Manortronics +44 (0)1273 834135 — was £89
With the huge growth in popularity of computerised GoTo telescopes, it's inevitable that users of PushTo instruments, particularly Dobsonian owners, should also wish to add digital setting circles (DSCs) to their 'scopes. While there have been a number of DSC kits marketed in recent years, there are few commercial units that simply provide the altitude and azimuth coordinates of where the telescope is pointed without being tied into a computerised hand controller database of some kind. This latest offering, the Astro-Fix, offers an attractive, easy-to-use, and quick to install alternative.
Measuring just 80 x 55 x 25mm, the metal-boxed Astro-Fix feels reassuringly robust. Rather like the Wixey reviewed elsewhere on this website, the Astro-Fix features an internal digital inclinometer that measures directly the altitude of any surface (e.g. telescope tube) against which it is placed. However, the really innovative feature of the unit is the separate azimuth sensor (which is essentially a digital compass) connected to the Astro-Fix via a metre-long ribbon cable.
If you've ever had to retrofit the optical encoders of traditional DSCs to a mount, then you'll know that this can be a fiddly, time-consuming process. Not so with the Astro-Fix. For the average Dobsonian, installation consists of first attaching the hand unit to the upper side of the tube with the self-adhesive Velcro pads provided, then using a similar method to affix the azimuth sensor (with the white arrow facing in the direction of the 'scope) to the side of the rocker box (angle bracket supplied) or the base — that's it.
Once you've installed the Astro-Fix and turned it on by pressing the appropriate button on the front of the unit, the single line LCD display appears dimly backlit in green (I have suggested to the developer, Terry Whitehouse, that red would be better to preserve dark adaption). The resolution of the display is 0.1° in both altitude and azimuth. Since the azimuth sensor is sensitive to ferrous metals, it has to be calibrated each session. Fortunately, this is easy to do: hold down the 'Cal' button for a few seconds to engage calibration mode, then leisurely rotate the 'scope in azimuth by 360° over the course of 10 seconds or more. Pressing and releasing the 'Cal' button then gives you an azimuth reading.
If you own a Pocket PC or Palm running a graphical planetarium package (Astromist springs to mind), then the computational element is performed for you with an intuitive, easy to interpret graphical user interface, rather than the two-line alphanumeric display of a typical DSC hand controller. Most palmtop programs will give you the realtime horizon coordinates of any screen object that you care to point the stylus at, coordinates that you'll be able to match on the display of the Astro-Fix.
The unit comes with a six-page A4 manual that tells you how to use calibration stars to 'fine tune' the altitude and azimuth readings given by the unit in order to improve pointing accuracy. Fortunately, this is a largely intuitive process and quick to master. The guide states that the sort of results you can expect to achieve are <0.5° in altitude and <1° in azimuth. In my tests with a 12-inch Sky-Watcher FlexTube Dobsonian I achieved, on average, a slightly better targeting accuracy than that.
While it may not have the sort of pointing accuracy one would associate with a commercial DSC system such as the Orion IntelliScope (<0.2°), the fact that the Astro-Fix is so easy to install on a wide variety of altazimuth mounts and is simple to calibrate and operate, makes it a system worthy of further consideration. For low power views, where the field is a degree or more wide, Astro-Fix will get the desired object in view. The unit feels well-engineered and I like the fact that it uses internal rechargeable batteries and comes supplied with a trickle charger. Recommended. Website: Manortronics.