[00-00] In the shops May10.indd

[00-00] In the shops May10.indd
In the shops
An eye on the iOptron MiniTower
Ian Morison takes a new mount designed to make alignment as simple as can be out into the field.
■ The iOptron MiniTower GOTO alt-az mount.
T
he iOptron
MiniTower is a
computerised alt-az
mount that is capable of
carrying telescopes up to 25
pounds (11.3 kilograms) in
weight. Rather than start by
giving its specifications let’s first
see how it performed in use –
that’s what really matters!
The mount’s ‘first light’
was under the watchful eye
of the amateur astronomers
attending a Society for Popular
Astronomy observing weekend. As
dusk fell and Jupiter appeared in the
south-west, my 80mm ED refractor
was mounted in the Vixen dovetail.
The mount has first to be set into
its ‘park’ position with the telescope
vertical and alt-az head aligned to
the south. The substantial tripod
was set up with its top approximately
level. The head is then positioned on
it, supported by three coupling rods
that can be finely adjusted whilst one
can easily observe and centre the air
bubble in its inverted cup, therefore
quickly giving a perfectly levelled
mount. There is an azimuth clamp
that must be loosened whilst this is
■ A Celestron six-inch SCT and an
Astronomica ED80 co-mounted on the
head of the MiniTower. Image: Ian Morison.
At a glance:
IOptron MiniTower Pro dual
alt-az mount
OTA connection:
Database:
Carry weight:
Price:
Available from:
dovetail
130,000 objects
11.3kg (25 pounds)
£749
Altair Astro (01263 731505)
Astronomia (01306 640714)
Green Witch (01954 211288)
Telescope Planet (01269 843888)
The Widescreen Centre (020 7935 2580)
78 | Astronomy Now | May 2010
done and this also allows the head to
be rotated to face south. Not being
able to see the Pole Star meant that
was not too accurate but, as you will
see, this was not a problem.
The mount was powered up
and after a short while the integral
GPS system had updated the
location and set the accurate time.
The next task with a computerised
mount would normally be to align
it before one is able to slew to an
object that you wish to observe, but
with the iOptron mount this is not
demanded of you. You can simply
apply the ‘Select and slew’ option
and choose the object that you wish
to observe. We selected Jupiter and
the telescope immediately slewed
around towards the giant planet but
ended up a little to its west – not
surprising given that our alignment
to the south was only approximate.
However, as the head was accurately
horizontal, the elevation should be
correct and the only significant error
would be in azimuth. A low speed
azimuth slew quickly brought Jupiter
into the centre of the low power
field. Moving to a higher power and
some very minor tweaks in position
In the shops
■ An ED80 refractor in the ‘park’ position.
Image: Ian Morison.
■ A counter-balanced Takahashi FS102 on the
iOptron MiniTower. Image: Ian Morison.
accurately aligned the mount on
Jupiter. At this point, ‘Sync to target’
is activated and the computer will
then internally compensate for our
inaccurate alignment south. This
took less time than it takes to read
this and we had effectively carried
out a one star align but with the
object of our choice. If you were
going to observe this object anyway,
as we were, then the alignment has
essentially taken no time. Brilliant!
The seeing was surprisingly good
and the belts and zones showed
up well.
We then slewed to the
Andromeda Galaxy high in the west.
It was an impressive sight using a
TMB 40mm Paragon eyepiece so
we became more ambitious and
slewed to M33 in Triangulum.
Heavy showers earlier in the day
had cleared the atmosphere and
M33 was easily seen with averted
vision. We wanted to try mounting
a TMB 110mm refractor so selected
the ‘Park scope’ item on the menu.
The telescope moved to the vertical
position and the head aligned
itself due south, so now we knew
accurately where south was. The
somewhat heavier telescope was
handled with ease but advancing
cloud soon ended our observing,
but not before leaving us with a very
favourable first impression.
GOTO precision
The following night the clouds cleared and an
observing site was found with good views from
the south-east around to the north. This time our
first target was the Pleiades cluster on which we
synchronised just as we had previously on Jupiter. Our
observations then took in the Orion Nebula, various
clusters in Auriga and Gemini and finally, as the
clouds encroached from the west, the galaxy pair M81
and M82. In all cases, using a TeleVue 20mm Plössl,
the objects were very close to the centre of the field of
view. The GOTO precision displayed by the mount
on those first two nights had been very impressive,
but what impressed our group most was how fast we
were able to begin our observations.
The next outing for the mount was at an
astronomy weekend at Burton Manor College.
