The C2 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 cameras usually require computer for operation control, image download, processing and storage etc. To operate the camera, you need a computer which:

1. Is compatible with a PC standard and runs modern 32 or 64-bit Windows operating system.

2. Is an x86 or ARM based computer and runs 32 or 64-bit Linux operating system.

   Remark:

   Drivers for 32-bit and 64-bit Linux systems are provided, but the SIPS camera control and image processing software, supplied with the camera, requires Windows operating system.

3. Support for x64 and ARM64 based Apple Macintosh computers is also included.

   Remark:

   Only certain software packages are currently supported on Mac.

C2 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.

The C2 cameras need an external 12 V DC power supply to operate. The wall adapter providing proper voltage is shipped with every camera.

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.

C2 Camera Overview

C2 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:

• Camera with Internal filter wheel.

• Camera with control port for External filter wheel. This model allows attachment of several variants of external filter wheels with various number of filter positions and sizes.

C2 camera model with Internal filter wheel accepts two sizes of filters:

• Filter wheel with 5 positions for unmounted D31 mm filters or filters in 1.25” threaded cells.

• Filter wheel with 6 positions for unmounted D27 mm (or 1”) filters.

There are two sizes of the External filter wheels, each capable to accept multiple sizes of filters, available for the C2 cameras:

• Extra small “XS” size wheel for 8 unmounted filters D31 mm or filters in 1.25” threaded cells.

• Extra small “XS” size wheel for 7 unmounted filters D36 mm.

• Small “S” size wheel for 12 unmounted filters D31 mm or filters in 1.25” threaded cells.

• Small “S” size wheel for 10 unmounted filters D36 mm.

• Small “S” size wheel for 7 unmounted D50 mm or 2" filter or filters in 2” threaded cells.

C2 cameras are manufactured with a wide range of CMOS sensors. Probably the most important differentiating factor, fundamentally affecting camera operation, is an electronic shutter implemented in the sensors. C2 cameras support sensors with:

• Global shutter, allowing capturing of the whole frame in the very same instance of time. This means all pixels are reset and start to capture light simultaneously. Global shutter is particularly suitable for capturing fast moving scenes, because they ensure image does not suffer from motion distortion, caused by rolling shutter sensors. On the other side, frame rate of global shutter sensors is lower compared to rolling shutter ones, because each frame must be fully digitized prior to start of next exposure.

• Rolling shutter, which resets individual image rows in a sequence. The exposure of each image row is delayed typically by a few tens of microseconds. Depending on this delay and number of rows, the first and last row exposure time may be shifted by up to several tenths of a second. The inherent feature of rolling shutter sensors is a distortion of fast-moving scenes, when image moves within the time individual rows are exposed. Luckily such fast moving scenes are very rare in astronomy. The plus side of rolling shutter is much higher FPS, as each image is already exposed while the previous image is digitized.

C2 Camera System

Components of C2 Camera system include:

1. C2 camera head with Internal Filter Wheel (5 or 6 positions)

2. C2 camera head capable to control External Filter Wheel

3. External Filter Wheel “XS” size (7 or 8 positions)

4. External Filter Wheel “S” size (10 or 12 positions)

5. C1 guider camera

   Remark:

   C1 cameras are completely independent devices with their own USB connection to the host PC. They can be used either on C2 OAG or on standalone guiding telescope.

   C1 cameras can share the Moravian Camera Ethernet Adapter with up to 3 other Cx cameras to be accessed over TCP/IP network.

6. Off-Axis Guider with M48 × 0.75 thread

7. Off-Axis Guider with M42 × 0.75 thread (T2)

8. Thick adapter base, compensating EFW thickness to achieve proper back focal distance for cameras without filter wheel

9. 1.75” dovetail rail for C2 camera head

10. Camera Ethernet Adapter (x86 CPU)

11. Camera Ethernet Adapter (ARM CPU)

    Remark:

    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 unlimited distance.

