Moravian Instruments C2 Series User manual

C2 Series
Astronomical Cameras
User’s Guide

Version 1.6
Modified on October 13th, 2023
All information furnished by Moravian Instruments is believed to be
accurate. Moravian Instruments reserves the right to change any
information contained herein without notice.
C2 cameras are not authorized for and should not be used within Life
Support Systems without the specific written consent of the Moravian
Instruments. Product warranty is limited to repair or replacement of
defective components and does not cover injury or property or other
consequential damages.
Copyright © 2000-2023, Moravian Instruments
Moravian Instruments
Masarykova 1148
763 02 Zlín
Czech Republic
phone: [phone]
web: https://www.gxccd.com/
e-mail: [email protected]

Table of Contents
Introduction .................................................................................................. 5
C2 Camera Overview ..................................................................................... 7
C2 Camera System .................................................................................... 9
C2 with global shutter CMOS Sensors ......................................................... 11
Camera Electronics .................................................................................. 12
Sensor linearity ....................................................................................... 13
Download speed ..................................................................................... 14
Camera gain ............................................................................................ 15
Conversion factors and read noise .......................................................... 15
Exposure control ..................................................................................... 16
Mechanical shutter ............................................................................. 16
C2 with rolling shutter CMOS Sensors ........................................................ 17
Camera Electronics .................................................................................. 17
Sensor linearity ....................................................................................... 17
Download speed ..................................................................................... 18
Camera gain ............................................................................................ 19
Conversion factors and read noise .......................................................... 20
Binning .................................................................................................... 20
Hardware binning ................................................................................ 21
Adding vs. averaging pixels ................................................................. 21
Binning in photometry ........................................................................ 23
Exposure control ..................................................................................... 23
Mechanical shutter ............................................................................. 24
GPS exposure timing ........................................................................... 24
Cooling and power supply ........................................................................... 27

Overheating protection ....................................................................... 29
Power supply ........................................................................................... 29
Mechanical Specifications ........................................................................... 32
Camera with Internal Filter Wheel .......................................................... 34
Camera with “XS” External Filter Wheel ................................................. 35
Camera without filter wheel ................................................................... 36
Back focal distance .................................................................................. 37
Adapters without back focal distance defined .................................... 38
Adapters with defined back focal distance ......................................... 40
Off-Axis Guider Adapter ...................................................................... 41
Optional accessories.................................................................................... 44
Telescope adapters ................................................................................. 44
Off-Axis Guider Adapter (OAG) ............................................................... 44
GPS receiver module ............................................................................... 46
GPS receiver module handling ............................................................ 47
Attaching camera head to telescope mount ........................................... 48
Camera head color variants .................................................................... 49
Camera Ethernet Adapter ....................................................................... 49
Adjusting of the telescope adapter ............................................................. 51
Camera Maintenance .................................................................................. 54
Desiccant exchange ................................................................................. 54
Exchanging the silica-gel...................................................................... 55
Changing Filters ....................................................................................... 57
Opening the camera head ................................................................... 57
Changing the Whole Filter Wheel ........................................................... 58
Changing the Telescope Adapter ............................................................ 58
Power supply fuse ................................................................................... 59

5
Introduction
Thank you for choosing the Moravian Instruments camera. The cooled C2
series CMOS cameras were developed for imaging under extremely low-
light conditions in astronomy, microscopy, and similar areas.
Mechanical design of this series inherits from earlier CCD-based G2 Mark II
cameras, which makes the C2 series fully compatible with vast range of
telescope adapters, off-axis guider adapters, internal or external filter
wheels, Camera Ethernet adapters, guiding cameras etc.
Rich software and driver support allows usage of C2 camera without
necessity to invest into any 3rd party software package thanks to included
free SIPS software package. However, ASCOM (for Windows) and INDI (for
Linux) drivers, shipped with the camera, provide the way to integrate C2
camera with broad variety of camera control programs.
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 slow-scan, cooled cameras
usually require computer for operation control, image download,
processing, and storage etc. To operate the camera, you need a computer
which:
1. Is compatible with a PC standard and runs modern 32 or 64-bit
Windows operating system.
2. Is compatible with a PC standard and runs 32 or 64-bit Linux
operating system.
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.
Only certain software packages are currently supported on Mac.

