Sky & Telescope - January 2024 - 68

S&T Test Report
The 200M is also no slouch when it comes
to lunar close-ups. This detailed, 2-panel
mosaic of the crater Copernicus was recorded
through a green filter on the same evening as
the photo of Jupiter seen on page 67.
pected. When I turned
to Jupiter and Saturn,
they also yielded high
frame rates, as did
the Moon and Sun
(through a proper solar
filter). Recording videos
with the full frame of
the 200M was useful
when including nearby
Galilean moons in
images of Jupiter. The
onboard 512 megabytes
of DDR RAM acting
as a frame buffer was
particularly useful
then. While operating
the camera using FireCapture,
the software's
status bar showed buffered frames
downloading for 10 seconds or so after
the recording had been completed,
and I never lost any data because of
dropped frames.
I briefly used the 200M as an
QHY5III678M
tBoth cameras are very
sensitive to wavelengths
beyond the visible spectrum,
as noted in the
text. These images show
Venus recorded on June
22, 2023, about 24 hours
apart through a Baader
Planetarium Venus filter
centered at 350 nanometers
in the ultraviolet. Both
photos were captured at a
frame rate of 209 frames per
second through the author's
12.5-inch Newtonian reflector
operating at f/20.
QHY5III200M
close-ups of the Moon,
planets, or the Sun. For
example, the 678M is an
excellent match for my
Celestron C14 at prime
focus in average seeing.
The 678M also claims even greater
autoguider when supernova SN 2023ixf
appeared in M101 late last May. PHD2
software had no problem detecting the
camera and got busy guiding without
a hitch.
QHY5III678M: Tiny Pixels,
and Lots of Them
As mentioned earlier, both cameras have
very similar field coverage. But due to
the smaller pixels in the 678M the camera
produces an image scale twice that
of the 200M. Those little pixels cover a
smaller area of the sky and so produce
an effect similar to using a higher-magnification
eyepiece. This translates to
extremely high resolution when imaging
with the 678M at prime focus of
the Schmidt-Cassegrains popular with
planetary imagers. You often may not
need additional focal extenders in the
optical path to produce high-resolution
tThe small pixels within the 678M combined
with its relatively wide field make the camera
attractive for lunar imagers seeking to create
high-resolution lunar photos. The author recorded
this 11-panel mosaic on the evening of
June 23, 2023, at the prime focus of his 12.5inch
Newtonian reflector through the camera's
included IR850 near-infrared-filtered chamber
window. He still missed a spot.
68 JANUARY 2024 * SKY & TELESCOPE
quantum efficiency than the 200M,
though it peaks at around 650 nanometers.
The camera's 8.4-megapixel sensor
produces up to 43 FPS when operating
in 8-bit mode, and 22 FPS in 16-bit
mode. Both generate a lot of data!
16-bit-mode is generally more useful
for deep-sky imaging, so I'd recommend
activating it and output FIT-format
images when targeting nebulae, galaxies,
and star clusters. In those cases,
you would record exposures many
seconds (or even minutes) long, rendering
the camera's frame rate irrelevant.
However, none of the cameras in the
QHY5III series includes thermoelectric
cooling, so the long exposures are generally
noisier than those captured with
a cooled deep-sky camera, particularly
on hot summer nights.
In contrast, the targets for highresolution
planetary imaging (as well
as solar and lunar photography) are
bright by comparison. As such, they are
well-exposed in fraction-of-a-second
exposures, so they don't benefit greatly
when recorded with a greater bit depth.
In these cases, speed is more important
than bit depth.
The little pixels in the 678M paired
with its generous field make the Moon a
particularly attractive target. Its expansive
detector produces a wide field at an
impressively high image scale, eliminat
Sky & Telescope - January 2024

Table of Contents for the Digital Edition of Sky & Telescope - January 2024
