Sky & Telescope - February 2019 - 63

adapter to thread this to the Evostar
body ($49) as well as an adapter to
connect my CCD camera to the ﬂattener. Note that with the reducer/ﬂattener, the scope is operating at a focal
length of 357-mm, producing a focal
ratio of just under f/5.
My ﬁ rst test was to shoot the Moon
with and without the reducer (see
below) with a Canon 5D Mark III
DSLR. In the center of the ﬁeld, the
Moon was sharp and well-deﬁ ned in
both cases, with no color fringing
evident photographically. Even without the ﬁeld-ﬂattener, the Evostar 72
can likely be used for objects near the
center of the ﬁeld of view.
Sky-Watcher states all Evostar refractors will satisfactorily cover an APS-Csized sensor or smaller without the use
of a ﬁeld-ﬂattener. I put a full-frame
DSLR on it just to see how large the
usable ﬁeld is, and I took a test shot
of M31 from my backyard. The image
shown on the opposite page is a single
calibrated and stretched frame which
shows just how wide the ﬁeld of view is.
I've superimposed a rectangle showing
the size of an APS-C sensor's coverage;
it's still plenty to capture all of M31.
Naturally, the stars at the edges

of the full-frame image are a good
bit elongated, but curiously, one of
the corners actually held up okay. It
is possible there was some tilt in my
prototype adapter, or perhaps some sag
with a heavy camera attached. Performance is better inside the crop-sensor
rectangle, of course, but still you can
see the correction fall off at the edges
and corners of the APS-C frame. Anything smaller than an APS-C should
produce round stars across the entire
image, while APS-C detectors will show
acceptable stars until you get to the
very corners of the frame.
Color-wise, there was some lateral color separation of stars radially
towards the center of the image, with
stars displaying a blue edge on one
side and a red one on the other. This is
normal for a doublet APO in this price
range without using a ﬁeld-ﬂattener,
and I've even seen worse on moreexpensive APO triplets.
A backyard on the far side of
Orlando from Disney World is not the
best place to do color images, and so I
thought I'd try some narrowband with
this little scope. A doublet APO should
excel when shooting with ﬁlters as a
much narrower range of wavelengths
needs to be focused in the same place.
Slightly under-sampled on a Starlight
Xpress Trius-SX694 monochrome camera at f/5, I knew I could get some nice
images with short 5-minute exposures,
even at narrowband wavelengths.
I focused all of these images by
hand using the stock focuser. Florida
summers are pretty stable temperaturewise, and I focused once and left it
for the night. I shot four targets total
over several nights in automated runs
that included meridian ﬂ ips, and the
focuser never slipped.

Conclusion
I started my astronomical life strictly a
visual observer, and now after several

t The Evostar 72 Apo performs well on the
Moon both with (near left) and without (far left)
Sky-Watcher's reducer/corrector for its ProED
80 refractor. With the reducer/flattener, the
telescope operates at 357 mm, f/4.9.

p Although the Evostar 72 can cover detectors
smaller than APS-C format with minimal aberrations as seen on the facing page, a field-flattener is recommended for optimal performance
for full-field correction on detectors as large as
24×36 mm. Additional adapters are necessary
to properly space your camera's detector from
the corrector for best performance.

years as a hardcore imager, I've only
recently returned to visual astronomy. I
must admit, I had forgotten the simple
joy of just taking ﬁve minutes to set up
a telescope for a quick look at an object
or two. It really was a pleasure, certainly better than my ﬁ rst experience
with a Go To mount and scope combination many years back, which was of
course the biggest scope I could afford
(the #1 mistake beginners often make).
The AZ-GTi is simple, stress-free, and
easy to use.
The Evostar 72 is a budget APO, and
yes, I could tell the difference between
it and some of my top-shelf scopes,
most of which, however, would require
adding an extra zero to the price. It has
good color performance in the middle
of the ﬁeld, with only a touch of color
visible at the edges when viewing the
brightest objects. For astrophotography,
I found the Evostar 72 to be a pretty
reasonable starter scope, and combined
with the AZ-GTi, it's also a nice, portable visual package.
■ RICHARD S. WRIGHT, JR. can often be
found sharing views of the night sky at
his local Starbucks.
sk yandtele scope.com * FE B RUA RY 2 019

http://www.skyandtelescope.com

Sky & Telescope - February 2019

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