The QSI 6162wsg8 camera employs a KAF-16200, 16 megapixel, full frame CCD image sensor with microlens technology that has been specifically produced for astrophotography. The 6-micron pixel size make this camera the ideal imaging partner for a wide range of focal length telescopes. The ability to ‘bin’ the CCD means the QSI 6162wsg8 is suitable for focal lengths right up to 2.5m and still stay around 1 arc second per pixel (recommended for successful imaging). The large APS-H 16mp CCD sensor with a 35mm diagonal works happily using 2” mounted or 50.8 mm unmounted filters on scopes as fast as f/2.8 with minimal vignetting. The camera is available with or without an Off-Axis Guider and the choice of a five or eight position filter wheel.
The ‘ws’ model comes with a shutter and filter wheel installed. The ‘wsg’ model is supplied with the Off-Axis Guider, Integrated Guider Port (IGP).
The QSI 6162wsg8 camera system is supported by industry leading image acquisition software plus a full camera control API is available for creating custom Windows or Linux applications.
High Performance Design
“The QSI 600 Series was designed from the ground up to attain the highest possible imaging performance from Kodak’s Full-Frame and Interline Transfer CCD image sensors.”
Two separate analogue processing chains, providing dual read rates, allow the QSI 600 Series to meet two seemingly incompatible imaging goals. The QSI 600 Series High Quality mode provides the highest possible Signal to Noise Ratio (SNR) for applications that require the lowest noise and widest possible dynamic range. High Speed mode has a read rate of 8MHz providing high speed reads at multiple frames per second. The read mode is easily changed under program control providing exceptional flexibility it tuning the camera’s performance to the desired imaging goals.
All significant performance characteristics, including Linearity, Read Noise, and Photon Transfer (Gain), are tested and confirmed during manufacture. Each camera’s timing and voltages are carefully set during manufacture to ensure maximum Charge Transfer Efficiency, and to minimize charge injection and other secondary noise sources. QSI’s exclusive Research Spec® profiling ensures optimal performance in every camera.
Sophisticated mixed-signal design practices are utilized throughout the camera. This permits a very compact design while eliminating interference from conducted and radiated noise. ROHS compliant multi-layer circuit boards and surface-mount components are used exclusively. A unique circuit board stacking methodology eliminates interconnecting wires that could reduce reliability.
A carefully designed and isolated switching power supply generates all of the voltages needed to operate the camera from a single 12VDC power source. Low noise design practices and advanced filtering techniques completely eliminate any measurable impact on camera noise performance.
Arguably, the most important aspect of a CCD camera design is the video processing subsystem. This is where almost all of the camera’s performance characteristics are established. The 600 Series video processing begins with a very low noise, precision preamp to accurately amplify the microvolt level pixel signal from the CCD image sensor. This signal is then processed through a Correlated Double Sampler (CDS) to reduce temporal read noise in the pixel signal. Subsequent signal conditioning then feeds the pixel level to a high-speed, precision 16-bit Analog to Digital Converter (ADC) where it is converted to a digital value between 0 and 65535.The Read Noise contributed by this entire subsystem is exceedingly small. So small in fact, that it is virtually undetectable, contributing less than 1/30 of the combined read noise of a typical KAF image sensor. The low read noise and carefully chosen camera gain yield excellent Dynamic Range. Linearity is also outstanding, limited only by the CCD image sensor itself.
CCD Cooler Subsystem
Key in the design of the QSI 6162wsg8 camera is a very efficient custom 2-stage thermoelectric cooler (TEC) subsystem. Intelligent, programmable cooling fans are integrated into the rear of the camera body to remove the heat generated by the cooler. Typically, forced air cooling lowers the regulated CCD temperature by up to 45°C below ambient utilizing 85% power. Tight +/- 0.1°C temperature regulation is maintained at temperature settings of 10°C below ambient and lower.
The cooled CCD image sensor is positioned in a hermetically sealed environmental chamber covered with an anti-reflection coated precision optical window. The chamber is purged with an ultra-dry noble gas to increase heat conduction and eliminate the possibility of frost forming inside the chamber. To extend the useful period before re-purging is required, a user-rechargeable microsieve desiccant is employed to scavenge water molecules that enter the chamber. It is located behind a sub-micron, gas-permeable membrane to prevent particulate contamination of the CCD chamber.
Cooling and Dark Current
Effective cooling of the CCD image sensor is essential for long exposure imaging, especially in astronomy. Thermally generated electrons accumulate in the pixels over time and compete with the photo-electrons that make up the image. This accumulation of thermal electrons is known as ‘dark current’. It lowers the dynamic range of the sensor and reduces the signal to noise ratio. Eventually the thermally generated electrons will swamp the image.
Fortunately, dark current can be reduced dramatically by cooling the CCD. Onsemi CCD sensors accumulate thermal electrons at a rate of roughly 4 electrons per second per pixel at 25°C. With every 6.3°C decrease in temperature the dark current is reduced by half. Where a 10-minute exposure might generate 2400 thermal electrons at 25°C, it will produce only about 10 at -25°C. This is a very small number when compared to the CCD read noise and pixel full well capacity.
