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Borg Mini Borg 50 Achromat Review

MiniBorg parts: Drawtube, EP holder, 50mm Achro’ and 45mm ED Objectives.

If my TMB175 is at one end of a spectrum of refractors that I can’t go beyond, then the MiniBorg is the other (see last photo). If a smaller, lighter, more compact astronomical telescope exists, then I don’t know about it.

This is a telescope that you could put in a pocket; then again, it’s the same aperture as a regular binocular barrel or most finders. Everyone wants a truly portable telescope, but can a 50mm telescope actually do anything useful beyond making a very configurable (and expensive) finderscope?

In fact, experience with quality 50mm scopes – like the classic Zeiss 50/540 – suggests they can do lots. But even more than larger scopes, they need to be really good. Is the MiniBorg good enough to overcome its meagre aperture? Let’s find out.

At A Glance

Telescope

Borg Mini Borg 50 Achro

Aperture

50mm

Focal Length

250mm

Focal Ratio

F5

Length

168mm

Weight

340g

 Data from Me/Hutech.

Design and Build

Borgs are modular. Read that again, because it’s by far the most significant thing about this unusual range of... well, of telescope parts really. With Borg you don’t buy a telescope, you buy a kit of parts to construct the telescope you need.

If I was seriously rich, I would buy the entire Borg parts list just so I could play constructor with it: you can imagine me sitting cross-legged on the floor of my study making weird looking scopes surrounded by tubes, lenses and adapters. What fun!

There is a serious side to this modular approach, though (and a downside too, you can probably guess what it is). Borgs are very flexible because all the components use common metric thread sizes. If you want to build a finder from the MiniBorg parts list, you can - or a terrestrial spotter, a camera lens, a little astro’ scope, a guider, a monocular.

That flexibility is great, but it’s also very expensive. By the time you’ve bought the 50mm lens, the drawtube body, a helical focuser (which you could fit in various places), some extensions, lots of adapters and then finally an eyepiece holder, you will have spent the equivalent of a very decent small fast-food apochromat.

If you want to equip the MiniBorg with a 60mm lens, or an apochromat lens, the cost goes up even more and can easily get into premium 60mm apochromat (Takahashi FS-60/Tele Vue TV-60) territory.

Optics

The basic MiniBorg 50 has an F5 achromatic doublet similar to that in many finderscopes, but of higher optical quality. The objective is really tiny, but incorporates a little dew shield. It connects to the tube by a standard M57 thread.

Tube

The way of the Borg is that there is no fixed answer. Well anyway not when it comes to building an OTA, which you could do many different ways. This is the standard basic MiniBorg set, but you could build a Series 80 tube set with the right adapter (you knew it) – Part #7459, in case you were wondering.

In this case, the objective is attached to a simple draw tube with a ¼-20 mounting for a photo tripod. The OTA construction is light weight, but high quality – all metal with a nicely blacked inside and a single baffle.

The threads on the lens cell and the back of the drawtube are standard M57 and so all sorts of accessories – camera adapters, push fit eyepiece holders, helical focusers etc – can be attached in a huge range of configurations. For use as a tiny astro’ scope, though, you can get away with Borg’s simple set-screw 1.25 adapter and the diagonal and eyepieces of your choice.

As I explained above, the Borg modular concept means you can substitute the basic 50mm achromatic objective with either a 45mm ED apochromat (see separate review) or a larger 60mm achromat or 60mm ED apochromat, extending the OTA with additional tube sections if required.

Focuser

The sliding drawtube shown here works fine as a focuser in most cases at moderate powers. But there are numerous helical focusers to choose from and Crayford and rack-and-pinion options too. The most commonly encountered is the tiny 1.25”-only helical shown below that threads into the MiniBorg draw tube.

A Mini Borg 50mm objective (actually the F8 50FL) in a Series 80 tube with larger helical focuser.

Mini helical focuser, threads into the MiniBorg tube in place of the eyepiece holder.

The Mini Borg drawtube carries a mounting block for tripod attachment.

Mounting

The Mini Borg 50 will go on the tiniest mini photo tripod. You can get a pair of diminutive tube rings, but in this arrangement the 1/4-20 standard tripod thread built into a mounting block on the drawtube is fine (you would need to remove it to fit the rings).

In Use – Daytime

At, say, 20x there is very little false colour during daylight use. Why is this? Is the Mini50 some kind of semi- apochromat or something? The reason is that for achromats, you will recall, there is a criteria for acceptable CA levels of F=1.22D, where F is the focal ratio and D is the aperture in cm. Now for a 6” refractor this is going to be about F18 (think Cooke refractor), but for a 2” it’s down at about F6, hence the Mini Borg’s modest false colour.

So for medium powers, daylight spotting and birding with the Mini 50 is very effective. Views are crisp and full of contrast and detail – much better than most small spotting scopes from mid-range manufacturers.

In Use – The Night Sky

General Observing Notes

I was surprised at how much I like the Mini 50. It may just be a finder with interchangeable eyepieces (and an expensive one at that), but it works well. Critically for a quick-view scope, cool-down is virtually instant, so you can use it straight from a warm house.

I tested the MiniBorg side-by-side with a 70mm Russian Maksutov: the Borg was much easier to use and unexpectedly provided nicer views on everything I pointed it at, Moon included.

The Moon

The MiniBorg Moon is nice, crisp and contrasty up to about 50x magnification, after which the chromatic aberration spoils the view a bit. But at low-medium powers false colour is not the problem you would expect if you’ve tried larger F5 achromats – like a Synta (Sky-Watcher etc) Short Tube 80 - on the Moon.

Planets

On planets ... well what do you expect from 50mm!? You can clearly see Jupiter’s moons, the main equatorial cloud belts and Saturn’s rings, but not the Cassini division.

Deep Sky

At lower powers, bright DSOs like the Orion Nebula and star fields are a delight, with a huge wide-field view on offer even from basic EPs like Plossls.

The MiniBorg 50 proves that for a super-portable small telescope a simple, quality achromat is all you need.

Summary

The Mini 50 has a definite charm and utility. No other usable scope comes close to being this portable. It’s not an apochromat, but is really about quick low power looks anyway. What’s more, that modular approach means if you get bored with using it as a quick-look astronomy scope, you can turn it into a finder (which I did).

Although it’s an F5 (with a vast field as a result), chromatic aberration is not a problem. At moderate powers the views are sharp and bright, day or night. So the Mini 50 could be used as an ultra-portable birding scope or spotter (which I also did).

In comparison, the much more expensive Mini 45ED, which gets a separate review, is a lot less charming; maybe mine was a bad one.

The MiniBorg 50 is the most portable proper astro-scope available and one of the most adaptable. Recommended.

Update: Borg have recently introduced several Canon/Optron (same as Takahashi) 50mm fluorite lenses in the Mini Borg format. I have tried and separately reviewed the 50FL.

Borg Mini 50 as a finder on my TMB175 – my smallest and largest telescopes united!