Moravian instruments, Inc., source: https://www.gxccd.com/art?id=653&lang=409, printed: 18.09.2021 22:22:48
|C1× cameras employ the same sensors like the C3 series — latest generation of Sony APS and Full-Frame (24 × 36 mm) CMOS sensors, offering exceptional quantum efficiency thanks to back-illuminated design and very low dark current. Despite relatively small pixels, full-well capacity exceeds 50 ke-, rivaling cameras with much greater pixels. Combined with full 16 bit digitization, perfectly linear response to light and exceptionally low read noise, these cameras are suitable for both aesthetic astro-photography as well as astronomical research. At the same time the C1× camera head is designed to be symmetrical, with as small front cross-section as possible.|
The C1× family of cameras combine large APS and Full-Frame sized sensors, used in the C3 series, with a compact body of C1+ cameras. The front cross-section of the C1× camera head is the same like the C1+ one, only its body is a bit longer to accommodate more complex electronics as well as more powerful cooling (here originates the name of the entire series – C1 eXtended). Similarly to the C1+ line, also the C1× cameras lack mechanical shutter.
Using of large sensors up to size 24 × 36 mm required also redesign of the telescope/lens adapters of the C1× line, the M42/M48 × 0.75 threads, used with C1+ camera adapters, are too small for such large sensors. So, the C1× adapters are equipped with new M56 × 1 thread. The front plate of the M56 × 1 adapter also contains four threaded holes, which makes it compatible with C3 camera body and thus the C1× can use the same External filter wheels and other accessories like the C3 line.
Rich software and driver support allow usage of C1× camera without a 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 and Linux driver libraries are shipped with the camera, provide the way to integrate C1× camera with broad variety of camera control programs.
C1× cameras are designed to be attached to host PC through very fast USB 3.0 port. While C1× cameras remain compatible with older (and slower) USB 2.0 interface, image download time is significantly longer.
Alternatively, it is possible to use the Moravian Camera Ethernet Adapter device. This device can connect up to four Cx (and CCD based Gx) cameras of any type (not only C1×, but also C1, C2, C3 and C4) 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.
Download speed is naturally significantly slower when camera is attached over Ethernet adapter, especially when compared with direct USB 3 connection.
The C1× cameras need an external power supply to operate. It is not possible to run the camera from the power lines provided by the USB cable, which is common for simple imagers. C1× cameras integrate highly efficient CMOS sensor cooling, shutter and possibly filter wheel, so their power requirements significantly exceed USB line power capabilities. On the other side separate power source eliminates problems with voltage drop on long USB cables or with drawing of laptop batteries etc.
Also note the camera must be connected to some optical system (e.g. the telescope) to capture images. The camera is designed for 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 large sensor can be, and at the same time to be robust and resilient.
C1× cameras are equipped with tiltable telescope interface and tripod mounting threaded holes. They are also compatible with external filter wheels designed for larger C2 and C3 cameras — camera head contains connector to control filter wheel. If the external filter wheel is used, the tiltable mechanism on the camera head is not accessible and tiltable adapters for external filter wheels are used instead. C1× cameras with external filter wheels are then compatible with vast range of other telescope and lens adapters including off-axis guider adapters etc.
C1× camera head is designed to be easily used with a set of accessories to fulfil various observing needs. Camera adapter base back focal distance is 16.5 mm and can be used directly to attach the camera to the telescope focuser using the M56 × 1 thread.
The adapter base is also equipped with four M3 threaded holes 44 mm apart. As the adapter base BFD is 16.5 mm — the same BFD like in the case of C2 and C3 cameras — there is a possibility to attach the External Filter Wheel to the C1× camera. Four sizes of the External filter wheels, capable to accept various sizes of filters, are available for the C1× cameras:
The filter wheels with D36 mm filters can be used with C1× cameras equipped with APS size sensors only. Cameras with Full-Frame sensors (24 × 36 mm) cannot use such small filters.
Note the S and M filter wheels are of very similar dimensions and hold the same number of the same filters. They differ in the adjustable adapter size only.
