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Main pageProductsCMOS & CCD cameras

C3 Series CMOS Cameras
 C3 cameras employ the latest generation of Sony IMX CMOS sensors, offering exceptional quantum efficiency thanks to back-illuminated design and very low dark current. Despite relatively small pixels, full-well capacity exceeding 50ke-. Combined with full 16bit digitization and perfectly linear response to light make these cameras suitable for both aesthetic astro-photography as well as astronomical research. Sensor formats from APS to photographic full-frame (24נ36mm) ensure wide field of view and optimally utilize capabilities of the optical systems most commonly used by amateur astronomers.

Mechanical design of the C3 series of astronomical CMOS cameras inherits from earlier CCD-based G3 Mark II cameras, which makes the C3 camera line fully compatible with vast range of telescope adapters, off-axis guider adapters, filter wheels, Ethernet adapters, guiding cameras etc.

Rich software and driver support allow usage of C3 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 and Linux driver libraries are shipped with the camera, provide the way to integrate C3 camera with broad variety of camera control programs.

The C3 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 cooled 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 based Apple Macintosh computers is also included.

    Remark:

    Only certain software packages are currently supported on Mac.

C3 cameras are designed to be attached to host PC through very fast USB 3.0 port. While C3 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 C3, but also C1, C2 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.

Hint:

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 USB3 connection.

The C3 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. C3 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.

C3 Camera Overview

C3 camera head is designed to be easily used with a set of accessories to fulfill various observing needs. The camera head itself is manufactured in several variants.

First, there are variants differing in the cooling performance:

  • Standard cooling

  • Enhanced cooling (11 mm thicker due to increased heat sink)

Second, there are variants differing in filter wheel control:

  • 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.

C3 camera model with Internal filter wheel accepts two sizes of filters:

  • Filter wheel with 5 positions for unmounted D50mm (or 2) filters or filters in 2 threaded cells.

  • Filter wheel with 7 positions for unmounted D36mm filters.

There are three sizes of the External filter wheels, capable to accept various sizes of filters, available for the C3 cameras:

  • Small “S” size wheel for 10 unmounted filters D36mm.

  • Small “S” size wheel for 7 unmounted filters D50mm or filters in 2 threaded cells.

  • Small “S” size wheel for 5 unmounted square filters 50נ50mm.

  • Middle “M” size wheel for 10 unmounted filters D36mm.

  • Middle “M” size wheel for 7 unmounted filters D50mm or filters in 2 threaded cells.

  • Middle “M” size wheel for 5 unmounted square filters 50נ50mm.

  • Large “L” size wheel for 9 unmounted D50 mm or filters in 2 threaded cells.

  • Large “L” size wheel for 7 unmounted square filters 50נ50mm.

Warning:

Both Internal and External filter wheels for D36mm filters can be used with C3 camera equipped with APS size sensors only. Cameras with Full-frame sensors (24נ36mm) cannot use such small filters.

Please note the camera head is designed to either accept Internal filter wheel or to be able to connect to the External filter wheel, but not both. If the Internal filter wheel variant is used, External filter wheel cannot be attached.

And third, there are two sizes of adjustable adapters, which can be used with C3 cameras:

  • Small “S” adapters, compatible with C2 cameras, are used for e.g. M48נ0.75 and M42נ0.75 threaded adapters, Nikon bayonet adapter, 2 barrel adapter etc.

  • Large “L” adapters, compatible with C4 cameras, intended for large diameter attachments between camera and telescope, e.g. M68נ1 threaded adapter or G3-OAG, which is also equipped with M68נ1 thread.

Adjustable adapters are mounted on adapter base when camera with internal filter wheel or camera without any filter wheel is used or directly on the external filter wheel front surface. This means both S and L adapter bases can be mounted on any camera, but external filter wheels are made for one particular adapter size only:

  • “S” external filter wheels are compatible with “S” adapters

  • “M” and “L” external filter wheels are compatible with “L” adapters

Remark:

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.

Camera head and numerous accessories comprise imaging system, capable to be tailored for many applications.

