Sky & Telescope - January 2024 - 69

ing the need to mosaic several frames
in order to capture the largest craters
when shooting with my Newtonian and
Schmidt-Cassegrain.
Under the typical seeing conditions
at my New Hampshire location, I often
didn't need any additional Barlow or
projection to produce good detail on
Jupiter using a Celestron C14 at its
Cassegrain focus, unless the atmosphere
was extremely steady, allowing me to
crank up the magnification. Nor did I
need anything but the 678M camera
in my 12.5-inch Newtonian reflector's
focuser to capture a fairly large image of
Venus on August 13, just half a day after
inferior conjunction, when the planet
was a 57″ crescent (seen at right).
I had two particularly notable
observations with the 678M. The first
was most likely due to those tiny pixels.
I found I needed to stack a lot more
images of my targets to get a smooth
result that held up to sharpening compared
to the 200M and other planetary
cameras I've used. Images taken with
the camera become " noisy " when applying
the same wavelet settings in RegiStax
6 that I would use with the same
target, scope, and number of frames.
For example, I often stacked about 33%
of 5,800 frames when targeting Jupiter
with the 200M camera on my C14 to
achieve a good result after sharpening.
Using the 678M in the same scope at
Both cameras are
smaller than the
typical 1¼-inch
eyepiece.
The 2-micron-square pixels in the 678M
camera make resolving the planets easy even
when imaging at relatively short focal lengths.
This shot of Venus was captured at prime focus
on the author's 12.5-inch f/5 Newtonian reflector
less than 12 hours after the planet passed
through inferior conjunction on August 13, 2023.
an identical image scale and frame rate,
I needed about 40% of the frames to
achieve a comparable result.
The other thing to be aware of
when considering the 678M is that
its 8.4-megapixel detector generates
massive files when working at full
resolution. Each video can be dozens of
gigabytes. And that onboard 512-megabyte
image buffer did some heavy-duty
lifting as I attempted several lunar
mosaics. When imaging with the camera
connected to my aging SurfacePro
laptop, I had to wait a good 15 seconds
or more before starting another video
as the buffer released its backlog of
frames. Be sure you have a computer
with a large hard drive and a fast write
speed. Solid-state drives are highly recommended
for planetary imaging. Also,
plan on investing in a multi-terabyte
portable drive in order to move and/or
store your videos.
A welcome option with such tiny
pixels is the ability to bin the chip 2×,
meaning the control software groups 4
pixels together to effectively function
as a single, larger pixel. This allows the
678M to perform just like the 200M in
most respects, producing a 2-megapixel
video as opposed to one with four times
the pixels. It's like having the ability to
reduce the image scale by half when the
seeing degrades, but without having to
swap Barlows or even change focus.
Both the QHY5III200M and the
QHY5III678M
QHY5III200M
Although both cameras performed admirably on each chosen target, images taken with
the 678M get noisy quickly when sharpened compared to those from the 200M. This pair
of Jupiter images was recorded through the same telescope and blue filter. Each utilizes
the same number of frames, though the 678M result at left is noticeably grainier than that
with the 200M. A simple remedy is to stack a higher percentage of frames.
QHY5III678M are excellent cameras for
imaging the Sun, Moon, and planets.
Although they offer similar fields of
view, the 678M is particularly attractive
for lunar imagers, and its binning
capability makes it versatile for imagers
who use a wide variety of telescopes
and focal lengths. The 200M is a fine
performer, especially if your focus is
exclusively with the major planets, or if
you're looking for a camera that functions
as both an imager and autoguider.
The QHY5III body is one of the most
compact designs available today and
will work in most any guidescope or offaxis
guider.
¢Associate Editor SEAN WALKER often
targets solar system bodies from his
backyard observatory in Litchfield, New
Hampshire.
sk yand tele scope .o r g * JANUARY 2024 69

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