ZWO ASI6200MM-Pro
The ZWO ASI6200MM Pro camera is built around the Sony IMX455 backside illuminated CMOS-sensor, similar to the Moravian C3-61000Pro. A full-frame sensor with a pixel-size of 3.8 µm. The resolution is an impressive 61MP. This sensor is a popular choice in the astrophotography world, especially when paired with telescopes that support full-frame sensor sizes.
Most cameras have a 16-bit readout, but often this is an upsampled 12- or 14-bit signal from the sensor. The ASI6200MM has a true 16-bit sensor readout, providing a lot more tonal information especially in the darker part of the image, the part most interesting for astrophotography. Coupled with an exceptionally high Quantum Efficiency of >90% and a pretty large full-well depth of 51.4ke, the camera is able to record 14 stops of dynamic range. The dual-gain setting of sensor switches hardware circuitry on-chip. This results in a drop in read-noise at gain 100 while maintaining the same 14 stop dynamic range as with gain 0.
Specifications
Resolution: 9576*6388 pixels (61 Megapixels)
Sensor-size: 36 x 24mm; 43.3mm diagonal
Quantum Efficiency: 91%
Full well capacity: 51.4ke
ADC: true 16-bit
Interface: USB3 (image download) and 2 x USB2 hub
Camera size: 90mm diameter, 700g
Field of View
The sensor of the ASI6200 is a full-frame size of 36x24mm, or the traditional film-size. The bigger the sensor, the bigger the Field of View. Coupled with the TOA-130, the horizontal FoV is 2.07°, twice as big as the 1.01° of the TOA-130/ASI1600 combination. The 43.3mm diagonal means that regular 1.25” filters are too small and that 50mm diagonal round or square filters are required. Also, the image circle of the telescope/flattener should be large enough to capture full frame. The 67-FL flattener on the TOA-130 projects an image circle of 90mm, more than large enough for the ASI6200.
Sensor: 61 Megapixels
Each image of the ASI6200 contains 61MP of information, and that is a lot. The file-sizes are significant, with roughly 100Mb/frame. Transferring these files from camera to acquisition computer takes significant effort. For a local connection, transfer time is less than 1 sec. When transferring over WiFi, this time increases to 20 sec, significantly longer than the 6 sec of the ASI1600. Storage is another point of interest, but storage gets cheaper every year. One can use the camera in bin2 or bin3 mode, which reduces resolution and file-size by a factor of 4 or 8 respectively.
Cooling
In ZWO-nomenclature, ‘Pro’ indicates ‘Cooled’. The sensor can be cooled to about 35°C below ambient temperature. Cooling reduces the dark-current, a component of the read noise. The dark current is very low in this camera. At -20°C it is 0.0006 e-/s/px. This is 10 times lower than the ASI1600 at the same temperature. Cooling further will add little to the noise reduction. Standardising temperature across sessions has the advantage that only one set of bias/dark frames is needed. -15°C is a good standard for year-round imaging. For cooling, 12V DC power needs to be supplied to the camera.