Camera CG-3000A (IMX265)- MORAVIAN

Sometimes the C0 or C1 camera cannot be used on OAG because of its shape. Both C0 and C1 cameras exceed the front plane, defined by the OAG front thread, and thus they can possibly interfere with the telescope's rear mounting interface. The CG cameras are designed not to exceed the OAG in the front. But otherwise, the CG cameras are essentially the C0 ones in the flat casing.

• Dimensions: 50 × 34 × 68 mm   
• Weight: 138 g     

C0, CG, and C1 camera models are equipped with Sony IMX global shutter CMOS detectors with 3.45 × 3.45 μm square pixels. Individual models differ in resolution only.

All used sensors utilize global electronic shutter. This means every pixel within the image is exposed in the same time, as opposed to rolling shutter sensors, which exposes individual lines one after another. There is no difference for long exposures of static objects, but imaging of moving objects using short exposure time using rolling shutter leads to image shape distortions.

Two camera lines are available depending on the available dynamic range (bit-depth of the digitized pixels):

• Cameras with Sony IMX sensors 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.
• Cameras with Sony IMX sensors 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.

CG-3000A use a 12Bit digitization only

Featrues of CG-3000A

• Sensor: IMX265   
• Resolution: 2064 × 1544 pixels   
• Pixel seize:  3.45 × 3.45 μm
• Sensor seize: 7.12 × 5.33 mm
  
  
  

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 C1 cameras shows very good linearity in response to light. This means the camera can be used also for entry-level research projects, like for instance photometry or brighter variable stars etc.

Download speed

As already noted, there are two lines of C0, CG, and C1 camera series, differing in the used sensor. The first series offers four different read modes:

• 12-bit fast mode with ~132 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.

Sensors used in C0, CG, and C1 cameras offer programmable gain from 0 to 24 dB, which translates to the output signal multiplication from 1× to 15.9×. Gain can be set with 0.1 dB step.

Remark:

Note the 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, many sensor characteristics depend on the used gain. Hence, we provide two lists of parameters for both minimal and maximal gain.

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

C0, CG, and C1 cameras are capable of very short exposures. The shortest exposure time is 125 μs (1/8000 of second). This is also the step, by which the exposure time is expressed. So, the second shortest exposure is 250 μs etc.

Long exposure timing is controlled by the host PC and there is no upper limit on exposure time. In reality the longest exposures are limited by saturation of the sensor either by incoming light or by dark current (see the following sub-chapter).
Sensor Cooling

Dark current is an inherent feature of all silicone circuits. It is called “dark”, because it is generated regardless if the sensor is exposed to light or not. Dark current, injected into individual pixels, appear in image as noise. The longer exposure, the greater amount of noise is present in every image. As it is generated by random movement of particles, it depends on the temperature exponentially (this is why the noise generated by dark current is also denoted “thermal noise”). Typically, lowering the sensor temperature by 6 or 7 °C halves the dark current.

While none of the C0, CG, or C1 cameras are equipped with active thermo-electric (Peltier) cooling, the C1 models employ a small fan, exchanging air inside the camera body. What is more, a small heat sink is located directly on the sensor to remove as much heat as possible (with the exception of C1-1500, which sensor is too small to be equipped with a heat sink). So, the C1 sensor cannot be cooled below the ambient temperature, but its temperature is kept as close to environment as possible. Compared to closed designs of the C0 and CG cameras, the sensor temperature in the C1 can be between 7 and 10°C lower and resulting dark current may be less than a half.

Other information

• Internal mechanical shutter: No
• Shortest exposure time: 125 μs
• Longest exposure time: Limited by chip saturation only
• CG head dimensions: 50 mm × 34 mm × 68 mm (including CS-mount adapter)
• Back focal distance:
       - 12.5 mm for 1/32 UN thread (CS-mount compatible)
        - 18.5 mm for M42 × 0.75 thread (T-mount)
• CG head weight: 138 g