that the aforementioned coma corrector is
a must-have. The rapidly converging light
cone of an f/4 Newtonian (regardless of the
instrument’s optical quality) has enough
coma to show up clearly even in photos
captured using a camera
equipped with an APS-C-
sized sensor—the config -
uration found in most
enthusiast DSLRs. (Orion
sells a variety of optional
coma correctors starting at
US$250.) In addition,
an auto-guider setup
will likely prove very
useful.
What’s not in the
box? Since this in -
strument is sold mainly as a
photographic tool, no eyepieces are
included. I, for one, was glad not to
pay part of the purchase price for
the privilege of having yet another
25mm eyepiece cluttering my eye-
piece drawer. The omission of a col-
limation cap, however, was surprising—
even an astrograph needs to have its
optics carefully aligned.
Once I had all the parts laid out in
front of me, I have to admit I was im-
pressed by what I saw. Everything was
attractively finished (mainly in gloss black)
and seemed well made. Considerable
attention to detail was evident. For exam-
ple, the hefty focuser is mounted with a
re inforcement plate inside the OTA toreduce the potential for flexure. All the
focuser fittings (including an extension
tube and a 1¼-inch adapter) utilize com-
pression rings instead of the usual locking
screws, which tend to scratch eyepiece bar-
rels. The instrument’s overall fit and finish
is very good.
I was excited to get the scope mounted
and out under the stars. For my testing,
I used a Nikon D5100 DSLR camera, a
Tele Vue Paracorr coma corrector and a
Celes tron NexGuide auto-guider mated
to a homemade 70mm guidescope, all rid-
ing on my venerable Sky-Watcher HEQ5
mount. However, as soon as I lifted the
Orion onto the mount and attached my
camera, I hit a snag—the OTA was notice-
ably front-heavy. I loosened the tube rings
and slid the scope rearward as much as
I could, then shifted the dovetail bar as far
back on the mount as possible, but the
assembly was still out of balance. The
dovetail section of the included mounting
bar is too short to allow enough back-
and-forth adjustment to accommodate
the 795-gram (28 oz) weight of my DSLR
and Paracorr combination. Fortunately,
I had another longer dovetail bar that
solved the problem.CATCHING PHOTONS
For the most part, my imaging sessions
went smoothly and were gratifyingly un-
eventful. The astrograph’s compact size and
relatively modest six-kilogram (13.2 lb)
weight—including finder, tube rings andSHARPENING UPThe biggest shortcoming of the Orion astrograph is
its fine-focus control, which lacks sufficient friction to move the camera
outward in certain tube orientations. In addition, the scope’s design places
the focal plane 6^3 ⁄ 4 inches (170mm) outside the optical tube assembly,
requiring the use of the included extension tube to reach focus with a
camera or an eyepiece.34 SKYNEWS •SEPTEMBER/OCTOBER 2019
COMETS, COMETS EVERYWHEREThe effect of coma is apparent
in this crop from the bottom left corner of a photo of the Double Cluster
captured without the aid of a coma corrector. While the stars at the centre
of the field in the full-sized image are sharp and round, those near the
edge are distorted into little comets.
PHOTO-READYThe author evaluated the
Orion astrograph using the configuration shown
here, consisting of a Sky-Watcher HEQ5 German
equatorial mount, a Tele Vue
Paracorr coma corrector
and a Celestron NexGuide
auto-guider (affixed to a
homebuilt guidescope).