Product Review: QHY 600
One needn’t look far to find the signs of the “CMOS revolution” in astrophotography. CMOS-sensor-based cameras have increasingly become the product of choice for experienced and budding astrophotographers alike. That said, there has been an option in CMOS technology that has been decidedly absent from the available offerings: a full-frame, monochrome sensor. QHY answered that call, however, with the release of the QHY600. Now, not only do astronomers now have a full-frame monochrome option, but one with excellent performance as well.
Overview:
The QHY 600 uses the impressive Sony IMX455 back-illuminated CMOS sensor. This chip has 3.76 micron pixels (perfect for short-to-medium focal length scopes) and packs over 60 million of them in the useable imaging area. Paired with a 16-bit A/D converter and over 87% peak QE (based on QHY’s internal tests), the QHY 600 is an extremely sensitive camera.
Perhaps one of the most unique features of the QHY 600 are the newly-implemented readout modes. On this camera, there are (currently) 3 different readout modes available, which change the way the camera reads the sensor, giving the user even more freedom and control over the performance. For example, see the following chart for mode 0 vs mode 1 in the camera:
|
Read Noise |
Dynamic Range |
Full-Well Depth |
|
|
Read Mode 0/Gain = 0 |
7.8 electrons |
13.4 stops |
85003 electrons |
|
Read Mode 0/Gain = 27 |
2.7 electrons |
13.26 stops |
27045 electrons |
|
Read Mode 1/Gain = 0 |
3.68 electrons |
13.75 stops |
50639 electrons |
|
Read Mode 1/Gain = 56 |
1.68 electrons |
13.65 stops |
21657 electrons |
What does this mean in practicality? From my experience, having shot targets both in Mode 0 and Mode 1, you can get great shots out of both modes (see images at the end of this review). However, from an optimization standpoint, Read Mode 1 at Gain = 56 will be the most often used mode. It yields you the lowest read noise while still maintaining a sizeable full-well depth. And, that is done without sacrificing much Dynamic Range (only 0.1 stops). I should also note, these values in the table above are taken from the QHY specifications, but they match nicely with the real-world numbers off the camera. Here is the BasicCCDParameters Script (PixInsight) readout for my camera in Mode 1, Gain = 56:
From this we can see the computed read noise is 1.718 electrons (vs 1.68 on spec), full well capacity is 21956 electrons (vs 21657 on spec), and the dynamic range is 12,780 steps, which translates to 82.13 dB or 13.64 stops (vs 13.65 stops on spec).
The camera used for this review was an early-bird version of the QHY600M. This means the camera is in the longer Professional Body, but doesn’t include the Professional hardware, namely the 2 x Gigabit Ethernet ports or programmable FPGA. As such, it is essentially a longer-bodied version of the Photographic Version of the camera. The camera comes nicely boxed by QHY, with the camera cushioned nicely above the accessories:
A stack of QHY600’s!
Camera upon opening the box
Oh so many pixels!
I paired the QHY600 with the new QHYCFW3L Filter Wheel, which is a substantial piece of equipment on its own. The CFW3L holds 7 x 50mm round filters, which I loaded with Chroma LRGB and 3nm Ha, OIII, and SII filters, perfect for the full-frame sensor of the QHY600. It can be controlled via USB (if used separately) or, if using a QHY camera, connects to the back of the camera with a 4-pin connector, allowing the need of only the USB and power cables from the camera to control and power both. In addition, the CFW3 comes with the necessary threaded holes to allow for the QHY off-axis guider (OAG) to be bolted directly on to it, reducing the OAG back focus consumption to only 13mm. Fully assembled, the camera, filter wheel, and OAG assembly are beefy, weighing in at 4.4 lbs with filters installed. It also consumes a convenient 57mm of backfocus, making it work well with most systems (within 1-2mm of the “standard” 55 - 56mm on many corrective optics).
CFW3 box – banana for scale
CFW3 loaded with Chroma Filters – banana for scale
Complete imaging train – again, banana for scale
Only a mere 4.4 lbs!
Connectivity:
Upon first getting the 600, there was concern about the need for a 64-bit program to be able to handle the size of the images (each image is 122mb in its full resolution). QHY recommended that and, upon my first trials, I experienced similar results. Sequence Generator Pro (a 32-bit program) was crashing due to file size limits. In order to combat this, I switched to NINA, which in its 64-bit version handled the camera like a dream. Not soon after, however, it was discovered that the driver for the 600 had a memory leak, which turned out to be the culprit for the apparent 32-bit issue. Updating to the latest version of the SDK solved the problem, allowing the camera to run on SGP now, as well. See our blog post on “Configuring and Connecting the QHY600” for a full explanation of the experience.
In all cases, configuring the computer to connect to the camera was simple, and everything needed is provided on QHY's software download page. I recommend downloading the "System Driver," "SDK," and "ASCOM Driver," as that will give the most flexibility for use with multiple software programs. If users are using TheSkyX, there is a specific TSX SDK plug-in that is also required.
