The 25x100 Monk Leviathan binoculars

Two eyes are often better than one. So what's it like to combine two 4-inch refracting telescopes into a single giant pair of binoculars? Neil Bone got to find out.

Small binoculars have long been the recommended instrument for newcomers to observational amateur astronomy. In particular, 7x40 or 10x50 models are seen as the ideal (binoculars are described in terms of first their magnification, x7 or x10 in these cases; and aperture in millimetres, 40 or 50mm respectively). The benefits of portability are obvious, while the wide field of view is a further advantage for observing many types of deep-sky object and variable stars.

Experienced amateurs may 'trade-up' to more powerful binoculars typically in the 15x80 range, enjoying the greater light grasp afforded by increased aperture. These however, are somewhat heavier and cannot be hand-held for any great length of time; 15x80s need to be mounted on a tripod.

Can still-larger binoculars be of use for astronomy? In the case of the 'Leviathan' 25x100s, imported from a military factory in China by the UK company Monk Optics, I think the answer has to be a resounding yes.

Specifications
Most observers who have used relatively small wide-field telescopes in the 100mm (4-inch) aperture class have probably wondered what it would be like to combine two such instruments into a binocular arrangement.
In essence, this is what the Leviathan binoculars come to. Assembled in a 65 by 25 cm (26 by 10 inch) cast aluminium housing with an elegant champagne paint finish, the optics work as side-by-side f/6.5 refractors. The optics are fully coated for optimal performance, and their light path is folded through porro prisms, emerging to eyepieces angled at 45 degrees which, for viewing most positions in the sky, the observer looks down into. The optical assembly has small internal baffles, and the housing also has a shield extending above the objective (front-end) lenses to further cut out stray light.

The eyepieces focus individually and can, of course, be adjusted to the observer's ideal separation. At x25, they offer an exit pupil of 4mm, which is ample for most people, with good eye relief (15mm), allowing use of the binoculars with spectacles if necessary. The field of view, 2.5 degrees, is about half that offered by a pair of 10x50s. An optional - special order only - version can be purchased with x40 eyepieces (1.5 degree field).

Monk Optics supply the Leviathan binoculars in a moulded foam carrying case. First impressions on removing them from the case centred on their weight - at a hefty 12kg (26lb), these are not the sort of binoculars to hang on a strap around your neck! Indeed, a substantial tripod is needed to hold them steady. During the period in which this review was conducted, Monk Optics set about designing a dedicated astronomical mount for the Leviathan allowing access to the sky to within six degrees of the zenith. This is a vast improvement on the original, which restricted viewing to within about 45 degrees of the horizon. The Monk alt-azimuth mount is another substantial piece of metalwork, which sits atop the sturdy wooden tripod.

Setting up of the modified mount is simplicity itself, and takes only a couple of minutes. Once a suitable garden location has been found for the evening's viewing, the tripod is extended, then the binoculars attached to the yoke mounting by a single large, knurled retaining screw which threads through the mount's base into a base plate on the housing. That done, you can get straight down to observing.


Field tests
I have been able to try out the Leviathan binoculars on several nights, ranging from balmy mid-July to the frosty depths of winter. Many of the views have been spectacular. Favourable first impressions were gleaned on 12-13th July last year for example, when the 25x100s were turned on the summer Milky Way in the constellations Scutum and Sagittarius.

The Scutum Star Cloud just south of Aquila was shown in magnificent detail, with the binoculars clearly revealing mottled dark nebulosity obscuring the light from the packed starfields beyond; this is something at which smaller instruments only hint! M11, the Wild Duck Cluster, was well resolved as a tight clump of stars with a brighter member at its eastern tip. Down in Sagittarius, the Swan Nebula, M17, was shown as a hook of cotton wool against the dark background sky.

Use of binocular vision gives an almost three-dimensional view of the sky. Having both eyes studying the field simultaneously has advantages, too, for resolution and detection of faint objects. In the Leviathan binoculars, it was easy to see individual stars in the outer parts of the spectacular Sagittarius globular cluster M22, while fainter objects like M28 and NGC 6712 (the latter back up in Scutum) were easily picked up.

