Moravian instruments, Inc., source: https://www.gxccd.com/art?id=525&lang=409, printed: 30.04.2025 16:26:53
Main page▹Product Overview▹Astronomical cameras▹Articles | 26.11.2020 |
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The cooled G2 series Mark II CCD cameras were developed for imaging under extremely low-light conditions in astronomy, microscopy and similar areas. Design of this series inherits from earlier G2 Mark I cameras but brings some significant enhancements. G2 cameras employ precise electronics providing uniform frames and extremely low read noise limited only by CCD detector itself. Modular mechanical construction allows various camera variants to be combined with rich set of accessories, including telescope adapters, off-axis guider adapters, internal or external filter wheels, Ethernet adapters, guiding cameras etc. |
All members of the G2 Mark II series of cooled CCD cameras are designed for low-light imaging applications, requiring very high sensitivity and very low noise and dark current. The G2 Mark II series comprises numerous model, each suitable for a particular application area in astronomical research, astro-photography, microscopy, life-sciences, material research etc. G2-0400, G2-1600 and G2-3200 models are equipped with Full-Frame, NABG detectors. Their features make them especially suitable for research applications:
G2-8300 still employs Full-Frame architecture CCD, but thanks to ABG this particular model is especially popular among astro-photographers:
G2-2000 and G2-4000 models use Interline-Transfer CCD detectors, bringing some unique features:
All members of the G2 Mark II series share the same design, making them powerful research and imaging tools:
No matter if your target is reliable scientific data or beautiful images of deep-sky objects, G2 Mark II cameras are able to provide both. G2 Mark II Camera OverviewG2 camera head is designed to be easily used with a set of accessories to fulfill various observing needs. Camera head itself is manufactured in two different variants:
G2 Camera Mark II without filter wheel (left), with Internal filter wheel (middle) and with attached External filter wheel (right) G2 camera model with Internal filter wheel accepts two sizes of filters:
There are two sizes of the External filter wheels, each capable to accept multiple sizes of filters, available for the G2 cameras:
Remark: Because G2 series of cameras can work with various sensors, not all filter wheel/filter variants can be used with every detector. For instance, G2-8300 camera works with CCD measuring 22.7 mm diagonally. Depending on the used optics f/ratio, 1” or even 1.25” filters can cause more or less significant vignetting when combined with such sensor. Warning: Please note the camera head is designed to either accept Internal filter wheel or to be able to connect to the External filter wheel, but not both. If the Internal filter wheel variant is used, External filter wheel cannot be attached. Components of G2 Mark II Camera system include:
The G2 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 the camera, you need a computer which:
G2 cameras require at last one free USB 2.0 port to communicate with a host PC. Alternatively, it is possible to use the Gx Camera Ethernet Adapter device. This device can connect up to four Gx cameras of any type (not only G2, but also G0, G1, G3 and G4) and offers 1 Gbps and 10/100 Mbps Ethernet interface for direct connection to the host PC. Because the PC then uses TCP/IP protocol to communicate with the cameras, it is possible to insert WiFi adapter or other networking device to the communication path. G2 Mark II Camera ModelsAvailable models of G2 Mark II cameras:
CCD detectorsG2 Mark II series of CCD cameras are manufactured with two kinds of CCD detectors:
Model G2-0400G2-0400 model uses 0.4 MPx OnSemi KAF-0402ME NABG Full-Frame CCD chip.
KAF-0402ME CCD chip specifications Model G2-1600G2-1600 model uses 1.6 MPx OnSemi KAF-1603ME NABG Full-Frame CCD chip.
KAF-1603ME CCD chip specifications Model G2-3200G2-3200 model uses 3.2 MPx OnSemi KAF-3200ME NABG Full-Frame CCD chip.
KAF-3200ME CCD chip specifications Model G2-8300G2-8300 camera uses 8 MPx OnSemi KAF8300 ABG Full Frame CCD detectors with 4/3 format.
KAF-0402ME CCD chip specifications Model G2-2000G2-2000 model uses 2 MPx OnSemi ABG Inteline-Transfer KAI-2020 CCD chip.
