Astronomy - USA (2022-06)

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