A 'bonus' observation in July 2001- again emphasising the benefits of binocular vision with such apertures - was of Comet 2002 A2 LINEAR. Using my 80mm f/5 'spotter' telescope, I suspected the presence of a narrow, straight faint ion tail. In the 25x100s there was no question it was there. The comet was also seen to be enveloped in an extensive diffuse halo of light (the outer coma)

Stellar targets were also well shown. Albireo was cleanly resolved into its orange and green components, whilst theta (_) Serpentis showed a closely- matched pair of white components. Bright stars like Vega focussed to sharp points.


Moon and Planets
As Autumn 2001 arrived, Jupiter and Saturn became available as test targets. Obviously at x25 neither was expected to reveal much disk details but it was just possible to make out Saturn's wide-open rings as distinct from the planet. Jupiter showed a hint of dark band (probably a combination of the NEB and SEB) and also brought out just a touch of optical colour fringing.

One truly superb view on the 25x100s came late on 9-10th October when the last quarter moon was about half a degree north of Jupiter. The 2.5-degree field presented the moon, Jupiter and the four Galilean satellites neatly arranged east-west order of orbital distance from the Giant Planet-all in the same view. Usually only visible when the moon is a thin crescent, earthshine was readily apparent in the non-sunlit portion of the lunar surface; clearly the 25 x 100s do a lot to boost contrast.

Surface detail on the moon was superb, the magnification being easily sufficient to reveal features like the terracing on the walls of Copernicus or craterlets in the floor of Clavius. Hints of blue colour fringing on the moons bright limb detracted little from the spectacle.
November forays into the winter skies again showed the usefulness of the Leviathan binoculars for hunting out nebulae. M1, the Crab Nebula in Taurus, can be a difficult object in moderate-aperture instruments, but showed up easily as an S-shaped patch in the 25x100s, even in somewhat hazy skies. As expected, the Orion Nebula was splendid. The showpiece Andromeda Galaxy and its satellite M32 filled the binoculars field of view.

These November observations, made using a test version of the new mounting, brought home the usefulness of the mount's fine-adjustment controls - something I had initially thought a bit of an unnecessary luxury. In fact, even with a 2.5 degree field, objects do drift from the centre quite quickly, and it is useful to be able to make small smooth shifts, using the hand control, in both altitude and azimuth (rather than 'nudging' the mount) to keep track on objects. The fine adjustment also comes into its own when 'star hopping' to faint targets. Each control is operated via a large knurled knob which turns a screw thread to effect motion. These were very easy to use, even with gloved hands on a frosty night.

One practical point which soon came to light was the need for a large-scale atlas showing stars to a reasonably 'deep' faint magnitude. The relatively small field of view dictates that the observer will have to hop from quite faint starting stars to locate some objects. I found Uranometria 2000.0 a useful in-field accessory when taking the Leviathan binoculars through their paces.

Dismounting the binoculars at the end of the session was as quick as set-up, but it is perhaps more of a consideration carrying the heavy, cold metal body after a couple of hours or more in the frost of a midwinter night!


Final impressions
Overall, my impression is that the Monk Leviathan 25x100 binoculars are a deep sky and comet observer's 'dream' instrument, and a good alternative to a large telescope. The 2.5-degree field is ideal for observing diffuse objects, and the optics are sufficiently contrasty to pull quite tricky targets out from the background.

These could be a 'career' instrument for an observer happy to eschew high-magnification telescopic work for the advantage of the wider view in cometary work. The 25x100s bring to mind the portrait photographs of the late George Alcock with his giant binoculars, used in his unparalleled visual searches for comets and novae. Perhaps the next great visual discoverer will regularly use a Leviathan!
Thanks to Monk Optics for supplying the review instrument and mounting.


Neil Bone is a Contributing Consultant to Astronomy Now, and has been observing the sky through a variety of instruments for more than 30 years.
For many years the standard advice to beginners in astronomy has been that binoculars offer the ideal first serious instrument.

Neil Bone is a Contributing Consultant to Astronomy Now. His trusty 10x50 binoculars have been used to make more than 11,000 variable star estimates since 1976.