Pocket Borg Review
The Pocket Borg is the lightest, most compact way to enjoy the Moon.
Doubtless quoting yourself is the first sign of madness or megalomania, but here goes. When I reviewed the MiniBorg a few years ago I wrote ‘if a smaller, lighter, more compact astronomical telescope exists, then I don’t know about it’. Since then Borg have introduced two smaller scopes to confound me. So I thought I’d try the smallest of them all – the 25mm Pocket Borg. Famous last words, but this really is the smallest astronomical telescope you will ever be able to buy.
Stop laughing. I know what you’re thinking. What possible use is a 25mm scope? This thing has the same focal length as the aperture on my TMB 175; half the aperture of its finder!
But if you’re thinking the Pocket Borg is useless, let me challenge you with two questions:
When you go on holiday or travel for business, how often do you take a scope with you?
How often have you found yourself on one of said trips, looking at something in the distance and thinking ‘wish I had a little scope with me’?
For me the honest answer to those questions would (still, having owned many supposed travel scopes) be ‘never’ and ‘regularly’.
If you’re much the same, then the Pocket Borg might just be for you. It’s so small that you could take it with you without thinking about it much, wherever you go. And when you get there, a one inch scope might be more useful than you think.
At A Glance
25mm / I”
~12cm Astro’ / 17cm monocular (incl visual back)
~175g (depending on visual back used)
Design and Build
Pocket Borg Objective.
One good thing (and we need to find a few) about a 25mm scope is that chromatic aberration is no longer an issue. It’s an achromat by design, but optical theory suggests the Pocket Borg should be almost APO-like at F7. So if the lens has been well-ground and polished, near-perfection is possible (and with so little aperture we’ll need it to see anything).
On the face of it, all we can say about the Pocket Borg’s objective is that it’s a tiny well-coated achromat in a threaded cell that’s integral with the dew-shield. It does look better and rather different to the objective on your average small finder: just like a MiniBorg objective unit, in fact, only much smaller!
One advantage of such a tiny focal length is the enormous field of view on offer. With a 1.25” eyepiece, the Pocket Borg has a maximum true field of almost 9°, wider than almost any binoculars.
Ridiculous? With a Pocket Borg and Ethos 13mm you get 13.5x magnification and 7.3° FOV!
Pocket Borg Components: Focuser, extension and objective.
The tube assembly is really where the Pocket Borg adds value. Borgs are well-known for their flexibility and the Pocket Borg is like their larger models in this respect. A tiny scope it may be, but Borg seem to have worked hard to make it as adaptable to different roles and configurations as possible. You could easily use it in any of the following ways:
1) A miniature astro’ scope with a diagonal and 1.25” eyepiece that mounts on a small photo tripod.
2) A straight-through spotter on a photo tripod.
3) A highly configurable 25mm finder, either right angle or straight-through, with an illuminated reticle eyepiece if you want.
4) A tiny hand-held monocular.
5) A miniature telephoto lens: natively 175mm F7, or pair it with a 2.5x TeleVue Powermate to create a, sharp 438mm F18 lens. Push things with a 5x Powermate and it still works at 837mm, but is very dim at F36, so you will need a tripod and high ISO.
Pocket Borg configured as a 12x monocular.
Pocket Borg configured as an illuminated finder.
Let’s look at how Borg have built-in this flexibility.
The white-painted part of the tube has an integral threaded extension section. This is because the Pocket Borg can be used straight through as a monocular, or as a DSLR lens (insert extension) or with a diagonal (remove extension). The photo on the Hutech (Borg’s US reseller) website shows the Pocket Borg on a tripod with the extension in place and a diagonal in the back: it’s wrong.
The rear section of the OTA – the satin black part – bells out to end in a in an M36.4 metric thread that accepts various 1.25” visual backs. The standard Borg visual back (part 7317) is one option, but has locking screws and will mar your diagonal barrel; I threaded-in a Takahashi unit which has a twist grip.
Finally, the OTA is properly designed to counter stray-light: there is a knife-edge baffle in the focuser tube and the inside of the OTA and focuser unit is ridged with machined-in micro-baffles.
Pocket Borg extension tube has machined-in micro-baffles to prevent stray light.
The Pocket Borg focuses by simply sliding the white tube over the black rear section. It sounds crude, but in practice it’s easy to get focus at any power the Pocket Borg will cope with.
That black rear OTA section incorporates a ¼-20 thread for a photo tripod which is handy: unlike the MiniBorg the thread is integral so there is no mounting block to get in the way if you want to use it as a finder or monocular.
Pocket Borg has ¼-20 thread built in.
It goes without saying that the lightest photo tripod is more than enough for the Pocket Borg. As shown above, mounted on a table-top mini tripod with a ball-head, it really is a complete system you could put in a pocket.
In Use – Daytime
At low powers with a decent Plossl the Pocket Borg gives good daytime views. In fact the view with a 25mm TeleVue Plossl at 7x is really excellent. It reminds you of how much erecting prisms take away, so absolutely sharp is the view and still plenty bright enough, even in dull weather. And just as we thought, the small aperture and longish focal length mean no apparent chromatic aberration and a decently flat field too.
Enlargement of daytime branches shows minimal chromatic aberration.
Getting the Pocket Borg to yield high powers is a problem. Theory suggests even a one-inch scope should cope with 30-50x magnification, but with only 175mm focal length that means eyepieces of 3-6mm focal length. Now that’s fine if you have £300 worth of Nagler Zoom to hand. But it’s a problem if not, because the Borg’s short focal length doesn’t work so well for conventional eyepieces - like Plossls and Orthos - below about 7mm F.L.; they seem to end up with almost no eye relief. The Pocket Borg works much better with eyepieces that have a built in barlow lens to increase the effective focal length of the objective.
