ZWO ASI178MMC camera – field test

Recently I had the opportunity to take the ASI178MMC camera out for a test run. I wanted to test a few things with this camera in the limited time I had. I used Sharpcap for the imaging, as this is a program I had downloaded and with with I could control both the camera and my Xagyl motorised wheel.

The things I wanted to test were:

  1. The focusing distance for this camera on my setup.
  2. The dark frame for 5 minute subs with gain set to 50 (I will need to test this for other gain levels i.e. 100, 200, 300 and 400).
  3. The ability of the cooling system to get the sensor temperature down to -20 degrees Celsius.
  4. Star test to see if my Skywatcher ED80 focus differs significantly with red, green, blue and luminance frames.
  5. The correct distance to place the autoguider on the Orion Off-axis guider to match with the focus for the ASI178MMC.
  6. Long exposure of the Horsehead nebula – 5 minute subs.

Unfortunately I ran into a problem of not being able to get the focus position of the autoguider right in the short time I had. Hence I was only able to do the first 4 tests. The remainder will have to wait until I have more time.

I managed to sort out item 1 easily, as with my Skywatcher ED80 with the Astro-Physics CCDT67 telecompressor (set at 101mm from sensor plane = 0.67x), Orion thin Off-axis guider, Xagyl 5 x 1.25″ motorised filter wheel, I was still able to have enough back focus (over 3 cm) for the ASI178MMC.

Item 2 – test of dark frame 300s sub Gain 50 with sensor temperature cooled to -20 degrees Celsius (I chose this level as it will be achievable during summer months as well). The first image is the single dark frame as it was captured, and second image is the same dark frame boosted by +3.94EV with Capture One Pro 8.

ASI178MMC: 300 sec dark frame Gain 50
ASI178MMC: 300 sec dark frame Gain 50

As you can see with big boost in exposure, there is a small amount of amp glow at the bottom two corners of the image, and a slight amount on the right edge close to the top right corner (less obvious).

Dark frame - boosted + 3.94 EV with Capture One Pro 8
Dark frame – boosted + 3.94 EV with Capture One Pro 8

So for me, this camera passes the dark frame test with Gain 50. I will test this with other gain levels in due course, in the hope of finding the best settings for doing Deep Sky Object imaging.

Item 3 – sensor cooling to -20 degrees Celsius. The outdoors temperature on the day of the test was about 3-4 degrees Celsius. As can be seen below, the sensor was able to get to -20 degrees Celsius easily using only 13% of the cooling capacity i.e. it was doing it with plenty of backup capacity.

Cooling of sensor to -20 degree Celsius
Cooling of sensor to -20 degree Celsius

Item 4 – below are just two images of the star test I did that night. I am now aware that there is definitely some shift in focus between the red channel and luminance channel and the blue and green, channel i.e. the Skywatcher ED80 is not as well corrected as a true Apo refractor. Hence to capture images which will stack better, I will need to readjust the focus for the red after the blue, green and luminance channels.

Star test using green filter
Star test using green filter
Star test - luminance filter
Star test – luminance filter

And I still need to work on item 5 and 6, and will write about these when they are done – hopefully with some nice pics as well. But I am impressed with this camera.

Boon