Schematic diagram of C3 camera with S size adapter system components

Schematic diagram of C3 camera with “S” size adapter system components

Schematic diagram of C3 camera with L size adapter system components

Schematic diagram of C3 camera with “L” size adapter system components

Components of C3 Camera system include:

  1. C3 camera head with Internal Filter Wheel

  2. C3 camera head with Internal Filter Wheel and Enhanced Cooling option

  3. C3 camera head capable to control External Filter Wheel

  4. C3 camera head capable to control External Filter Wheel with Enhanced Cooling option

  5. 1.75 dovetail rail for C3 camera head

  6. Moravian Camera Ethernet Adapter (x86 CPU)

  7. Moravian Camera Ethernet Adapter (ARM CPU)

    Remark:

    The Camera Ethernet Adapter allows connection of up to 4 Cx cameras of any type on the one side and 1Gbps Ethernet on the other side. This adapter allows access to connected Cx cameras using routable TCP/IP protocol over unlimited distance.

  8. 7-positions internal filter wheel for unmounted D36mm filters

  9. 5-positions internal filter wheel for 2/D50mm filters

  10. 10-positions filter wheel for “S” or “M” housing for unmounted D36mm filters

  11. 7-positions filter wheel for “S” or “M” housing for 2/D50mm filters

  12. 5-positions filter wheel for “S” or “M” housing for 50נ50mm square filters

  13. External Filter Wheel “S” size (5, 7 or 10 positions)

  14. M42נ0.75 (T-thread) or M48נ0.75 threaded “S” size adapters, 55mm BFD

  15. Canon EOS bayonet lens “S” size adapter

  16. Nikon bayonet lens “S” size adapter

  17. External Filter Wheel “M” size (5, 7 or 10 positions)

  18. External Filter Wheel “L” size (7 or 9 positions)

  19. 9-positions filter wheel for “L” housing for 2/D50mm filters

  20. 7-positions filter wheel for “L” housing for 50נ50mm square filters

  21. C1 auto-guiding camera

    Remark:

    The C1 cameras are completely independent devices with their own USB connection to the host PC. They can be used either on C3 OAG or on standalone guiding telescope.

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

  22. M68נ1 threaded “L” size adapter, 47.5mm BFD

  23. Canon EOS bayonet lens “L” size adapter

  24. Off-Axis Guider with M68נ1 thread, 61.5mm BFD

CMOS Sensor and Camera Electronics

C3 cameras are equipped with Sony IMX rolling shutter back-illuminated CMOS detectors with 3.76נ3.76μm square pixels. Despite the relatively small pixel size, the full-well capacity over 50ke- 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.

Remark:

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.

Both IMX571 (used in C3-26000) and IMX455 (used in C3-61000) sensors are supplied in two variants:

  • Consumer grade sensors. The sensor manufacturer (Sony Semiconductor Solutions Corporation) limits their usage to consumer still cameras only with operation time max. 300 hours per year.

  • Industrial grade sensors, intended for devices operating 24/7.

All sensor characteristics (resolution, dynamic range, ) are equal, sensors differ only in target applications and usage time. C3 is technically digital still camera, only specialized for astronomy. If it is also “consumer” camera strongly depends on users. Cameras used for causal imaging (when weather permits) only rarely exceeds 300hours of observing time per year. Cameras permanently installed on observatories, utilizing every clear night and possibly located on mountain sites with lots of clear nights exceed the 300hours/year within a couple of months. This is why C3 cameras are offered in two variants:

  • C3-26000 and C3-61000 with consumer grade sensors, intended for max. 300hours a year operation.

  • C3-26000PRO and C3-61000PRO with industrial grade sensors.

