Revelation 16-inch f/4.5 M-CRF Truss Dobsonian

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Revelation 16-inch f/4.5 M-CRF Truss Dobsonian

Vital Stats

Price: 
£1520.00
Aperture: 
406mm (16 inches)
Focal Length: 
1800mm (f/4.5)
Weight: 
64kg
Supplier: 
Telescope House
Telephone: 
01342 837610
Website: 
www.telescopehouse.com
A large-aperture Dobsonian telescope at an affordable price, this is a decent scope that yields great deep-sky views but doesn’t cost a fortune.

Over the past decade, a move towards manufacturing astronomy equipment in the Far East has led to big reductions in price, with little or no noticeable drop in engineering quality. An good example of this is the Revelation f/4.5 M-CRF, a Dobsonian reflector that boasts a 16-inch aperture yet costs just a little over £1,500. Even at that low price it has a host of good features and well-made parts.

Dobsonians provide big mirrors and light grasp, and sit on a simple rocker-box platform without the need for an expensive equatorial mount, which makes them ideal if you just want to enjoy the riches of the night sky.

This one comes packed in four large boxes. The rocker-box platform requires construction and putting it together takes just a few minutes. Three wide struts connect the top and bottom of the scope, rather than the more traditional and stiffer eight-pole truss setup. Assembling these components into a complete telescope involves placing the mirror unit in the rocker box, attaching the three wide struts to it with hand screws and then fixing the top of the scope to the struts. You may want an extra pair of hands to help with the last step, but with or without them it’s only a five-minute job to piece together the whole scope, which looks elegant with its gloss black finish.

The scope needs to be collimated before use to give the best views. Adjustment of the secondary mirror is done with three fiddly Philips screws, so don’t drop your screwdriver on the primary mirror! At the bottom end, the main mirror adjustment uses hand knobs and the mirror centre is spotted, both of which help to speed up collimation. Subsequent reassemblies only require a small collimation adjustment each time, provided you keep the struts in the same relative locations. Having just three support struts gives the scope a slight bit of flexure, which does seem to cause a small change in collimation – especially going from 45° to horizontal – but it’s nothing that will seriously affect the view.


Smooth moves

A Dobsonian’s night-time usability is dictated by the design of its altitude and azimuth bearings. They need to be smooth, especially at slow speed, and have the right amount of residual friction to hold the scope in place. This one does move smoothly in altitude and has the right amount of friction, but the bearing diameter is quite small and this affects its stability, leading to some slight springiness in use. The azimuth bearing on the M-CRF is based around a large-diameter ‘lazy Susan’ ball-bearing turntable: this is more stable, but moves a little too easily; with more friction it would better match the performance of the altitude bearing. Three PTFE pads in the base are fitted for this purpose but, unfortunately, they are not thick enough to contact the plastic foil bottom of the wooden base.

After evaluating the scope’s construction, it was time to test its viewing capability. Once assembled and collimated the scope was left to cool while the summer sky slowly darkened. With the supplied 30mm Superview eyepiece inserted and the scope pointed at some favourite deep-sky objects, the large aperture hit home, giving great views of globular clusters like M13 in Hercules and M71 in Sagitta, as well as M10 and M12 in Ophiuchus. If you’re used to smaller aperture views of these then you’re in for a real treat, as the 16-inch aperture resolves numerous stars in each cluster. The Ring Nebula and the nearby Dumbell Nebula were also big, bright and impressive.

While there are signs of over-correction in the primary mirror, views of the planets are acceptable, and the scope gave us sharp, contrasting views of the Moon, while star images were nice and round. The scope was comfortable to use and we enjoyed sweeping through Cygnus and drinking in the full majesty of the Milky Way during the review period.

If you’ve hankered after a decent big telescope that will yield great deep-sky views but thought such a thing would be too expensive, this could be the scope that changes your mind.

A solid mirror cell

The 16-inch, 30mm-thick primary mirror is held in a nicely made die-cast metal, 18-point support cell, which wouldn’t be out of place on a far more expensive telescope. The cell’s well-ventilated design helps keep the mirror closer to ambient temperature, reducing convection currents that might disturb the view. Thermal acclimatisation is helped by a DC fan that blows onto the rear face of the mirror. This is powered by a 12V battery pack that sits on the base and plugs into a socket on the mirror cell.

The alignment of the mirror cell is set by adjusting three strongly sprung black hand screws, and lightly locked off with three white ones. The cell also has three large rubber feet on the outer edge. The inclusion of these feet may not sound like much but it allows you to sit the whole bottom part of the scope on the ground during assembly without disturbing or damaging the collimation knobs – a welcome feature.


Eyepieces - The scope comes with two eyepieces: a 2-inch, 30mm focal length, wide-field ‘Superview’ and a narrower-field 1.25-inch, 9mm Plössl. A 2-inch, 35mm extender-adaptor is also included with the scope. Both eyepieces gave pleasing views in the central region of the field.

Finder - The addition of a 8x50 finder is a real bonus, especially for star-hopping under suburban skies where there are often too few naked-eye stars to easily use a red-dot finder. The finder has cross-wires to help with centring, and its alignment arrangement – using two screws and a opposing sprung rod – works really well.

Altitude axis - The scope has two beautifully machined altitude axes, fixed to adjustable rails on the mirror box. The bearings have large adjuster knobs that can be used to increase or decrease the friction. These are also used to grip the mirror box when lifting it into position in the base.

Adjustable balance - With the mirror unit out of the base, the altitude bearings can be moved along graduated rails and locked in position. This feature allows you to easily accommodate weight changes to the scope and avoids the need to mess around with counterweights to achieve the correct balance.

Focuser - The scope includes a good-looking and functional 2-inch focuser with a 2- to 1.25-inch adaptor and brass compression rings for both sizes. Focusing is smooth and well-controlled with no noticeable backlash and has a 10:1 slow-motion knob at one end for critical focusing. It also features a friction-control thumbscrew.


This review originally appeared in the October 2013 issue of BBC Sky at Night Magazine.

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