[This is just one of many articles in the author’s Astronomy Digest.]
These are computerised mounts that any amateur astronomer would be proud to own. They mounts will have a greater load capacity than less expensive mounts – useful if one were astroimaging with a large refractor or Schmidt-Cassegrain, guide scope, cooled CCD camera and filter wheel. They will have larger diameter drive gears which should allow for more precise tracking, their ‘GoTo’ precision will be higher and will either be used with substantial tripods or be used mounted on a fixed pier. Some are ‘portable’ and some definitely not and will often be installed in an dome or ‘Roll on,Roll off roof’ observatory. It is only possible to cover a few in this article including two that I own and use – which is, I hope some recommendation. As premium mounts are made in far smaller quantities, their costs are high but they can sometimes be bought second hand using a website, such as ‘https://www.astrobuysell.com/uk/’, at significant savings on their new prices.
The Track the Stars TTS-160 Panther Telescope Mount
This is a portable Alt-Az mount which also allows for precision equatorial tracking and is, perhaps, the most portable of any of those mentioned in this article. With a load capacity of 20 kg, it can be set up and aligned in around 7 minutes with no levelling or polar alignment required. For astrophotography, TTS provide a ‘rOTAtor’ mounted between the head and the Telescope Tube assembly (OTA) which allows for total exposures of from 1 to 3 hours dependent on the sky position of the object. In common with all Alt-Az mounts, there is no ‘meridian flip’ as an object crosses the meridian – a great help when astroimaging. As with many Alt-Az mounts it can either be used with one telescope and counterweight or with two telescopes. Including the rOTAtor, it costs from ~£5,000 from Peak2Valley.co.uk . I have to say that I would really like to own one of these mounts.
The Losmandy equatorial mounts.
Losmandy is an American company which provides a range of four mounts beautifully constructed entirely of machined aluminium and stainless steel with load capacities ranging from 13.6 kg up to 45 kg. The lowest cost is the GM8, at ~£3,000, which is equipped with the Gemini 2 ‘Goto’ drive system. I bought an un-computerised version, no longer available, some 17 years ago and it has given me sterling service over that time. As its tripod and head are not too heavy (7 and 9.5 kg respectively), it is easy to transport and I now use it to take to star parties. I equipped mine with encoders and an Argo Navis computer controller to provide a ‘push-to’ mount – made very easy to use due to its variable tension clutches on both axes.
Their next product was the G11, now costing ~£4,000, owned and used with great effect by a colleague. This more substantial mount has a load capacity of 27 kg with the equatorial head weighing some 15 kg and the tripod 16 kg – so not so portable. More recently, they have brought out a mount called the GM811G which, at a cost of ~£3,400, amalgamates much of the GM8 mount with the GM11 RA drive. This has a larger RA drive gear so giving smoother tracking for photographic use and an enhanced load capacity of 22 kg. I suspect that this may now be a better buy than the GM8.
At the top of their range is the GM11 GT at a cost of ~£4,700 which has a more substantial ‘Titan’ RA axis drive which as load capacity for photographic use of 34 kg and with tracking performance of equal or better than +/- 5 arc seconds.
Premium mounts may well be equipped with ‘absolute encoders’ rather than what are, in effect, ‘incremental encoders’ when the pointing is determined by counting the steps made by the stepping motors. This greatly improves the ‘GoTo’ and tracking performance of the mount. For example, the Astro-Physics Mach2GTO described below uses absolute encoders with an accuracy of a quarter of an arc second giving a tracking performance with a similar periodic error so autoguiding is not required.
Some premium mounts such as those made by Software Bisque and 10micron can employ what is called ‘TPoint’ assisted pointing accuracy. By synchronising the mount on stars spaced around the sky, a ‘model’ of the telescopes uncorrected positional errors is made which is then used to compensate for systematic errors in the mounts ‘goto’ performance so giving the mounts a very precise pointing accuracy.
The Astro-Physics Mach2GTO
This is perhaps one of the highest load capacity mounts that can be regarded as portable and is an upgrade of the Mach1 mount, that I have been using for some years and permanently mounted in my garden on its combination pier/tripod. The Mach1 could well be worth buying second-hand if one can be found. One nice feature is that the electronic control unit can be easily removed and brought inside so eliminating any damp problems if, as mine, the mount is permanently located outside – in the open, but well covered. The Mach2 has a load capacity of 34 kg and is equipped with absolute encoders to provide superb pointing and tracking performance. A good feature is that these two mounts will not do a ‘meridian flip’ as the object crosses the meridian providing that the scope will clear the mount. This is really useful as one is often imaging when an object lies highest in the sky towards the south.
Their lowest cost mount is the GM1000 HPS at ~£7,600 from Tring Astronomy Centre which has a load capacity of ~25 kg and powered with 24 volts DC. As with the Mach2 mount, it will usefully track for 30 degrees past the meridian. Its TPoint modelling can include 100 stars and the absolute encoders give a tracking accuracy of ~1 arc second without autoguiding. A very solid tripod is available at a cost of ~2,000. This could thus perhaps be regarded as a portable mount and 24 volt 28 Ah batteries are available, designed for eBikes. The separate electronics control package can be stored ‘in house’ so avoiding any damp problems. If a higher load capacity is required, three further mounts are available including the GM2000 HPS II ‘Ultraport’ German Equatorial Mount having a payload of 50 kg at a cost of ~£12,000.
Software Bisque Paramounts
Their lowest cost mount is the MYT portable system with the equatorial head costing ~£6,500 and available from Rother Valley Optics. It has a load capacity of 23 kg and a maximum periodic error before correction of 7 arc seconds. It employs a belt driven to remove backlash and provides around 1 arc second tracking after periodic error correction. A portable tripod at £2,900 or pier/tripod at £1,300 are available but I suspect that they will usually be pier mounted in an observatory. Larger mounts with greater load capacities of 45 kg and 109 kg are available at greater cost. All mounts are supplied with a 240 volt mains power supply supplying 48 volts, so perhaps making them more suitable for permanent installation. The mount also uses the TPoint modelling system to give 30 arc second pointing accuracy.