The skies only cleared for a short while during one
morning but gave our group a chance to see if the Sun
had come out of its deep sleep. It hadn’t – not a single
sunspot could be seen! Unlike many computerised
mounts, the MiniTower does allow one to move to
and then synchronise on the Sun, after a suitable
warning of course. This time we mounted an eightinch Celestron Schmidt–Cassegrain on the mount and
used the supplied counterweight along with another
of similar weight to balance it. The mount had no
problems slewing or tracking smoothly, indicating
that the MiniTower can support a telescope of this
size. For safety, the finder objective was covered
and the telescope eyepiece pointed down to project
an image onto card. The Sun’s image was easily
centralised and synchronised on. Then we were able
to do something that I, personally, have never been
able (or dared) to do before – find Venus in daylight
just nine degrees from the Sun. Having executed a
slew to Venus, it was immediately
seen as a tiny gibbous disc virtually
in the centre of the field-of-view.
The MiniTower provides
three options for its power supply.
Perhaps the neatest is to use eight
AA batteries that fit into the tower
unit. It was pleasing to find that
rechargeable Ni-MH batteries
worked well, giving over three
hours of use. Alternatively, a mains
adapter and a 12-volt plug and
cable for use with rechargeable
battery packs are provided.
The mount’s hand controller
has a large, informative, eight-line
display. I did find the controller’s
backlit buttons rather ‘squishy’
but at least it does means that one
is unlikely to activate a button
by mistake! Pressing the ‘Menu’
button brings up the main menu
that includes eleven options. The
most used will be ‘Select and slew’,
which opens up the object menu
that has eight sub-menus to reach
the ~130,000 objects in its database
including the planets, Sun and
Moon, all the usual catalogues,
190 comets, 4,096 asteroids, 88
constellations, up to 256 user
objects and the ability to enter the
RA and declination of an object.
The controller also has an USB
port to enable the mount to be
computer controlled.
May 2010 | Astronomy Now | 79
In the shops
■ iOptron dealers can supply an adapter puck priced from £29.50,
which enables use of the Altair modular Telescope Mounting System
to provide additional stability when attaching Vixen or Losmandy bars.
■ A counterbalanced Alter 500
Maksutov on the iOptron Minitower.
Image: Ian Morison.
Balance
The MiniTower has the capability
of putting a supplied counterweight
on the opposing side of the mount
to balance the telescope – obviously
a good thing in order to minimise
wear and give the best possible
slewing and tracking performance.
For light telescopes though,
iOptron state that a balance weight
is not needed. Even better, a second
dovetail is provided that may be
located on the balance arm so that a
80 | Astronomy Now | May 2010
second telescope can be mounted in
parallel with the first. Very neat!
The mount uses 12-volt DC
servomotors that are very quiet in
operation (great if you have close
neighbours) and the positioning
is monitored and controlled
using optical encoders having a
resolution of one arcsecond. With
an accurately levelled mount, the
selected object was always close
to the centre of the field-of-view
of a medium power eyepiece. To
enhance the GOTO performance it is also possible to
carry out a two star align that will correct for any small
errors in setting up the mount. The next important
requirement is that, once an object has been centred
in the field-of-view, it remains there as the mount
tracks the object across the sky. For this test, a sixinch Schmidt–Cassegrain was set on the mount and a
7mm eyepiece used to view Jupiter. Having centred the
planet in the 20-arcminute field-of-view it was good
to find that it was still precisely centred well over an
hour later.
It is often said that an alt-az mount cannot be
used for astrophotography due to the fact that the
field-of-view rotates with respect to the sky. In
fact, lunar photography and webcam imaging of
the planets present no problems, but long exposure
CCD imaging is not possible. However, by stacking
a number of short exposure images, it is possible
to make deep sky images by using a program such
as DeepSkyStacker that automatically de-rotates the
images before combining them.
All parts of the mount except for the tripod fit
within a compact aluminium flight case so the mount
is very portable making it a superb ‘pick-up and
go’ package, ideal if you want to get away from the
lights of your town and set up in a dark sky location.
As I hope I have shown, it is very quick to set up
and its GOTO ability and tracking could not be
faulted. What more could one want? This year, I gave
myself a new year’s resolution not to buy any more
telescopes but I had omitted to include telescope
mounts. Good!
Professor Ian Morison is a radio astronomer at Jodrell Bank
Observatory, is the Gresham College Professor of Astronomy
and is the SPA's equipment expert.
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