12. 5-positions internal filter wheel for 1.25”/D31 mm filters

13. 6-positions internal filter wheel for 1”/D27 mm filters

14. 8-positions external filter wheel “XS” for 1.25”/D31 mm filters

15. 7-positions external filter wheel “XS” for D36 mm filters

16. 12-positions external filter wheel “S” for 1.25”/D31 mm filters

17. 10-positions external filter wheel “S” for D36 mm filters

18. 7-positions external filter wheel “S” for 2”/D50 mm filters

19. M42 × 0.75 (T-thread) or M48 × 0.75 threaded adapters, 55 mm BFD

    Remark:

    Other standard adapters are available, for instance threaded 2" barrel adapter etc.

20. Canon EOS bayonet lens adapter

21. Nikon bayonet lens adapter

C2 with global shutter CMOS Sensors

C2 camera models equipped with Sony IMX global shutter CMOS detectors with 3.45 × 3.45 μm or 4.50 × 4.50 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.

Three lines of C2 cameras are available depending on the available dynamic range (bit-depth of the digitized pixels) and pixel size:

• C2 cameras with Sony IMX sensors with 3.45 × 3.45 μm pixels, supporting 8- and 12-bit digitization. Because every 12-bit pixel occupies two bytes when transferred to host PC, 12-bit image download time is longer compared to 8-bit image. Maximal FPS in 8-bit mode is then significantly higher.

• C2 cameras with Sony IMX sensors with 3.45 × 3.45 μm pixels, supporting 12-bit digitization only. As the 12-bit read mode is always used for long-exposure applications (astronomical photography, scientific research) either way, lower theoretical download time in 8-bit mode brings no limitations for real-world scenarios. All other parameters being same (sensor size, resolution, pixels size, noise, …), lower price of these cameras may be then very attractive.

• C2 cameras with Sony IMX sensors with 4.50 × 4.50 μm pixels and 12-bit digitization only. Greater pixels mean higher dynamic range (more electrons can be stored in each pixel before it saturates), but also higher read noise. Still the theoretical S/N is almost the same because of higher signal camera can accumulate. This camera is more suitable for longer focal length telescopes, where small pixels provide oversampled images, and also for research applications, where dynamic range is important.

C2 camera models with 3.45 × 3.45 μm pixels and 8- and 12-bit digitization:

C2 camera models with 3.45 × 3.45 μm pixels and 12-bit digitization only:

C2 camera models with 4.50 × 4.50 μm pixels and 12-bit digitization only:

Camera Electronics

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).

Sensor linearity

The sensors used in C2 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.

Download speed

As already noted, there are two lines of C2 camera series, differing in the used sensor. The first series with 3.45 × 3.45 μm pixels offers four different read modes:

• 8-bit slow mode with ~132 MPx/s digitization speed

• 12-bit slow mode with ~72 MPx/s digitization speed

• 8-bit fast mode with ~263 MPx/s digitization speed

• 12-bit fast mode with ~132 MPx/s digitization speed

The “A” version of C2 cameras with 3.45 × 3.45 μm pixels offers only single read mode:

• 12-bit fast mode with ~132 MPx/s digitization speed

And the “A” version of C2 cameras with 4.50 × 4.50 μm pixels offers also only one read mode:

• 12-bit fast mode with ~151 MPx/s digitization speed

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.

Camera gain

Sensors used in C2 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.

Conversion factors and read noise

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 sensors with 3.45 × 3.45 μm pixels:

Camera/sensor parameters for sensors with 4.50 × 4.50 μm pixels:

Exposure control

C2 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).

Mechanical shutter

C2 cameras are equipped with mechanical shutter, which is an important feature allowing unattended observations (fully robotic or just remote setups). Without mechanical shutter, it is not possible to automatically acquire dark frames, necessary for proper image calibration etc.

Mechanical shutter in the C2 cameras is designed to be as reliable as possible, number of open/close cycles is virtually unlimited, because there are no surfaces rubbing against each other. The price for high reliability is slow shutter motion. Luckily, mechanical shuttering is not necessary for exposure control, only for taking dark frames and possibly bias frames — all used CMOS sensors are equipped with electronic shuttering.

