Moravian instruments, Inc., source: https://www.gxccd.com/art?id=383&lang=409, printed: 30.04.2025 20:12:21
Main page▹Product Overview▹Astronomical cameras▹Articles | 27.6.2018 |
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Cooled CCD cameras of G4 series contain detectors with 36 × 36 mm area, which is 50% more than photographic full-frame format. G4 camera dimensions are the same like dimensions of G3 series. Also camera handling, software control, power supply and connection to the host PC using fast USB 2.0 interface is the same like in the case of G3 cameras. Filter wheel for 50 × 50 mm square filters (round filters of 50 mm diameter cause vignetting on such large CCD chips) cannot be placed inside the camera head due to limited space. But it is possible to connect external filter wheels for 5 or 7 large filters to the G4 camera, the camera head already contains connector for external filter wheel control. |
G4 cameras contain Full-Frame CCD chips OnSemi KAF with 36 × 36 mm detector area. These detectors are equipped with so-called anti-blooming gate (ABG), which drains the over-abundant charge from saturated pixels. ABG ensures the round images of bright stars, without disruptive blooming spikes. On the other side, compromising of the CCD linearity by ABG is only negligible. G4 cameras can be used for astrometric and photometric applications as well as for astrophotography. No matter if your target is reliable scientific data or beautiful images of deep-sky objects, G4 cameras are able to provide both. G4 Camera OverviewG4 camera head is designed to be easily used with a set of accessories to fulfill various observing needs. G4 cameras do not allow usage of internal filter wheel as they require large 50 × 50 mm filters. External filter wheel is then the only option for G4 camera. There are two sizes of the external filter wheel available for the G4 cameras:
Camera head and numerous accessories comprise imaging system, capable to be tailored for many applications.
G4 cameras are designed to work in cooperation with a host Personal Computer (PC). As opposite to digital still cameras, which are operated independently on the computer, the scientific slow-scan, cooled cameras usually require computer for operation control, image download, processing and storage etc. To operate G3 camera, you need a computer which:
G4 Camera ModelsG4 series contains the following camera models:
G4 CCD Cameras Technical SpecificationsCCD chipG4 cameras use OnSemi Full-Frame CCD detectors with ABG (anti-blooming gate), ensuring images without excessive charge leaks from the overexposed portions of the image (blooming), e.g. bright stars in the field of view. ABG of these CCDs is designed for relatively low light levels (100× of saturation signal, compared to e.g. 300× of saturation signal ABG level of KAI-4022 CCD or 1000× of saturation signal ABG level of KAF-8300 CCD, intended for taking of images against sun etc.). Low ABG level does not to disrupt linear response to light. Model G4-9000G4-9000 model uses 9 MPx OnSemi KAF-09000 CCD.
KAF-09000 CCD specifications Model G4-16000G4-16000 uses 16 MPx OnSemi KAF-16803 CCD.
KAF-16803 CCD specifications Camera Electronics16-bit A/D converter with correlated double sampling ensures high dynamic range and CCD chip-limited readout noise. Fast USB interface ensures image download time within several tens of seconds. Maximum length of single USB cable is 5 m. This length can be extended for instance to 10 m by using single USB hub or USB active extender cable. Up to 100 m extension can be achieved with third-party extender.
Camera electronics specifications Image download time depends on the CCD chip used in particular camera model. Also the read noise depends on the chip as well as on the read mode.
Model G4-9000
G4-9000 electronics specification The gain in binning modes of G4-9000 cameras was adjusted from 2.5 e-/ADU to 1.7 e-/ADU beginning with system driver version 2.3 to utilize the full A/D converter dynamic range, because particular detector output node cannot pass higher output signal levels either way. Model G4-16000
G4-15000 electronics specification G4-16000 cameras use the same gain for unbind and binned reading when used with system driver version 2.3 and higher. When older driver is used, stated gain 1.6 e-/ADU is used for 1×l binning only, while all other binning use 2.7 e-/ADU. Gain setting was unified to utilize the full A/D converter dynamic range, because particular detector output node cannot pass higher output signal levels either way. Notes:
Power and USB connectors on the back side of the camera head. External filter wheel connector in the middle. Chip CoolingRegulated thermoelectric cooling is capable to cool the CCD chip from 42 to 47 °C below ambient temperature, depending on the camera type. The Peltier hot side is cooled by a fans. The CCD chip temperature is regulated with ±0.1 °C precision. High temperature drop and precision regulation ensure very low dark current for long exposures and allow proper image calibration. G4 cameras are available in two variants, differing in the cooling performance:
Chip cooling specifications Notes:
Power supplyThe 12 V DC power supply adapter enables camera operation from arbitrary power source including batteries, wall adapters etc. Universal 100–240 V AC/50–60 Hz, 60 W brick adapter is supplied with the camera.
