56 ASTRONOMY • JUNE 2022
pixel at its position. It does this with
transistors surrounding each photosensi-
tive pixel. Initially, this created two
problems. First, the transistors took up
real estate where more pixels could go;
second, after a certain level of exposure,
amplifier glow fogged the image.
But CMOS chips were easier to make
and thus less expensive. They also
required considerably less power to run.
In addition, CMOS chips have signifi-
cantly higher frame rates, allowing users
to take successive images faster because
the readout is quicker. Manufacturers
kept improving CMOS chips until they
had lower noise and higher resolution
than their CCD counterparts.
With the advent of commercially
available back-illuminated chips, sensi-
tivity and quantum efficiency skyrock-
eted. In such a chip, all the electronics
are grouped behind the pixels, allowing
all the space facing the sky to be filled
with photoreceptors. This
means that all incoming
photons strike the pixels.
Back-illuminated chips
also increased the deep well capacity —
how many photons can be recorded
before the photo receptor site “fills up”
and can’t record any more data. The
Sony Corporation accomplished much of
this progress and most of today’s high-
end CMOS astronomy cameras contain
Sony chips.
In fact, many manufacturers have
ceased to make CCDs.
Enter the QHY 600
The QHY600PH mono CMOS chip
camera that I am currently using is
the beneficiary of all this history and
technology. It is the brainchild of Qiu
Hongyun, more commonly known as Dr.
Qiu, who founded QHYCCD in 2003. Dr.
Qiu has degrees in optical science and
engineering, including spe-
cialties in noise reduction
as it appears in hardware
and software — quite use-
ful when designing astronomy cameras.
The QHY 600 camera utilizes the lat-
est Sony IMX 455 CMOS BSI chip. (BSI
stands for backside illuminated.) The
pixel size is 3.76 microns. In the full
35mm frame, this creates an image
that is 9576x6388 pixels in resolution,
or 61 megapixels in size. That pairs
nicely with wide-field telescopes like
small refractors.
The camera can also be binned 2x2
(where four pixels are combined to act as
one) for approximately 7-micron pixels
and lower file size. I do this when I use
my Planewave CDK17, which has a focal
length of 3,000mm and matches well
with 7-micron pixels.
The QHY 600 mono camera works
well with the QHY CFW3 medium filter
wheel, which attaches to the camera and
plugs into it. The wheel is threaded for 2"
mounted filters and the openings are
50.8mm. If you use 50.0mm filters like
those from Chroma, you’ll need spacers
Four 10-minute shots
through R, G, and B
filters allowed the QHY
600 to produce this
image of the Orion
Nebula (M42). TONY HALLAS