Camera firmware optimizes the shutter operation to avoid unnecessary movements. If a series of light images is taken immediately one after another, the shutter remains open not to introduce quite significant delay of the close/open cycle between subsequent light images. If the next image is a dark or bias frame, shutter closes prior to exposure and vice versa — shutter remains closed if a series of dark frames is acquired and opens only prior to next light frame. If no exposure is taken for approx. 5 seconds while the shutter is open, camera firmware closes the shutter to cover the sensor from incoming light.

GPS exposure timing

The C2 cameras with global shutter can be equipped with GPS receiver module (see the Optional Accessories chapter). The primary purpose of the GPS receiver is to provide precise times of exposures taken with the camera, which is required by applications dealing with astrometry of fast-moving objects (fast moving asteroids, satellites, and space debris on Earth orbit, ...).

The GPS module needs to locate at last 5 satellites to provide exposure timing information. Geographic data are available if only 3 satellites are visible, but especially the mean sea level precision suffers if less than 4 satellites are used.

The camera SDK provides functions, allowing users to access precision exposure times as well as geographics location. The SIPS software package main imaging camera control tool window contains the “GPS” tab, which shows the state of the GPS fix.

A huge advantage of the global-shutter CMOS sensors, compared to rolling-shutter ones, is very simple and straightforward way to determine the exact exposure time. As opposed to rolling-shutter sensors, all pixels are exposed at exactly the same time, returned by the GPS receiver, and there is no need to calculate with line time and pixel y-coordinate.

Remember to always use the latest version of SIPS or latest camera drivers (ASCOM or Camera SDK DLLs in Windows, INDI or libraries in Linux) available on the web. Also, always update the firmware in the Moravian Camera Ethernet Adapter if the camera is connected over Ethernet.

C2 with rolling shutter CMOS Sensors

C2 series of CMOS cameras with Sony IMX rolling shutter CMOS detectors employs sensors of two different sensor families, differing in pixel size and dynamic range:

As opposed to global-shutter sensors, rolling-shutter sensors expose individual lines in sequence.

Camera Electronics

Controlling of the rolling shutter sensors differs significantly from controlling of the global shutter sensors. The camera internals differ significantly according to different electronic shutter.

The C2 cameras with rolling shutter contain 256 MB of onboard memory, capable to store up to 14 full-resolution frames of the C2-9000 camera or 2 full-resolution frames in the case of C2-46000 camera. Camera API allows for sequential exposures, during which short-exposure images are stored into memory possibly faster than the host computer is able to read them. Sequential exposures are paused when the internal memory is filled with images, not yet read by the host PC. As explained earlier, rolling shutter sensors are capable to perform image exposure while digitizing the previous image.

Sensor linearity

The IMX sensors used in C2 cameras show very good linearity in response to light. This means C2 cameras can be used for advanced research projects, like the photometry of variable stars and transiting exoplanets etc.

Download speed

Thanks to C2 camera onboard RAM, downloading of the image to the host computer 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.

The C2-9000 camera significantly speeds up the download if only a sub-frame is read. 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 download speedup is not as proportional to the downloaded area in the case of C2-46000 camera because of the sensor-imposed limitations, but it is still significant.

C2 camera electronics supports in-camera 2×2 binning. If this binning mode is used, download speed increases because of less amount of data read from camera.

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 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 C2-9000 full frame is less than 0.5 s.

C2-9000 camera gain

Sensors used in the C2-9000 camera offer programmable gain from 0 to 36 dB, which translates to the output signal multiplication from 1× to 63×.

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:

C2-46000 camera gain

The C2-46000 camera offers programmable gain from 0 to 16 dB, which translates to the output signal multiplication from 1× to 6.5×.

Camera driver accepts gain as a number in the range 0 to 500. This number does not represent gain in dB nor in multiply value. 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:

C2-9000 conversion factors and read noise

Generally, many sensor characteristics depend on the used gain. Also, the sensor used in the C2-9000 employs 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.

