The OnSemiconductor (formerly Truesense and Kodak) KAF-8300 Image Sensor is a 22.5 mm diagonal (Four Thirds Format) high performance color or monochrome full frame CCD (charge-coupled device) image sensor designed for a wide range of image sensing applications including digital imaging.
Each pixel contains blooming protection by means of a lateral overflow drain thereby preventing image corruption during high light level conditions.
For the color version, the 5.4 μm square pixels are patterned with an RGB mosaic color filter with overlying microlenses for improved color response and reproduction.
The sensor utilizes the TRUESENSE Transparent Gate Electrode to improve sensitivity compared to the use of a standard front side illuminated polysilicon electrode.
The embedded microprocessor of the AST8300 provide the capability for a new software approach to readout: instead of the classical analogue CDS, the AST8300 uses a multi sample digital CDS.
The idea is to sample the reset and the data level multiple times and reduce the noise by averaging the data: the more times you sample the levels, the more accurate is the measurement of the pixel value.
Averaging 16 samples for the reset and data levels, the AST8300 can readout the photo at typically as low as 6.5e- total noise. Having the capability of digitally sampling the levels and onboard calculation power, makes it possible to experiment custom readout modes to further improve the noise levels.
(R1+R2+...+RN) - (D1+D2+...+DN)
The AST8300-B series cameras feature very low power consumption: less than 2.4A @ 12V in fully operative state.
This is obtained by an efficient cooling system that lowers the regulated CCD temperature by up to 42°C below ambient.
The cooling system consists on: low-vacuum sealed chamber + custom shaped cold finger + 2-stage thermoelectric cooler (TEC) + heat-sink + fan.
The camera case consists of two main units: Sensor Unit (SU) and Processor Unit (PU).
The SU is a sealed chamber; through a vacuum pump connected to the valve on the rear of the camera body it is possible to pump-out the air from the chamber. This has two fundamental effects: it eliminates the possibility of frost forming inside the chamber and minimize the convention up and down heat transfer inside the SU, optimizing the heat removal via the cold finger.
Every camera is tested to maintain a proper vacuum level inside the SU for at least one week. The vacuum level can be controlled through the manometer incorporated in the vacuum pump and eventually adjusted in less than a minute. No dessicant is needed.
The cold finger is a small block of aluminium properly shaped to provide the best conductive thermal link between the rear of the CCD and the TEC.
The TEC is a two-stage thermoelectric cooler with the cold side connected to the cold-finger and the hot side to the heat sink. Its activity is controlled by the Processor through the feedback from a precision temperature sensor positioned on the cold-finger just close to the CCD rear allowing tight +/- 0.1°C temperature regulation.
The aluminium heat-sink consists on a wide 60x60x25mm flat base with an array of pins that are embedded into the base. Pin fin heat sinks are extremely effective as they feature a low thermal resistance for a given volume. The smooth pins reduce resistance to incoming airstreams and enhance air turbulence between the pins. The omnidirectional structure maximizes the entrance of fresh air into the pin array from every possible direction and simultaneously allows the hot air to exhaust from the pin array in every possible direction provided by the air flow forced by the fan.
The fan is 60x60x15mm with an air flow of 25.2CFM and thanks to the "maglev" tecnology guarantees high rated speed (5400RPM) at limited noise emission (36.2dB(A)).
The AST8300-B series cameras are powered by a 1000MHz Cortex-A9 Processor.
Thanks to this "intelligence", the AST8300 can do onboard all the operations that other cameras can only do by means of an external PC.
Similar to a powerful astrophotography-oriented DSRL, the AST8300 offers a complete suite of easy to use graphical applications that can be accessed using the large 5" touchscreen monitor, including photo sequences programming with filters management, temperature setting and monitor, liveview and focus modes, images review and postprocessing.
The camera software includes all the tools needed for easy and intuitive operations and administration. More advanced applications like standalone autoguiding using an external USB camera/webcam are foreseen in a near future. Moreover, thanks to the completely Open Source license of the software and the Linux OS, other applications can be easily added by the users, giving the camera more and more capabilities: our aim is to create a community of AST8300 users and software developers which will add leading edge contents, ranging from innovative readout modes to web enabled applications. The same applications are accessible from any network connected device, including PC and smartphones/tablets, avoiding the need of learning different interfaces.
The user can control the camera in a conventional mode through a PC connected via an Ethernet cable.
The calculation capacity and the rich set of embedded peripheral of the processor adds to these cameras further innovative use modes: the Wireless mode and the Stand-Alone mode.
The Wireless mode let the user communicate with the camera through a wireless link established between his PC / Tablet / Smartphone and the integrated WiFi module of the camera. No wire exists between the Camera and the PC, so that the user can do all the actions comfortably and no one can risk to stumble on a wire destroying the work of hours.
