Explore Scientific Ultra Light 16-inch Dobsonian Generation II review

Dobsonian reflectors on their large, stable altaz mounts are very popular among visual observers who love their ease of use and quick set-up times.

Combine this with a big aperture and you have the potential for a great, user-friendly visual instrument, capable of revealing many thousands of deep-sky objects and pulling out detail and contrast in objects barely visible in smaller scopes.

Explore Scientific produces a range of elegant lightweight truss tube Dobsonian reflectors with mirrors ranging in diameter from 10-inch, to a whopping 20-inch.

We tested their Generation II 16-inch option, which has been upgraded recently to improve its mechanics.

The scope came extremely well packed in a huge 52kg box.

Once we’d unbundled it, we started assembly but were soon scratching our heads.

The problem was that the design of some of the altitude bearing components has been upgraded but the manual hasn’t been updated accordingly.

Some online picture checking was needed to work out how it all went together, particularly the attachment of the altitude bearings to the mirror box.

With these attached, the rest of the assembly involved fixing the truss poles to the mirror box and then attaching the head to the pole tops.

The former was easy but the latter less so; it’s a tricky job requiring you to keep a good hold on the head, close to the heavier focuser, until all four truss tube pairs are securely connected with screw knobs.

Collimation made easy

A lot of thought has gone into the collimation method.

Secondary adjustment is achieved via three spring-loaded knobs while the adjustment of the primary is accomplished by use of a specially supplied pole with a hex key at the end.

This then engages with one of three socket screws around the front of the mirror.

You can adjust both the secondary and primary whilst looking through the focuser, which is handy.

With the scope assembled and collimated we inserted a low-power, wide-field eyepiece and started exploring the skies.

A thin crescent Moon was low in the west as dusk fell and we had a lovely crisp and detailed view of the lunar landscape.

As the sky darkened we found the open clusters M36, M37 and M38, all three of which were sharp and high contrast.

Although we were observing from a suburban site, the large aperture did its job collecting lots of photons and we started searching out some of the numerous galaxies in the spring sky.

First, we found the Leo triplet, M65, M66 and NGC 3628, then some of the brighter ones in the Virgo cluster including the lovely, edge-on NGC 4762.

M51 at the zenith with its companion was easy and at higher power gave hints of spiral structure.

Later, the globulars M13 and M3 were well resolved and the session rounded off with a nice view of Jupiter low in the southeast sporting several darker belts.

Combatting stray light

The optics performed well once cooled down and the large, foam light baffle opposite the focuser helped keep the field dark and the contrast up.

If you’re troubled by nearby lighting, though, you might want to consider rigging up a lightweight shroud around the truss poles to help keep out stray illumination.

It also helps reduce the likelihood of the optics dewing up in damp conditions.

There were a couple of niggles.

The body of the red dot finder was so loose it kept going out of alignment and even at the lowest settings was much too bright.

Although the scope movement was smooth and easy thanks to its low-friction PTFE-on-glass-board bearings, it was perhaps a little too low-friction when it came to altitude.

This meant the balance had to be just right or the scope would rise or fall on its own depending on what altitude you were at.

There are adjustable side blocks on the base to centralise the mirror box which are supposed to control the altitude friction, but we couldn’t get the things to work.

Instead the secret was to add or remove counterweights from the mirror box until it balanced at our desired altitude.

Although the Explore 16-inch is a big aperture scope, its design makes it relatively simple and lightweight to assemble and use.

The few annoying niggles shouldn’t stop you having many enjoyable hours scanning the night sky.

Outstanding feature: Lightweight design

A 16-inch scope is a big piece of equipment and often back-wrenchingly heavy.

The Explore design brings the weight right down while maintaining strength and rigidity.

It does this by abandoning the particle board used by other manufacturers for the mirror box and the base, and instead uses aluminium for many of the telescope’s main components and structure.

The total weight of the scope is an impressively low 40kg.

The base box is made of aluminium panels riveted to an aluminium frame, making it a very light but sturdy unit.

The mirror box uses similar build principles and even with the 14kg mirror inside it, it is not too difficult to lift the whole bearing box in and out of the base when you’re setting up or breaking down the scope.

You can do this by grabbing onto the tops of the attached aluminium altitude bearings, which double up as very convenient handles.

The poles and the head are also aluminium, with steel only used for the secondary spider to give extra rigidity.

Focuser

The focuser is a handsome, smooth-action, solid aluminium unit with both coarse and fine (10:1) tuning controls and friction control.

Taking the 1.25-inch adaptor out allows 2-inch eyepieces to be used.

A locking screw underneath allows you to tension the focuser when using heavier eyepieces.

Truss poles

The well-made metal truss poles are in four hinged pairs, reducing the number of parts you have to transport and speeding up the process of fixing the mirror box to the head.

Screws in the corner of the mirror box slide into slots in the truss hinges, which, when tightened, grip the poles in place.

Four screwed knobs then attach the poles to the head.

Main mirror

The 16-inch (405mm) f/4.5 mirror is made of low-expansion glass, 43mm thick, and has a laser-engraved centre ring to help you collimate the scope before use.

The mirror has a well-designed support system and two rollers at the bottom edge to support the mirror weight at low altitude.

Mirror cooling

The mirror box is an open design with plenty of space around it to help it cool down to air temperature.

To speed things up, two 12V fans sit in the side of the mirror box, one wired to suck and the other to blow.

A battery packtaking D cells is provided to power the fans.

Compact storage

For a 16-inch scope, it’s more transportable than you might expect.

The scope packs away very nicely when the poles are removed: the head sits on the lid of the closed mirror box to form a compact unit 55x55cm and only 75cm high.

This review originally appeared in the July 2018 issue of BBC Sky at Night Magazine