Sensor dynamic range, defined as full well capacity divided by read noise, is greatest when using gain 0, despite somewhat higher read noise:

• At gain = 0, dynamic range is 50,800 / 3.81 = 13,333×

• At gain = 2750, dynamic range is 16,500 / 1.55 = 10,645×

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.

So, which gain settings is the best? This depends on the particular task.

• Gain set to 2750 can be utilized if imaging through narrow-band filter with appropriately short exposures, so the background noise does not exceed the read noise. This is typical for aesthetic astro-photography, where the lowered full well capacity does not negatively influence the result quality.

  But even without narrow-band filters, the extremely low read noise allows stacking of many short exposures without unacceptable increase of the stacked image background noise, caused by accumulation of high read noise of individual exposures.

• Gain set to 0 offers maximum full well capacity and the greatest sensor dynamic range, which is appreciated mainly in research applications. Pass-bands of filters used for photometry are relatively wide and dominant source of noise is the sky glow.

  But also for RGB images, used for aesthetic astro-photography, higher dynamic range allows longer exposures while the bright portions of the nebulae and galaxies still remain under saturation and thus can be properly processed.

C2-46000 conversion factors and read noise

The sensor read noise and full well capacity depend on the used gain.

Binning

The camera driver and user’s applications offer wide variety of binning modes up to 4 × 4 pixels as well as all combinations of asymmetrical binning modes 1 × 2, 1 × 3, 1 × 4, 2 × 4 etc. To allow such flexibility, binning is performed only in the camera driver (software binning) and does not rely on the limited capabilities of the hardware binning.

The negative side of software binning is the same download time like in the case of full-resolution 1 × 1 mode. For typical astronomy usage, the small fraction of second download time is irrelevant, but for applications sensitive to download time, the hardware 2 × 2 binning can be useful.

Hardware binning

The C2-9000 camera implements 2 × 2 binning mode in hardware in addition to normal 1 × 1 binning.

Hardware binning can be turned on and off using the parameter HWBinning in the 'cXusb.ini' configuration file, located in the same directory like the 'cXusb.dll' driver DLL file itself.

[driver]
HWBinning = true

When the HWBinning parameter is set to true, the in-camera hardware binning is used. This mode brings faster download time, but also introduces several restrictions:

1. Maximal binning is limited to 2 × 2, higher binning modes are not available.

2. Asymmetrical binning modes (1 × 2, 2 × 1, ...) are not allowed.

Adding vs. averaging pixels

The traditional meaning of pixel binning implies adding of binned pixels. This originated in CCD sensors, where pixel charges were literally poured together within the sensor horizontal register and/or the output node. Binning with CMOS sensors can behave differently, pixels can be either added or averaged.

In theory, the resulting S/N ratio of binned pixel remains the same regardless if we add or average them. Let's take for example 2 × 2 binning:

• If we add 4 pixels, signal increases 4-times and noise increases 2-times — three additive operations increase noise by √((√2)^2×(√2)^2 ). Resulting S/N increases 2-times, but only until the sum of all pixels is lower than the pixel capacity.

• If we average 4 pixels, signal remains the same but the noise is lowered to 1/2 as noise is averaged √((√2)^2×(√2)^2 )/4. Resulting S/N also increases 2-times, but only until the noise decreases to lowest possible 1-bit of dynamic range.

But in reality, resulting S/N ratio can be affected either by overflow (saturation) of resulting pixel when adding binned pixels or by read noise underflow (dropping below 1 bit) when averaging them.

While the bigger siblings of the C2 cameras (C1×, C3 and C5) utilize CMOS sensors with full 16-bit dynamic resolution, the sensor used in C2 models offers only 14-bit or even 12-bit conversion. So, up to 4 pixels (2 × 2 binning) can be added and still the resulting pixel cannot overflow the 16-bit dynamic range of each 2 bytes long pixel. This is why the default binning behavior of the C2 camera uses pixel adding instead of averaging on both software binning and in-camera (hardware) binning.

