QSI 690
The QSI 690 model camera employs an 9.19mp Sony CCD image sensor. This new generation of Sony sensor offers remarkable sensitivity with peak QE of over 75%. The high senstivity, wide dynamic range, dual read rates, low noise performance and internal 5 or 8-position color filter wheels make the QSI 690 ideally suited to a broad range of demanding scientific, medical, astronomical, and industrial imaging applications.
The QSI 690wsg is available with an Integrated Guider Port (IGP) allowing astronomers to guide using the light from the main telescope while picking off the light from the guide star in front of the filters.
The 690 camera system is supported by industry leading astronomy and microscopy image acquisition software plus a full camera control API is available for creating custom Windows or Linux applications.
High Performance CCD Image Sensor
9.19mp Image Sensor.
The 3388×2712 sensor in the QSI 690,provides extremely high resolution with its 3.69µm pixel.
The compact design and internal color filter wheel of the QSI 690ws allows unvignetted, filtered images even with very fast optical systems.
The QSI 690 camera employs a Sony ICX814 9.19 megapixel interline transfer CCD image sensor with microlens technology.
The Sony ExView sensor has exceptional sensitivity across the visual band with peak quantum efficiency of 77% along with remarkably low dark current. The sensor has antiblooming protection and a fast electronic shutter. Micro lenses cover the surface of the CCD to focus the light into each 3.69µm pixel to increase optical response. See the Specifications tab below for additional details.
Leading Edge Technical Performance
Two separate analog 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 ResearchSpec® 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 image sensor. The low read noise and carefully chosen camera gain yield excellent Dynamic Range. Linearityis also outstanding, limited only by the CCD image sensor itself.
Refined Design
Small enough to practically hide behind a CD-ROM, the medium format QSI 600 Series family sets new standards for full-featured, high performance scientific CCD cameras. The striking appearance, refined design and superior fit and finish only hint at the advanced technical performance lurking inside. Some have described it as a work of art.
A defining feature of the 600 Series is the flexible design that permits three progressively configured body styles with a minimal impact on overall size. A camera’s body size depends on the internal features installed. The Slim body is the thinnest version and can be used with CCDs incorporating an electronic shutter. The Medium body provides addition space for an internal mechanical shutter. The Full body allows the installation of both the shutter and a five position filter wheel with interchangeable filters.
Engineered with extensive use of sophisticated CAD-CAM design tools, the QSI 600 Series is CNC machined from aircraft grade aluminum alloy. The finely finished anodized body components are assembled with corrosion resistant stainless steel hardware throughout.
Small, Light-Weight and Thin
The 600 Series is designed to support image sensors with a maximum diagonal measurement of 22.5mm. For this class of camera they are surprisingly compact. At just 4.45″ square, the Slim body camera is just 1.68″ deep, occupying less than 30 cubic inches and weighing in at under 26 ounces. Even a Full body camera with shutter and color filter wheel is only 2.5″ deep and a mere 40 ounces. In fact, the small footprint is the practical limit for a camera with a 5 position filter wheel using standard 1.25″ threaded or 31mm unmounted filters.
Keeping the depth of the camera to a minimum was an early design goal. Not only is backfocus minimized, but the camera moment-arm is reduced resulting in greater stability. The shutter and filter wheel were placed inside the body, very close to the image sensor reducing backfocus and overall depth. The motion control electronics are actually buried in the 0.12″ thick shutter/filter mounting plate to reduce depth further. Pulling the cooling fans and heat sinks into the body resulted in another significant reduction in depth. Finally, having all electrical cables and the optional liquid heat exchanger recirculation hoses exit the body in the same direction and perpendicular to the optical axis insured an interference-free fit in tight spaces.
Efficient, Low Power CCD Sensor Cooling
CD Cooler Subsystem
Key in the compact design of the 600 Series cameras 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. A slim liquid heat exchanger (shown at right) can be attached to the rear of the camera body to increase the cooling further, up to 55°C below the temperature of the circulating fluid.
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. Sony ExView CCD sensors accumulate thermal electrons at a rate of roughly 0.002 electrons per second per pixel at -10°C. Where a 10 minute exposure might generate 2000 thermal electrons at 25°C, it will produce only about 1 at -25°C, making noise from thermal current insignificant even on very long exposures.
Two Shutters and a Filter Wheel
Electronic Shutter
The QSI 690 utilizes the electronic shutter built into the Sony ICX814 CCD image sensor to control exposures. Shutter timing is very precise and can range from as short as 100 microseconds up to 240 minutes. The very fast acting shutter is possible due to two key features of the interline transfer architecture.
Any existing electrons can be removed from the pixels instantly with a single electronic pulse, beginning the exposure.
After the specified exposure duration, the entire image field can be instantaneously moved into a light-shielded holding area on the CCD. The image is then read out at the normal rate without being contaminated by any light still illuminating the CCD surface.
Mechanical Shutter
The Model 690s model incorporates the optional internal, even-illumination mechanical shutter in the ‘mid-size’ camera body configuration. When operating with an interline transfer CCD, the mechanical shutter is not used to actually make the exposure. This is still the responsibility of the electronic shutter. The mechanical shutter is employed to cover the CCD and simplify the creation of Dark and Bias frames for subsequent image processing.
Filter Wheel
The Model 690ws adds an internal five position filter wheel to the camera in a ‘full-size’ camera body. The 690ws-8 incorporates a larger 8-position filter wheel. Even with the large 4mp sensor, the short backfocus and close spacing provided by the internal color filter wheel allows the 690ws or ws-8 to work even with optics faster than f/2.8 with no vignetting. The filter wheel accepts any standard threaded 1.25″ or unmounted 31mm 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.
Innovative Integrated Guider Port
Integrated Guider Port
Selecting the best guiding solution for deep sky imaging has always required a compromise. The 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 600 Series WSG models 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 backfocus 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 Integrated Guide Port (IGP) built into 600 Series WSG models is designed to support any camera with 12.5mm of back focus or less that can be attached using C-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 WSG using a C-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.