C3 camera models with consumer-grade sensors include:

Model C3-26000 C3-61000 C3-26000C C3-61000C
CMOS sensor IMX571 IMX455 IMX571 IMX455
Sensor grade Consumer Consumer Consumer Consumer
Color mask None None Bayer RGBG Bayer RGBG
Resolution 6252נ4176 9576נ6388 6252נ4176 9576נ6388
Pixel size 3.76נ3.76μm 3.76נ3.76μm 3.76נ3.76μm 3.76נ3.76μm
Sensor size 23.51נ15.70mm 36.01נ24.02mm 23.51נ15.70mm 36.01נ24.02mm

C3 camera models with industrial-grade sensors include:

Model C3-26000 PRO C3-61000 PRO C3-26000C PRO C3-61000C PRO
CMOS sensor IMX571 IMX455 IMX571 IMX455
Sensor grade Industrial Industrial Industrial Industrial
Color mask None None Bayer RGBG Bayer RGBG
Resolution 6252נ4176 9576נ6388 6252נ4176 9576נ6388
Pixel size 3.76נ3.76μm 3.76נ3.76μm 3.76נ3.76μm 3.76נ3.76μm
Sensor size 23.51נ15.70mm 36.01נ24.02mm 23.51נ15.70mm 36.01נ24.02mm

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 C3 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.

Response of IMX455 sensor in 16-bit mode

Response of IMX455 sensor in 16-bit mode

Download speed

C3 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 frame depends on USB connection type.

Model C3-26000 C3-61000
Download time on USB 3.0 (5 Gbps) 0.5s 1.0s
Download time on USB 2.0 (480 Mbps) 1.6s 3.3s

Download speed when using the Moravian Camera Ethernet Adapter depends if the 100Mbps or 1Gbps Ethernet is used, if USB2 or USB3 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 USB3 and 1Gbps Ethernet is directly connected to the host PC, download time of the C3-61000 full frame is approx. 2.5s.

Camera gain

Sensors used in C3 cameras offer programmable gain from 0 to 36dB, which translates to the output signal multiplication from 1 to 63.

Remark:

Note the C3 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:

Gain number Gain in dB Gain multiply
0 0.00 1.00
1000 2.34 1.32
2000 5.82 1.95
3000 11.46 3.74
4000 32.69 43.11
4030 35.99 63.00

Conversion factors and read noise

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. 10dB), where the full well capacity drops from more than 50ke- to ~17ke-. The read noise then drops from ~3.2e- RMS to ~1.5e-RMS.

Gain number Gain in dB Gain multiply Conversion factor Read noise RMS Full well capacity
0 0.0 dB 1 0.80 e-/ADU 3.51 e- 52,800 e-
2749 9.7 dB 3 0.26 e-/ADU 3.15 e- 17,100 e-
2750 9.7 dB 3 0.26 e-/ADU 1.46 e- 16,900 e-
4030 36.0 dB 63 0.18 e-/ADU 1.39 e- 11,600 e-

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 52,800/3.51=15,043

  • At gain=2750, dynamic range is 16,900/1.46=11,575

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 4e-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.

Remark:

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.

Exposure control

The shortest exposure time C3 cameras depends on the used sensor type.

  • C3-26000 shortest exposure time is 73ms.

  • C3-61000 shortest exposure time is 126ms.

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).

Cooling and power supply

Regulated thermoelectric cooling is capable to cool the CMOS sensor from 40 to 45C below ambient temperature, depending on the camera type. The Peltier hot side is cooled by a fans. The CCD chip temperature is regulated with 0.1C precision. High temperature drop and precision regulation ensure very low dark current for long exposures and allow proper image calibration.

C3 cameras are available in two variants, differing in the cooling performance:

  • Standard cooling cameras achieve regulated temperature difference up to 40C under environment temperature.

  • Enhanced cooling cameras can regulate temperature up to 45C under environment temperature. Compared to standard variant, enhanced cooling cameras are somewhat bulkier due to bigger heat sink, slightly heavier and somewhat noisier because of more powerful fans.

Comparison of the C3 standard cooling camera and enhanced cooling version

The cooling performance depends on the environmental conditions and also on the power supply. If the power supply voltage drops below 12V, the maximum temperature drop is lower.

CCD chip cooling Thermoelectric (Peltier modules)
Standard cooling ΔT 43C below ambient maximum
40C below ambient typical
Enhanced cooling ΔT 48C below ambient maximum
45C below ambient typical
Regulation precision 0.1C
Hot side cooling Air cooling (two fans)
Optional liquid coolant heat exchanger

Chip cooling specifications

Standard cooling C3-61000 (left) and Enhanced cooling C3-16000EC (right) cameras reaching -40C and -45C sensor temperature

Remark:

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.

