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90
FIRST light
See an interactive 360° model of this scope at
www.skyatnightmagazine.com/willops715
William Optics Star 71
five-element
apo refractor
A compact imaging scope that offers great sharpness and colour
VITAL STATS
• Price £799
(introductory offer)
• Aperture 71mm
(3 inches)
• Focal length 350mm
(f/4.9)
• Optical design
Five-element patented
lens arrangement
• Tube length 324mm
dew shield retracted,
356mm extended
• Focuser 2.5-inch
dual-speed rack
and pinion
• Weight 2.05kg;
2.4kg with tube rings
and Vixen bar
• Extras Dew shield,
tube rings, Vixen
dovetail bar, Canon
DSLR adaptor
• Supplier The
Widescreen Centre
• www.widescreencentre.co.uk
• Tel 020 7935 2580
WORDS: PAUL MONEY
SKY SAYS…
ver since the days of Galileo,
correction. Overall triplets work
the refractor has been the
Stars were sharp well, but still leave fast apo
most familiar form of
refractors with some field
to the edges as
telescope to anyone thinking
distortion around the edges.
we’d expect from
of exploring the night sky. Early
a scope designed
refractor designs suffered from a variety
specifically for
of optical problems, especially when
One way to fix this problem is to
used for astrophotography – and so
buy an external flat-field corrector.
a flat field
today manufacturers strive to perfect the
William Optics has gone even better
ideal imaging refractor. It is this ambition
here, opting for a five-element arrangement:
that has led to William Optics’s Star 71
a triplet as the front objective and two correcting
five-element apo instrument.
lenses, one of which is flat field.
The package comprises an optical tube, tube
As the Star 71 is expressly intended for imaging,
rings with a Vixen dovetail bar, 2.5-inch dual-speed the back of the focusing unit ends in a male M48
rack and pinion focuser with built-in thermometer,
thread – which means you can’t add a regular star
front and rear metal covers and an M48-Canon
diagonal for visual observing. William Optics has
EOS adaptor ring. If you have a non-Canon DSLR,
stated that it will be stocking a custom 1.25-inch
you’ll need to buy a suitable adaptor.
90° dielectric mirror diagonal to allow visual use,
Cheap refractors suffer from chromatic
but this was not available in the UK at the time
aberration, a defect where not all colours are
of review. However we did discover we had a
brought to the same focus, as well as field curvature.
suitable adaptor that allowed us to attach an
Combined, these lead to distorted star shapes at the
eyepiece for straight-through viewing with our
edge of the image field of view. Visually a doublet
own 26mm and 17mm eyepieces.
design can improve chromatic aberration, but
The Vixen mounting bar has a tripod thread,
triplet lenses are often used in scopes intended for
allowing us to attach the scope to a standard tripod.
imaging as they provide a higher degree of colour
We enjoyed crisp wide field views with our 26mm >
E
WWW.THESECRETSTUDIO.NET X 4, PAUL MONEY X 2
SLIGHT AND LIGHT
The combination of compactness and lightness,
even with the tube rings and Vixen dovetail bar
attached, make this a viable travel telescope as well
as one that can capture great wide-field vistas. The
telescope tube weighs just 2.05kg; even with the ring
and dovetail bar attached it’s only 2.4kg, and at
324mm long it can fit in airline hand luggage. Its
size and weight makes it suitable for any of the travel
mounts reviewed in these pages, enabling you to take
it abroad to capture large deep-sky objects that are not
visible from your regular observing sites. Add to that
the excellent colour, field correction and fast focal
length, and you’ll find that lots of short image
exposures of a minute or so will give great results.
skyatnightmagazine.com 2015
Flat out success
FIRST LIGHT JANUARY 91
TUBE RINGS AND VIXEN BAR
The scope is supplied with a sturdy and nicely crafted pair of tube rings,
which are lightweight and easy to use. There are threaded holes on
the top of each one so that you can add other accessories, such as a
guidescope. The rings attach via a Vixen-style mounting bar.
FOCUSER
The dual-speed rack and pinion
focuser built into the rear of the
telescope was a delight to use. The
screw at the base enables you to lock
the focus position and didn’t move
even with our DSLR attached, though
there was a tiny image shift when
initially locking it.
DEW SHIELD
The retractable dew shield was
smooth to use, being easy to retract
for storage and capable of being
locked in place with a thumbscrew.
Though the shield seemed a little
short, it gave good protection from
dewing up under normal conditions.
Þ Our four-minute hydrogen-alpha exposures revealed the Veil Nebula
Complex in its entirety save for a faint region in the western section
Þ Our final stacked images of the Pleiades in Taurus showed a healthy
amount of nebulosity as well as the cluster stars themselves
skyatnightmagazine.com 2015
92 FIRST LIGHT JANUARY
OPTICS
FIRST light
The patented five-element design incorporates a multicoated
triplet objective lens at the front and two further lenses
farther down the tube to provide additional colour and field
correction. The lenses made of FPL-53 low-dispersion glass
for colour-free apochromatic performance.
INTERNAL
BAFFLES
There are internal
baffles at both ends
and these are coated
with matt paint to cut
down on stray light
bouncing around
inside the tube. They
do a good job in
preventing internal
reflections, which
would otherwise spoil
the contrast of faint
deep-sky objects.
WWW.THESECRETSTUDIO.NET, PAUL MONEY X 2
> eyepiece and slightly more magnified views with
the 17mm. Stars were sharp to the edges as we’d
expect from something designed specifically for
a flat field; there’s every indication that with the
custom diagonal the Star 71 can be turned into
a visual instrument if you so wish.
But this is primarily an imaging instrument so
we attached our Canon EOS 50D DSLR to the scope
and set them on an NEQ6 Go-To mount, giving
us the ability to capture exposures of up to four
minutes without guiding. The camera’s APS-C
sensor, coupled with the Star 71, equates to an
image scale of 3.65° by 2.4°, a nice wide field of view.
Full format camera sensors will give an even wider
view of 5.9° by 3.9°, which is large enough to
photograph sprawling targets such as the Veil
Nebula and Andromeda Galaxy comfortably.
We imaged the Pleiades star cluster, taking a
series of exposures of 30 seconds each to ensure
no trailing. Stars at the corners were still crisp
and well rounded with no sign of distortion. The
final stacked image, made from two sets of data
on different days, showed an enjoyable amount
of nebulosity too. We also experimented with
taking hydrogen-alpha images of the Veil Nebula
Complex, partly because of moonlight and partly
due to the scale of the object. We achieved
12 exposures of four minutes each at ISO 3200,
showing the whole complex bar a fainter section
of the western section.
Overall, William Optics has produced a good
looking, compact imaging telescope that gives
sharp stars out to the field edges and good colour
correction. We can recommend it to anyone
interested in wide-field imaging. S
skyatnightmagazine.com 2015
< Our composite of the
Beehive Cluster, made
from 20 exposures
lasting 60 seconds
< The Star 71 has a field
of view of 3.65º by 2.4º
– so targets such as the
Moon appear quite small
SKY SAYS…
Now add these:
1. Soft case
2. 50mm
guidescope
and rings
VERDICT
BUILD & DESIGN
EASE OF USE
FEATURES
IMAGING QUALITY
OPTICS
OVERALL
+++++
+++++
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3. William Optics
1.25-inch 90°
dielectric mirror
diagonal