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Borg 67FL Review

The Borg 67FL was a limited production run and is no longer available new. But when one came up for sale I had to have it. The reason is simple – it’s insane optical spec’ makes for a pocket-size (really) telescope that performs much like a good 3” apochromat. You want extreme portability and performance? Here you go.

Once I’d bought it, though, I held it in my hand and had doubts. Would its radical numbers make for a poor optic? Let’s find out.

At A Glance

Telescope

Borg 67FL

Aperture

67mm

Focal Length

300mm

Focal Ratio

F4.5 (F3.8 with 0.85x reducer)

Length

270mm visual

Weight

880g visual

 Data from: Me

What’s in the Box?

It’s a Borg, so just lots of component parts in little boxes.

Borg 67FL configured in a Series 80 OTA with helical focuser.

Design and Build

The 67FL objective threads straight onto Series 80 tubes, or onto Mini Borg tubes using the flared adapter you see above. Apart from that, it’s impossible to be specific, because there are numerous different combinations of focusers and drawtubes you could combine depending on your needs.

Optics

Borg 67FL and Takahashi FS-60 objectives for comparison.

The Borg 67FL has a fluorite doublet made by Canon/Optron in Japan, like others in the Borg range and like many Takahashis. A laser test shows the fluorite element is at the front in a conventional Fraunhofer configuration, like older ‘FS’ Takahashi’s, rather than recent (and also much older) ‘FC’ Tak’s that have the fluorite at the back as a Steinheil.

In my opinion, the front-element makes for a slightly better optic (though many will disagree) if only because having the more transmissive fluorite up front makes for a slightly more transparent lens (fluorite transmits more light than glass, hence its lack of scatter in the laser test).

So far, so typical. However, in terms of its focal ratio the Borg 67FL is a radical beast. Why? Consider the Takahashi FS-60 (see above), for many years the definitive small, fast apochromat. The FS-60 has an aperture of 60mm and a focal length of 355mm giving F-5.9.  In comparison, the Borg 67FL has a focal length of just 300mm, giving an F-ratio of just F-4.5, even though its aperture is larger.

Now F-4.5 is incredibly fast for any refractor, but for a doublet it’s pretty amazing. Fast is good for imagers, decreasing exposures and widening the field. But all aberrations tend to increase with aperture and shorter f-ratios. We might expect the 67FL to show lots of false colour and off-axis field curvature and to be limited to low powers. However, the 67FL has an air gap between the elements in its objective, compared to the FS-60 that just has little foil spacers. That air gap allows better correction of aberrations and helps explain how the 67FL can get away with being 1.5 F-stops faster than the FS-60.

Tube

In this case, the 67FL is in a Series 80 (i.e. 80mm o.d.) tube that allows a 2” visual back, but it still weighs just 880g in visual trim – even an FS-60C weighs 25% more. Meanwhile, the objective comes with a flared adapter to fit 60mm Mini Borg components which would make an even lighter OTA.

That size you see in the photos isn’t due to a drawtube or the need for extensions – it really is that short in use, in fact for some eyepieces you need to shorten the tube! That length also includes the fixed dew-shield.

Borg 67FL and Takahashi FS-60C compared.

Focuser

The focuser is Borg’s standard helical, part 7835, to fit Series 80 tubes. It is decent, but lacks travel and can get stiff under heavy loads.

Mounting

The 67FL is small enough to mount on the lightest photo tripod.

Accessories

Borg’s own 80mm tube ring is very light, but a bit thin and short on padding. A nicer option is the 80mm Takahashi tube ring for the FS-60C which has an offset plate which helps with balance. Borg make lots of other useful accessories, such as an extra-wide T-mount (see OTA in reducer configuration below).

The only reducer sold with the Borg 67FL was the doublet 0.85x MiniBorg reducer (part 7885) which only works with APS-C. I’ve discussed this in detail below.

It’s possible other Borg reducers will work. I got some incredibly good terrestrial images with the new 0.72x 90FL reducer, but wasn’t able to test it on the night sky.