Power supply

The 12VDC power supply enables camera operation from arbitrary power source including batteries, wall adapters etc. Universal 100-240V AC/50-60Hz, 60W “brick” adapter is supplied with the camera. Although the camera power consumption does not exceed 40W, the 60W power supply ensures noise-free operation.

Camera power supply 12VDC
Camera power consumption <8W without cooling
47W maximum cooling
Power plug 5.5/2.5 mm, center +
Adapter input voltage 100-240 V AC/50-60 Hz
Adapter output voltage 12VDC/5A
Adapter maximum power 60W

Power supply specification

Warning:

The power connector on the camera head uses center-plus pin. Although all modern power supplies use this configuration, always make sure the polarity is correct if other than the supplied power source is used.

Remark:

Power consumption is measured on the 12VDC 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 14V. However, some parameters (like cooling efficiency) can degrade if the supply drops below 12 V.

C3 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.

12 V DC/5 A power supply adapter for C3 camera

12 V DC/5 A power supply adapter for C3 camera

Mechanical Specifications

Compact and robust camera head measures only 154נ154נ65mm (approx. 6נ6נ2.6inches) for the model with standard cooling. Enhanced cooling increases camera depth by 11mm.

C3 camera without filters and standard cooling (far left) and with enhanced cooling (left), camera with internal filter wheel and standard cooling (right) and with enhanced cooling (far right)

C3 camera without filters and standard cooling (far left) and with enhanced cooling (left), camera with internal filter wheel and standard cooling (right) and with enhanced cooling (far right)

The head is CNC-machined from high-quality aluminum and black anodized. The head itself contains USB-B (device) connector and 12VDC power plug, no other parts, except a “brick” power supply, are necessary. Another connector allows control of optional external filter wheel. Integrated mechanical shutter allows automatic dark frame exposures, which are necessary for unattended, robotic setups.

Internal mechanical shutter Yes, blade shutter
Standard cooling camera dimensions 154mmנ154mmנ65mm (without filters)
154mmנ154mmנ77.5mm (internal wheel)
Enhanced cooling camera dimensions 154mmנ154mmנ76mm (without filters)
154mmנ154mmנ88.5mm (internal wheel)
Back focal distance 33.5mm (base of adjustable adapters)
Standard cooling camera weight 1.6kg (without filter wheel)
1.9kg (with internal filter wheel)
2.5kg (with “S” external filter wheel)
2.5kg (with “M” external filter wheel)
2.8kg (with “L” external filter wheel)
Enhanced cooling camera weight 1.8kg (without filter wheel)
2.1kg (with internal filter wheel)
2.7kg (with “S” external filter wheel)
2.7kg (with “M” external filter wheel)
3.0kg (with “L” external filter wheel)

Mechanical specification

Remark:

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 44mm).

Stated back focal distance already calculates with glass permanently placed in the optical path (e.g. optical window covering the sensor cold chamber).

Mechanical shutter

C3 cameras are equipped with mechanical shutter, which is very 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 C3 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 each pair of subsequent light images. In the case next image has to be dark or bias frame, shutter closes prior to dark frame 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 a few seconds while the shutter is open (this means after a light image exposure), camera firmware closes the shutter to cover the sensor from incoming light.

Camera front view

C3 camera front cross-section is the same for cameras with Internal Filter Wheel or without filter wheel, as well as for variants with standard and enhanced cooling.

C3 camera head front view dimensions

C3 camera head front view dimensions

Camera without filter wheel

C3 camera head side view dimensions

C3 camera with Enhanced cooling head side view dimensions

Camera with Internal Filter Wheel

C3 camera with Internal Filter Wheel head side view dimensions

C3 camera with Internal Filter Wheel and Enhanced cooling head side view dimensions

Camera with the “S” size External filter wheel

C3 camera head with the S External filter wheel front view dimensions

C3 camera head with the “S” External filter wheel front view dimensions

C3 camera head with “S” External filter wheel side view dimensions

The “M” and “L” sized External Filter Wheels diameter is greater (see External Filter Wheel User's Guide), but the back focal distance of all external filter wheels is identical.

