Sky & Telescope - July 2022 - 68

S&T Test Report
measure, I applied a film of light grease
to the threads of the FRA500's set,
avoiding any issues with binding during
my testing.
Like the FMA230, the FRA500
includes tube rings and a dovetail
mounting plate. The top handle on the
rings is slotted to accommodate other
accessories, such as a small guidescope.
The bottom plate is a 4-inch-wide
Losmandy-style plate. Those wanting to
pair this scope on a mount that accepts
only the narrower Vixen-style dovetail
bars will need to replace this piece.
Orienting your camera with this
instrument is a bit different than the
FMA230 since the focuser itself doesn't
rotate, and turning the entire tube to
reorient the focuser requires an Allen
key to loosen the tube rings, which is an
inconvenience. Instead, the focuser has
a locking camera-angle adjuster that
turned smoothly and did not shift focus
when rotated. So, framing a camera was
easy, though there are no angle markings
on the rotator for making precise
turns, which would be helpful when
shooting mosaics.
Although each Askar instrument
came with a signed inspection certificate,
my FRA500 arrived with some
minor cosmetic blemishes. But, overall,
the unit is well-made.
FRA500 Optics
The focuser of the bigger FRA500 offers
an M86 male thread, which accommodates
either the conical camera adapter
set or the included 2-inch visual back.
All the eyepieces I tested reached focus
with a 2-inch star diagonal. Under
high-magnification testing, stars in
focus showed a nearly perfect Airy disk
and clean first diffraction ring, with no
astigmatism, even on cold winter nights
when optics can be pinched by contracting
lens cells.
In focus, bright stars were colorless,
with no blue or magenta halos
of chromatic aberration. Extra-focal
diffraction patterns showed a touch of
asymmetry either side of focus, indicating
slight spherical aberration. The
diffraction pattern had a mild magenta
rim inside focus and a cyan rim outside
68 JULY 2022 * SKY & TELESCOPE
The FMA230 (left) comes in a gift box but does not include a carrying case, though it is small
enough to slip into a typical camera bag. The FRA500 (right) comes with a foam-fitted aluminum
case that holds the scope (with rings attached) and space for the camera adapters.
of focus from residual longitudinal
chromatic aberration. Ditto on crater
rims and the limb of the Moon - they
were colorless in focus but showed the
same slight tints when just out of focus.
I compared the FRA500 to a Sharpstar
94EDPH, a similar-sized telescope
from Askar's companion brand. In
star tests, images in the two telescopes
looked identical, and both scopes
cleanly resolved close double stars
such as Castor, with generous dark sky
between the component suns.
Photographically, star images in the
Askar 500 appeared sharp right across
images produced by a full-frame sensor,
though stars at the extreme corners
were elongated ever so slightly. This
is field-flatness performance as good
as I've seen in the many apo/flattener
combinations I've tested over the years.
Recommendations
The little FMA230 is suitable for framing
wide Milky Way star fields and dark
dust lanes, and even small constellations.
While a 200-mm telephoto camera
lens can provide a similar field of
view, most will need to be stopped down
to f/4 or f/5.6 to approach the image
quality of the FMA230. And a camera
lens won't have the ease of image rotation
and mounting features offered by
astrographs like these Askar models.
At about $630 from U.S. suppliers, the
FMA230 is also less expensive than
most 200-mm telephoto lenses, though
of course the FMA lacks features such
as auto-focus and aperture diaphragms.
The small astrograph's size and
light weight make it ideal for overseas
trips to exotic locations, while its short
focal length is a good match for a star
tracker mount - a compact and portable
combination.
Out of the box, the bigger FRA500
is a superb visual and photographic
instrument. The optional f/3.9 reducer
should provide the attractive choice
of an even wider field and faster speed
when needed, but not having a sample
of the reducer for testing, I can't say how
well that combination works. However,
the FRA500's native f/5.6 speed is fast
enough for most imaging purposes with
the aid of a guidescope and autoguider,
and it will work well mated to a small
equatorial mount for a lightweight
observing rig to take to dark skies.
The similar telescope in the Sharpstar
line, the 94EDPH, also works very
well (I know, I own one!), and it costs
about $200 less than the $2,000 for the
FRA500, once you factor in the $300
for the required EDPH reducer. But the
FRA500 offers the flexibility of being
able to work photographically at two
focal lengths and fields of views, though
by adding its extra cost f/3.9 reducer.
We are certainly spoiled for choice
these days, and this pair of Askars are
fine options for anyone looking for a
wide-field astrograph. Or two!
¢ ALAN DYER is coauthor with Terence
Dickinson of the new fourth edition of
The Backyard Astronomer's Guide, described
at BackyardAstronomy.com.

http://www.BackyardAstronomy.com

Sky & Telescope - July 2022

Table of Contents for the Digital Edition of Sky & Telescope - July 2022