Power supply specifications Notes:
Warning: The power connector on the camera head uses center-plus pin. Although all modern power supplies use this configuration, always make sure the polarity is correct if you use own power source. Mechanical SpecificationsCompact and robust camera head measures only 154 × 154 × 65 mm (approx. 6 × 6 × 2.5 inches). The head is CNC-machined from high-quality aluminum and black anodized. The head itself contains USB-B (device) connector, 8-pin RJ45 connector for external filter wheel and 12 V DC power plug, no other parts (CPU box, USB interface, etc.), except a brick power supply, are necessary. Integrated mechanical shutter allows streak-free image readout, as well as automatic dark frame exposures, which are necessary for unattended, robotic setups. Filter wheel if not integrated into camera head, it is necessary to use external filter wheel with 5 positions for 50 × 50 mm square filters. This external filter wheel is driven by the electronics already included into G4 camera head. Only single short 8-wire cable connects the filter wheel with the camera head and no separate power or communication cables are necessary for the external filter wheel. Also software (camera drivers, image acquisition applications) does not distinguish between internal and external filter wheel, camera works the same way like the G2 or G3 camera with integrated filter wheel.
Mechanical specification Regardless if the camera has standard or enhanced cooling, the front view dimensions are the same. Also mounting adapter holes are the same, so both camera variants are compatible with the same set of telescope/lens adapters. The only different dimension is the camera thickness. Enhanced cooling requires thicker camera back shell. Notes:
Optional accessoriesCamera head can be combined with various accessories according to the requirements of the target application (optical system, used filters, guiding, etc.). Telescope adaptersLarge diagonal dimension of CCD detectors used in G4 cameras (52 mm) does not allow usage of common adapters, typically limited to 2 inches diameter (50.8 mm), like T-thread M42 × 0.75, M48 × 1 thread, Nikon bayonet etc. This is why G4 cameras are by default shipped with M68 × 1 threaded adapter. Another alternative if Canon EOS photographic lens adapter, which has enough diameter not to cause significant vignetting. Adapter is designed for G4 cameras with external filter wheel, with which it keep the 44 mm back focal distance between bayonet front plate and CCD detector.
External Filter WheelsBecause large detectors if the G4 camera require large 50 × 50 mm filters, filter wheel cannot be placed inside the camera head and G4 cameras rely on external filter wheels only. There are two sizes of external filter wheels for G4 cameras available:
Remark: There is a possibility to use round D50 mm filters with the G4 camera. Normally these filters cause significant vignetting as the CCD diagonal measures 52 mm and filter clear aperture is 47 mm. But it the used optics does not cover the whole detector (e.g. standard camera fish-eye lens), D50 mm filters increase number of available position from 5 to 7 in the case of M wheels and from 7 to 9 in the case of L wheels. External filter wheels for 5 filters 50 × 50 mm (left) and for 7 filters D50 mm or with M48 × 0.75 threaded cells (right) External filter wheels are described in detail here. Off-Axis Guider adapterThe G4 off-axis guider (OAG) is designed to allow attachment of any guiding camera with 1.25" eyepiece nose, although the nose must be somewhat shorter to achieve focus. G0 cameras are designed to achieve focus with G4 OAG and a special shorter version of 1.25" nose with C-mount thread is available for all G1 cameras. Any camera with CS-mount (short version of C-mount standard) can use this adapter to be attached to G4 OAG. The G4 OAG offers the M68 × 1 thread on the telescope side. The back focal distance is 61.5 mm. Off-Axis Guider adapters are described in detail here. Guiding camerasG0 and G1 cameras are completely independent devices with their own USB connection to the host PC. They are mentioned here only not to omit an important part of the whole system. G1-0301 standalone guiding/imaging camera is equipped with USB connection and standard AutoGuider port G0 and G1 cameras can be used on the G4 OAG, on standalone guiding telescope or for any other imaging purpose, like Moon or planetary imaging etc. Both G0 and G1 camera can share the Gx Camera Ethernet Adapter with up to 3 other Gx cameras to be accessed over network. G0 and G1 guider cameras are described in detail here. Attaching camera head to telescope mountG4 cameras are equipped with two tripod 0.250-20UNC threads on the top side of the camera head. This thread can be used to attach 1.75 inch dovetail bar (Vixen standard). It is then possible to attach the camera head, e.g. equipped with photographic lens, directly to various telescope mounts