Enhanced cooling C3 camera head with “S” External filter wheel side view dimensions

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.

C3 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 adapters without strictly prescribed back focal distance are M48נ0.75 thread for C3 cameras with the “S” adapter base or the “S” sized External Filter Wheel and M68נ1 thread for C3 cameras with the “L” adapter base or the “M” and “L” sized External Filter Wheel.

Remark:

Let us note the M48נ0.75 threaded adapter is sometimes used with 55mm BFD, e.g. when used with optical correctors. This is why two models of this adapters are available “short” variant with as low BFD as possible and “long” variant, which preserves the 55mm BFD.

C3 camera back focal distances with short M48נ0.75 adapter without filter wheel (left), with Internal Filter Wheel (center) and with External Filter Wheel (right)

C3 camera back focal distances with thin M68נ1 adapter without filter wheel (left), with Internal Filter Wheel (center) and with External Filter Wheel (right)

Adapters with defined back focal distance

There are three basic variants of C3 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 33.5mm, 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 33.5mm 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 33.5mm BFD. Thickness of this adapter base equals the thickness of the External Filter Wheel shell.

C3 camera with thin 55mm BFD M48נ0.75 adapter without filter wheel (left), with Internal Filter Wheel (center) and with External Filter Wheel (right)

C3 camera with Canon EOS bayonet adapter without filter wheel (left), with Internal Filter Wheel (center) and with External Filter Wheel (right)

C3 camera with Nikon bayonet adapter without filter wheel (left), with Internal Filter Wheel (center) and with External Filter Wheel (right)

C3 camera with C3-OAG without filter wheel (left), with Internal Filter Wheel (center) and with External Filter Wheel (right)

Optional accessories

Various accessories are offered with C3 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.

C3 camera without filter wheel and with “S” size External filter wheel

Telescope adapters

Various telescope and lens adapters for the C3 cameras are offered. Users can choose any adapter according to their needs and other adapters can be ordered separately.

Adjustable telescope/lens adapters are attached slightly differently depending if the External filter wheel is used or not:

  • If no External filter wheel is used, C3 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 MarkII External filter wheel front plate is already designed to hold the spring and it also contains threads to fix respective adapters.

C3 cameras are offered with two sizes of adjustable adapter base:

  • Small “S” adapters (also used with C2 cameras)

  • Large “L” adapters (also used with C4 cameras)

Adjustable adapters are mounted on adapter base when camera with internal filter wheel or camera without any filter wheel is used or directly on the external filter wheel front surface. This means both “S” and “L” adapter bases can be mounted on any camera, but external filter wheels are made for one particular adapter size only:

  • “S” external filter wheels are compatible with “S” adapters

  • “M” and “L” external filter wheels are compatible with “L” adapters

Comparison of the S size external filter wheel with S adapter (left) and M size external filter wheel with L adapter (right)

Comparison of the “S” size external filter wheel with “S” adapter (left) and “M” size external filter wheel with “L” adapter (right)

Small “S” size adapters:

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

  • T-thread short M42נ0.75 inner thread adapter.

  • T-thread with 55 mm BFD M42נ0.75 inner thread adapter, preserves 55mm back focal distance.

  • M48נ0.75 short adapter with inner thread M48נ0.75.

  • M48נ0.75 with 55 mm BFD adapter with inner thread M48נ0.75, preserves 55mm back focal distance.

  • Canon EOS bayonet standard Canon EOS lens adapter (“S” size). Adapter preserves 44mm back focal distance.

  • Nikon F bayonet standard Nikon F lens adapter (“S” size), preserves 46.5mm back focal distance.

Large “L” size adapters:

  • M68נ1 adapter with M68נ1 inner thread and 47.5mm back focal distance.

  • Canon EOS bayonet standard Canon EOS lens adapter (“L” size). Adapter preserves 44mm back focal distance.

  • Nikon F bayonet standard Nikon F lens adapter (“L” size), preserves 46.5mm back focal distance.