However, both software and hardware binning modes can be switched to sum binned pixels instead of average them by the BinningSum parameter in the 'cXusb.ini' configuration file:

[driver]
BinningSum = true

Let us note there is one more possibility to bin pixels — in the application software. This time binning is not performed in camera hardware nor in the camera driver. Full resolution 1 × 1 image is downloaded from the camera and software itself then performs binning. The SIPS software adds pixels instead of averaging them, but at the same time SIPS converts images from 16-bit to 32-bit dynamic range. This means S/N of the binned images always increases, pixels never saturate and read noise newer approaches lower limit. The negative side of this option is two-time bigger images.

Binning in photometry

Saturated pixels within bright stars are no issue for aesthetic astro-photography, but photometry measurement is invalid if any pixel within the measured object reaches maximum value, because it is not possible to determine the amount of lost flux. Software performing photometry (e.g. the SIPS Photometry tool) should detect saturation value and invalidate entire photometric point not to introduce errors.

But binning efficiently obliterates the fact that any of the binned pixels saturated (with the exception of all binned pixels reached saturation value). So, using of binning modes for research applications (photometry and astrometry) can lead to errors caused by lost flux in saturated pixels, which cannot be detected by the processing software due to binning.

This is why the behavior of both software and hardware binning modes is user-configurable through the BinningSaturate parameter in the 'cXusb.ini' configuration file:

[driver]
BinningSaturate = true

If the BinningSaturate parameter is set to true, resulting binned pixel is set to saturation value if any of the source pixels is saturated. For aesthetic astro-photography, keeping this parameter false could result into slightly better representation of bright star images, but for research applications, this parameter should always be set to true.

Exposure Control

The shortest theoretical exposure time is 49 μs for the C2-9000 camera and 108 μs for the C2-46000 model. However, such short exposures have no practical application, especially in astronomy. The camera firmware rounds exposure time to a multiply of 100 μs intervals, so in reality the shortest exposure time is also 100 μs.

There is no theoretical 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).

Mechanical shutter

Mechanical shutter of the rolling-shutter C2 cameras works the same way like in the case of global-shutter C2 variants.

GPS exposure timing

C2 cameras can be equipped with GPS receiver module (see the Optional Accessories chapter). The primary purpose of the GPS receiver is to provide precise times of exposures taken with the camera, which is required by applications dealing with astrometry of fast-moving objects (fast moving asteroids, satellites, and space debris on Earth orbit, …).

The GPS module needs to locate at last 5 satellites to provide exposure timing information. Geographic data are available if only 3 satellites are visible, but especially the mean sea level precision suffers if less than 4 satellites are used.

The camera SDK provides functions, allowing users to access precision exposure times as well as geographics location. The SIPS software package main imaging camera control tool window contains the “GPS” tab, which shows the state of the GPS fix.

Determination of exact exposure time is quite complicated because of the rolling-shutter nature of the used sensors. Camera driver does all the calculations and returns the time of the start of exposure of the first line of the image. Still, users interested in precise exposure timing need to include several corrections into their calculations:

• Individual image lines are exposed sequentially. The time difference between start of exposure of two subsequent lines is 12.194 μs (this time is determined by the IMX533 sensor) or 26.985 μs (again determined by the IMX492 sensor).

• If the image is binned, single line of resulting image contains signal from multiple added (or averaged) lines, each with different exposure time start. The exposure start of individual lines of the binned images differs by the single line time difference, multiplied by the vertical binning factor.

• If only a sub-frame is read, it must be considered that the sensor imposes some restrictions to the sub-frame coordinates. If the required sub-frame coordinates violate the sensor-imposed rules, camera driver enlarges the sub-frame region to fully contain desired sub-frame and then crops it by software. The provided start exposure time then concerns the first line actually read from the camera, not the first line of the resulting (software cropped) image.

  Note the camera SDK offers function AdjustSubFrame, which returns the smallest sub-frame, fully containing the requested sub-frame, but also fulfilling the sensor-imposed sub-frame coordinate restriction. If adjusted sub-frame is read, no software cropping occurs and image exposure time concerns the first line of the image. The SIPS software offers the “Adjust Frame” button, which adjusts defined sub-frame.