In Use – Daytime Viewing

The 67FL makes an excellent spotting scope when used with eyepieces designed to cope with F4.5, like Tele Vue’s.

An old 15mm Panoptic gave wonderful wide-field views at 20x.

At 60x (about max for most spotting scopes) with a 5mm Nagler, the view is still absolutely sharp, quite flat, detailed and with minimal false colour. Things stay this way to at least 100x – impressive.

At 120x with a 2.5mm Nagler the view is still quite sharp, but shows quite a bit of false colour, perhaps a little more than Takahashi’s FS-60 (an Optron fluorite doublet of similar spec’), but smaller than the extra aperture and shorter focal ratio of the Borg might suggest.

In Use – Daytime Photography

For terrestrial photography, test images of silhouetted branches show very similar false colour levels to Takahashi’s FS-60; however, without a flattener, the Borg has much more severe off-axis curvature as you would expect due to its very challenging f-ratio.

0.85x MiniBorg doublet reducer (part 7885)

This small and quite cheap APS-C only reducer came with the 67FL, the only one sold with it as a package and apparently the reducer best suited to it.

Terrestrial images using the 7885 reducer (see below for connecting it) are good with an APS-C chip (for which it is designed). Used like this, the 67FL converts into an F3.8 255mm telephoto that works well and produces sharp images to the corners of an APS-C frame.

For the recent Jupiter/Venus conjunction I was up at four and got my big scope out. But in the event, the planets only appeared for a minute or two over my neighbours’ roof before the clouds closed in. A hand-held snap from the very corner of my balcony with the Borg 67FL was all I got – at F3.8 it is fast enough to use hand-held in low light.

0.72x Quadruplet 90FL Reducer (part 7872)

I also tried the 0.72x quadruplet reducer for the 90FL and 71FL which threads directly into the M57 thread on the focuser. In this configuration, the reducer is designed for a focal length of 400mm (i.e. the 71FL), so it’s not quite right for the 300mm focal length of the 67FL.

Nonetheless, I got some really fabulous terrestrial images (see below) – razor sharp to the edge, with loads of fine detail zoomed in and with minimal false colour at 216mm F3.2 and proving what a fine objective the 67FL is.

Connecting a reducer - example

This section is intended as a resource for anyone wanting to figure out how to connect their camera to a Borg 67FL; if that’s not you, skip it!

Borg’s great strength and pain-in-the-*** is all the adapters they sell to allow almost anything to fit anything else. To fit a reducer to your camera will take a few of these adapters because you need to get the spacing right or you’ll have nasty off-axis aberrations.

As an example, connecting the basic 0.85x APS-C reducer (part 7885) to my Fuji X-mount camera needed the following parts (there are other solutions):

7885 - Reducer

7920 – M57 to M49.8 female

7602 – M57 extension 20mm

7000 – M57 to M49.8 male

5016 – Borg X-mount adapter (ends in a M49.8 thread)

 

Now, I’ll go through a sample calculation with my Fuji X-mount camera to show you why you need the 20mm extension.

For the 0.85x doublet APS-C reducer (Part 7885), the distance from reducer’s interface flange to the camera’s image plane needs to be 55mm.

The Fuji X-mount has a focal flange distance of 17.7mm (this is a key fact about your camera which you can easily check online, it is the distance between the mount surface and the sensor). To the flange distance, you need to add 7mm for the Borg X-mount adapter (the standard T-mount adapter is too long), another 8mm for the M57 adapter on the back of the reducer (part 7920) and a further 5mm for the X-mount M49.8 to M57 adapter (part 7000). That lot sums to 37.7mm, leaving a further 17.3mm to space out. The closest Borg come to that is the M57 20mm extension tube S, (part 7602), or just use the 20mm eyepiece holder which is also a 20mm M57 tube! Job done … eventually.

Borg 67FL configured with MiniBorg 0.85x reducer.

Terrestrial image with Borg 67FL + 0.85x reducer: Fuji X-Trans APS-C camera.

Terrestrial image with Borg 67FL + 0.72x quadruplet super-reducer: Fuji X-Trans APS-C camera.