KAI-2020 CCD chip specifications Model G2-4000G2-4000 model uses 4 MPx OnSemi ABG Inteline-Transfer KAI-4022 CCD chip.
KAI-4022 CCD chip 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 seconds. Maximum length of single USB cable is approx. 5 m. This length can be extended to 10 m or 15 m by using single USB hub or active USB extender cable. Up to 5 hubs or active extenders can be used in one connection. Gx Camera Ethernet Adapter device allows connection of up to four Gx cameras of any type through Ethernet interface and TCP/IP network. Because TCP/IP protocol can be routed, the distance between camera and host PC can be virtually unlimited.
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 G2-0400
G2-0400 electronics specifications Model G2-1600
G2-1600 electronics specifications Model G2-3200
G2-3200 electronics specifications Model G2-8300
G2-8300 electronics specifications Model G2-2000
G2-2000 electronics specifications Model G2-4000
G2-4000 electronics specifications Notes:
Cooling and power supplyRegulated thermoelectric cooling is capable to cool the CCD chip up to 50 °C below ambient temperature. The Peltier hot side is cooled by fan. 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. Bottom side with connectors of the camera without filter wheel (left) and with internal filter wheel (right) The camera head contains two temperature sensors — the first sensor measures directly the temperature of the CCD chip package. The second one measures the temperature inside the camera shell. The cooling performance depends on the environmental conditions and also on the power supply. If the power supply voltage drops below 12 V, the maximum temperature drop is lower.
Chip cooling specifications Remark: Maximum temperature difference between CCD and ambient air may be reached when the cooling runs at 100% power. However, temperature cannot be regulated in such case, camera has no room for keeping the CCD temperature when the ambient temperature rises. Typical temperature drop can be achieved with cooling running at approx. 85% power, which provides enough room for regulation. Power supplyThe 12 V DC power supply 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. Although the camera power consumption does not exceed 40 W, the 60 W power supply ensures noise-free operation.
Power supply specification 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 other than the supplied power source is used. Remark: Power consumption is measured on the input (AC side) of the supplied power adapter. Camera consumes less energy from 12 V power supply than state here. The camera contains its own power supplies inside, so it can be powered by unregulated 12 V DC power source — the input voltage can be anywhere between 10 and 14 V. However, some parameters (like cooling efficiency) can degrade if the supply drops below 12 V. G2 camera measures its input voltage and provides it to the control software. Input voltage is displayed in the Cooling tab of the Imaging Camera control tool in the SIPS program. This feature is important especially if you power the camera from batteries. Mechanical SpecificationsCompact and robust camera head measures only 114 × 114 × 65 mm (approx. 4.5 × 4.5 × 2.6 inches). The head is CNC-machined from high-quality aluminum and black anodized. The head itself contains USB-B (device) connector and 12 V DC power plug. Integrated mechanical shutter allows streak-free image readout, as well as automatic dark frame exposures, which are necessary for unattended, robotic setups. Camera head with integrated Internal filter wheel is 77.5 mm thick. Filter wheel offers 5 positions for standard 1.25-inch threaded filter cells. A variant of filter wheel with 6 positions for unmounted D26 mm filters is also available.