Remember to always use the latest version of SIPS or latest camera drivers (ASCOM or Camera SDK DLLs in Windows, INDI or libraries in Linux) available on the web. Also, always update the firmware in the Moravian Camera Ethernet Adapter if the camera is connected over Ethernet.

Cooling and power supply

Regulated thermoelectric cooling is capable to cool the CMOS sensor up to 45 °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 sensor measures directly the temperature of the CMOS sensor package. The second one measures the temperature inside the camera shell.

The cooling performance slightly depends on the amount of heat generated by a sensor used in the camera:

• In general, lower resolution sensors generate less heat and thus reaches lower temperature.

• The “A” version cameras, using sensors with limited read modes, also generate less heat and reaches lower temperature.

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.

Overheating protection

The C2 cameras are equipped with an overheating protection in their firmware. This protection is designed to prevent the Peltier hot side to reach temperatures above ~50°C sensor cooling is turned off to stop heat generation by the hot side of the Peltier TEC modules.

Turning the overheating protection on results in a drop in cooling power, a decrease in the internal temperature of the camera and an increase in the temperature of the sensor. However, when the camera cools its internals down below the limit, cooling is turned on again. If the environment temperature is still high, camera internal temperature rises above the limit an overheating protection becomes active again.

Power supply

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 40 W, the 60 W power supply ensures noise-free operation.

Mechanical Specifications

Compact 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.

Camera with Internal Filter Wheel

Camera with “XS” External Filter Wheel

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.

Camera without filter wheel

If 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.

Back focal distance

The stated back focal distances (BFD) include corrections for all optical elements in the light path (cold chamber optical window, sensor cover glass, ...), fixed in the camera body. So, stated values are not mechanical, but optical back focal distances. However, no corrections for filters are included, as the thicknesses of various filters are very different.

C2 cameras are manufactured in many variants and can be connected with various accessories, which leads to many possible back focal distance values.

There are two groups of the telescope and lens adapters, differing in back focal distance definition:

• Adapters without strictly defined BFD. These adapters are designed to provide as low BFD as possible.

• Adapter with defined BFD. These adapters are typically intended for optical correctors (field flatteners, coma correctors, ...) and also for photographic lenses. Keeping the defined BFD is necessary to ensure proper functionality of correctors or to be able to achieve focus with photographic lenses.

  Remark:

  Special variant of adapter with defined BFD is Off-Axis Guider adapter. Keeping its distance from the sensor is then necessary to achieve focus with guiding camera when the main camera is focused.

Adapters without back focal distance defined

Most commonly used adapter without strictly prescribed back focal distance is M48 × 0.75 thread.

Adapters with defined back focal distance

There are three basic variants of C2 camera, differing with back focal distance of the camera head front shell — camera without internal filter wheel, with Internal Filter Wheel with External Filter Wheel. But adapters preserving back focal distance are always designed with the same thickness. Their dimension counts with the BFD of the tiltable adapter base 33.5 mm, which corresponds with BFD of the camera with External Filter Wheel.

However, adapters not mounted on the External Filter Wheel tiltable base, must be mounted on standalone tiltable adapter base attached to the camera head. Such adapter base is designed to provide exactly the same 33.5 mm BFD when mounted on camera with Internal Filter Wheel.

If a camera without filter wheel is to be used with adapter preserving the defined BFD, it is necessary to use a thick tiltable adapter base, which also provides the 33.5 mm BFD. Thickness of this adapter base equals the thickness of the External Filter Wheel shell.

Optional accessories

Various accessories are offered with C2 cameras to enhance functionality and help camera integration into imaging setups.

External filter wheels

When 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.

Telescope adapters

Various telescope and lens adapters for the C2 cameras are offered. Users can choose any adapter according to their needs and other adapters can be ordered separately.

• 2-inch barrel — adapter for standard 2" focusers.

• T-thread short — M42 × 0.75 inner thread adapter.

