78 | Astronomy Now | May 2010

In the shops

An eye on the iOptron MiniTowerIan Morison takes a new mount designed to make alignment as simple as can be out into the fi eld.

The 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

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

At a glance: IOptron MiniTower Pro dual

alt-az mount

OTA connection: dovetailDatabase: 130,000 objectsCarry weight: 11.3kg (25 pounds)Price: £749Available from: Altair Astro (01263 731505) Astronomia (01306 640714) Green Witch (01954 211288)

Telescope Planet (01269 843888) The Widescreen Centre (020 7935 2580)

■ The iOptron MiniTower GOTO alt-az mount.

■ A Celestron six-inch SCT and an Astronomica ED80 co-mounted on the head of the MiniTower. Image: Ian Morison.

In the shops

May 2010 | Astronomy Now | 79

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 showedup 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 precisionThe 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 eight-inch 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.

■ A counter-balanced Takahashi FS102 on the iOptron MiniTower. Image: Ian Morison.

■ An ED80 refractor in the ‘park’ position. Image: Ian Morison.

80 | Astronomy Now | May 2010

In the shops

BalanceThe 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

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

■ 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.

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 six-inch 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.