Moravian instruments, Inc., source: https://www.gxccd.com/art?id=590&lang=409, printed: 06.06.2020 3:34:00
|C1+ camera models are designed to fulfill the gap between small and lightweight C1 models, intended as Moon and planetary cameras and auto-guiders, and C2 cameras, equipped with active sensor cooling and mechanical shutter and thus intended for more serious astronomical imaging and research. C1+ cameras are able to work as C1 ones, only being somewhat heavier and bulkier, and at the same time C1+ can replace the C2 models, only with slightly less cooling performance and lack of mechanical shutter.|
Mechanical design of this series makes it fully compatible with vast range of telescope adapters a external filter wheels, Camera Ethernet adapters, etc.
Rich software and driver support allows usage of C1+ camera without necessity to invest into any 3rd party software package thanks to included free SIPS software package. However, ASCOM (for Windows) and INDI (for Linux) drivers, shipped with the camera, provide the way to integrate C1+ camera with broad variety of camera control programs.
C1+ cameras are designed to be connected with the host PC through USB 3.0 interface, operating at 5 Gbps. Cameras are also compatible with USB 2.0 port to communicate with a host PC.
Alternatively, it is possible to use the Moravian Camera Ethernet Adapter device. This device can connect up to four Cx (with CMOS sensors) or Gx (with CCD sensors) cameras of any type 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.
Please note that the USB standard allows usage of cable no longer than approx. 5 meters and USB 3.0 cables are even shorter to achieve very fast transfer speeds. On the other side, the TCP/IP communication protocol used to connect the camera over the Ethernet adapter is routable, so the distance between camera setup and the host PC is virtually unlimited.
Note the camera must be connected to some optical system (e.g. the telescope) to capture images. The camera is capable of long exposures, necessary to acquire the light from faint objects. If you plan to use the camera with the telescope, make sure the whole telescope/mount setup is capable to track the target object smoothly during long exposures.
C1+ camera head is designed to be as small and compact as a cooled camera with rich features and compatible with broad set of accessories can be.
C1+ cameras are equipped with tiltable telescope interface and threaded holes for mounting on tripod or dovetail bar. They are also compatible with external filter wheels designed for larger C2 cameras — camera head contains connector to control filter wheel. If the external filter wheel is used, the tiltable mechanism on the camera head is inactive and tiltable adapters for external filter wheels are used instead. Therefore, C1+ cameras can utilize vast range of telescope and lens adapters including off-axis guider adapters.
C1+ camera models are equipped with Sony IMX global shutter CMOS detectors with 3.45 × 3.45 μm square pixels. Individual models differ in resolution only.
All used sensors utilize global electronic shutter. This means every pixel within the image is exposed in the same time, as opposed to rolling shutter sensors, which exposes individual lines one after another. There is no difference for long exposures of static objects, but imaging of moving objects using short exposure time using rolling shutter leads to image shape distortions.
C1+ camera models with 8- and 12-bit digitization:
C1+ camera models with 12-bit digitization only:
Cameras limited to 12-bit read mode are marked with letter A, following the model number. For instance, if C1+12000 marks camera with both 8- and 12-bit read modes, C1+12000A denotes camera model with only 12-bit read mode. All other parameters (sensor size, pixel resolution) are equal.
CMOS camera electronics primary role, beside the sensor initialization and some auxiliary functions, is to transfer data from the CMOS detector to the host PC for storage and processing. So, as opposite to CCD cameras, CMOS camera design cannot influence number of important camera features, like the dynamic range (bit-depth of the digitized pixels).
The sensors used in C1+ cameras shows very good linearity in response to light. This means the camera can be used also for entry-level research projects, like for instance photometry or variable stars etc.
The slow variant of both read modes can be used to slightly lower the amount of heat generated by the sensor, as the communication interface operates at half speed compared to fast mode. Also, when the camera is connected using USB 2.0 interface, fast read mode provides data at higher speed than the USB 2.0 can handle and thus causes more interruptions of image digitization process.
The digitization speeds mentioned above are valid for USB 3.0 connection. Also please note the digitization speeds do not necessarily lead to corresponding FPS, because every image downloaded has to be processed and displayed, which also consumes time. This time is negligible, if slow-scan camera needs many seconds for image download, but in the case of fast CMOS cameras, time for image processing in the PC (e.g. calculation of image standard deviation etc.) can be longer than image download itself.
Despite one byte per pixels is transferred from camera to PC in the 8-bit read mode, many astronomical processing software packages work with 16-bit or 32-bit images only (e.g. SIPS). So, images occupy the same space in the computer memory regardless of the read mode.
Also, standard format for image storage in astronomy is FITS. While this format supports 8-bit per pixel, this variant is rather unusual and 16 or 32-bit integer or 32-bit floating-point pixels are typically stored to disk files to achieve as wide compatibility as possible.
Sensors used in C1+ cameras offer programmable gain from 0 to 24 dB, which translates to the output signal multiplication from 1× to 15.9×. Gain can be set with 0.1 dB step.
Note the C1+ camera firmware supports only analog gain, which means real amplification of the signal prior to its digitization. The used sensors support also digital gain control, which is only numerical operation, bringing no real benefit for astronomical camera. Any such operation can be performed later during image processing if desired.
Generally, many sensor characteristics depend on the used gain. Hence, we provide two lists of parameters for both minimal and maximal gain.
Camera/sensor parameters for minimal gain 0 dB (1×):
Camera/sensor parameters for maximal gain 24 dB (15.9×):
Please note the values stated above are not published by sensor manufacturer, but determined from acquired images. Results may slightly vary depending on particular sensor and other factors (e.g. sensor temperature), but also on the software used to determine these values.
