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Telescope Drive Master

One of the most difficult problems in astrophotography and scientific CCD measuring techniques of "instrumental" astronomical observations is the sufficiently accurate tracking ability of various mounts. Even the most precise "semi-pro" mounts, designed especially for advanced amateurs (e.g. Paramount ME), have some periodic and non-periodic tracking errors. Due to this type of errors, the length of exposure must be limited in time. This limitation obviously depends on other factors as well, such as focal length of certain telescope, horizontal altitude of the object observed (refraction problem), correct polar alignment of the mount, etc. Moreover, these factors have rather complex interrelation to each other; e.g., you can use shorter focal distances keeping star-swinging problem at low level on the surface of the CCD sensor in spite of the higher tracking errors of your mount.

For avoiding these kinds of problems and imperfections, the commonly used solution in instrumental astronomical observations nowadays is referred to as "auto-guiding". Another possibility to eliminate the effect of the periodic tracking error is the so-called PEC (Periodic Error Correction) software. Although both of the above-mentioned systems can remarkably improve the tracking accuracy of your mount, each of them has certain difficulties. Sometimes, it is quite laborious to find a guiding star in the observed object's region in the sky, which is bright enough for accurate tracking process and, at the same time, you surely will not be able to find two tracking periods with exactly the same shapes for using your PEC algorithm efficiently enough.

Anyway, the better the tracking accuracy of your mount is, the better imaging possibilities you have, independently from the other parameters of your astronomical equipment. This is a well-known and widely accepted general rule among highly qualified amateur astronomers worldwide.

This is why our team has developed an extremely accurate driving correction system called "Telescope Drive Master" (TDM), applicable for almost any type of mass-produced equatorial mounts and installed subsequently onto the mount. The system's patent procedure is in progress; its registration number is: P0700280HU.

Our system has got two main parts: a high precision encoder unit attached directly onto the RA shaft of the mount and an electronic device (let's say a sort of "black-box"), which receives the electrical signals arriving from the encoder unit and sends control instructions to its own mount's driver via its auto-guider input connector.

The Telescope Drive Master is able to provide roughly ±1 arc-second tracking accuracy, depending on the mechanical features of the mount concerned and the tracking correction speed of its driver to be used. Any type of controller unit may be used with Telescope Drive Master that has a standard auto-guider input and its tracking correction speed can be 0.5x of sidereal speed or lower.

So far, three types of mechanical adapters have been developed, attaching the encoder unit to the mount: for Synta (SkyWatcher) EQ6 (or Orion Atlas EQ-G in the US), Celestron CGE and any type of Fornax mounts. (However, in the near future more and more new adapters will be developed and produced for the other popular mounts as well like Losmandy, Vixen, LX200, etc.) It means that while a typical EQ6 (EQ-G) mount can easily have 20-30" (or higher) periodic error as "out-of-box result", Telescope Drive Master can reduce it by more than one order of magnitude, down to 2-2.5" peak-to-valley total or less, which is better than the same feature of the very expensive premium category mounts. Certainly, the better quality of mounts will also be able to provide higher accuracy (even less than ±1" or 2" total) using Telescope Drive Master.

The first curve shows the "out-of-box" tracking error of an EQ6 mount (cca. ±20"):


The second curve shows the same EQ6 mount corrected by Telescope Drive Master (cca. ±1"):


(Both curves were created by K3CCDTools3 and a free copy of PEAS software.)

You can see on the second chart that Telescope Drive Master is able to keep the tracking error of an "average-quality" EQ-6 (Atlas EQ-G) mount within ±1" range at least in the 95% of the total exposed time. (A better mount can perform better with Telescope Drive Master as well.)

No adjustment or external initializing is required after installing the hardware. You only need to switch on your telescope driver first and if you then switch on the Telescope Drive Master, it will automatically perceive both the Northern-Southern hemisphere usage of the mount and it will also recognize the Eastern-Western position of the equatorial mount during its one-second self-test and self-initialization process. Telescope Drive Master recognizes your driver's GoTo or your other manual positioning movements as well (if the speed of these movements is higher than 1.5x sidereal speed for longer than 1 second duration) and blocks its own corrections during these movements.

This version of Telescope Drive Master does not allow the simultaneous use of any auto-guider system (except SBIG AO-7 or AO-8 used together with their ST series cameras) and any of your manual correction applied by lower speed than 1.5x sidereal rate (or higher speed but with less than 1 second duration) will be compensated by Telescope Drive Master.

The long term tracking accuracy of your mount supported by Telescope Drive Master will be determined and limited exclusively by the precision of the polar alignment of your mount and air refraction. E.g. the attached photograph below (NGC1161) was captured by a 10 minutes' (!) long exposure using a 16" LX200R OTA (and SBIG ST-8) with 2.5m (!) reduced focal length on around 70 degrees horizon altitude without conventional autoguider and, as you can see, the shape of the stars are free of any kind of visible elongation or distortion. At the same time, for example, if you are hunting just about 25-30 degrees above the horizon (and far from the local meridian) with a 1000-1200mm APO refractor, you will be able to apply around 1 minute exposure time only due to the exponentially increasing refraction rate at low altitudes.


10 min. long expo sure (RAW) using TDM without conventional autoguider or PEC sw (shot by Zsolt Kereszty)




Finally, Telescope Drive Master is highly recommended, first of all, for observatory using; mainly for "semi-pro" amateurs who want to have as many measuring sessions as they can night-by-night (supernova, comet and asteroid hunters, variable star observers, exo-planet discoverers, gamma-ray burst watchers, spectroscopic observers, etc.). These astronomers will hopefully be happy with this controller, because Telescope Drive Master will help them to create a fully automated system. On the other hand, anyone can also use this system with pleasure in the field, if he/she has experiences in applying Scheiner and/or King method in quickly enough way to achieve accurate polar alignment before observing.

One of the ultimate solutions can be using Telescope Drive Master together with SBIG AO-7 or AO-8 adaptive optics, because Telescope Drive Master can compensate all type of tracking errors of your mount (independently from the amplitude of its PE) and AO-X can compensate air refraction and scintillation as well. So, you do not need to waste a lot of time for finding an appropriate guide-star for each of your exposures and, a narrow band filter (e.g. H-alfa) will not block the light in front of your guiding chip. The only case when you really need to use a conventional autoguider system is measuring a celestial object with high proper motions (comets and asteroids) or applying extra long exposure time on low altitudes.

original solarflare design by rhuk
modified by MDA-TelesCoop