All telescope/lens adapters of the C3 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.

Adjusting the telescope adapter tilt (left) and removing tiltable the adapter (right)

Off-Axis Guider adapter

C3 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.

Position of the OAG reflection mirror relative to optical axis

Position of the OAG reflection mirror relative to optical axis

The C3-OAG offers the M68נ1 thread on the telescope side. The back focal distance is 61.5mm.

Warning:

Note the C3-OAG is manufactured for “L” size adapter base, so it is compatible with “M” and “L” external filter wheels only.

While C2-OAG (with M48נ0.75 or M42נ0.75 inner thread) for “S” size adapter base can be technically mounted to “S” size external filter wheel, the mirror is so close to optical axis, that it partially shields sensors used in C3 cameras and C2-OAG is not recommended for C3-61000 camera.

When used on camera with Internal filter wheel, thin adapter base is used.

OAG on C3 camera with internal filter wheel

OAG on C3 camera with internal filter wheel

If the OAG is used on camera without filter wheel, thicker adapter base must be used to keep the Back focal distance and to allow the guiding camera to reach focus.

OAG guider port is compatible with C1 cameras with CS-mount adapter. It is necessary to replace the CS/1.25 adapter with a short, 10mm 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.

Attaching camera head to telescope mount

C3 cameras are equipped with two “tripod” 0.250-20UNC threads on the top side of the camera head, as well as four metric M4 threaded holes.

Location of the threaded holes on the top part of the C3 camera head (left), 1.75" bar for standard telescope mounts (right)

These threaded holes can be used to attach 1.75inch “dovetail bar” (Vixen standard). It is then possible to attach the camera head, e.g. equipped with photographic lens, directly to various telescope mounts supporting this standard.

Spare desiccant containers

The C3 cameras are supplied with silicagel container, intended to dry the sensor cold chamber. This container can be unscrewed and desiccant inside can be dried in the owen (see the camera User's Manual).

The whole desiccant container can be baked to dry the silica-gel inside or its content can be poured out after unscrewing the perforated internal cap and baked separately

The whole desiccant container can be baked to dry the silica-gel inside or its content can be poured out after unscrewing the perforated internal cap and baked separately

Remark:

This is why the container itself does not contain any sealing, which could be damaged by high temperature in the owen. The sealing remains on the 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. Containers intended for enhanced cooling cameras are prolonged as the camera thickness is greater in the case of this variant.

Containers for standard and enhanced cooling cameras also in variants allowing tool-less manipulation

Containers for standard and enhanced cooling cameras also in variants allowing tool-less manipulation

It is possible to order spare container, which makes desiccant replacement easier and faster. It is possible to dry the spare container with silicagel and then only to replace it on the camera. Spare container is supplied including the air-tight cap.

Spare container can be supplied also in a variant that allows manipulation without tools. But this container is longer and exceeds camera outline. If the space behind the camera is not critical, this container can make desiccant exchange even easier.

Silicagel container with slot (left) and variant for tool-less manipulation (right)

Silicagel container with slot (left) and variant for tool-less manipulation (right)

Camera head color variants

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

C3 camera color variants

C3 camera color variants

Moravian Camera Ethernet Adapter

The Moravian Camera Ethernet Adapter allows connection of up to 4 Cx cameras of any type on the one side and 1Gbps Ethernet on the other side. This adapter allows access to connected Cx cameras using routable TCP/IP protocol over practically unlimited distance.

The Moravian Camera Ethernet Adapter device (left) and adapter with two connected cameras (right)

Moravian Camera Ethernet Adapter devices are described in detail here.

Software Support

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.

SIPS controlling whole observatory (shown in optional dark skin)

SIPS controlling whole observatory (shown in optional dark skin)

But SIPS is capable to do much more than just camera and observatory control. Many tools for image calibration, 16 and 32bit FITS file handling, image set processing (e.g. median combine), image transformation, image export etc. are available.

SIPS handles FITS files, supports image calibration and processing

As the first “S” in the abbreviation SIPS means Scientific, the software supports astrometric image reduction as well as photometric processing of image series.