6
C2 cameras are designed to be attached to host PC through very fast
USB 3.0 port. While C2 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 Gx) cameras of any type
(not only C2, but also C1, C3 and C4) and offers 1 Gbps and 10/100 Mbps
Ethernet interface for direct connection to the host PC. Because the PC
then uses TCP/IP protocol to communicate with the cameras, it is possible
to insert WiFi adapter or other networking device to the communication
path.
Please note while the USB standard allows usage of cable no longer
than approx. 5 meters, the TCP/IP communication protocol used to
connect the camera over the Ethernet adapter is routable, so the
distance between camera setup and the host PC is virtually unlimited.
Download speed is naturally significantly slower when camera is attached
over Ethernet adapter, especially when compared with direct USB 3
connection.
The C2 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. C2 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.

7
C2 Camera Overview
C2 camera head is designed to be easily used with a set of accessories to
fulfil 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.
Figure 1: C2 Camera without filter wheel (left), with Internal filter wheel (middle)
and with attached External filter wheel (right)
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 D26 mm (or 1”)
filters.
There are two sizes of the External filter wheels, each capable to accept
two sizes of filters, available for the C2 cameras:

8
 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.
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.
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.

9
C2 Camera System
Figure 2: Schematic diagram of C2 camera system components

10
Components of the 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
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 camera can share the Moravian Camera Ethernet Adapter
with up to 3 other Cx or Gx cameras to be accessed over
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)
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. 6-positions internal filter wheel for D27.5 mm filters
13. 5-positions internal filter wheel for 1.25”/D31 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
20. Canon EOS bayonet lens adapter
21. Nikon bayonet lens adapter

11
C2 with global shutter CMOS Sensors
C2 series of CMOS cameras with Sony IMX global shutter CMOS detectors
have pixel size 3.45 × 3.45 μm or 4.50 × 4.50 μm.
Three lines of C2 cameras with global shutter 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 speed 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 “A” 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.

12
C2 camera models with 3.45 × 3.45 μm pixels and 8- and 12-bit digitization:
Model C2-3000 C2-5000 C2-12000
CMOS sensor IMX252 IMX250 IMX253
Resolution 2064 × 1544 2464 × 2056 4112 × 3008
Pixel size 3.45 × 3.45 μm 3.45 × 3.45 μm 3.45 × 3.45 μm
Sensor size 7.12 × 5.33 mm 8.50 × 7.09 mm 14.19 × 10.38 mm
C2 camera models with 3.45 × 3.45 μm pixels and 12-bit digitization only:
Model C2-3000A C2-5000A C2-12000A
CMOS sensor IMX265 IMX246 IMX304
Resolution 2064 × 1544 2464 × 2056 4112 × 3008
Pixel size 3.45 × 3.45 μm 3.45 × 3.45 μm 3.45 × 3.45 μm
Sensor size 7.12 × 5.33 mm 8.50 × 7.09 mm 14.19 × 10.38 mm
C2 camera models with 4.50 × 4.50 μm pixels and 12-bit digitization only:
Model C2-7000A
CMOS sensor IMX428
Resolution 3216 × 2208
Pixel size 4.50 × 4.50 μm
Sensor size 14.47 × 9.94 mm
Cameras limited to 12-bit read mode are marked with letter A, following
the model number. For instance, if C2-3000 marks camera with both 8-
and 12-bit read modes, C2-3000A denotes camera model with only 12-
bit read mode. All other parameters (sensor size, pixel resolution) are
equal.
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).

13
Sensor linearity
The sensors used in C2 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.
Figure 3: Response of the Sony IMX sensors with 3.45 × 3.45 μm pixels (IMX252)
Figure 4: Response of the Sony IMX sensors with 4.50 × 4.50 μm pixels (IMX428)

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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 slow variant of both read modes can be used to slightly lower the
amount of heat generated by the sensor, as the communication
interface operates at half speed compared to fast mode. Also, when
the camera is connected using USB 2.0 interface, fast read mode
provides data at higher speed than the USB 2.0 can handle and thus
causes more interruptions of image digitization process.
The “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.
Despite one byte per pixels is transferred from camera to PC in the 8-
bit read mode, many astronomical processing software packages work
with 16-bit or 32-bit images only (e.g. SIPS). So, images occupy the
same space in the computer memory regardless of the read mode.

