WHY are the QHY600 monochrome CMOS cameras more expensive than models from other manufacturers that also use the Sony IMX 455 BSI CMOS sensor?
Image sensors are THE basis of ALL imaging in astronomical photography. The performance of the camera - i.e. the read out raw image after exposure - is based on the quality of the CMOS or CCD sensor and its performance.
Image sensors of many manufacturers are produced in different qualities: In very high quantities the "consumer-grade" sensors and in much lower quantities - and therefore much more expensive - the "industry-grade" sensors, which have to pass more extensive and tougher quality controls before delivery. The monochrome "Industrial-grade" IMX 455 sensor is certified by Sony for 24/7 continuous operation!
QHYCCD is one of the few manufacturers of amateur-priced cameras that uses the Sony IMX BSI sensor in "industry-grade" quality in all mono version of QHY600 series use IMX455 industry grade sensor (Grade-K) – except the QHY600-L. WHY?
FRAMOS - a world leader in industrial, scientific and medical imaging technologies and custom camera development - comments on the choice of "consumer-grade" and "industry-grade" sensors and recommends the following to customers): (www.framos.com/en/products/sensors/consumer-sensors/)
Similar to area scan sensors, images produced by consumer grade sensors, provide a fast, high-resolution capture of the entire field of view. The main difference between them and industry grade ones is that consumer sensors have a shorter life span, a shorter MTBF (Mean Time Between Failures) and, as a result, may cost much less than an equivalent industry sensor.
If you have a product that needs to be guaranteed for a long time, have a consistent image between each vision product, or if you need it to last for several years versus just one year you will want to consider an industry sensor instead. If you are purchasing hundreds of thousands of sensors per year and you have satisfied the other requirements, then consumer sensors may be the right choice for your application".
Another important difference between "consumer" and "industry" sensors is the so-called "package" - the housing in which the sensor is embedded. In the case of consumer sensors, this package is often made of plastic, while in the case of industrial sensors ceramic is often used as the base material, which is much more temperature stable and guarantees a high degree of flatness of the sensor array with deep cooling.
The Sony IMX 455 "industry grade" sensor is part of a so-called LGA package. LGA stands for "Land Grid Array" and the base material must be materials that minimize thermo-mechanical stresses as much as possible. This enables a wide temperature working range and the sensor can be used even under extreme environmental conditions.
The industry grade sensor is designed for longer life under normal use and can therefore withstand repeated cooling/heating cycles with less thermal stress, resulting in a longer life for a cooled camera. AND industrial sensors have a significantly lower number of pixel defects.
! The price difference between the "consumer" and "industry" version of the Sony IMX 455 is more than 500 US Dollar in purchasing !
Other advantages and features that ONLY the QHY600 models offer comparing to other camera models with the Sony IMX 455 sensor.
The different readout modes of the QHY 600 PHOTO / 600 PRO and the QHY600 PH-L
The "Readout Mode" selection is a new function developed for the QHY600 and other newer QHYCCD cameras. With the QHY 600 Photo there are (currently, more to follow) 4 different readout modes available, which change the way the image sensor is read out. This is giving the user freedom and control over the performance of the sensor.
The following table shows the differences in the data between mode 0 and mode 1 at different gain (source QHYCCD)
|Read Mode 0/Gain = 0||7.8 e-||13.4 stops||85003 ke-|
|Read Mode 0/Gain = 27||2.7 e-||13.26 stops||27045 ke-|
|Read Mode 1/Gain = 0||3.68 e-||13.75 stops||50639 ke-|
|Read Mode 1/Gain = 56||1.68 e-||13.65 stops||21657 ke-|
What does this data mean in practice for the user? In readout mode 0 the readout noise of the QHY600 PH is drastically reduced between a gain setting of 25 and 26. It is therefore recommended to set the gain as a starting point to 26. At this gain the full well capacity is 27ke- and the readout noise is only 2.7e-. For longer exposure times, where the readout noise is not so critical, reducing the gain will result in a higher full well capacity. Recommended e.g. for images of objects with a large contrast range (dynamic range), such as the Andromeda nebula or the Orion nebula.
From the optimization point of view, readout mode 1 with gain = 56 will be the most commonly used mode. It offers the lowest readout noise while providing considerable full well capacity. And this practically without loss of dynamic range. Recommended for taking pictures of fainter objects at shorter exposure times.
Readout mode 2 (Extended Full Well Mode, EDR) increases the full well capacity enormously. In this "Ultra-High" Full Well Mode the QHY600 reaches an unbinned Full Well capacity of more than 80.000 ke-. In 2x2 binning mode, full well is greater than 320,000 ke- and in 3x3 binng, full well capacity is greater than 720,000 ke-. High full well values guarantee a wide dynamic range between bright and faint details of the object under observation.
The EDR technology is not new, but is used exclusively by QHY cameras with the Sony IMX 455 sensor. Usually it is used to scale the image to 16 bit data depth in sensors with 12 or 14 bit AD conversion. Now the QHY 600 and the QHY 268C are already cameras with true 16 bit AD conversion. The Extended Dynamic Range readout mode 02 increases the full well capacity from over 51,000 ke- to just over 80,000 ke- with the pixels measuring only 3.76mü - and thus the image dynamics of the raw image also increase. The EDR mode also allows a wider range of gain values to be used without saturating the pixels. This way, extremely "deep" luminescence and RGB raw images can be captured, resulting in full detail and extreme dynamic differences in the raw image - without tricks and "pull-ups" in the final image processing.