Shutter and Filter Subsystem
The QSI 6162wsg8 camera achieves its unique configuration flexibility though an innovative shutter/filter subsystem. Both the mechanical shutter and filter wheel can be installed internally while keeping the growth of the camera dimensions at a minimum. This results in minimal loss of back focus as these features are added. The compact design also reduces vignetting with fast optical systems.
Shutter and Filter Wheel
The QSI 6162wsg8 camera incorporates QSI’s proprietary internal, even-illumination mechanical shutter and adds an internal five or eight position filter wheel to the camera. The filter wheel accepts any standard threaded 2″ or unmounted 50.8 mm filters. The filter wheel can be easily removed and replaced to change or clean the glass filters. Additional filter wheels can be purchased allowing quick interchange of different filter set configurations. The shutter is not only used for timing exposures, but can be left closed to produce ‘dark frames’ for subsequent image processing. Exposures can be as short as 0.03 seconds or as long as 240 minutes. The shutter is rated for more than 1 million cycles.
Integrated Guider Port
Selecting the best guiding solution for deep sky imaging has always required a compromise. The optional available Integrated Guider Port (IGP) solves many of the problems associated with existing guiding solutions.
The Right Guiding Solution
Guiding with a separate guide scope provides the most flexibility, but differential flexure can be an issue, especially with long focal length scopes. With an internal guide chip, you’re forced to guide with light through your filters and you can’t guide at all while the shutter is closed or an image is being downloaded. This is especially problematic for narrowband imagers. To get around those issues, you could add an external off-axis guider, but a traditional OAG can add an inch or more of back focus plus more weight and two new mounting surfaces that need to be held rigidly.
Guide with Light from in Front of the Filter Wheel
The QSI 6162wsg model solves the problems with other guiding solutions by integrating a Precision Off-Axis Guider directly into the camera body with the pick-off prism positioned in front of the integrated color filter wheel – right where it belongs.
Never Struggle with Finding a Guide Star
One of the main challenges when using a camera with an internal guide chip is to find a star bright enough to guide by within the limited field of view of the internal guide sensor. When shooting through red, green or blue filters, ⅔ of the available light is blocked by the filter and not transmitted to the internal guider chip, guaranteeing lower signal-to-noise stars for guiding. This problem is compounded with narrowband filters where as little as 1% of the total light from a star reaches the guide chip. By positioning the pick-off prism in front of the filters, you always have all the star’s light available for guiding.
Integrated Guide Port Supports Fast Optical Systems
By integrating the Off-Axis Guider into the camera, we’re able to position the pick-off prism very close to the internal filter wheel adding minimal back focus and eliminating any possibility of flexure or rotation compared to a traditional OAG. The large ½” square pick-off prism is optimally positioned close to the internal filter wheel, supporting the use of guide cameras with large sensors, while preventing any vignetting of the main sensor even with very fast optical systems.
Flexible Guide Camera Options
The optional Integrated Guide Port (IGP) when installed on the QSI 6162wsg8 model is designed to support any camera with 12.5mm of back focus or less that can be attached using C-mount, STi mount or T-mount threads. Many cameras are designed with 12.5mm of back focus to be compatible with CS-mount lenses. CS-mount lenses use the same thread as C-mount (1″ x 32tpi) but with 12.5mm of back focus as opposed to 17.5mm for C-mount.
Easy, Rigid Guide Camera Focusing
The guide camera attaches to the OAG using a C-mount, Sti mount or T-mount threaded adapter (specified at time of order). The threaded adapter sits on top of the focus ring and allows the guide camera to be rotated to any position. The focus ring threads onto the focus base to allow 3mm of travel when focusing the guide camera. Once focus is achieved, the focus ring is locked with a set screw. The guide camera can still be rotated manually if desired without changing the focus. The end result is a rigid, easily focused guide camera that will not move or flex while your mount tracks the apparent motion of the night sky.
|Sensor Type||CCD – KAF-16200|
|Horizontal Resolution||4499 pixels|
|Vertical Resolution||3599 pixels|
|Pixel Size||6 µm x 6 µm|
|Readout Noise||8e- typical value high quality mode|
|Gain Factor||High gain and low gain modes|
|Dark Current||>0.25 electrons/second at 0°C|
|Interface||USB 2.0 high speed|
|Power||12v DC 3.5A|
|Maximum Exposure Length||Unlimited|
|Minimum Exposure Length||50 ms|
|Cooling||Thermoelectric set point with max ΔT -50°C|
|Download speed||High speed 3 seconds
High quality 23 seconds
|Weight: approx.||2.9 kg for wsg-8
2.8 kg for ws -8
OAG weight 0.15kg
|Dimensions||5 pos: 189 x 189 x 87.5mm
8 pos: 238 x 238 x 87.5mm
|Back Focus||Standard all models – 31 mm (38 mm with front plate adaptor)
Optional wsg add on – 51 mm (61 mm with front plate adaptor)
Optional low profile – 31 mm (35mm with front plate adaptor) for use with Canon/Nikon lens adaptors
|Adapter threads currently||M54 x 0.75 mm, standard all models
Optional wsg add on, M68 x 1 mm internal thread
External 3” connection to fit standard 3” draw tube
|In the box||Power adaptor
USB drive with software
M54 to 2” eyepiece adaptor