QHY461M PH, BSI Medium Format CMOS Camera, gekühlt

QHY461M PH - especially for ambitious amateur astrophotographers

The monochrome QHY461 PH (Photo) is a completely new development of the larger, scientific camera of the monochrome model QHY461 PRO. It has a more compact body and does NOT have the scientific features of the  QHY461 M/C PRO, BSI Cooled Scientific Cameras (various versions available) . These include the two 2 x 10 GB fiber interfaces, GPS timing, programmable FPGA and the external trigger input. An optional additional water cooling is also not available.

Data is transferred to the PC via a standard USB 3.0 interface. Otherwise, the performance of the QHY461 PH is essentially identical to the scientific version. The main advantage of the QHY461 PH is that it offers all the features and performance important for astrophotography at a much lower price than the QHY461 PRO.

High resolution scientific CMOS sensor Sony IMX461 with 102 megapixels

The Sony IMX461 is a BSI Exmore R sensor with similar architecture to its bigger brother, the IMX411. The sensor measures 44mm x 33mm with a 55mm image diagonal. The array has 11,656 x 8,742 pixels (102 megapixels) at 3.76 µm square pixels. It has maximum quantum efficiency while maintaining high dynamic range.

The compact QHY461 PH with the Sony IMX461 BSI sensor

True 16 bit analog digitization with 65,536 gray levels

The IMX is the world's first scientific CMOS sensor with the AD converter "on board". The data output provides true 16 bit with 65,536 gray levels. In contrast, most CMOS sensors deliver only 12- or 14-bit resolution (4,096, or 16,385 gray levels, respectively). This means a coarser sampling rate and, for example, in the field of astronomical photometry, an inaccurate resolution with weak signals. Compared to cameras 12/14 bit sensors the QHY461 PH offers a higher sampling resolution and the system gain is less than 1e-/ADU with very low readout noise.

Very low readout noise of only 1 electron with high gain

The QHY461 PH has only one electron of readout noise (1 e-) at high gain and a high - for the large dimension of the sensor - readout speed of 1.3 frames per second (fps) at 16 bit, or 2.7 frames per second at 8 bit AD conversion.

One electron of readout noise means that the camera can achieve a signal-to-noise ratio (SNR) >3 (SNR) with only 3 to 4 photons of signal. This is a near perfect performance when only a very weak signal (photons) is available during image acquisition. Thus, the camera is optimal for both short exposure times (lucky imaging) and long exposure times, which are necessary for narrow band imaging in RGB mode, for example. The size of the sensor is also ideal for wide angle views of the sky.

Quantum efficiency and low dark current noise

The BSI technology of the IMX461 sensor results in exceptionally high quantum efficiency (max. 90% at 540nm) and features extremely low dark current thanks to SONY's Exmor BSI sCMOS technology. This means that the camera's high sensitivity and low readout noise make it suitable not only for short exposures but also for long exposures, where dark current noise often dominates. To further reduce dark current noise, the QHY461 PH features QHY's proprietary thermal noise reduction technology and two-stage thermoelectric cooling to lower the temperature of the sensor below ambient.

The quantum efficiency of the IMX461 as a function of wavelength.

Full-well capacity of 50 ke- in standard mode, up to 720 ke- in extended mode

Another advantage of the BSI CMOS structure is the increased full-well capacity. This is especially important for sensors with small pixel dimensions. Even with unbinned 3.76 µm pixels, the QHY461 PH has a full-well capacity of 50 ke-. When binning 2x2 to 7.5 µm, the full-well capacity is already 204 ke- and when binning 3x3 to 11 µm, it is 408 ke-. As a further technical highlight, QHY461 PH offers 4 different readout modes of the sensor, including an extended full-well mode. In extended mode, the full-well capacity is 80 ke- unbinned, 320 ke- binned 2x2 and 720 ke- binned 3x3.

True raw data

Many DSLR cameras have RAW image output, but it is usually not entirely in RAW format. Upon closer inspection, some traces of noise reduction and hot/coll pixel removal are visible. This can have a negative effect on the image in astronomy. However, the QHY461 PH (and also the other QHY models with a 16 BIT AD conversion) provides a REAL RAW IMAGE OUTPUT and produce an image consisting of only the ORINAL SIGNAL), maintaining maximum flexibility for astronomical imaging programs and other scientific imaging applications.

Anti-dew technology and amplifier readout glow

The QHY461 Photo's technology is based on nearly 20 years of experience in developing cooled CMOS cameras and provides solutions for icing and dew control. The optical entrance window has a built-in heater to protect dew condensation on the entrance window and the sensor chamber from internal moisture condensation. The sensor itself is kept dry with our desiccant tube base design to control humidity in the sensor chamber. The QHY461 PH shows no readout amplifier glow even with long exposure times.

Advanced high-tech features

Restarting the camera with power on/off

The camera's electronics are designed to use the +12V power supply to reboot the camera WITHOUT having to disconnect and reconnect the USB interface. This means that you can restart the camera by simply disconnecting the +12V and then reconnecting it. This function is absolutely essential for remote operation of a telescope ! You can simply use a remotely controllable power supply to restart the camera.

Random thermal noise suppression function

Certain types of thermal noise can change over time in BSI CMOS cameras (keyword: aging of electronic components). As a result, each image has a unique thermal noise characteristic, making it difficult to reduce by subtracting a dark image.

 The QHY461 PH employs innovative proprietary technology that significantly reduces the amount of random thermal noise.

Optimizing USB speed to minimize horizontal banding

CMOS sensors typically exhibit some horizontal banding (see figure). Typically, these random horizontal bands are removed by adding multiple raw images so that they do not affect the final image.

However, the so-called periodic horizontal banding is not removed during stacking, so it may become visible in the final image. By adjusting the USB transfer speed in single image or live image mode, the user can adjust the frequency of the CMOS sensor driver, optimizing the transfer frequency and thus suppressing horizontal banding. This optimization is very effective in eliminating periodic banding in most cases.

Left, an example of typical periodic horizontal noise at standard USB transmission frequency. On the right after optimization of the transmission frequency with strong reduction of banding.

The most important operating data show the following curves

The mechanical dimensions are shown in the following picture

Here we describe in detail the advantages of the modern Sony IMX 461 CMOS sensor in comparison with a CCD sensor, which was the first choice in amateur astronomy imaging for many years.

Baader Blogpost:
A comparison of the technical data between the Sony CMOS sensor IMX 461 and the Kodak CCD KAF 16803 sensor - CMOS vs.CCD

This entry was posted on March 9, 2023 by Dipl.-Ing. Wolfgang Paech

Further detail information can be found on the original webpage of QHYCCD

 If you have any further questions, please send us an email to kontakt (at) baader-planetarium.de.