2 Megapixel CCD Image Sensor

The standard 520i model camera employs a Kodak KAI-2020M 2 megapixel interline transfer CCD image sensor with microlens technology. The KAI-2020M sensor has a photoactive array of 1600W x 1200H pixels. It has excellent quantum efficiency between 350nm and 1000nm with significant enhancement at the blue end of the spectrum. Low dark current and high pixel charge capacity result in a dynamic range exceeding 74db. The sensor employs a vertical overflow drain that provides both antiblooming protection and a fast electronic shutter. Micro lenses cover the surface of the CCD to focus the light into each pixel to increase optical response. See the Specifications tab for more detail.

  High Performance Design

"The QSI 500 Series scientific camera family was designed from the ground up to attain the highest possible imaging performance from Kodak's KAF and KAI CCD image sensors."

• Sophisticated mixed-signal design practices are utilized throughout the camera. This permits a very compact design while eliminating interference from conducted and radiated noise. All of the many internal clock and bias voltages are set via high precision Digital to Analog Converters (DACs) under computer control, allowing automated optimization during manufacture. 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.
   
• 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 500 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.
   
• An internal pipelined data architecture with a large FIFO memory buffer is employed to achieve a constant 500,000 pixel/second read rate from the CCD. The multi-controller design effectively decouples the camera pixel read operation from the USB transfer process while ensuring maximum throughput.
   
• 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.
   
• 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.

CCD Cooler Subsystem
 
Key in the compact design of the 500 Series cameras is a very efficient 12 watt thermoelectric CCD cooler 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 38°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 45°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 minimize the frost point and heat conduction. 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, 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 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. Kodak KAF 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 of 15 electrons and the pixel capacity of 100,000 electrons. At -35°C, a 1 hour exposure will generate less than 20 thermal electrons per pixel!
 

Electronic Shutter
 
The 520ci utilizes the electronic shutter built into the KAI-2020CM 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 520csi camera incorporates the optional internal mechanical shutter in the 'mid-size' camera body configuration. When operating with an interline transfer CCD, a 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 520wsi adds an internal five position filter wheel to the camera in a 'full-size' camera body. The filter wheel accepts any standard 1.25" filter and can be purchased with various filter configurations. The filter wheel can easily be removed and replaced to change or clean the glass filters. Additional filter wheels can be purchased allowing quick interchange of different filter set configurations. (Note how the RGB filters reflect the complimentary color in the picture at the right.)

LRGB Filter Set
 
Astronomik Type IIc LRGB filters are the standard filters available with the 504ws camera (filter sets from other manufacturers are available by request.) The Astronomik filters are optimized for astronomical color imaging and the bandpass is designed to accurately match the color sensitivity of the human eye. Infrared cutoff down to 1150nm is integrated into each filer eliminating the need for an extra IR filter. These thickness-matched filters are par-focal with excellent transmission to nearly 100%. The chart below illustrates the bandpass characteristics of each filter.

The connector panel, shown above, is thoughtfully recessed into the body of the camera for protection and provides access for all external connections. The two threaded holes on the back of the body are used to attach an optional cable restraint system to support the electrical connections as well as the recirculation hoses if the liquid heat exchanger is employed.

USB Interface

All 500 Series cameras utilize a standard USB 2.0 (USB 1.1 compatible) port for connection to the host computer and imaging application software. Read and transfer time for an entire 1600x1200 image frame is typically less than five seconds.

Guider/Control Port

A four channel optically isolated control port is accessible through a standard 6 pin modular connector. The signal pin-out is compatible with most modern telescope mount drive correctors and is intended to be used for telescope guiding under MaxIm/DL and CCDSoft. The outputs can also be used for other control purposes when developing your own applications with the 500 Series ActiveX software development toolkit. The outputs are common emitter, open-collector and can sink up to 50ma. The maximum voltage should not exceed 50v.

Power Requirements

One of the defining features of the 500 Series cameras is power efficiency. A fully configured 520wsi camera operates from a single 12v DC supply and only consumes 18 watts at full cooling, with both fans at maximum and the filter wheel moving. Other camera model configurations have power consumption as low as 3.5 watts. Included with each camera is an approved 12 volt DC power supply with an input voltage range of 90-240V, 50-60HZ.

Notification

Both visual and audible notification is built into all 500 Series cameras. A multi-color LED status display provides visual indication of the various states of camera operation. The behavior of the indicator is configurable and can be disabled by user command. A unique internal beeper provides audible feedback of camera operation and status. Like the visual display, the beeper can be configured and disabled by the user.

Support

Every 500 Series camera is accompanied by a collection of software applications and tools that allow you to begin imaging immediately or develop custom camera control applications to precisely match your requirements.

MaxIm LE

MaxIm LE is based on the award winning MaxIm DL version 4.5 from Diffraction Limited providing the fastest and easiest way to image the night sky. All QSI Series 500 cameras are supported for imaging and auto-guiding, plus most popular guider cameras are supported as well. MaxIm LE is available with any 500 Series camera. You can also upgrade to MaxIm DL/CCD for an attractive price at the time of purchase. Details >>

Drivers for Software Bisque's CCDSoft

Realizing that one shoe doesn't fit all, QSI also supplies the necessary drivers for CCDSoft, the popular Image Processing and Camera Control Software from Software Bisque.

Windows Custom Application Development

QSI provides an ASCOM-compatible API (Application Programming Interface) enabling users to write their own custom camera control applications. The camera control API is an automation component that communicates with the camera device driver and exports a COM automation interface. COM automation provides an interface which Microsoft Office, VB, VBA, C++, and other Windows applications can use to control the camera. The API is available as part of the QSI Software Development Kit (SDK), available for download from the QSI website.

Learn more about the ASCOM Initiative.

QSI provides a camera control C++ API for Linux users on Intel x86-compatible platforms. The API provides full camera control and image capture capabilities via the USB interface. The API is implemented as a shared library providing an easy to use camera object that exposes all of the features and capabilities of the camera. It is well suited for both simple scripting, and more sophisticated imaging application development.

View complete 500 Series Software details >>.

Field Upgradeable Firmware

All 500 Series cameras can be upgraded to the latest firmware in the field. The latest firmware is always available for download from the QSI Software page. QSI supplies a simple fail-safe Updater application that handles all the details.