I tested the camera with Sequence Generator Pro (SGP), N.I.N.A., and TheSkyX and had success in connecting, cooling, and downloading images in all three. It is worth noting that N.I.N.A. allows for connectivity via the native driver, which produces MUCH faster download times. In my experience, when connected in SGP via the ASCOM driver, my average download times are approximately 20 seconds per file (over USB 3.0). On NINA, however, over the same hardware connection, the download times dropped to approximately 2-3 seconds!
With large sensors, spacing and tilt become even more sensitive (especially with faster systems). Initial imaging tests showed a small amount of tilt in the image. This seemed to stem from the connection between the camera and the adapter on the back of the filter wheel. I added 3 small layers of 1mil Kapton Tape to half of the front of the dovetail flange on the camera and this eliminated the tilt. All other physical connections are solid and repeatable.
Imaging:
I have imaged with the camera on two different telescope configurations: first with my Astro-Physics 130GTX @ f/4.5 using the Astro-Physics Quad-TCC, then on my TEC 180 @ f/5, also using the Astro-Physics Quad-TCC. The first configuration yields an image scale of 1.32 “/pixel and a field of view of 3.52 x 2.34 degrees. The small pixels on the camera allow it to sample well at short focal lengths, yielding wide fields of view while still allowing high-resolution imaging. For example, I took this image of M31 using the A-P 130 configuration. I can easily fit the entirety of the galaxy in the FOV, but still get excellent resolution on the galactic details:
M31 – Full Image FOV. AP 130 GTX with Quad-TCC (585mm focal length). Image scale = 1.32”/pixel. Imaged in Mode 0, Gain = 27. Image Credit: Matt Dahl
Same M31 image, 1:1 resolution. Note the fantastic detail on the dust lanes, as well as the nice resolution of the star cloud NGC 206. Many HII regions are visible, as well as some cataloged globular clusters. Image Credit: Matt Dahl
Similarly, attaching the camera to my TEC 180, also with the Quad-TCC (bringing the scope to f/5), this configuration yields an image scale of 0.85 “/pixel and field of view of 2.26 x 1.5 degrees. Still a very comfortable FOV for large objects, but with a much higher-resolution image scale. This image of the Horsehead Nebula was taken with this configuration, yielding not only a large field around Barnard 33, but highlighting some very cool features of the region, as well:
Horsehead Nebula – Full Image FOV. TEC APO 180FL with Quad-TCC (907mm focal length). Image scale = 0.85”/pixel. Imaged in Mode 1, Gain = 56. Image Credit: Matt Dahl
Same Horsehead image, focused on NGC 2023, 1:1 resolution – Image Credit: Matt Dahl
It is hard to overstate how fantastic a full-frame imaging camera is, and at the same time it is challenging to describe the impact sensor size makes on an image. As someone who started with a full-frame camera, then migrated to a 4/3 sensor, I was always longing to get back to full-frame imaging. But, I enjoyed the resolution I got out of the smaller pixels on my 4/3 sensor. The QHY600 blended the best of both worlds. To highlight this, I shot a comparison image (or, as close to a comparison as I could get) to something I had shot in the past. Below is a 4-panel mosaic of the Heart Nebula I shot at 616mm of focal length using my 4/3 sensor (22mm diagonal):
Heart Nebula, 4-panel mosaic. Shot at 616mm of focal length, 4/3 sensor (22mm diagonal) – Image Credit: Matt Dahl
Here is the same region of sky shot at 585mm of focal length, using the QHY600, in a SINGLE PANEL:
Heart Nebula, Single Panel. Shot at 585mm of focal length, QHY600M – Image Credit: Matt Dahl
What is also notable in the images above is that, in addition to needing 4 panels on the 4/3 chip, I also had to use DrizzleIntegration, a process that improves resolution in under sampled images, at the expense of noise being added to the image. This allowed me to achieve a similar print resolution in the mosaic that is achievable natively with the 600 (the mosaic is 11312 x 7968 pixels, compared to the 600's 9576 x 6388 pixels). Additionally, there is less data in each region (the total imaging time on the 4 panel mosaic was 17 hours - about 3-4 hours per panel - whereas the 600 image had almost 11 hours over the entire field). These two things combine to make the mosaic image far noisier, losing a lot of the extended nebulosity that you can see in the 600 image.
"Fish Head" region of the nebula, registered for the same alignment, zoomed to the same 1:2 zoom level. The mosaic image is on the left, the 600 image on the right – Image Credit: Matt Dahl
Summary:
The QHY600 is the camera the astronomical community has been looking for. A high-QE, large-format sensor with pixels designed for today’s ubiquitous short focal length imaging scopes was unavailable until now. I’ve found this camera to be well-built and well-thought out. QHY has produced stable drivers that reliably control the camera and they have been responsive and supportive when I had questions. The camera has performed to spec, and calibration and post-processing have been straight-forward. I feel I have produced some of my best images to-date using the QHY600, and I continue to look forward to each new image I produce with it. If you are looking to step-up your imaging to a full-frame sensor, taking advantage of all the benefits thereof, seriously consider the QHY600. You’ll be glad you did.