• T-thread with 55 mm BFD — M42 × 0.75 inner thread adapter, preserves 55 mm back focal distance.

• M48 × 0.75 short — adapter with inner thread M48 × 0.75.

• M48 × 0.75with 55 mm BFD — adapter with inner thread M48 × 0.75, preserves 55 mm back focal distance.

• Canon EOS bayonet — standard Canon EOS lens adapter, preserves 44 mm back focal distance.

• Nikon F bayonet — standard Nikon F lens adapter, preserves 46.5 mm back focal distance.

All telescope/lens adapters of the C2 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 C2 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.

• C2 adapters are not mounted directly on the camera head. Instead a tilting adapter base, holding the circular spring, is always used.

• If the External filter wheel is used, the adapted base is not necessary, as the External filter wheel front plate is already designed to hold the spring and it also contains threads to fix respective adapters.

Off-Axis Guider Adapter (OAG)

C2 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.

C2-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 C0 and C1 cameras (and also older G0 and G1). 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 C2-OAG.

GPS receiver module

The C2 cameras, both global-shutter and rolling-shutter variants, can be equipped with an optional GPS receiver module, which allows very precise timing of the exposure times. Geographic location data are also available to the control software through specific commands.

The used GPS receiver is compatible with GPS, GLONASS, Galileo and BeiDou satellites.

The GPS receiver can be attached to the back side of the camera head. If the GPS module is removed, the GPS port is covered with a flat black cover.

Attaching camera head to the telescope mount

C2 camera heads are equipped with “tripod” thread (0.25”) as well as four M4 threaded holes 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.

Tool-less desiccant containers

C2 cameras employ the same desiccant container like the larger 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.

Container shipped with the camera by default does not exceed the camera head outline. It is equipped with a slot for tool (a plastic tool is included with every camera, but e.g. some coin can be used, too), allowing releasing and also tightening of the container.

This design also allows usage of some optional parts:

• Threaded hermetic cap, allowing sealing of the dried container when it is not immediately attached to the camera head.

• Alternate (somewhat longer) desiccant container, modified to be able to be screw in and tightened (as well as released and screwed out) without any tool.

Camera head color variants

Camera head is available in several color variants of the center plate. Visit manufacturer's web pages for current offering.

Moravian Camera Ethernet Adapter

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 support

Always use the latest versions of the system driver package for both Windows and Linux system. Older versions of drivers may not support new camera models or latest versions or existing series.

If the camera is controlled through the Moravian Camera Ethernet Adapter, make sure the device firmware is updated to the latest version available.

Also, always use the latest version of the SIPS software package, older versions may not support latest cameras correctly. If a driver for 3^rd party software package is used (e.g. ASCOM or INDI drivers), always update the driver to the latest available version.

SIPS

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.

Automatic guiding

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.

Advanced reconstruction of color information of single-shot-color cameras

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.

Drivers for 3^rd party programs

Regularly updated Sofware Development Kit for Windows allows to control all cameras from arbitrary applications, as well as from Python scripts etc.

There are ASCOM standard drivers available together with native drivers for some 3^rd party programs (for instance, TheSkyX, AstroArt, etc.). Visit the download page of this server to see a list of all supported drivers.

Libraries and INDI standard drivers for 32-bit and 64-bit Linux working on x86 and ARM processors are available as well. Also drivers for TheSkyX running on macOS are supplied with all cameras.

Shipping and Packaging

C2 cameras are supplied in the foam-filled, hard carrying case containing:

• Camera body with a user-chosen telescope adapter. If ordered, the filter wheel is already mounted inside the camera head and filters are threaded into place (if ordered).

• A 100-240 V AC input, 12 V DC output “brick” adapter with 1.8 m long power cable.

• 2 m long USB 3.0 A-B cable for connecting camera to host PC.

• USB Flash Drive with camera drivers, SIPS software package with electronic documentation and PDF version of User's Manual.

• A printed copy of camera User's Manual

Image Gallery

Example images captured with C2 cameras.

All images published with permission of their respective authors.