Kg counter-weight is ample and the mount dampens vibration well with a scope of this size. Here you can see it on a light Berlebach wooden tripod. The whole rig is very lightweight and super-portable, whether in and out of the house or on and off a plane. I love the idea of a complete RA-driven mini-observatory system I can carry about fully set-up and the FS-60Q/Teegul fills that role better than anything I know. Even a Questar system ends up being significantly heavier due to the weight of its tri-stand.

Because both the FS-60Q and the Teegul break down into small sub-assemblies, it makes an obvious choice for eclipse-chasers.

If you’re considering the Teegul, please note! The Teegul is sold in various configurations. As a basic setup it works as a single-arm fork, not a German equatorial.  As a single-arm fork, the Teegul is a strange beast that won’t give you whole-sky coverage, even with the FS-60C. Clearances are so tight that FS-60Q won’t work with this setup – it’s too long. So to use the Teegul with the FS-60Q you will need to get the kit that turns into a German equatorial and this is how the Teegul is setup in the photos here.

For these tests, I also mounted the FS-60Q piggybacked atop my AP 1200 mount for maximum stability.

Fs-60Q_1

FS-60Q Piggy-backed atop my TMB175/AP1200

In Use – Daytime

Having first screwed-in the CQ 1.7, I turned the now lengthened scope on the field across the way with a 25mm Plossl giving 24x. The view is immediately impressive – sharp, bright, with snappy focus.

Next I pushed the power to 120x with a 5mm T6 Nagler, about the maximum I’d ever use in a 60mm scope and a power that had the basic FS-60C turning slightly fuzzy. Expletive. Wow. Why? Because the FS-60Q is a scope transformed. The high-power daytime views are extremely sharp, even at high power. Even at 120x the FS-60Q remains sharp and free from in-focus chromatic aberration, even focusing on tree branches silhouetted against a bright sky, with just a trace of residual CA either side of focus.

With a 3.5mm Nagler, giving an extreme 171x and an over-the-top 70x per inch, the daytime view remained completely crisp and free of false colour: quite usable if a bit dim.

Overall, high-power daytime views are among the best: the FS-60Q has great potential as a high-power daytime spotter or birding scope.

In Use – The Night Sky

General Observing Notes

The FS-60Q takes just a little longer to cool than the base FS-60C, but is still delivering high-power views 10-15 minutes from a warm room, which is what you need in a quick-look scope.

The focuser on this FS-60 is a good one in the first place: smooth and with little image shift, as I said above. But with the basic FS-60 you really need a micro-focuser for high powers, because the sweet spot of perfect focus is so small. The CQ module changes that. The extended sweet spot that the longer F10 light-cone gives makes finding perfect focus a doddle, even at 170x and that’s true for imaging too. On this example, the focus lock works perfectly - i.e. it doesn’t alter the focus! For modest loads the lock isn’t necessary to prevent rack-out and I only used it when slewing with a DLSR attached.

The star test is decent, but not perfect. This is a limitation of this particular FS-60C objective, which is diffraction limited but no better. In practice, this limitation shows up much less with the Q module in place than in the basic F5.9 scope.

The Moon

The FS-60Q makes an excellent small lunar scope, despite its limited aperture. Lots of detail is available at 120x and the view is still perfectly sharp and reasonably bright at 170x. Contrast is excellent for the aperture. The whole Moon fits into the field of a 5mm T6 Nagler at 120x and the flat field makes it a very enjoyable view.

On a low Gibbous Moon at 120x, I was able to study the slumped walls of craters Tycho and Copernicus, their central peaks, the retreating dawn shadow in Marius, the arcing crater chain in Clavius and the Apennine mountains.

There is almost no chromatic aberration on a bright Moon, even focusing through the limb at 170x. Flare around the limb of the Moon is also very well controlled (something that might have been a problem with the extra glass surfaces introduced by the module, but isn’t).

This means that the FS-60Q is one of those scopes that excels when looking at Lunar mountains right on the limb highlighted against space. I always like doing this because you see the mountains’ real form – rounded and smooth – rather than the exaggeratedly jagged look they have on the terminator.

When I returned to my first draft of this review, I thought I was over-egging the pudding a bit regarding the FS-60Q’s view of the Moon. So I went back and checked it out again with the same result. Enjoying crisp and very detailed views at 120x, let alone 171x, just isn’t what I expect from this aperture. Usually I would stick at below 100x on the Moon in a 60mm scope, but with the FS-60Q I always found myself using 120x and sometimes more.

Mars

The prospect of good performance on Mars was one of the main things that got me interested in the FS-60Q. With some favourable oppositions coming up over the next few years, I have been auditioning portable/travel scopes for the Red Planet. So how does it perform?

Near a fairly unfavourable opposition, with Mars at maybe 15” apparent diameter, the FS-60Q was able to reveal significant albedo detail at 120x and 171x. On one occasion, in good seeing, Mare Acidalium was very obvious, as was Syrtis Major on another. The polar caps were both just about visible, although much diminished in the Martian summer.  Some other albedo detail was glimpsed as well, including the dark band stretching from Syrtis Major towards Solis Lacus and I think I could make out a patch of bright limb cloud too.

