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!