Sky-Watcher Explorer-150PL
Newtonian OTA
Optical Vision Ltd. — +44 (0)1359 244200 — £99
Ah, nostalgia. That's what I felt when I first saw an advert for
the Sky-Watcher Explorer-150PL, a 6-inch f/8 Newtonian imported
into the U.K. by
Optical Vision Ltd. and sold through their
network of stockists. I regard such instruments
with affection since it was with a self-built Newtonian of just
this size that I had my first detailed views of the Moon three
decades ago. In the 1970s, a 6-inch reflector was an instrument to
be reckoned with. Sadly, many contemporary observers severely
underestimate what a quality telescope of this size is capable of
revealing.
Optical Vision sells this 'scope mounted on an EQ3-2 German
equatorial with eyepieces and a 2x Barlow for a SRP of £249, but
the company has recently offered the OTA plus tube rings, a long
Vixen dovetail, 10mm and 25mm eyepieces, 6x30 finder and a coated
2x achromatic Barlow for just £99. At that price I was sceptical of
the optical and build quality, but I was pleasantly
surprised.
The fit and finish of the Explorer-150PL is typical of contemporary
Sky-Watcher products — in other words, extremely good for the
money. The rigid yet lightweight rolled steel tube has an
unobtrusive seam and the gorgeous slightly metallic sky blue paint
finish contrasts nicely with the rounded black tube end
castings.
The lockable rack and pinion focuser has a generous 6cm of smooth
travel and the 1.25-inch drawtube unscrews to reveal a T-mount
camera thread. (Astrophotographers may care to note that one of the
tube rings has a 1/4-20 thread for piggy-backing a camera). I had
no problems bringing any of my 1.25-inch eyepiece collection to
focus. The 6x30 finder is surprisingly bright for its aperture and
of good optical quality. I was pleased to see that the finder's
adjustment consisted of just two screws at right angles to one
another acting against a spring-loaded third; aligning it with the
main 'scope is therefore an easy and precise process.
Sky-Watcher doesn't seem keen for inexperienced users to tinker
with the factory settings of their primary mirrors (which is a good
thing), hence they like to put a steel cover plate on the bottom of
their Newtonians. This is retained by three easily removed Phillips
screws revealing a 148mm clear aperture primary supported by cork
shims at its periphery. With the back of the mirror exposed in this
fashion, cool down time is particularly rapid (I chose to leave the
cover off). Collimation of the primary is similarly
straightforward.
Sky-Watcher advertising makes a point about the 'ultra-thin'
secondary mirror supports used on their Newtonians, and it has to
be said that the diffraction impact of the 0.5mm thick spider vanes
is minimal. The 'scope was perfectly aligned out of the box, but
should you ever need to adjust the secondary mirror then you will
need a small Allen key in order to do so. The primary mirror is
also centre marked for ease of collimation.
Optical tests
At the time of the Explorer-150PL's evaluation I fortunately still
had the Orion Optics
OD150L De-luxe 6-inch f/11
Dobsonian on loan, so it made for an interesting comparison. Late
into the evening of July 7th I used both 'scopes to scrutinise
Jupiter under surprisingly good seeing for a planet at such a low
altitude. At close to 21h UT I watched the start of a transit of
Ganymede, Jupiter's largest moon, which appeared like a bright bead
against the dusky limb of its parent planet. Both 'scopes revealed
much detail along the border of the North Equatorial Belt and North
Tropical Zone in moments of excellent seeing.
The smaller central obstruction (25mm vs. 36mm) and Hilux coatings
of the OD150L gave it the edge for planetary work, but the
Explorer-150PL held up against its more expensive competitor
staggeringly well. Star testing of the 150PL revealed a tiny amount
of overcorrection, but with smoothly polished mirrors. M13, the
great Hercules globular cluster, was a magnificent sight despite
urban light pollution with resolved components across the core and
innumerable peripheral stars.
Verdict
A reborn classic that I can't recommend highly enough for the
price.