Mechanical specifications Remark: Filter wheel with 6 positions can cause vignetting (shielding of the detector corners) if large CCD detector is used. Back focus distance is measured from the sensor to the base on which adjustable adapters are mounted. Various adapters then provide back focal distance specific for the particular adapter type (e.g. M48 threaded adapter back focal distance is 55 mm). Stated back focal distance already calculates with glass permanently placed in the optical path (e.g. optical window covering the CCD cold chamber). When the adjustable adapter base, intended for camera with Internal filter wheel, is mounted on camera without filter wheel, the resulting back focal distance is only 21 mm. Camera with Internal Filter WheelCamera with XS External Filter WheelThe S sized External filter wheel diameter is greater (viz. External Filter Wheels), but the back focal distance of all external filter wheels is identical. Camera without filter wheelIf the camera model, intended for usage with External filter wheel, is used without filter wheel at all, two types of adjustable adapter bases can be used. When a thin adapter base, intended for camera with Internal filter wheel, is used, the back focal distance is only 21 mm. Thick adapter base has the same thickness like the External filter wheel. This means all adapters, attached to this thick base, keep the same back focal distance like if attached directly to External filter wheel shell or to a camera with Internal filter wheel and “thin” adapter base. Optional accessoriesVarious accessories are offered with G2 Mark II cameras to enhance functionality and help camera integration into imaging setups. External filter wheelsWhen there is no filter wheel inside the camera head, all electronics and firmware, intended to control it, stays idle. These components can be utilized to control external filter wheel with only little changes. Also the camera front shell can be manufactured thinner, the space for filter wheel is superfluous. G2 Mark II camera with attached External filter wheel Telescope adaptersVarious telescope and lens adapters for the G2 Mark II cameras are offered. Users can choose any adapter according to their needs and other adapters can be ordered separately.
All telescope/lens adapters of the G2 Mark II series of cameras can be slightly tilted. This feature is introduced to compensate for possible misalignments in perpendicularity of the telescope optical axis and sensor plane. The Mark II camera telescope adapters are attached using three pulling screws. As the adapter tilt is adjustable, another three pushing screws are intended to fix the adapter after some pulling screw is released to adjust the tilt. Adjustable telescope/lens adapters are attached slightly differently depending if the adapter is attached directly to the camera head (e.g. when camera is equipped with internal filter wheel) or to the External filter wheel case.
Off-Axis Guider Adapter (OAG)G2 camera can be optionally equipped with Off-Axis Guider Adapter. This adapter contains flat mirror, tilted by 45° to the optical axis. This mirror reflects part of the incoming light into guider camera port. The mirror is located far enough from the optical axis not to block light coming to the main camera sensor, so the optics must be capable to create large enough field of view to illuminate the tilted mirror. G2-OAG is manufactured in two variants, one with M42 × 0.75 thread (T-thread) and another with M48 × 0.75 thread. Both variants are designed to be compatible with external filter wheels and to preserve 55 mm distance from the sensor. If the OAG has to be used on camera with internal filter wheel, the OAG is mounted to adapter base like any other adapter. Resulting Back focal distance remains the same. OAG guider port is compatible with G0 and G1 cameras. It is necessary to replace the CS/1.25” adapter with short, 10 mm variant in the case of G1 cameras. Because G1 cameras follow CS-mount standard, (BFD 12.5 mm), any camera following this standard with 10 mm long 1.25” adapter should work properly with the G2-OAG. Attaching camera head to telescope mountG2 Mark II camera heads are equipped with tripod thread (0.25”) on the top side. 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. Tool-less desiccant containersG2 Mark II cameras employ the same desiccant container like the larger G3 and G4 cameras. The whole container can be unscrewed, so it is possible to exchange silica-gel without the necessity to remove the camera from the telescope. The whole desiccant container can be baked to dry the silica-gel inside or its content can be poured out after unscrewing the perforated internal cap and baked separately 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. New containers have a thin O-ring close to the threaded edge of the container. This O-ring plays no role in sealing the CCD cold chamber itself. It is intended only to hold possible dust particles from entering the front half of the camera head with the CCD chamber optical window, shutter and possibly internal filter wheel. While the O-ring material should sustain the high temperature during silica-gel baking, it is possible to remove it and put it back again prior to threading the contained back to the camera. 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. This design also allows usage of some optional parts:
Comparison of the standard and tool-less container (left), optional cap, standard and tool-less variant of the container Camera head color variantsCamera head is available in several color variants of the center plate. Visit manufacturer's web pages for current offering. Moravian Camera Ethernet AdapterThe Moravian Camera Ethernet Adapter device allows connection of up to 4 Gx cameras of any type on one side and 1 Gbps Ethernet interface on the other side. So, this device allows attaching of cameras to virtually unlimited distance using the routable TCP/IP protocol. The Moravian Camera Ethernet Adapter device (left) and the adapter with connected two cameras (right) Moravian Camera Ethernet Adapter device is described in detail here. Software SupportPowerful SIPS (Scientific Image Processing System) software, supplied with the camera, allows complete camera control (exposures, cooling, filter selection etc.). Also automatic sequences of images with different filters, different binning etc. are supported. With full ASCOM standard support, SIPS can be also used to control other observatory equipment. Specifically the telescope mounts, but also other devices (focusers, dome or roof controllers, GPS receivers etc.). SIPS also supports automatic guiding, including image dithering. Both autoguider port hardware interface (6-wire cable) and mount Pulse-Guide API guiding methods are supported. For hi-quality mounts, capable to track without the necessity to guide at last during one exposure, inter-image guiding using the main camera only is available. But SIPS is capable to do much more than just camera and observatory control. Many tools for image calibration, 16 and 32 bit FITS file handling, image set processing (e.g. median combine), image transformation, image export etc. are available. As the first S in the abbreviation SIPS means Scientific, the software supports astrometric image reduction as well as photometric processing of image series. SIPS focuses to advanced astrometric and photometric image reduction, but also provides some very basic astro-photography processing SIPS software package is freely available for download from this www site. All functions are thoroughly described in the SIPS User's Manual, installed with every copy of the software. 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. Also INDI drivers for 32 bit and 64 bit Linux running on x86 and ARM are available. Also drivers for TheSkyX package running on macOS are supplied with the camera. 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 Advanced reconstruction of color information of single-shot-color camerasColor CCD detectors have red, green and blue filters applied directly on individual pixels (so-called Bayer mask). Schematic diagram of color CCD detector with Bayer mask (left) and magnified crop of raw image captured by color camera (right) Every pixel registers light of particular color only (red, green or blue). But color image should contain all three colors for every pixel. So it is necessary to calculate missing information from values of neighboring pixels. There are many ways how to calculate missing color values — from simple extending of colors to neighboring pixels (this method leads to coarse images with visible color errors) to methods based on bi-linear or bi-cubic interpolation to even more advanced multi-pass methods etc. Bi-linear interpolation provides significantly better results than simple extending of color information to neighboring pixels and still it is fast enough. But if the telescope/lens resolution is close to the size of individual pixels, color artifacts appear close to fine details, as demonstrated by the image below left. The above raw image with colors calculated using bi-linear interpolation (left) and the same raw image, but now processed by the multi-pass de-mosaic algorithm (right) Multi-pass algorithm is significantly slower compared to single-pass bi-linear interpolation, but the resulting image is much better, especially in fine details. This method allows using of color camera resolution to its limits. SIPS offers choosing of color image interpolation method in both Image Transform and New Image Transform tools. For fast image previews or if the smallest details are significantly bigger than is the pixel size (be it due to seeing or resolution of the used telescope/lens) the fast bi-linear interpolation is good enough. But the best results can be achieved using multi-pass method. Shipping and PackagingG2 Mark II cameras are supplied in the foam-filled, hard carrying case containing:
G2 cameras are shipped in the foam-filled carrying case (left), larger case is used if camera is ordered with external filter wheel (right) Image GalleriesExample images captured with G2 cameras.
G2-0402, G2-1600 and G2-3200 Image GalleryG2 CCD cameras with KAF detectors are primarily intended for research work. They are only occasionally used for aesthetics astrophotography. Following examples represent both science observations and astrophotography images. Astronomy researchG2 cameras are appreciated by both professional researchers and amateur astronomers involved in scientific observations. Here are only a few examples, chosen from huge amount of observations, be it extragalactic novae discovery, minor planet photometry and astrometry, variable star discovery and regular observations, exoplanet transit observations etc.
Only 0.8mmag RMS difference from ideal light cure
This discovery is a record in the size of telescope, used to discover nova in M81. The second smallest has 750mm diameter.
Microscopy and material science
Near-IR radiation of semiconductor (solar cell) samples
Field emission microscope images, camera field of view is 800nm (1.5nm/pixel). Astrophotography
All images published with permission of their respective authors. |