As the weather has not been suitable for imaging, I decided to do some master dark frames with the ZWO ASI178MM-cooled at different gain settings. I chose to cool the sensor down to -20 degrees Celsius, as I thought that this would still be achievable when imaging during summer nights – allowing me to use just one set of master dark frames throughout the year.
I set my computer up in my conservatory as it is unheated and hence much cooler than the house – but it was still only 12 degrees Celsius, so not as cool as I would have hoped for. The first 4 images were done at different gain levels but at -20 degrees Celsius. The last two were done at -25 degrees Celsius, although the sensor’s temperature fluctuated between -22.0 and -25.0 degrees Celsius i.e. when the sensor was capturing images, it did heat up a little and exceeded the cooling capacity of the camera (but 34 degrees below ambient temperature is still pretty good).
All images were captured using Demo Nebulosity 4,with between 5-8 frames captured for each gain setting. They were then stacked in Deep Sky Stacker as .tiff files, opened and then saved as .tiff (16-bit) files with Registax 6 so that it could be read by Capture One Pro 8. They were then boosted to +4.0 EV with Capture One Pro 8, to show the amp glow present.
300 second sub with Gain 0 @ -20 degrees Celsius – a tiny bit of glow at the bottom two corners.
300 second sub with Gain 100 @ -20 degrees Celsius – slightly more glow at the two bottom corners.
300 second sub with Gain 200 @ -20 degrees Celsius – some more glow in the bottom two corners and on the right top corner/side.
300 second sub with Gain 300 @ -20 degrees Celsius – more obvious glow at the top right corner, and more glow compared to the others in the two bottom corners.
Now images where cooling was set to -25 degrees Celsius.
300 second sub with Gain 100 @ -25 degrees Celsius – similar to that of the -20 degrees Celsius master dark frame.
300 second sub with Gain 200 @ -25 degrees Celsius still visible glow at the top right corner, as well as both bottom corners.
Looking at the amp glow with higher gain levels, I will probably not image above gain 200. I don’t think that there is that much difference between the amp glow with Gain 0 and 100, so I might set Gain 100 (19%) as my preferred setting unless shooting with a very fast lens i.e. F2.0, where I would set to Gain 0.
I am pretty impressed with the dark frames I am getting out of this imager – definitely less noisy than the Olympus E-PL5.