SkyNews – September 2019

C

APTURING PHOTOS of nebulas,

clusters and galaxies is undeniably

satisfying, and the barriers to pro-

ducing superb results have never been

lower. Suitable cameras, mounts and tele-

scopes are readily available at a price that

was unheard of as recently as a decade ago.

For astrophotographers, these really are the

best of times. If you have a DSLR (or “mir-

rorless” interchangeable-lens camera) and

want to go beyond the capabilities of basic

lenses, attaching your camera to a telescope

is the logical next step. But what kind of

scope is best?

A high-quality apochromatic refractor

is a very popular choice, but such astro-

graphs are pricey enough to discourage be-

ginners. Fortunately, expensive refractors

aren’t the only option. For would-be astro -

photographers on a budget (and even ex-

perienced imagers), Newtonian reflector

telescopes offer many significant benefits.

ISAAC NEWTON

TO THE RESCUE

Newtonians are available in a wide range of

apertures and focal lengths, all with one

thing in common: perfect colour correc-

tion. Reflectors are also much less expen-

sive per inch of aperture than any other

design. For astrophotographers, there are

many mod els that combine useful focal

lengths with fast focal ratios—a one-two

punch yielding both a generous image scale

and relatively short exposure times. Sounds

good, right? Yes, but as you probably sus-

pect, there’s a reason why apochromatic

refractors are so popular.

Fast reflectors (those with focal ratios of

f/5 or lower)

have two significant strikes against them.

First, most will require additional optics to

correct for coma—an aberration that causes

stars near the edge of the field to smear into

blurry little comets. Second, you’ll have to

learn how to accurately align the optics

in a process called collimation. Neither of

these are deal breakers. Coma correctors

are easy to find (you may already have

one for visual use), and collimation isn’t

nearly as difficult to accomplish as you may

have heard. (You can find detailed collima-

tion instructions on my personal website:

http://www.GarySeronik.com.)

Clearly, Orion Telescopes believes the

reflector option is an appealing one. The

company offers 6-, 8- and 10-inch Newto -

nian astrographs, each similarly spec’d. We

opted to evaluate the least expensive model,

the 6-inch f/4, which can be purchased

as an optical tube assembly (OTA) for

US$400. No question, this is still real

money. However, keep in mind that the

lowest-priced astrographic refractor Orion

offers (an 80mm f/6 apochromat) comes

in at US$950! It makes the much bigger

Newto nian seem like quite a deal. And with

the Orion 6-inch, you get a lot of astropho-

tographic niceties for your $400.

OUT OF THE BOX

The Orion astrograph sports a dual-speed

2-inch Crayford-style focuser, felt-lined

tube rings, an 8×50 finderscope and a

Vixen-style dovetail bracket. Of course, you

must supply your own camera, T-adapter

and mount, but the basics are all accounted

for. What else might you need? I’d argue

SEPTEMBER/OCTOBER 2019 •SKYNEWS 33

WORTH 1,000 WORDSThis image of the

famed Double Cluster, in Perseus, neatly

summarizes the capabilities of the Orion

6-inch f/4 astrograph—a generous field of

view with good star images from corner

to corner when an optional coma correc-

tor is used. To create this photo, the author

stacked five 2-minute exposures shot at

ISO 800 with a Nikon D5100 DSLR camera

and a Tele Vue Paracorr coma corrector.

THE COMPLETE PACKAGE
The Orion 6-inch f/4 astrographic
reflector includes a heavy-duty
2-inch focuser, an 8×50 finderscope
(with spring-loaded bracket),
felt-lined tube rings, a dovetail bar,
a focuser extension tube and
a 1¼-inch eyepiece adapter.