Sky and Telescope - June 2017 - 60

S&T Test Report

tener's 2-inch tube was squarely inserted
into the focuser. Despite the focuser's
2-inch collar having a compression ring,
I found I could tighten the collar's three
thumbscrews and still have the ﬂattener
tilted, which would result in unevenly
distorted stars across the ﬁeld.

Mechanical Quality
The telescope is quite light for its aperture, weighing just 4.1 kilograms (9
pounds) without rings or other accessories. (By comparison, the premium
apo I compared it to weighs 5.8 kg,
even though it has a carbon ﬁber tube.)
The FCD 102-mm will work well with
a light "grab-and-go" mount, such as
Explore's own Twilight alt-azimuth
model, at least for visual use. I used the
scope on a similar Astro-Tech Voyager
mount, a combination that worked well.

Of course, long-exposure photography
requires a heavier equatorial mount.
The FCD100 series comes with
Explore Scientiﬁc's standard HEX
focuser, a Crayford-style unit with both
coarse and 10:1 ﬁne focus adjustments.
It has a relatively short 44 mm of travel.
So to allow for the varied back-focus
demands of eyepieces and cameras, the
FCD100 comes with three extension
tubes, one short and two longer ones,
plus a ﬁnal screw-on collar that accepts
2-inch accessories.
For visual use the one short extension tube sufﬁced to enable all the
eyepieces I tried, from low-power 2-inch
to high-power 1¼-inch eyepieces, to
reach focus with the excellent 2-inch
mirror diagonal supplied as standard
equipment. For photographic use with a
DSLR, one additional longer extension

tube was required. Attaching a CCD
camera might require the third tube,
depending on the spacing requirements
of the camera.
The extension tubes screw on with
ﬁne threads that might be easy to crossthread. Also, if they weren't on tight, I
found they could loosen and turn under
the weight of a star diagonal and heavy
eyepiece if they were tilted towards the
left side of the focuser, causing them
to unscrew and ﬂop down unnervingly.
There are no lock screws to secure the
extension tubes.
On the plus side, by not using any
extension tubes I could get my Baader
binoviewer and its own low-proﬁle
diagonal to reach focus without requiring any Barlow lens. That produced a
lovely 2° ﬁeld with a pair of 24-mm Tele
Vue Panoptic eyepieces.

With the optional ﬁeld ﬂattener, stars appeared as pinpoints across most of the ﬁeld, only exhibiting aberrations at the corners. This image of NGC 7000, the North America Nebula, is a stack of ﬁve 6-minute exposures at ISO 1600 with a modiﬁed Canon EOS 5D MkII camera.

60

J U N E 2 0 1 7 * SK Y & TELESCOPE

Sky and Telescope - June 2017

Table of Contents for the Digital Edition of Sky and Telescope - June 2017

Contents
Sky and Telescope - June 2017 - Cover1
Sky and Telescope - June 2017 - Cover2
Sky and Telescope - June 2017 - 1
Sky and Telescope - June 2017 - Contents
Sky and Telescope - June 2017 - 3
Sky and Telescope - June 2017 - 4
Sky and Telescope - June 2017 - 5
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Sky and Telescope - June 2017 - 7
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