Vixen AX103S and Atlux mount

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Magazine Verdict: 
Vixen AX103S and Atlux mount

Vital Stats

103mm (4 inches)
Focal Length: 
825mm; f/8
None supplied
01582 726522
The beautifully engineered, heavy-duty, cream-finished Atlux mount has a 34kg load capacity, making it a very sturdy platform for both visual and imaging use.

The Vixen Atlux AX103S is a substantial, high-end product that comes with some rather interesting features. The telescope has a richly finished white aluminium tube with a retractable dew shield and a dual-speed, 10:1 high-precision rack-and-pinion focuser. However, what makes this scope special compared to most other refractors is that it has a rear field-correction lens as well as its extra-low dispersion, apochromatic, multicoated 4-inch triplet objective (main) lens. The rear lens corrects a problem common to normal refractors, the views of which suffer from ‘field curvature’. This is when light passing through the edge of the lens is brought to focus closer to the lens than light passing through the centre, so image quality drops off towards the edge of the field of view.

The beautifully engineered, heavy-duty, cream-finished Atlux mount has a 34kg load capacity, making it a very sturdy platform for both visual and imaging use. The mount is a Go-To, but it’s no normal Go-To. It’s matched up to Vixen’s Star Book controller that incorporates a complete full-colour 22,725-object planetarium as well as the Go-To system itself.

We wanted to test the system by using it for both observing and imaging. First, we carried out an extensive observing session to get accustomed to the Star Book controls. Opticron supplied us with 20mm and 5mm Lanthanum eyepieces, a flip mirror and a finderscope for this review since these accessories aren’t included.

Assembly of the components was straightforward and we found the well-designed polar alignment scope very simple to use. Although we were surprised that the Star Book’s 10 control buttons weren’t illuminated, they were very intuitive in use and we quickly felt at one with the unit.

We carried out a two-star alignment, choosing Vega and Aldebaran so we could examine these two very different stars. Bright blue Vega sparkled crisply and the out-of-focus views of the Airy discs (the patterns of diffraction) either side of the point of focus revealed a very well matched pair of concentric rings, confirming the excellence of the optics. Vega remained beautifully formed right out to the edge of the field of view.

Accurate star-hopping

With Vega as our first alignment star, we were pleased to see the obvious red hue of Aldebaran appear in our 20mm eyepiece when we slewed to it to complete the star alignment. Subsequent slews confirmed the high accuracy of the Go-To system. Our first hop was back to the region of Vega for a look at M57, the Ring Nebula, and we were rewarded with a lovely view of this celestial smoke ring. Nearby, the Double-Double quadruple star (Epsilon Lyrae) was split with ease using the 5mm eyepiece, and the high contrast view was stunning.

Heading for closer prey, Jupiter was a small but glorious sight with obvious bands and beautifully bright, pin-prick moons. The full Moon was framed well in the 20mm eyepiece and the lack of colour fringing was a testament to the excellent optics. The Pleiades, too, was a memorable sight, although we couldn’t fit the whole cluster into the field of view of the 20mm eyepiece.

Digital camera sensors really show the effects of field curvature, so we were keen to see how well this refractor coped with this problem. We analysed an image of the sky to see how ‘flat’ it appeared and were very impressed with the result, with pin-point stars right to the edge of the frame. Some of our two-minute unguided images showed star trailing, but long exposures can be autoguided via the standard autoguider port on the Star Book.

With its excellent build quality and rich feature set, we thoroughly recommend this system if you’re looking to upgrade from your current setup.

Consummate controller

We are accustomed to feature-rich hand controllers being supplied with modern Go-To mounts, but the Star Book takes things to a new level. In addition to storing your location and maintaining an accurate clock and calendar, this innovative hand controller has a 119mm 320x240 pixel LCD colour display. The display and 10 buttons give access to a comprehensive planetarium and full control of the mount.

There are two main modes: chart mode and scope mode. In chart mode you can simply navigate around the built-in planetarium, zooming in and out of the objects shown on the screen, or select them from the Messier, NGC, IC, Solar System, Star, Constellation, Famous Object and Comet databases. The catalogues helpfully only show objects currently above your horizon.

Having chosen your object, selecting scope mode will automatically slew the telescope to that object. From here you have the opportunity of selecting it as an alignment object (up to 19 can be chosen) or simply enjoying the view.

Focuser - We tend to expect Crayford focusers in high-end telescopes, but a well-designed rack-and-pinion focuser such as this one makes focusing very simple. The 10:1 speed reduction drive was very smooth indeed and no slippage was detected, even with a heavy CCD camera attached.

Polar scope - A good polar alignment is important for both Go-To accuracy and reliable tracking, especially while imaging. This polarscope was neatly incorporated in a semi-recessed position in the Atlux mount and was extremely easy to use. The brightness of the illuminated reticule was fully adjustable and the view was excellent.

Tripod - A sturdy mount requires a sturdy tripod and the one supplied by Vixen is certainly that. The 48mm-diameter black-finished tubular legs with cream fittings make for a substantial base that’s very attractive too. We particularly liked the spring-loaded extension legs, which made assembly very straightforward.

Mount - This very sturdy mount is an excellent platform for both observing and imaging. We particularly liked the fact that the electronics cables didn’t move with the rotation of the mount, making cable snags a thing of the past. The RA and Dec. clutches latched easily and securely into place and the latitude and azimuth adjustment bolts were smooth to operate.

Optics - The optics included in this telescope are rather unusual, consisting of two modules: the primary lens at the front and the rear field-correction lens. The primary lens is an apochromatic triplet designed to banish chromatic aberration, while the rear lens ensures sharp images across the whole field.

This review originally appeared in the February 2010 issue of BBC Sky at Night Magazine.

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