In Use – Astrophotography

The reducer gives very wide and flat APS-C frames – so wide you can start to image whole regions of sky. Another advantage of such a short focal length is that you only need rough polar alignment for exposures up to a minute or two, which will be enough for most purposes if stacking. The 40s image of M31 below was taken by just rough-aligning the Teegul mount and one minute plus showed no tracking errors. Coverage is excellent on APS-C.

With such a wide, fast field, things appear in single raw frames that I’ve never seen before – such as the North American Nebula. The field is commendably flat too, with stars developing no more than a trace of coma/astigmatism in the corners. There is some violet bloating on bright O-A stars, but it’s no too bad at all. Sadly, I never got a chance to try the 0.72 reducer on the night sky.

At its native F4.5, or with a reducer, the 67FL has just too little image scale for the Moon, but Moon-rise shots will work out fine.

Pleaides with Borg 67FL, no reducer: 30s at ISO 3200, Fuji X-Trans APS-C.

M31 with Borg67FL + 0.85x reducer: 40s at ISO 3200, Fuji X-Trans APS-C.

In Use – The Night Sky

General Observing Notes

I have tested a lot of small refractors now and I was pretty sure what the Borg 67FL would be – an astrograph compromised for visual use. I was quite wrong.

At higher powers, Naglers delivered a reasonably flat field. At lower powers, there is a lot of curvature, along with some coma and astigmatism from about 60% field width. Even so, the central section is large and flat enough to give great views of almost anything, without the off-axis aberrations intruding. Other, lesser eyepieces, work less well with the F4.5 focal ratio (Naglers are tested to F4, but few others can say the same).

The configuration shown worked well for a range of 1.25” eyepieces from a 32mm TV Plossl to a 2.4mm Nagler zoom. But for big 2” eyepieces you would need to replace one of the white tube segments with a drawtube (which Borg sell) for more focus travel, but why would you bother?

You see, the 67FL requires some conceptual recalibration. A 32mm Plossl (maximum FOV for 1.25”) gives a magnification of 9x and a field width of 5.2 degrees, well into binocular territory. However, at this magnification exit pupil is 7mm and to older eyes DSOs will look no brighter than through a 50mm scope. Now plug in a 55mm Plossl and you get a magnification of 5.5x and a field of 8.8 degrees – wider than almost any binoculars, great. But at that magnification, the exit pupil is a stupid 12mm. No one has pupils that big and so the 67FL just became a 40mm scope, even for young eyes (which can dilate much more than older ones).

Cool Down

Instant, except on the frostiest night, when it’s very fast.

Star Test

Good. Better than you have a right to expect at F4.5.

The Moon

A night with a first quarter Moon, scudding clouds and periodic showers is where a tiny scope like the Borg comes into its own: put it out, get observing almost straight away and then whip it back in if the weather turns ugly.

You would expect a 67mm F4.5 doublet to show semi-APO levels of false colour on the Moon and at 60x with a 5mm Nagler I’m prepared for lilac wash; but it’s not there. At this magnification, the Moon looks fantastic – cold fluorite whites and hard greys, with no false colour to note, even focusing through the limb.

At this point many owners who have bought this little scope as a wide-field astrograph are going to run out of eyepieces. Fortunately I like tiny APOs, so I can push on to a 3.5mm Nagler. This eyepiece normally gives the highest power I will ever use in a small scope, but in the 67FL it magnifies the image by just 86x - still well within the Borg’s capabilities. That expected softness and chromatic aberration still haven’t materialised.

What now? Who owns eyepieces shorter than 3.5mm? I bought a 2.5mm type 6 Nagler for rare occasions like this: the tiny Borg is one of the few scopes where it’s of any use. Now I have a magnification of 120x. It’s a good thing that these Naglers are parfocal and I can keep the focus point from the Nagler 3.5mm, because that helical focuser is struggling: the steep light cone means you really need a micro-focuser at this power.

