WWW.ASTRONOMY.COM 57
to fill in the small gap. Several are avail-
able online and work well.
The IMX 455 CMOS chip is the first
to capture data in true 16 bits. Most cam-
eras use chips that capture data in 14 bits
and interpolate up to 16 bits. True 16-bit
data has an incredible number of tonal
values so stretching can be performed
without the image falling apart. By cap-
turing in 16 bits, you have the full range
of 65535 density levels, which allows you
to pull out more detail during process-
ing. If you’re simply stretching 8-bit data,
it doesn’t look good because of the lim-
ited number of tonal values.
The QHY 600 is available in both
mono and color versions, and in a variety
of configurations depending on how you
plan to use the camera. I spoke at length
about shooting color versus mono in my
review of the QHY 410C color camera,
which appeared in the February issue.
To sum it up, traditionalists like myself
prefer shooting mono with separate fil-
ters for the RGB and narrow bands.
It does get a bit more complicated,
however. A color camera records all
colors simultaneously utilizing a Bayer
matrix. This makes creating colored
images a lot easier and can be an advan-
tage for imaging certain objects, like
comets. If you are used to working with
a mono CCD camera, the switch to a
CMOS mono camera should not be
difficult.
The one difference that I have found
between the two is that because CMOS
has such low noise, you only need RGB
exposures to create an image, with no
luminance exposure required. If you feel
you do need a luminance, you can fabri-
cate one by averaging all the color data.
Due to the large size of the files and
the fast download
speeds, QHYCCD built
in a 2-gigabyte DDR3
image buffer to smooth
data transfer to the host
computer. The data
from the QHY 600, in
addition to its real 16-bit depth, are also
true raw data, meaning the recorded
data have undergone no adjustments,
such as noise suppression or hot pixel
removal. It is the original signal, which
can be processed and manipulated as the
situation necessitates. The camera has
one other great feature: There’s zero
amplifier glow even with extended expo-
sure times.
Dew, condensation, and ref lections
have always been problems with digital
cameras. The QHY 600 addresses them
with a desiccant plug for the hermetically
sealed CMOS chamber, high-end anti-
ref lective coatings on all glass surfaces,
and a heater to keep external windows
moisture-free. The sensor is cooled by a
regulated two-stage thermocouple device
to maintain a constant temperature.
Creating images
I try to keep my processing as simple
as possible, yet I sacrifice nothing in
producing the final results. I use MaxIm
DL for my initial processing: the creation
of master darks, f lats, and bias frames. I
also use it to reduce and combine all my
data files. I find that the sigma combine
function works great to maintain as
much information as possible and still
remove outliers like hot pixels. Be careful
with these. Some hot pixels change value
so that the dark frame does not remove
them completely. You need outlier rejec-
tion and at least five frames to affect
their removal.
After creating the master files, I save
them as a 16-bit TIFF file. I then import
it into Photoshop, stretching it with
curves or levels to bring out all the detail.
CMOS data have such low noise that cer-
tain plug-ins work wonders. These typi-
cally are Luminar, Topaz II, and the real
secret weapon, the sharplet filter in the
Redfield suite. There are numerous star
reduction methods, which include Russ
Croman’s Star Shrink and the minimum
filter in Photoshop. In all cases, I use
these powerful tools with the stars
selected and feathered.
Large stars can be reduced using the
liquefy filter and choosing the pucker
tool. If it sounds like there are a lot of
tricks to make striking images, you’re
right. But the challenge can be part of
the fun.
If noise does show up in your image,
it’s usually in the shadows. Make a dupli-
cate layer, generously apply the noise
The optional filter
holder is seen here,
attached to the
QHY 600. QHYCCD
PRODUCT
INFORMATION
QHY600PH
Sensor: Sony IMX455 back-illuminated
Sensor size: 36mm x 24mm (full frame)
Image buffer: 2 gigabytes
Pixel size: 3.76x3.76 micrometers
Effective pixel area: 9576x6388
Output: 16-bit with 65535 levels
Exposure range: 40ms to 3600s
Computer interface: USB 3.0
Weight: 30 ounces (850 grams)
Dimensions: 5.2 x 3.5 inches
(131.8mm x 90mm)
Price: $4,599