Aperture: 130mm (5 inches)
Focal Length: 905mm (f/7)
Supplier: Altair Astro
Telephone: 01263 731505
There is something rather special about a large refractor – and with an aperture of 5 inches and a focal length of 905mm, Altair Astro’s Wave Series 130 EDT is certainly a large instrument.
The fit and finish of the component parts is really excellent and the telescope exudes quality.
It is supplied in a fairly lightweight aluminium ‘flight case’, but this is probably not rugged enough for extended use.
Attached to the top of the attractive tube rings is a useful carrying handle.
We were not too keen on the modified Vixen-style dovetail bar (this had to be installed to ensure the necessary spacing to fit the handle) as this had a minimum amount of contact area in the saddle.
For astrophotography purposes, we would advise upgrading this to a Losmandy-style dovetail bar.
The rack and pinion focuser performed smoothly and precisely, allowing stars to snap into focus with ease, irrespective of magnification, while its Teflon-coated rotation system made camera alignment a simple process.
Views through the 130 EDT were excellent.
Despite numerous clouded out sessions, we enjoyed some very memorable sights.
Globular clusters M13, M92 and M56 were particularly good, as were planetary nebulae M27 and M57; the latter looked particularly strong with very nicely defined central darkness.
We turned to star hunting next.
The beautiful colour-contrasting components of double star Albireo in Cygnus looked fabulous at various magnifications and the Garnet Star, Mu Cephei, displayed amazingly vivid colour.
Splitting the Double Double, Epsilon Lyrae, revealed a distinct dark space between the individual stars, which looked very impressive through our 5mm eyepiece.
Star shapes remained excellent out to about 85 per cent of the field of view, with a gentle deterioration in shape and star colours reddening towards the field edges as seen with our 68° apparent field of view eyepieces.
The view had good contrast, no doubt assisted by the CNC-machined baffles in both the optical and focuser tubes.
We were keen to try imaging with the telescope, attaching our own cooled CCD camera and off-axis guider for this purpose.
This combination yielded a field of view a fraction under 1.5° by 1°.
It was at this point that we realised just how good the self-centring eyepiece holder was.
The inner surface comprises a smooth, matt finish nylon sleeve with a generous 20mm-deep gripping surface.
This excellent system allowed for easy and smooth insertion of the imaging equipment, and a quick turn of the capstan resulted in a very firm and well-aligned grip.
The operation of the capstan was so silky that it almost made the focuser rotator redundant for the purposes of orientating the camera to suit the object being imaged.
The rack and pinion focuser was more than capable of holding our camera when pointing towards the zenith and its operation was very smooth.
Imaging conditions were pretty poor during the review period, not helped by the limited available darkness.
Our images of the North America Nebula’s ‘Mexico’ region (also known as ‘The Wall’) showed good star colouring.
We noted a small level of vignetting that was easily corrected by applying flat frames.
Star shapes towards the edges of the field of view became elongated due to field curvature, but this is normal for a triplet design such as this.
Altair Astro’s Wave Series 130 EDT would be a good choice for intermediate astronomers, for both observing and imaging – though for deep-sky imaging we would recommend the addition of a focal reducer to improve star shapes at the outer edges of the field of view.
Certified lens quality
The refractor’s multicoated triplet lens is designed to give good colour correction, and it is this type of objective lens that gives the telescope its apochromatic (apo) credentials.
A standard refractor, known as an achromat, uses two lens elements.
These bring both red and blue light to the same point of focus, but there is still colour fringing on bright objects.
The three elements in an apo like the 130 EDT additionally bring green light to the same point of focus as the red and blue light, producing vibrant and accurate colours with minimal colour fringing.
To further improve colour fidelity, the lenses are made of Ohara FPL-51 extra-low dispersion glass. Each lens is also supplied with an optical report.
The lens cell itself can be collimated via three pairs of opposing bolts, which are accessible from the front of the telescope once the dew shield is removed.
Our initial star test showed that the review instrument had arrived perfectly collimated.
Retractable Dew Shield
The retractable dew shield has an inner diameter of 167mm and extends 150mm in front of the primary lens.
The inner surface has a matt black paint finish to keep reflections to a minimum and increase contrast, and there is a very effective locking knob to hold it in the extended position.
Rack and Pinion Focuser
The substantial, baffled 2.5-inch focuser is of a rack and pinion design, the gears for which are manufactured to very close tolerances in the UK.
With a 10:1 reduction drive, the focus feel is very good indeed, with no backlash evident when changing direction.
There is a very generous 97mm of movement.
Self-Centring Eyepiece Holder
The focuser tube has a 68mm female thread, onto which is attached a 2-inch eyepiece holder with a built-in capstan.
The capstan operates a very smooth and precise self-centring mechanism for gripping a standard 2-inch eyepiece, but it also held our imaging camera rigidly.
A self-centring adaptor for 1.25-inch eyepieces is also supplied.
A very handy carry handle is attached to the top of the tube rings.
This is ideal for manoeuvring a telescope of this size and weight onto the mount’s saddle clamp.
However, the handle has to be removed if you want attach a guidescope to the top of the tube rings.
The beautifully crafted and shaped tube rings are CNC machined.
A flat top with three tapped holes allows a guidescope or other accessories to be attached for imaging purposes, while a smaller flat area with a single tapped hole caters for a finderscope.
This review original appeared in the September 2014 issue of BBC Sky at Night Magazine.