Attaching such exotic eyepieces to a small cheap scope seems and looks odd, but works. Daytime views at 35x with a 5mm Nagler Type 6 (an eyepiece that costs three times as much as the scope) are close to ideal for terrestrial use in bright conditions, but not at dusk or when it’s very dull. The view remained bright and sharp, with just a trace of chromatic aberration creeping in out of focus.
In Use – Night Sky
With so little aperture perfect optics are essential and fortunately the Pocket Borg has them. The star test is virtually identical either side of focus with nice evenly illuminated rings and perfect collimation.
With such a small aperture even the full Moon isn’t blindingly bright, even at low powers – a real advantage if you enjoy looking at the full Moon’s brilliant ray system.
At higher powers, the Pocket Borg gives good views of the Moon at 50x with a 3.5mm Nagler T6: perfectly sharp and with minimal in-focus chromatic aberration. On a gibbous Moon in twilight, I was able to watch sunrise highlighting just the rims of the crater arc within Clavius, whilst the rest of crater remained in darkness; ditto the central peak in Tycho. I could easily make out the dark patches in Alphonsus and just resolve the Great wall. Mons Piton and Pico stood out clear and bright from the Mare.
On another night, I was quite surprised to find that a 2.5mm T6 Nagler giving 70x also worked well on a Moon just past full. Two highlights were the mountains around the rim of Mare Criseum and the Messier twin craters with their double ray. The bright limb was surrounded by a dark purple halo, but this did nothing to spoil the view or the contrast.
This is a situation where the Pocket Borg refutes the idea that a one-inch scope is useless: no hand-held binoculars will show you that level of Lunar detail. Put it another way: the Pocket Borg would outperform anything available to Galileo or his contemporaries.
Unlike binoculars or terrestrial spotters - encumbered with prisms that cause flare on small bright objects - the Pocket Borg does well on planets for its aperture.
At 30-50x it will just about show you Jupiter’s equatorial belts and polar hoods and Galilean moons, but little else. Still, that’s again better than any hand-held binocs.
Venus shows its phase with no untoward flare and just a touch of chromatic aberration, whilst you can tell Mars isn’t a star, but would struggle to guess its phase (gibbous or full).
In truth, the Pocket Borg really doesn’t do deep sky. Averted vision on the Double Cluster? The Pleiades looked pretty good, with sharp stars, but lacked their usual diamond-dust sparkle. Even a bright open cluster like M38 needed averted vision to see more than just the faintest fuzzy patch.
The Great Nebula in Orion (M42) looks much better in most binoculars because of their greater light grasp.
Overall, for portable deep sky you would be better even with a good pair of 8x32 binoculars … but of course they would be much bulkier and heavier to pack than the Borg.
Daytime shot through Pocket Borg as a 175mm telephoto lens: very sharp on-axis, but quite curved at the edges.
The Pocket Borg makes a very lightweight 175mm F7 telephoto lens – just add a suitable T-mount. You can see a snap taken with it above. Ahhh, I hear you saying, but 200mm lenses are cheap as the proverbial these days. Well indeed, but the Pocket Borg is a telescope so it’s optic is sharper on-axis than a typical camera lens. There follows a shot of the Moon at prime focus through the Pocket Borg (no barlow or Powermate) and then cropped. The result is impressively sharp and detailed – better than I could achieve with my Nikon 200mm lens. Off axis a camera lens is better corrected of course.
Moon through Pocket Borg: crop of original prime focus image, but with no PhotoShop enhancements.
For some buyers the Pocket Borg will doubtless be a route into a customised small finder, perhaps by combining it with an erect-image diagonal or an illuminated reticle eyepiece. But though I’d hate to think of children or beginners getting a Pocket Borg as a starter scope, because it’s much too limited for that, it does have a use beyond being a premium finder. For Borg have engineered this tiny scope with a well-finished objective capable of higher magnifications and a properly baffled tube, to create a sub-binocular sized setup that can do some things better than any hand-held binoculars.
If not as a finder, then the Pocket Borg’s main use is as a travel scope for all those times (let’s face it, most times) when you wouldn’t otherwise take any scope at all. Whilst the 25mm aperture is seriously limiting for any kind of deep sky apart perhaps from bright clusters like the Pleiades, there are three reasons I can see for why you might want a Pocket Borg in your travel bag:
1) First and foremost, use it as a miniature daytime spotter in bright conditions and at moderate magnifications. Pop it in your luggage at the last moment, then deploy it on the patio table of your holiday villa, next to a glass of Barolo, for distant views of that Tuscan hill town or smoking Sicilian volcano in the distance.
2) When it’s getting dark, turn the Pocket Borg on the Moon. No it isn’t going to let you hunt for TLPs or Gruithuisen’s Lunar City, but the aesthetics of the view –typical of small refractors - reward just gazing at a rising Moon over the darkening sea at low power, without binocular shakes or softness. If you have a short enough eyepiece, the Pocket Borg will show you a satisfying level of quick-look Lunar detail at 30-70x.
3) For quick looks at the planets, Pocket Borg also gives a more satisfying view than binoculars. So if you’re still enjoying a quick observing session from your Tuscan Terrace, you can see Venus’ phase, Jupiter’s main belts and moons, Saturn’s rings.
The only caveat is that to get powers above binocular level you will need an exotic eyepiece or two, preferably something light like a Nagler zoom, to avoid spoiling that travel portability.
I cautiously recommend the Pocket Borg despite the severe limitations of its 25mm aperture, but only as a travel scope in extremis – for those trips (for me almost all trips) when otherwise the only distance magnifier to hand would be miniature binos.