If the External filter wheel is used, the tiltable base directly on the camera head stays inactive. Instead, another tiltable base, intended for C3 adapters, is manufactured directly on the External filter wheel front shell. So, if the External filter wheel is used, adapters for the M56 × 1 thread cannot be used. Instead, adapters designed for C3 cameras, must be used.
C1× cameras are equipped with Sony IMX rolling shutter back-illuminated CMOS detectors with 3.76 × 3.76 μm square pixels. Despite the relatively small pixel size, the full-well capacity over 50 ke- rivals the full-well capacity of competing CMOS sensors with much greater pixels and even exceeds the full-well capacity od CCD sensors with comparable pixel size.
The used Sony sensors are equipped with 16-bit ADCs (Analog to Digital Converters). 16-bit digitization ensures enough resolution to completely cover the sensor exceptional dynamic range.
While the used sensors offer also lower dynamic resolution (12 and 14 bit), C3 cameras do no utilize these modes. Astronomical images always use 2 bytes for a pixel, so lowering the dynamic resolution to 14 or 12 bits brings no advantage beside the slightly faster download. But cooled astronomical cameras are intended for very long exposures and a fraction of second saved on image download is negligible compared to huge benefits of 16-bit digitization.
C1× camera models with consumer-grade sensors include:
C1× camera models with industrial-grade sensors include:
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 the C1× cameras show very good linearity in response to light. This means the camera can be used for advanced research projects, like the photometry of variable stars and transiting exoplanets etc.
C1× cameras are equipped with on-board RAM, capable to hold several full-resolution frames. Downloading of the image to the host computer thus does not influence image digitization process, as the download only transfers already digitized images from camera memory.
Time needed to digitize and download single full frame depends on USB connection type.
If only a sub-frame is read, time needed to digitize and download image is naturally lower. However, the download time is not cut proportionally to number of pixels thanks to some fixed overhead time, independent on the sub-frame dimensions.
The driver is sometimes forced to read bigger portions of the sensor than the user defined because of a sub-frame position and dimension limitations imposed by the sensor hardware. Sometimes it is even necessary to read a whole sensor.
It is recommended to click the Adjust Frame button in the Frame tab of the SIPS camera control tool. The selected frame dimensions are then adjusted according to sensor limitations. Adjusted frame is then read from the sensor, without a necessity to read a bigger portions or even whole sensor and crop image in firmware.
Download speed when using the Moravian Camera Ethernet Adapter depends if the 100 Mbps or 1 Gbps Ethernet is used, if USB 2 or USB 3 is used to connect camera to Ethernet Adapter device, but also depends on the particular network utilization etc. When the camera is connected to the Ethernet Adapter using USB 3 and 1 Gbps Ethernet is directly connected to the host PC, download time of the C1×61000 full frame is approx. 2.5 s.
Sensors used in C1× cameras offer programmable gain from 0 to 36 dB, which translates to the output signal multiplication from 1× to 63×.
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.
Camera driver accepts gain as a number in the range 0 to 4030, which corresponds directly to sensor register value. This number does not represent gain in dB nor it is an exact gain multiply. However, the driver offers a function, which transforms the gain numerical value to gain expressed in dB as well as multiply. Some selected values are shown in the table:
Generally, many sensor characteristics depend on the used gain. Also, the used sensors employ two conversion paths. One path offers very low read noise, but cannot utilize full sensor dynamic range. Another conversion path offers maximum pixel capacity, but at the price of higher read noise. The cross point is set to gain 3× (approx. 10 dB), where the full well capacity drops from more than 50 ke- to ~17 ke-. The read noise then drops from ~3.2 e- RMS to ~1.5 e- RMS.
Also, it is worth noting that in reality the noise floor is not always defined by read noise. Unless the camera is used with very narrow narrow-band filter (with FWHM only a few nm) and under very dark sky, the dominant source of noise is the sky glow. When the noise generated by sky glow exceeds approximately 4 e- RMS, extremely low read noise associated with gain set to 2750 or more is not utilized and dynamic range is unnecessarily limited by the lowered full well capacity.
Please note the values stated above are not published by sensor manufacturer, but determined from acquired images using the SIPS software package. Results may slightly vary depending on the test run, on the particular sensor and other factors (e.g. sensor temperature, sensor illumination conditions etc.), but also on the software used to determine these values, as the method is based on statistical analysis of sensor response to light.