The Stand-Alone mode is based on the availability of the Astrel 5" Touch Screen LCD. This (removable) display is connected to the processor through a dedicated LCD bus on a flex cable and tied to the camera body with a set of adjustable junctions that let the user fix the proper position for optimized view and touch control. In this way the user has complete control of the Camera without the use of a PC, which is usually not built to be used in harsh environment and forgetting the risk of exhausted battery. The user can also work using a mini wireless keyboard in place of the touch screen, if prefer. The applications can be run using a night mode graphical interface, while the LCD backlight can be maintained off when not in use.
ALL THE USE MODES USE THE SAME SOFTWARE GRAPHICAL INTERFACE
The table below summarize the several use mode:
The AST8300B provides the following ports:
Display Port: Touch-screen LCD
USB HS (2x) Host Port: Guide camera, memory pen drive, GPS module, HUB, ...
Ethernet: Gbit data network or direct PC connection
External In/Out 1 (UART, I2C, GPIO, PWR): sensors, LEDs, lens resistive heater, ...
External In/Out 2 (SPI, GPIO, PWR): mount motor control, ...
Finally the camera provides also a buzzer to notify camera operations and status, fully configurable by the user.
The AST8300-B series incorporate an internal seven position filter wheel.
The filter wheel accepts unmounted 27 to 27.6 mm filters.
The customers can select the proper configuration among a rich set of filters available on Astrel web site from Astronomik at the moment of purchasing the camera in order to get a fully equipped camera. For any other filter brand please contact us.
The customer can also change filters by himself following the indications on the user manual without any problem.
The eighth position of the filter-wheel is occupied by the shutter.
The exact position of the filter-wheel is controlled through the feedback of an optical sensor that provide also the filter identity to the processor.
The camera provides a complete set of onboard applications to make and manage photos. The applications are displayed on the touch LCD in stand alone mode or are available via VNC when used with PC / Tablet / Smartphones. The applications have two customizable skins: the daylight mode and the night mode.
At startup the camera shows a desktop that allows the user to access to the onborad applications.
The Astrel Desktop appears on a typical Linux Desktop where are the icons af a set of third-party preinstalled apps.
When in liveview mode, the camera is put in 10x5 binning, giving very high sensitivity and very fast readout: with a few seconds exposure, even faint objects will be visible on the display, allowing a quick and easy framing of the target. Exposure can be increased and decreased on the fly.
The user can enable the focus mode by selecting a star on the display. The camera starts downloading a small area around the selected star as fast as 2-3 frames per second, while showing the FWHM and profile graph, thus allowing a fast and precise focus. The dimension of the area surrounding the star and the exposure can be changed on the fly.
Control and make photos
For each filter, the user can define and make a sequence of exposures, with different binning, exposure time and readout mode. The user can choose the name of the photo and save/load presets to speedup operations.
The user selects a temperature setpoint as well as the minimum number of seconds required to ramp up and down the peltier. After the ramp is complete, the program takes control of the peltier power using a PID algorithm. A plot of the temperature covering the previous 5 minutes is showed to monitor the accuracy of the temperature control.
Status monitoring and logging
This graphical interface is used to monitor the photo sequence. It shows the photo info, the current exposure in the sequence, the remaining time, the current temperature, the TEC power and the supply voltage. When touching the image, the corresponding image intensity value is displayed in the value box.
The Filterwheel tool is used to control, where available, the integrated filter wheel, to select a filter for the Find and focus tool. At powerup the filterwheel is automatically moved to its default position. The go button moves the wheel to the selected filter position and together with direction and step +/- buttons are needed during the filter installation procedure.
The camera comes with third party KStars/Ekos and Cartes du Ciel planetarium apps already installed. With them the camera could control any telescope mount compatible with the INDI standard (most mounts)
The autoguider tool is based on Lin_guider Linux program and used to compensate for the tracking errors of the telescope mount during the exposure time.
This sw is compatible with most guide cameras and mount actuators.
Both video and actuator parameter are fully configurable.
While guiding is possible to monitor drift graph, current values of corrections and
Online help, filter calibration, file manager, text editor, safe shutdown, USB eject, Image Viewer, ...
Considering the high level of integration (incorporated filter-wheel) and the on-board intelligence (a PC inside!) the AST8300B series features very compact dimensions: it consists on a cylinder-shaped camera body with a diameter of 130 mm and an height of 76 mm.
The case is entirely made of aluminium alloy made by high-precision CNC lathe and milling machines with no die cast elements.
The aluminium is finished with a double treatment: complete anodization and external high resistance coating.
The case consists of two main units: Sensor Unit (SU) and Processor Unit (PU). The SU includes the PCB with the sensor and its drivers and the filter-wheel; the PU include the PCB with the Processor, its memories and all the related communication and controlling logic. The two units are perfectly separated and communicate only through an internal sealed connector: this allows the vacuum sealing of the SU and minimize any EMC effect from the PU the CCD sensor output.
The weight is also limited: 880g (including filter-wheels, without filters) and the building parts are positioned get the best balance resulting in greater stability on the mounts.