15
Also, standard format for image storage in astronomy is FITS. While
this format supports 8-bit per pixel, this variant is rather unusual and
16 or 32-bit integer or 32-bit floating-point pixels are typically stored
to disk files to achieve as wide compatibility as possible.
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.
Note the C2 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.
Conversion factors and read noise
Generally, all sensor characteristics depend on the used gain. So, we
provide two list of parameters for both minimal and maximal gain.
Camera/sensor parameters for sensors with 3.45 × 3.45 μm pixels:
Digitization 12-bit 12-bit 8-bit 8-bit
Sensor gain 0 dB 24 dB 0 dB 24 dB
Full well capacity 11000 e- 1100 e- 2600 e- 1100 e-
Conversion factor 2.8 e-/ADU 0.3 e-/ADU 10.0 e-/ADU 4.4 e-/ADU
Read noise 2.2 e- RMS 2.0 e- RMS 4.2 e- RMS 9.7 e- RMS
Camera/sensor parameters for sensors with 4.50 × 4.50 μm pixels:
Digitization 12-bit 12-bit
Sensor gain 0 dB 24 dB
Full well capacity 26000 e- 2100 e-
Conversion factor 6.3 e-/ADU 0.5 e-/ADU
Read noise 5.3 e- RMS 3.9 e- RMS
Please note the values stated above are not published by sensor
manufacturer, but determined from acquired images using the SIPS

16
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
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.

17
C2 with rolling shutter CMOS Sensors
C2 series of CMOS cameras with Sony IMX rolling shutter CMOS detectors
currently contain single model with Sony IMX533 sensor with pixel size
3.76 × 3.76 μm:
Model C2-9000
CMOS sensor IMX533
Resolution 3008 × 3008
Pixel size 3.76 × 3.76 μm
Sensor size 11.31 × 11.31 mm
The sensor belongs to the same family like sensors used in the C1×, C3
and C5 camera lines, only the digitization precision is 14-bit instead of
16-bit of the larger sensors.
Camera Electronics
Controlling of the rolling shutter sensors differs significantly from
controlling of the global shutter sensors. The camera internals differ
significantly from other C2 models.
The C2-9000 contains 256 MB of onboard memory, capable to store up to
14 full-resolution frames. 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 imaged, 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 IMX533 sensor used in C2-9000 camera shows 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.

18
Figure 5: Response of the Sony IMX rolling-shutter sensor (IMX533)
Download speed
Thanks to C2-9000 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.
 Full-frame, USB 3.0 (5 Gbps): 0.06 s
 Full-frame, USB 2.0 (480 Mbps): 0.40 s
If only a sub-frame is read, time needed to digitize and download image is
naturally lower. However, the download time is not cut proportionally to
number of pixels thanks to some fixed overhead time, independent on the
sub-frame dimensions.
 1024×1024 sub-frame, USB 3.0 (5 Gbps): 0.02 s
 1024×1024 sub-frame, USB 2.0 (480 Mbps): 0.05 s

19
The driver is sometimes forced to read bigger portions of the sensor
than the user defined because of a sub-frame position and dimension
limitations imposed by the sensor hardware. Sometimes it is even
necessary to read a whole sensor.
It is recommended to click the Adjust Frame button in the Frame tab
of the SIPS camera control tool. The selected frame dimensions are
then adjusted according to sensor limitations. Adjusted frame is then
read from the sensor, without a necessity to read a bigger portions or
even whole sensor and crop image in firmware.
C2-9000 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.
 Full-frame 2×2 binning, USB 3.0 (5 Gbps): 0.03 s
 Full-frame 2×2 binning, USB 2.0 (480 Mbps): 0.11 s
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.
Camera gain
Sensors used in C2-9000 camera offer programmable gain from 0 to 36 dB,
which translates to the output signal multiplication from 1× to 63×.
Note the C2 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’s register value. This number does not

20
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:
Gain number Gain in dB Gain multiply
0 0.00 1.00×
500 1.13 1.14×
1000 2.43 1.32×
1500 3.96 1.58×
2000 5.82 1.95×
2500 8.19 2.57×
3000 11.46 3.74×
3500 16.75 6.88×
4000 32.69 43.11×
4030 35.99 63.00×
Conversion factors and read noise
Generally, many sensor characteristics depend on the used gain.
Gain number 0 4030
Sensor gain 0.0 dB 36 dB
1× 63×
Full well capacity 50000 e- 950 e-
Conversion factor 3.05 e-/ADU 0.06 e-/ADU
Read noise 3.90 e- RMS 2.67 e- RMS
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.
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