The QHY 168C from QHYCCD is a one-shot colour camera with an APS-C sized sensor, a size format commonly used in non-full-frame DSLRs. A built-in, two-stage Peltier thermoelectric cooling (TEC) system can bring the camera’s sensor down to 35˚C below the ambient (air) temperature, reducing thermal noise and, in theory, producing cleaner images.
The QHY 168C uses a Sony IMX071 colour CMOS sensor, the same type as Nikon uses in several of its DSLR models.
This chip provides a 16 megapixel array of 4.8 micron square pixels arranged in a 4,952×3,288 array.
The camera uses an internal memory buffering system and, together with USB 3.0 connectivity, it’s able to maintain high-speed PC transfer rates.
In use the full-frame transfer time was quick enough that it didn’t really register there was any delay.
Recording natively as 14-bit images, it’s possible to output 8- or 14-, or expanded 16-bit images from this camera.
Jack of all trades
Despite having a DSLR-class sensor, the QHY 168C offers far greater functionality than a regular DSLR.
Exposure times range from 30 microseconds to 1 hour (3,600 seconds) and the camera supports region of interest (ROI) definition.
ROI is used to define a smaller area of the imaging array as active, while pixels outside the area are ignored.
As such, the camera is a jack of all trades when it comes to astrophotography, being both suited to wide-field deep-sky imaging, as well as the tiny fields used for imaging the planets.
The shorter end of the camera’s exposure range permits ‘lucky imaging’. Here, you basically take lots of images in rapid succession in the hope that some appear hardly distorted by the atmosphere.
These are then extracted, registered and averaged together to give a result which should exceed the quality of an individual frame.
Obviously, using a large sensor like the IMX071 for lucky imaging at full resolution will take a toll on the number of frames per second you can record, the onboard memory buffer and USB 3.0 connectivity are efficient but still have limits on how much data you can convey to a PC.
This is where ROI comes into its own, because a smaller active area results in a smaller amount of data per image.
For example, at full resolution, peak rates hit 10 frames per second but using a small 240×240 pixel array, this increases to 130 frames per second.
As is common with astronomically dedicated cameras, you are responsible for sourcing and installing control software to operate the QHY 168C. Fortunately, there are several free or low-cost options available.
For our testing we used FireCapture and SharpCap. FireCapture is brilliant for high-speed captures, but less well-suited for long exposure astrophotography.
SharpCap is a good all-rounder, V2.9 or above working well with the QHY 168C.
An ASCOM driver is also available, allowing you to use the camera with any ASCOM-compliant applications.
We found operating the camera using SharpCap to be intuitive and were imaging in no time.
When we tested it on a bright deep-sky object such as the Orion Nebula, M42, we found it was easy to burn out the core of the nebula with just a few seconds of exposure using our test 4-inch (100mm), f/9 refractor.
This high sensitivity is excellent if you need to keep exposures short. With longer exposures and a degree of light pollution, we were able to delve into the gas that inhabits the dimmer parts of the nebula with ease.
Turning our attention northeast towards the Horsehead Nebula, this proved a reasonable target for our 4-inch setup.
The shape of the silhouetted horse’s head was seen during test 60-second exposures.
We also viewed a comet, C/2017 T2 PanSTARRS, which was close to the open cluster M36.
The faint comet did register but was a bit lost in the wide-field coverage offered by the camera.
A lucky imaging test capture of the Moon also confirmed that the QHY 168C is a great performer for Solar System imaging.
The QHY 168C is an excellent all-round colour camera. It offers superb sensitivity, wide-sky coverage with the appropriate optics and is easy to handle.
The camera’s Sony IMX071 sensor offers high sensitivity and low noise.
The large APS-C chip size is ideal for capturing wide deep-sky images and offers up to 3×3 binning to improve light sensitivity, albeit at the expense of resolution and colour.
Colour sensitivity peaks around 525nm in green with both red and blue sensitivity peaks not far behind.
Peak red sensitivity is around 605nm with the all-important hydrogen-alpha (656.3nm) response being around 80 per cent of the peak red value.
Full pixel well-depth, the maximum amount of charge (electrons) a pixel site can store, is 46ke.
Although typically most pixels in an astronomical image don’t even get close to this value, it should be clear that the sensor’s average readout noise of 3.2 electrons is very low in comparison.
This is the noise introduced when a pixel’s charge is converted to a voltage during readout.
We also detected no amp glow, even when the capture gain was set high. Amp glow is an effect where heat from components near the sensor can create an unwelcome glow along
an edge or image corner.
Heated optical window
One problem with an efficient cooling system is fogging or even frost appearing on the optical window that fronts the sealed sensor cavity. The QHY 168C addresses this issue by providing an optical window heater. This raises the temperature of the window, dissipating any fogging or the unwanted build-up of ice crystals.
Two-stage TEC cooling
The QHY 168C uses a two-stage Peltier cooling system to lower the sensor temperature down to a possible 35˚C below ambient (air) temperature. Cooling is fast and maintains the selected temperature well. The sensor chamber is air-tight to prevent moisture getting in. Desiccant keeps the chamber moisture free with spare provided should replacement become necessary.
Camera image buffer
A buffer where image data can be stored en route to the host PC is provided by 128MB of internal DDR2 memory. This helps prevent bad frames caused by the computer should it unexpectedly pause the transfer. It also assists high frame-rate captures where the host’s USB transfer rate is perhaps performing slower than desired.
The QHY 168C connection ports are located on the rear of the camera
body and are minimal, with just 12V power and a USB 3.0 port provided.
A car-plug cable is provided with the camera, allowing you to power the
168C from your own 12V battery. A 1.5m USB 3.0 cable is also provided.
A 2-inch M54/0.75 T ring-adaptor is provided. This presents a standard 2-inch T-threaded barrel at the telescope end and a M54/0.75mm male thread towards the camera. An additional ‘fast installation connector ring’ is included. This locks onto the camera’s forward collar via three thumb screws, presenting a female M54 thread into which the 2-inch adaptor screws.
Sensor IMX071 colour CMOS 14-bit (APS-C, 23.77×15.78mm, 28.53mm diagonal)
Pixel array 4,952×3,288 (16 megapixels), 4.8×4.8micron square pixels
Exposure range 30 microseconds to 3,600 seconds
Size 105x90mm (supplied 2-inch M54/0.75 T-ring adaptor adds 35mm)
Backfocus 18mm with 2-inch adaptor ring fitted
Supplier Modern Astronomy
Tel 020 8763 9953
This review originally appeared in the January 2020 issue of BBC Sky at Night Magazine.