120x frames the Moon to perfection – it almost fills the field. Surprisingly, it’s still a good view – reasonably sharp and bright and detailed. The central peak in Alphonsus is just catching the morning sun. Strange Cassini crater is still surrounded by dark shadow. Hyginus rille is easy to spot with its craters. Leaning back from the eyepiece, it’s hard to believe the view is from this finder-sized telescope, a scope too light for the counterweight on the Teegul, that makes a TV-60 or FS-60 look big.

I tried a back-to-back comparison with the FS-60C on a waning crescent one frosty pre-Christmas dawn and found that the 67FL showed no more chromatic aberration, was just as sharp and significantly brighter – no apparent downside to that short (F4.5 vs F5.9) focal ratio.

I am surprised what a good view this tiny astrograph gives of the Moon – if you have the right eyepieces.

Mars

Low in the morning sky and at just four arcsecs in size, in the run-up to next year’s (2018) opposition, Mars was a tough target for a small scope. The Borg held up at 150x with a 2mm Nagler zoom and delivered a perfect tiny gibbous disk with just a touch of flare and false colour.

Jupiter

Jupiter focused crisp and without false colour. I saw the equatorial belts and polar darkening, a hint of GRS, at 100x-150x with a Nagler zoom.

Deep Sky

The Pleaides were lovely and sparkly with hints of nebulosity through a 13mm Ethos, or 15mm Panoptic. The field curvature is obvious at the edge, but doesn’t spoil the view. The clusters running up through Auriga (M35-37) looked lovely, with pin-sharp stars and strong colours, likewise the double cluster. I had great views of the double cluster too – masses of sparkly stars.

Orion’s sword region was less positive. The Great Nebula (M42) looked good with pin-sharp stars and the Trapezium easily resolved at 20x with a 15mm Panoptic; some structure in the nebula too. But stars in other parts of the sword were then severely distorted by field curvature and astigmatism, spoiling the overall view.

You wouldn’t expect an F4.5 scope to resolve much in the way of doubles, but with the 2mm setting on a Nagler zoom giving 150x, epsilon-Lyrae resolved nicely in good seeing, with epsilon-1 easy at 2.6” and epsilon-2 a bit harder at 2.3”.

The 67FL makes a surprisingly good all-round visual scope.

Summary

The Borg 67FL is a good example of why I enjoy reviewing small telescopes, because it really surprised me. I expected a dedicated astrograph, but what I discovered was the smallest general purpose astronomical telescope I have tested. Most of the views through it were typical of a good 3”-class APO, but this is a scope that makes a TV-76 seem huge and unwieldy.

The 67FL is not a super-APO, but false colour levels are typical of a 60mm F6 doublet – an FS-60 or TV-60. It can easily take powers that would trouble an expensive spotting scope by day. By night, only Venus really generates much nasty purple fringing. The Borg 67FL gives excellent views of the Moon and planets that would trouble a Questar; much better than an old TV Ranger, too.

Field curvature is strong at low powers on deep sky, but the sweet spot is large enough for most things. With a reducer giving under F4, some incredible wide-field images are possible, with lots of nebulosity in single frames straight from a DSLR. With the helical focuser and fast f-ratio, it works well as a handheld telephoto, too.

There are a few downsides. The 67FL is too light to balance, even on the Teegul micro-mount. It is capable of magnifications well over a 100x, but needs eyepieces shorter than 3mm to do so, eyepieces most people don’t own. Then again, even for lower powers you are going to need premium eyepieces to cope with F4.5. The basic reducer is fine for APS-C, but not ideal for full frame. Finally, that standard Borg helical focuser is stretched with this lens. It would be an even better scope with a Feathertouch.

All that is just nit-picking, though, because if you need a proper telescope the size of a finder, this is it. If the TV-60 is a ‘briefcase scope’, the 67FL is a ‘handbag scope’. The Borg 67FL is probably my favourite ultra-portable scope to date: too bad they only made a few.

The Borg 67FL just shouldn’t be any good – F4.5 seems silly in a doublet. But in fact, it is excellent for visual on anything you point it at. No other ‘proper’ telescope comes close to being this portable (or arguably this flexible either). For imaging, there is some violet bloat; but stunningly wide, fast frames are possible with a reducer.

 

 

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