The ZWO ASI178MC is a camera with a 14 bit ADC and a back illuminated 6.4 MP Sony IMX178 CMOS sensor with 7.4 x 5 micro metre pixels which use STARVIS and EXMOR R technologies.
These technologies produce higher sensitivity and lower noise as well as reducing rolling shutter distortion. The back illumination avoids the internal circuitry in the sensor obstructing some of the light falling on the sensor before it reaches the photodiode. This allows for the reduction in size of the pixels and higher pixel counts on the sensor without increasingly the proportion of the light that is attenuated before it reaches the photodiode. The global shutter reset reduces the rolling shutter distortions that can occur if the subject moves (In astronomical imaging, the only movement should be due to seeing. However, some people image while the object drifts across the field of view or manually nudge the scope to keep the object in the field of view).
This test was done on a night with a low, 94% waxing Moon in the sky. This produced relatively poor seeing and a sky filled with Moon glow.
The ZWO ASI178MC camera was placed at the Newtonian focus of a Skywatcher, f/5, 130PDS Newtonian mounted on a Celestron AVX EQ, GOTO mount. Two overlapping 500 frame SER files were captured at full resolution (3096 x 2080). The best 95% of the frames were stacked in Autostakkert! 3.1 running in Wine. The resulting images were wavelet processed in Registax 5.1, and stitched into a single image using Microsoft ICE, both running in Wine. The final image was post processed in the Gimp 2.10.
Deep sky on a moonlit night
The ZWO ASI178 has a 14 bit ADC unlike many of the CMOS astronomical cameras which have 12 bit ADCs. This means that it can capture images with 16384 levels of brightness, compared with a 12 bit ADC which produces 4096 levels of brightness.
AstroDMx Capture for Linux saves the 14 bit data, mapped to the lower or the upper bits of a 16 bit container. This is still not up to the 16 bit ADCs of traditional CCD based astronomical cameras, but it is a substantial improvement on 12 bit devices.
With the bright Moon illuminating the sky, the ZWO ASI178MC in the same configuration was used to capture 40 x 40s exposures of the Ring nebula.
Screenshot of AstroDMx Capture for Linux capturing images of M57.
The display was using Gammalog, but could be changed to show more contrast if required, but as all that is usually required is to correctly position the object of interest, no further adjustments were made. It should be remembered that the display controls are non destructive, so do not affect the data being captured.
The best 90% of the images were stacked in Deep Sky Stacker running in Wine, and post processed in the Gimp 2.10.
Performance and real-time display are still being improved, but a release will not be far away.
