focuser extension—allowed the HEQ5
mount to carry the scope without difficulty.
To save weight and make room for my
auto-guiding scope, I omitted the supplied
8 ×50 finderscope and used my own red-dot
finder for rough aiming.
The greatest difficulty I encountered
was achieving perfect focus. Although the
supplied dual-speed focuser is sturdy and
free of play, I found that getting sharp star
images involved more effort than expected
due to the unit’s balky fine-focus control.
No matter how I set the tensioning thumb-
screw, I could never get the fine focus to
perform reliably. Adjusting inward—when
the camera’s weight exerts a downward
force—worked fine, but when I tried to
focus outward, the fine-motion control
failed. It simply didn’t provide enough
friction to lift the camera’s weight. I was
able to work around this by rotating the
OTA so that the focuser was parallel to the
ground (a position that wasn’t always con-
venient) or by using the coarse adjustment
to position the camera outside of focus and
then utilize the fine control to creep in to
focus. Thankfully, most eyepieces in my
collection are light enough not to present a
problem when using the scope visually.
To keep the OTA short, Orion opted
to position the focal plane 6^3 ⁄ 4 inches
(170mm) out the side of the tube. That’s
a lot. Even with the focuser racked all the
way out, I was unable to reach infinity focus
for my camera unless I used the supplied
extension tube. This accessory was also
required for visual use—and even then, I
had to slide some eyepieces partway out
the drawtube to achieve focus. One notable
consequence of this arrangement is that
balancing the scope becomes difficult in
many orien tations—the farther the mass of
the camera (or eyepiece) is positioned away
from the optical axis, the more unbalanced
the assembly is when pointed toward the
zenith, even after the OTA is correctly ad-
justed for balance in right ascension and
declination.
There’s another problem with having
the focal plane positioned so far outside
the tube. Bench and field testing revealed
that the 63mm secondary mirror is barely
big enough to intercept the converging
cone of light arriving from the primary
mirror. There’s zero margin for error in
correctly placing the diagonal during col -
limation, and there’s a 0.4-magnitude
brightness drop at the edge of images shot
with my camera. In practice, this degree
of vignetting isn’t a great worry, since most
image-processing software can readily cope
with it. Even so, I couldn’t help wondering
why Orion didn’t eliminate the problem
by moving the diagonal mirror one inch
closer to the front of the tube. That would
allow the focuser height to decrease by
one inch and provide a little collimation
leeway. There’s more than enough extra
tubing at the front of the scope to accom-
modate this repositioning.THE RIGHT FIT?
Despite the design quirks, balance issues
and balky fine-focus control, there’s a lot to
like about the Orion 6-inch f/4 astrograph.
It’s an excellent choice for DSLR shooters
working with APS-C cameras. As you can
see from the examples shown here, the tele -
scope is certainly capable of producing
pleasingly sharp photos. And though I
didn’t spend a lot of time evaluating its
visual capabilities, it performed well as
a rich-field instrument delivering up to a
4.3-degree-wide field of view. Once in a
while, I’d pop in a low-power eyepiece and
sweep the Milky Way just by cradling the
scope in my lap. Quick and easy observing!
Does the Orion 6-inch astrograph de-
serve a place in your sky-shooting arsenal?
To a large extent, the answer depends on
how useful the image scale offered by a
610mm focal length is for the kind of
astrophotography you want to do. With my
camera and coma-corrector combination,
the instrument delivers a two-degree-wide
field. That’s a chunk of sky big enough to
encompass many large deep-sky objects,
such as the Double Cluster, in Perseus, or
the Pinwheel Galaxy (M33), in Triangulum.
The focal length is also nearly ideal for
recording the Orion Nebula (M42). Is
the telescope good value for the money?
Absolutely. Just imagine what a comparable
f/4 refractor with perfect colour correction
would cost! Maybe Isaac Newton was on to
something after all. ✦SEPTEMBER/OCTOBER 2019 •SKYNEWS 35
Approximate retail price:
US$400
http://www.telescope.com
Summary: An attractively priced
astrograph well suited to DSLR
astrophotography.PLUSES- A sturdy instrument built with
quality components - Good optical performance
- Generous assortment of included
accessories
MINUSES- Fine-focus control prone to slipping
- OTA difficult to balance with supplied
dovetail bracket - Secondary mirror barely big enough
ORION 6-INCH F/4
ASTROGRAPHIC
TELESCOPEVULPECULA’S DUMBBELL NEBULAAlthough the Orion 6-inch f/4 astrograph is best suited
to large targets, it does pack enough resolution to do a credible job with smaller objects, such as
plan etary nebula M27. This full-frame image is a stack of five 1-minute exposures taken at ISO 800
with a Nikon D5100 DSLR and a Tele Vue Paracorr coma corrector.