C1+ cameras are capable of very short exposures. The shortest exposure time is 125 μs (1/8000 of second). This is also the step, by which the exposure time is expressed. So, the second shortest exposure is 250 μs etc.
Long exposure timing is controlled by the host PC and there is no upper limit on exposure time. In reality the longest exposures are limited by saturation of the sensor either by incoming light or by dark current (see the following sub-chapter).
As mentioned in the introduction, C1+ cameras can operate only with USB power. Camera is then capable to acquire images and to control (guide) telescope mount via “autoguider” port. However, active sensor cooling (as well as filter wheel operation) is available only if external 12 V DC power supply is connected.
Camera fan operates even without 12 V DC power attached, only with lower fan speed. This helps to keep the camera electronics temperature close to environment temperature. When the external power is plugged in, the fan turns to full speed to remove the heat generated by the Peltier thermo-electric cooler.
Regulated thermoelectric cooling is capable to cool the CMOS sensor more than 40 °C below ambient temperature. The Peltier hot side is cooled by fan. The sensor 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.
The camera head contains two temperature sensors – the first thermometer measures directly the temperature of the CMOS sensor. The second one measures the temperature inside the camera shell.
The cooling performance also 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.
The stated values are valid for C1+3000A camera. As noted above, maximum ΔT of higher resolution sensors (C1+5000A, C1+12000A) is slightly lower as well as ΔT of corresponding non-A camera versions.
Maximum temperature difference between CMOS sensor 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 sensor temperature when the ambient temperature rises. Typical temperature drop can be achieved with cooling running at approx. 90% power, which provides enough room for regulation.
The 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 25 W, the 60 W power supply ensures noise-free operation.
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.
Power consumption is measured on the DC side of the supplied power adapter. Camera consumes more energy from the AC outlet than stated 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.
C1+ 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.
A lot of astronomical telescope mounts (especially the mass-manufactured ones) are not precise enough to keep the star images perfectly round during long exposures without small corrections. Cooled astronomical cameras and digital SLR cameras allow perfectly sharp and high-resolution images, so even a small irregularity in mount tracking appears as star image deformations. C1+ cameras were designed with automatic mount guiding on mind.
C1+ cameras were designed to operate without any mechanically moving parts (with the exception of magnetically levitating fan). Electronic shutter allows extremely short exposures and also obtaining thousands of images in a short time, which is necessary for quality guiding.
C1+ cameras work in connection with a host computer (PC). Guiding corrections are not calculated in the camera itself, it only sends acquired images to the PC. The software running on the PC calculates the difference from required state and sends appropriate corrections to the telescope mount. The plus side of using a host PC CPU to process images is the fact, that current PCs provide overwhelming computational power compared to any embedded processor inside the guiding camera. Guiding algorithms then can determine star position with sub-pixel precision, can match multiple stars to calculate average difference, which limits the effects of seeing, etc.
Calculated corrections can be sent back to mount using PC-to-mount link. If the mount controller does not support so-called Pulse Guide commands, it is possible to use Autoguider port. It is enough to connect the C1+ camera and the mount using standard 6-wire cable and guide the mount through the camera.
The maximum sinking current of each pin of the C1+ camera is 400 mA. If the mount does not treat the autoguider port as logical input only, but switches the guiding motors directly by these signals, a relay box must be inserted between the camera and the mount. The relay box ensures switching of currents required by the mount.
The Autoguider port follows the de-facto standard introduced by SBIG ST-4 autoguider. The pins have the following functions:
Compact and robust camera head measures only 78 × 78 × 80 mm (approx. 3.1 × 3.1 × 3.2 inches). The head is CNC-machined from high-quality aluminum and black anodized. The head itself contains USB-B (device) connector, Autoguider port connector, connector for External Filter Wheel and 12 V DC power plug.
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 sensor cold chamber).
C1+ cameras can be equipped with the same external filter wheels like the C2 cameras. In such case the C2 compatible adapter has to be used as a base for the External filter wheel.
The filter wheel can be used only if the C1+ camera is plugged to 12 V DC external power supply.
If the external filter wheel is used, tiltable adapters for C2 or G2 Mark II cameras have to be used with it.
The S sized External filter wheel diameter is greater (viz. External Filter Wheels), but the back focal distance of all external filter wheels is identical.
Various accessories are offered with C1+ cameras to enhance functionality and help camera integration into imaging setups.
For illustration of adapter options, see the figure in the C1+ Camera Overview chapter.
C1+ camera heads are equipped with tripod thread (0.25”) on the bottom 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.
Another possibility is to use four metric M4 threaded holes, also located on the bottom side of the camera head.
C1+ cameras employ the same desiccant container like the larger C2, C3 and C4 cameras, aw well as CCD based G2, 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.
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 sensor 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 sensor cold chamber itself. It is intended only to hold possible dust particles from entering the front half of the camera head with the sensor 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 (or for just a coin), allowing releasing and also tightening of the container.
The Moravian Camera Ethernet Adapter device allows connection of up to four Cx 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.
Moravian Camera Ethernet Adapter device is described in detail here.
Software and driver support of the Cx series CMOS cameras is as rich as is the case of their Gx series CCD camera siblings.
The SIPS (Scientific Image Processing System) software package version 3.18 or later is necessary to control C1+ cameras.
Support for CMOS based Cx cameras was gradually added to individual SIPS version. While previous minor SIPS versions could be able to recognize C1+ cameras, always use v3.18 or later for reliable camera operation.
Powerful 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 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, 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.
SIPS 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 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.
Color sensors have red, green and blue filters applied directly on individual pixels (so-called Bayer mask).
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.
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.