Sudden Offset (and gain) Change

ASI's Range of Specialised CMOS camera's

Moderators: Sam, Sean.Wang

Post Reply
bellavia
Posts: 18
Joined: Mon Nov 27, 2017 2:15 am

Sudden Offset (and gain) Change

Post by bellavia » Sat Oct 13, 2018 11:51 am

Last night the offset (and maybe the gain) suddenly changed on my ZWO ASI 183MM Pro cooled camera.

These are the events that happened:

1. I connected the camera through SharpCap to do a Polar Alignment with the main imaging camera and scope. When complete, I disconnected the camera and closed SharpCap

2. I then connected the camera through APT, using Shift-Connect and set the Gain to 140 and Offset to 20, and began cooling.

3. While cooling I went to connect the ZWO ASI224MC guide camera in PHD2, but accidentally chose the main camera, the ZWO ASI183MM. I disconnected and connected the correct camera, but after that could not get the 183 to work in APT, and tried to disconnect and reconnect, losing cooling, but that did not work.

4. I shut down and restarted APT and reconnected , using the Shift-Connect, set the Gain to 140 and Offset to 20, and began cooling again.

5. Once cooled I began imaging. The images had a larger minimum than I recall for that offset, and previews (using Nebulosity) showed them to be washed out and grainy. But I let it image for over an hour, not sure if this was normal or not.

6. Then, while previewing, after the 12th 5-minute image, subsequent images became completely different. The offset had dropped back down to "normal", and the mean was nearly half of the previous images, which were now much cleaner and nicer looking.

The file header still showed the same 140 gain (and offset is not reported from these cameras, a complaint I have made before).

I don't know what went wrong, but I don't want this to ever happen again. I lost over an hour of non-recoverable imaging time (which is precious for me)


Any help is appreciated
Attachments
offset-gain_anomaly.png

User avatar
Sean.Wang
Posts: 713
Joined: Mon Apr 24, 2017 10:08 am

Re: Sudden Offset (and gain) Change

Post by Sean.Wang » Mon Oct 15, 2018 1:51 pm

Hi there
Not sure about this, but I really suspect dew happened on the lens. Maybe it vanished and get better SNR.
The offset had dropped back down to "normal". What is normal means?
ZWO | Marketing Consultant
Location:lon=120.6 lat=31.3
SuZhou China

motto:
Don't face one's fate, can't be a real man;
Don't know manners, can't be gentle;
Don't know meaning behind the words, can't understand man's heart.

bellavia
Posts: 18
Joined: Mon Nov 27, 2017 2:15 am

Re: Sudden Offset (and gain) Change

Post by bellavia » Mon Oct 15, 2018 5:13 pm

Sean.Wang wrote:Hi there
Not sure about this, but I really suspect dew happened on the lens. Maybe it vanished and get better SNR.
The offset had dropped back down to "normal". What is normal means?
Definitely not dew. The optics and the sky were clear throughout the night.
I have over an hour's worth of images that are identical, and then very suddenly another 35 minutes worth that are also identical (and much better), and there was no change in the sky or the optics.
This was an electronic/software mishap.

By "normal" I mean approximately 300 to 500 ADU's (in 16-bit) as the minimum. The minimum was well over 1,000, closer to 2,000. I have never seen that before at this gain and offset setting.

I tried it again, but this time just connecting to the camera with SharpCap and then disconnecting, and it was fine after that.

I am pretty sure it was PHD2 that took hold of the driver, and changed the settings. Not sure why it didn't let go after I disconnected it, but I will be careful to not accidentally do that again.

Thanks

User avatar
Sean.Wang
Posts: 713
Joined: Mon Apr 24, 2017 10:08 am

Re: Sudden Offset (and gain) Change

Post by Sean.Wang » Fri Oct 19, 2018 5:41 am

bellavia wrote:
Sean.Wang wrote:Hi there
Not sure about this, but I really suspect dew happened on the lens. Maybe it vanished and get better SNR.
The offset had dropped back down to "normal". What is normal means?
Definitely not dew. The optics and the sky were clear throughout the night.
I have over an hour's worth of images that are identical, and then very suddenly another 35 minutes worth that are also identical (and much better), and there was no change in the sky or the optics.
This was an electronic/software mishap.

By "normal" I mean approximately 300 to 500 ADU's (in 16-bit) as the minimum. The minimum was well over 1,000, closer to 2,000. I have never seen that before at this gain and offset setting.

I tried it again, but this time just connecting to the camera with SharpCap and then disconnecting, and it was fine after that.

I am pretty sure it was PHD2 that took hold of the driver, and changed the settings. Not sure why it didn't let go after I disconnected it, but I will be careful to not accidentally do that again.

Thanks
Thank you, Beliavia. if the issue can be repeat, tell us how to repeat this issue, we will be able to fix it.
ZWO | Marketing Consultant
Location:lon=120.6 lat=31.3
SuZhou China

motto:
Don't face one's fate, can't be a real man;
Don't know manners, can't be gentle;
Don't know meaning behind the words, can't understand man's heart.

Post Reply