supporting this standard. Spare desiccant containersThe G4 cameras are supplied with silicagel container, intended to dry the CCD cold chamber. This container can be unscrewed and desiccant inside can be dried in the owen (see the camera User's Manual). Remark: This is why the container itself does not contain any sealing, which could be damaged by high temperature in the owen. The sealing remains on the CCD cold chamber instead. Container shipped with the camera by default does not exceed the camera head outline. It is equipped with a slot for tool (of for just a coin), allowing releasing and also tightening of the container. Containers intended for enhanced cooling cameras are prolonged as the camera thickness is greater in the case of this variant. Containers for standard and enhanced cooling cameras also in variants allowing tool-less manipulation It is possible to order spare container, which makes desiccant replacement easier and faster. It is possible to dry the spare container with silicagel and then only to replace it on the camera. Spare container is supplied including the air-tight cap. Spare container can be supplied also in variant, allowing manipulation without tools. But this container is longer and exceeds camera outline. If the space behind the camera is not critical, this container can make desiccant exchange even easier. Camera head color variantsCamera head is available in several color variants of the center plate. Visit manufacturer's web pages for current offering. Gx Camera Ethernet AdapterGx Camera Ethernet Adapter allows connection of up to 4 Gx cameras of any type on the one side and 1 Gbps Ethernet on the other side. This adapter allows access to connected Gx cameras using routable TCP/IP protocol over practically unlimited distance. The Gx Camera Ethernet Adapter is available in several variants, but their functionality is basically the same Gx Camera Ethernet Adapter devices are described in detail here. Software SupportPowerful SIPS (Scientific Image Processing System) software supplied with the camera allows complete camera control (exposures, cooling, filters) with automatic sequences and complete image calibration. SIPS also supports advanced tools like Image Add tool with automatic sub-pixel image alignment, (L)RGB Add tool, Image Blink tool, image filters and many more functions. SIPS software package is freely available for download from this www site. Drivers for ASCOM standard as well as native drivers for third-party software are also available (e.g. TheSkyX, MaxIm DL, AstroArt, etc.). Visit the download page of this web site for current list of available drivers, please. Automatic guidingSIPS software package allows automatic guiding of the astronomical telescope mounts using separate guiding camera. Proper and reliable automatic guiding utilizing the computational power of Personal Computer (e.g. calculation of star centroid allows guiding with sub-pixel precision) is not simple task. Guiding complexity corresponds to number of parameters, which must be entered (or automatically measured). The SIPS Guider tool window The Guiding tool allows switching of autoguiding on and off, starting of the automatic calibration procedure and recalculation of autoguiding parameters when the telescope changes declination without the necessity of new calibration. Also swapping of the German Equatorial mount no longer requires new autoguider calibration. There is also a graph showing time history of guide star offsets from reference position in both axes. The length of graph history as well as the graph range can be freely defined, so the graph can be adjusted according to particular mount errors and periodic error period length. Complete log of calibration procedure, detected offsets, correction pulses etc. is also shown in this tool. The log can by anytime saved to log file. An alternative to classic autoguiding is the inter-image guiding, designed for modern mounts, which are precise enough to keep tracking with sub-pixel precision through the single exposure, and irregularities only appear on the multiple-exposure time-span. Inter-image guiding then performs slight mount position fixes between individual exposures of the main camera, which eliminates traveling of the observed objects through the detector area during observing session. This guiding method uses main imaging camera, it does not use another guiding camera and naturally does not need neither OAG nor separate guiding telescope to feed the light into it. Inter-image guiding controls in the Guiding tab of the Imager Camera tool window Shipping and PackagingG4 CCD cameras are supplied in the foam-filled, hard carrying case containing:
G3 and G4 CCD cameras are shipped in the foam-filled carrying case (left), larger case is used if camera is ordered with external filter wheel (right) Image GalleryExample images captured with G4 cameras.
All images published with permission of their respective authors. |