Sky & Telescope - July 2022 - 65

and their fine helical focusing, while
superb for astrophotography, make
them less than ideal for most terrestrial
targets, except perhaps for those at a
fixed distance like a bird feeder or nest.
I found the closest focus point for the
FMA230 to be 15 meters (50 feet).
The larger FRA500's name refers to
the 500-mm focal length of its main
lens, though astronomers are more
likely to think of it as the 90-mm aperture
telescope it really is. The instrument
is a Petzval design that includes
a pair of lenses (a front three-element
and a rear doublet) to achieve the stated
f/5.6 focal ratio.
An optional 0.7× reducer lens takes
the FRA500 to f/3.9 and 350-mm focal
length. However, at the time of my testing
in early 2022, this accessory reducer
was undergoing design changes, and a
sample unit was not available to us.
At the time of testing, the FRA500
was the newest in a family of FRA astrographs.
The FRA400 has a 72-mm lens,
while the FRA600 has a 108-mm lens,
both at f/5.6 with a quintuplet design
like the mid-sized FRA500. An even
newer 60-mm f/5 FRA300 has since
been announced.
The FMA230 Mechanics
The little FMA230 has a solidly built,
black-metal tube that can be separated
into several components for air travel
All the FMA230's parts can unscrew from each other. The metal dew cap extends 50 mm (2
inches) and is threaded to accept 58-mm photographic filters.
or inspection at airport security. The
modular design reminds me of the Japanese
Borg brand of astrographs.
The scope includes red anodized
tube rings and mounting plates. While
fashionable and attractive, I find such
finishes are easily scratched. In particular,
the dovetail plates soon become
marked by the clamps and set screws
of some mounts. The FMA230 includes
an 18-cm-long (7-inch), Vixen-style
standard dovetail for attaching it to a
mount or star tracker.
The aforementioned helical focuser's
motion proved smooth and precise,
though in the sub-freezing temperatures
of a Canadian winter night, the
lubrication stiffens, making the focuser
control difficult to turn. I also found
that the focuser's tiny lock screw is
impossible to adjust with gloves on.
The tube components are well blackened
inside, though in some test images
I did notice an odd flare, likely produced
by a bright star just outside of the camera
frame.
The rear adapter ring on the reducer
has 48-mm threads on the camera
side to accept large-aperture T-rings
for DSLR and mirrorless cameras, or
the nosepiece tubes of cooled CMOS
cameras. The adapter ring separates
from the reducer to reveal a recessed,
threaded well on the telescope side
that accepts standard 48-mm filters.
However, as with any such recessed
filter wells, screwing filters in and out is
fiddly, with fingers inevitably touching
the filter. Changing filters also requires
removing the camera.
There is no rear camera-angle
adjuster as such. Rotating the camera
is a matter of loosening the four bolts
on the felt-lined tube rings and rotating
Without camera adapters, the FRA500 is
38 cm (15 inches) long with its dew shield
retracted and weighs 5.4 kg (11.9 lb).
The larger FRA500 astrograph presents a
4° by 2.7° field with full-frame sensors, perfect
for many targets along the Milky Way such
as these nebulae in Auriga. This is a stack of
ten 6-minute exposures at f/5.6, with a stock
Canon R6 camera at ISO 800.
sk yand tele scope .o r g * JULY 2022 65
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Sky & Telescope - July 2022

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