New readout mode # 03:
QHYCCD extends from August 2020 the readout modes of the QHY 600 models by the # 03 Extend Fullwell 2CMSIT mode (yellow curve). The advantage of mode # 03 is that it has the same fullwell value and the same system gain as mode #02 Extend Fullwell, but that the readout noise is reduced about 1.3 times. (see graphic, Figure #03).
This readout mode requires an upgrade of the control software to version SDK 2020.6.26 or later. If your software does not show mode # 03, please download the QHY AllInOne installation package to upgrade the SDK (Software Development Kit) in the software. The mode is available for all models of QHY 600 series.
The exact dependencies between readout noise, gain, full well and image dynamics are shown in the graphs of the 3 readout modes.
FPGA stands for Field Programmable Gate Array
The QHY 600 and the QHY 268C camera integrate a FPGA semiconductor chip in the camera electronics. Among other things, the camera firmware is stored in these chips. The firmware itself takes up only 10% of the resources, so that 90% of the hardware logic resources are available to the user for many customer-specific functions. In addition to the customer-specific functions, an online upgrade of future firmware updates via the USB 3.0 port is possible at any time. For example, to implement further, upcoming readout modes.
The internal image memory
The QHY 600 has an internal DDR 3 image memory with a capacity of 1 or 2 Gbyte. Thus the available memory is 4 to 8x larger than in the cameras with IMX 455 sensor of the co-suppliers. What does this mean for the photographer?
The extremely large number of individual pixels of the latest generation of CMOS sensors leads to an increased memory requirement, both for temporary intermediate storage and permanent storage on the computer. For example, the QHY600 Photo Sony IMX 455 sensor generates about 120 MB of data per frame. The transfer of such large amounts of data necessarily requires that the camera itself has a sufficiently large internal buffer memory.
A frame rate of 2.5 frames per second at full resolution generates a data volume of 300 MB in just one second. If the memory has a capacity of only 256 MB, it overflows within 1 second and this can mean a loss of data. With a memory capacity of 1 GB it is possible to bridge about 3 seconds in extreme cases, e.g. if the CPU of the computer is busy with other functions.
Although the cost of the 1 GB image memory is significantly higher than of a 256 MB memory, it makes sense to make the large storage capacity available in the QHY 600 Photo so that the sensor can be read out immediately. BECAUSE: A CMOS BSI image with Rolling Shutter technology is exposed until it is 100% read out - otherwise this leads to irregularities in the image.
The QHY Noise Suppression Technology
Normally, the thermal noise of CMOS and CCD image sensors changes in a reproducible way depending on exposure time and sensor temperature. However, there is another type of thermal noise that some Back Side Illuminated CMOS sensors have, which overlays the characteristics of the reproducible, typical noise with a random noise pattern that is independent of exposure time and sensor temperature (Random Noise).
Each image thus has its own noise characteristic, making a dark image print to reduce thermal noise less effective. The electronics of the QHY600 versions and the QHY 268 C use an innovative technology to suppress random thermal noise, which significantly reduces its influence, as the image examples clearly show. This technology delivers significantly smoother and noise-free backgrounds of the raw image.
Random horizontal noise optimization
The Sony IMX455 sensor offers a number of different readout modes that allow the user to control the image output. In high gain mode, the sensor delivers extremely low readout noise at very high gain. To further improve this mode, QHYCCD has developed an optimization that allows the sensor to deliver a noise-free image beyond factory specifications even at extremely high gain.
Because this effect is usually only visible in mode # 01 (high gain mode), the "Random Noise" optimization is effective in all readout modes and improves the performance of the QHY600 camera in every imaging mode. The hardware and software for optimization is integrated in all QHY models delivered from the beginning of 2020.
The monochrome and the olour version of QHY 600 PRO are optionally available with water cooling. This cools the sensor temperature about 10 degrees lower than the models with standard air cooling. A delta T of 45 degrees to the ambient temperature is achieved. This is an important option if the camera is to be used in regions where night temperatures are well above 20 degrees Celsius in some seasons. The water cooling must be ordered when placing an order, it cannot be retrofitted. We describe further advantages of a water cooling system here.
Highly precise time allocation for exposure time
The QHY 600 PRO models have an interface to connect the QHY GPS Box. The GPS Box provides extremely precise time information about the beginning and end of the exposure time worldwide. The time allocation plays a major role in astronomical observations of objects that change their brightness during the observation time. For example, in the photometry of minor planets or variable stars, in the observation of star occultations and exo planetary transits.
In the many years since the foundation of QHYCCD, engineers and developers have gained experience with CMOS sensors in numerous camera models, thus optimizing hardware and software. You buy this "know-how" with every QHY CMOS or CCD camera.
Further information and links to QHY600:
- Test of the linearity of the QHY 600 Photo:
In general CMOS sensors - compared to CCD sensors - do not work linear at higher full well values, which means that they are not well suited for photometric (brightness measurement) investigations.
- Testing the Absolute of the QHY 600 CMOS Camera
- EA general description of the optimal choice of gain and offset for CMOS cameras for astronomical photography
- Product Review QHY 600 (US dealer)
- Comparing the Sony IMX 455 (indrustry-grade) and KAF 11002 sensor
- New Technology in the QHY600 and QHY 268C CMOS Cameras
- "First Light" with the QHY600 EB: A field report by Christioh Kaltseis
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