SIPS focuses to advanced astrometric and photometric image reduction, but also provides some very basic astro-photography processing

SIPS software package is freely available for download from this www site. All functions are thoroughly described in the SIPS User's Manual, installed with every copy of the software.

Drivers for ASCOM standard as well as native drivers for third-party software are also available (e.g. TheSkyX, MaxIm DL, AstroArt, etc.). Visit the download page of this web site for current list of available drivers, please.

Also INDI drivers for 32bit and 64bit Linux running on x86 and ARM are available. Also drivers for TheSkyX package running on macOS are supplied with the camera.

Warning:

Make sure to always use the latest versions of available software and drivers. Minimal versions or the respective software packages, supporting the C3 cameras, are:

  • SIPS version 3.30

  • Moravian Camera Ethernet Adapter firmware version 50

  • ASCOM drivers version 5.5

  • INDI drivers in Linux version 1.7-3

  • Linux libraries version 0.6.3

  • TheSkyX drivers version 3.0

  • AstroArt drivers version 4.0

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 SIPS Guider tool window

The SIPS “Guider” tool window

The “Guiding” tool allows switching of autoguiding on and off, starting of the automatic calibration procedure and recalculation of autoguiding parameters when the telescope changes declination without the necessity of new calibration. Also swapping of the German Equatorial mount no longer requires new autoguider calibration. There is also a graph showing time history of guide star offsets from reference position in both axes. The length of graph history as well as the graph range can be freely defined, so the graph can be adjusted according to particular mount errors and periodic error period length. Complete log of calibration procedure, detected offsets, correction pulses etc. is also shown in this tool. The log can by anytime saved to log file.

An alternative to classic autoguiding is the inter-image guiding, designed for modern mounts, which are precise enough to keep tracking with sub-pixel precision through the single exposure, and irregularities only appear on the multiple-exposure time-span. Inter-image guiding then performs slight mount position fixes between individual exposures of the main camera, which eliminates “traveling” of the observed objects through the detector area during observing session. This guiding method uses main imaging camera, it does not use another guiding camera and naturally does not need neither OAG nor separate guiding telescope to feed the light into it.

Inter-image guiding controls in the Guiding tab of the Imager Camera tool window

Inter-image guiding controls in the Guiding tab of the Imager Camera tool window

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

Color CCD detectors have red, green and blue filters applied directly on individual pixels (so-called Bayer mask).

Schematic diagram of color CCD detector with Bayer mask (left) and magnified crop of raw image captured by color camera (right)

Every pixel registers light of particular color only (red, green or blue). But color image should contain all three colors for every pixel. So it is necessary to calculate missing information from values of neighboring pixels.

There are many ways how to calculate missing color values from simple extending of colors to neighboring pixels (this method leads to coarse images with visible color errors) to methods based on bi-linear or bi-cubic interpolation to even more advanced multi-pass methods etc.

Bi-linear interpolation provides significantly better results than simple extending of color information to neighboring pixels and still it is fast enough. But if the telescope/lens resolution is close to the size of individual pixels, color artifacts appear close to fine details, as demonstrated by the image below left.

The above raw image with colors calculated using bi-linear interpolation (left) and the same raw image, but now processed by the multi-pass de-mosaic algorithm (right)

Multi-pass algorithm is significantly slower compared to single-pass bi-linear interpolation, but the resulting image is much better, especially in fine details. This method allows using of color camera resolution to its limits.

SIPS offers choosing of color image interpolation method in both “Image Transform” and “New Image Transform” tools. For fast image previews or if the smallest details are significantly bigger than is the pixel size (be it due to seeing or resolution of the used telescope/lens) the fast bi-linear interpolation is good enough. But the best results can be achieved using multi-pass method.

Shipping and Packaging

C3 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).

  • A100-240VAC input, 12VDC output “brick” adapter with 1.8m long power cable.

  • 2m long USB3.0 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'sManual.

  • Aprinted copy of camera User'sManual

C3 cameras are shipped in the foam-filled carrying case (left), larger case is used if camera is ordered with external filter wheel (right)

 
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