Chromatic aberration is not a problem on Mars in focus, but just a touch was visible either side of focus at high power. Nonetheless, the FS-60Q gives a more satisfying view of Mars than many small doublet APOs I have tested, the FS-60C and Sky-90 included.

Jupiter

Jupiter can be a difficult subject due to its low contrast, but the FS-60Q gives one of the best views of it I’ve had in a small scope. On a night of steady seeing, a lot of subtle detail was visible at 120x and even more at 170x, including banding in the polar hoods, width variations in the equatorial belts, the Great Red Spot (even in its current pale and diminished state) and the thickened region downwind of it. I was also able to watch Ganymede in shadow transit. On a really good night, the Galilean moons stand out as four hard tiny balls of slightly different size and colour, the way they do in much bigger instruments.

Deep Sky

With just 60mm aperture, the FS-60Q is not a deep sky scope, but the flat field and tight stellar images produce some great views of brighter DSOs. The Pleiades were particularly sparkly, as they tend to be in scopes with low off-axis aberrations and a tight PSF. Clusters like those in Auriga looked good through the FS-60Q too. Fainter, smaller Messier objects – e.g. globular clusters M15 and M2 and the Ring and Crab Nebulae - were a bit dim due to the small aperture.

Doubles

Rigel is challenging for a small scope because the faint companion tends to get lost in the diffraction ring. Nonetheless, The FS-60Q split it comfortably at 120x. In good seeing the twin dumbbells of the 2.3” ‘Double Double’ just resolve into discrete Airy discs.

In Use - Astrophotography

You’d think taking an F-ratio of 5.9 and bolting in a module to extend that to F10 would kill the astrographic potential of the FS-60Q, but that’s not really the way it works out. Sensitive CCDs and stacking techniques can get around slow F-ratios to some extent. Meanwhile, the larger image scale is more often a help than a hindrance, unless trying to image very extended objects. The high optical quality, absolute focus snap and longish sweet-spot make it easy to get perfect focus when using a DSLR with Live View.

The following image of M42, straight from the camera, together with a 100% crop of the top right corner, demonstrates excellent flatness, coverage and low chromatic aberration, just as promised.

Full-frame image of M42 and 100% crop of corner below: Canon EOS5D at 59s and ISO 1600 with no post-processing.

As you can see below, allowing for its modest aperture and resolution, the FS-60Q takes an exceptionally sharp and detailed image of The Moon. In fact, the FS-60Q takes better images of the Moon than any other ultra-portable telescope I’ve tested, Questar included.

The FS-60Q would be perfect for taking art shots of Moon rises and eclipses, something I intend trying with mine.

 

FS60QCMoonCrop

The Moon through FS-60Q: single, cropped but otherwise unprocessed image with Nikon D5100

Lunar eclipse through the FS-60Q: cropped but unprocessed frame with Fuji XM-1

In Use – Terrestrial photography

The FS-60Q also works very well as a terrestrial telephoto lens too, as you can see in the following photo of autumn leaves. Below it I’ve included a crop of the top right corner to show the fine edge performance and limited chromatic aberration.

FS-60QLeaves

FS-60Q: This crop of the top right corner shows the flat field and just a trace of chromatic aberration (much less than most camera lenses)

Summary

The FS-60Q is honestly one of the most exciting scopes I’ve tested for a while. It offers new buyers two excellent, but quite different, refractors for the price of one. Alternatively, It gives FS-60C owners an interesting (and for Takahashi inexpensive) way of expanding the capabilities of their existing telescope.

The CQ module is both literally (because of those amazing coatings) and metaphorically transparent – you never detect its presence as a separate item, it just makes the FS-60 into a completely new telescope. Obviously the FS-60Q is still only a 60mm refractor, so don’t expect miracles, but performance is exceptional for the aperture, especially on the solar system. For my money it beats a Questar in most areas and is actually more portable when paired with the Teegul mount.

The CQ module enhances FS-60C performance in several key ways:

1)     The FS-60Q takes high magnification far better than the FS-60C.

2)     The longer focusing sweet spot of the F10 optics means finding focus at high power is much easier than with the FS-60C.

3)     The FS-60Q has lower levels of chromatic aberration and spherochromatism than the FS-60C and continues to perform into the red. It gives great views of Mars, something the FS-60C can’t do.

4)     The FS-60Q has a much flatter field than the FS-60C, so extended objects look great and image really well too.

5)     The greater image scale, sharpness and flatter field make the FS-60Q much better suited to imaging eclipses.

The FS-60Q is still very portable when built-up, but break it down and you have one of the lightest and most portable of Solar System scopes, ideal for eclipses.

Finally, is the Q version good just because my FS-60 was a good one to start with? Absolutely not! In fact the objective of this FS-60 is not as good as the first one I owned and probably not much better than diffraction limited. So I would have thought any FS-60 would perform as well as this one if fitted with the CQ 1.7x extender module.

The FS-60Q is a specialist scope and of course you can get much more sheer performance for the same cost in a larger aperture. But it still gets my highest recommendation, if you’re looking for an ultra-portable refractor with a huge range of capabilities.

 

 

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