MARCH 2021

Thoughts about Telescope mounts: 3 – £800 to £1,200 mounts

[This is just one of many articles in the author’s Astronomy Digest.]

This article continueslooks at some further, more expensive, mounts. This text also discusses howthey can be upgraded or, having been used for some time, serviced to improvetheir performance.

TheLosmandy AZ8 Alt Az mount

This impressive mount, costing £999, isconstructed entirely of machined aluminium and stainless steel and can supporttwo telescopes having weights of just under 16 kg, such as a 127 mm refractorand a ~200 to 230 mm Schmidt-Cassegrain – so providing complementary views andmaking an excellent mount for use at star-parties! [Note that counterweightswould be needed, on the opposite side of the mount, if only a single telescopewere to be mounted. This is in order to balance the mount so that the telescopecan be accurately controlled.] The total weight of the mount, riser and tripodis approximately 12 kg with the riser included so that the azimuth variableslip clutch under the head can be adjusted. Large knurled knobs control thevariable slip clutches for each motion so one can quickly move the telescopesto the desired object and then use the integrated slow motion controls to trackthe object across the sky using additional flex cables if desired.

TheAustralian company Astro Devices also provide a “Losmandy AZ8 Encoder  Kit” for use with the AZ8 employing 311,296step encoders giving a resolution of ~4 arc-seconds[NW1] . When used with a suitable controller such as the“Astro Devices Nexus DSC” this gives the mount a “Push To” capability that canbe controlled with star chart software such as Cartes du Ciel. [Search for“Losmandy AZ8 Encoder  Kit.”]

The iOptron CEM26

The new CEM26, at a cost of around £1,000 when it shortly becomes available in the UK, weighs only 4.5 kg but can support a payload of up to a 11 kg. Its innovative ‘centre-balanced’ design places the weight of the payload weight directly over the centre of the tripod providing great stability.  As the optional polar scope (included in the CEM26B) is not blocked by the declination shaft it is accessible at all times.  The Go2Nova® Hand Controller employs a large 4-line LCD screen and its database includes over 21,000 objects!  It allows for permanent periodic error correction to provide accurate tracking so useful when astroimaging and has a built-in Wi-Fi capability. 

Sky-Watcher provide two mounts

At a cost of £995, is the Sky-Watcher AZ-EQ5GT . This can be used in both alt-azimuth  and equatorial modes. The former mode isessentially for visual observing and, in this mode, the mount can support twotelescopes. The latter can be used for either visual or astroimaging withoutsuffering from the problem of ‘frame rotation’. Frame rotation occurs ifanything more than a single short exposure image is taken through a telescopethat is not polar aligned, as an equatorial mount should be. Weighing 7.7kg(excluding the tripod) and mounted on a tripod with 1.75 inch (44 mm) diameterlegs it can support two telescopes, each of up to 15 kg, on either side of themount, in visual mode or a single telescope up to 15 kg in equatorial mode.Balancing the telescope with counterweights, on the other side of theequatorial mount to the telescope, helps ensure that the telescope tracksobjects more accurately. The drive system incorporates a belt drive to givequieter slewing and smoother tracking than gear driven mounts and has a dualencoder system so that it can be moved manually without losing its positional informationgiving great flexibility during observing sessions. The polar scope isoptional. It’s Synscan hand controller includes a 42,900+ object database. Themount allows for periodic error correction in equatorial mode and includes an autoguiding port so, coupled with the belt drive, would make a superbmount for astro-imaging.

Also in this price range, at a cost of £1,099is the “HEQ5 Pro GOTO Mount with Rowan Belt Drive Modification” asdiscussed below.

The websites of reputable astronomical equipment suppliers provide farmore information than I can supply here as they quote detailed specificationsfrom the manufacturers. I suggest that you do your research by makingcomparisons on their websites. I have found the website of Rother Valley Opticsparticularly useful when learning about the wide variety of equatorial mountsthat are available. First Light Optics, who advertise in this magazine, alsohave extensive information on their website. Rother Valley Optics also providea DVD – “The RVO Beginner’s Guide to Equatorial Mounted Telescopes” –at a cost of £6.99.  Information andreviews of telescope mounts, from manufacturers and users, can also be found onYouTube and the manufacturers’ websites.

Upgrades and servicingto mounts

Rather than at some future time upgrading to a “premium” mountcosting sometimes well over £1,000, lower cost mounts can often be upgraded or“tuned” to improve their performance. One example is the Sky-Watcher HEQ5 Promount whose spur gears can be replaced with a “Rowan Belt Drive” system. Thiseliminates the noise produced by the gears when slewing and also improves thetracking performance. A kit for self-assembly can be bought for around £100 butcompanies will install it for you and, as mentioned above, one can evenpurchase an already equipped mount.

After a time, the performance of any mount will fall offpartly due to the degrading of the grease used to lubricate the bearings.Skilled amateurs can dismantle their mounts, re-grease them, and check andadjust the gear alignments, but others will employ a firm such as “DarkFrame”who can provide a “StellarDrive’” upgrade to a mount that will, for example,ultrasonically clean and re-grease all components and replace the worm gearbearings with those made from low friction hybrid-ceramic material. Telescope mountsare precision pieces of manufacturing, but manufacturing tolerances can beimproved with the fine-tuning that the “StellarDrive” upgrade also provides. Thetypical periodic tracking errors of a standard AZ-EQ5GT mount is 20-25arc-seconds and, with fine-tuning, this is reduced to 4-6 arc-seconds  – a great help when astroimaging. Thecost of such an upgrade is not small but will bring the mount’s performance upto those costing far more.

In a YouTube video “Best Mounts forAstrophotography” DarkFrame is visited and there is a demonstration of theRowan Belt Drive.

© Ian Morison