There is no practical limit on maximal exposure length, but in reality, the longest exposures are limited by saturation of the sensor either by incoming light or by dark current (see the following chapter about sensor cooling).
Regulated thermoelectric cooling is capable to cool the CMOS sensor by approx. 35 °C below ambient temperature, depending on the camera type. The Peltier hot side is cooled by a 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 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.
Maximum temperature difference between the 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 50 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 12 V DC side. Power consumption on the AC side of the supplied AC/DC power brick is higher.
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.
Compact and robust camera head measures only 78 × 78 × 108 mm (approx. 3.1 × 3.1 × 4.4 inches). The head is CNC-machined from high-quality aluminum and black anodized. The head itself contains USB-B (device) connector, connector for External Filter Wheel and 12 V DC power plug.
The front side of the C1× camera body is not intended for direct attachment of the telescope/lens adapter. It is instead designed to accept tiltable adapter base, on with the telescope and lens adapters are mounted.
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. Canon EOS bayonet adapter back focal distance is 44 mm).
Stated back focal distance already calculates with glass permanently placed in the optical path (e.g. optical window covering the sensor cold chamber).
The S, M and L sized External Filter Wheels diameter is greater (viz. External Filter Wheels), but the back focal distance of all external filter wheels is identical.
The M48, Canon and Nikon adapters, intended for the M56 × 1 thread, cannot be used with the External filter wheels. However, the External filter wheel is equipped with adapter base for C2 and C3 adapters and thus all adapters, designed for these cameras, can be used with C1× and External filter wheel.
Various accessories are offered with C1× cameras to enhance functionality and help camera integration into imaging setups.
Various telescope and lens adapters for the C1× cameras are offered. Users can choose any adapter according to their needs and other adapters can be ordered separately.
If the External filter wheel is attached to the C1× base, telescope/lens adapters are attached to the External filter wheel. In such case adapters compatible with the C2 or C3 cameras are used.
All telescope/lens adapters of the C1× 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.
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.
Because the necessity to adjust two screws (one pushing, one pulling) at once is inconvenient, the adapter tilting mechanism is also equipped with ring-shaped spring, which pushes the adapter out of the camera body. This means the pushing screws can be released and still slight releasing of the pulling screw means the distance between the adapter and the camera body increases. The spring is designed to be strong enough to push the camera head from the adapter (fixed on the telescope) regardless of the camera orientation.
Only after the proper tilt is reached, the pushing screws should be slightly tightened to fix the adapter in the desired angle relative to camera head. This ensures long-time stability of the adjusted adapter.
If the External filter wheel is used, the adjustment screws on the camera body are not accessible and they are not used to adjust the tilt. Instead, an adjustable adapter base on the External filter wheel is used to correct possible tilt.
The Off-Axis Guider adapter (OAG) can be used with the C1× camera only if the External filter Wheel is used. Then the C3-OAG with M68 × 1 thread can be attached to the M or L External filter wheel.
Technically also the C2-OAG with M48 × 0.75 thread can be attached to the XS and S External filter wheels, but C2-OAG mirror is positioned too close to the optical axis with respect to relatively small sensors of the C1+/C2 camera lines. So, the C2-OAG mirror would partially shadow large sensors use in the C1× cameras.
OAG 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.
The C3-OAG is manufactured with M68 × 1 thread with the back focal distance 61.5 mm.
The OAG guider port is compatible with C0 and C1 cameras with CS-mount adapter. It is necessary to replace the CS/1.25” adapter with short, 10 mm variant in the case of C1 cameras. Because C1 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 C3-OAG.
C1× cameras are equipped with a tripod 0.250-20UNC thread, as well as four metric M4 threaded holes, on the bottom side of the camera head.
These threaded holes 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.
C1× cameras employ the same desiccant container like the larger Enhanced cooling variants of the C3 and C4 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.
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 allows connection of up to 4 Cx cameras of any type on the one side and 1 Gbps Ethernet on the other side. This adapter allows access to connected Cx cameras using routable TCP/IP protocol over practically unlimited distance.
Moravian Camera Ethernet Adapter devices are described in detail here.
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, 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.
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.