I tried to run off a few subs last night after the moon set but was confronted with the images as shown in the attachments. I aborted the imaging session after these five frames and gave up.
The camera is a QSI683 which I have had since 2014 and it has been performing very nicely with no problems during this time. The telescope is a TSA120 refractor. I have never seen this type of issue previously. Note that I always cool down the sensor to -20c over a five minute period before kicking off the imaging session. In the time that I have had the camera I have not touched the desiccant or removed it for recharging.
I initially thought that I may have had ice or condensation on the sensor but when I look at the images in sequence I can see that the 'fog' is gradually reducing from one sub to the next. These are 3 minute exposures with the Luminance filter.
This video here on my Dropbox shows this clearly. Given this I am wondering if the issue was actually dew on the lens that took a while to dissipate. I didn't actually check the front lens of the telescope when I kicked off the imaging session though I did after I had closed everything down and it was clear.
I have two working theories therefore that I would like opinions on to see what others think.
Theory one is that I had ice or condensation on the sensor and I need to bight the bullet and recharge the desiccant.
Theory two (which I prefer) is that it was actually dew on the lens given that it was quite humid last night and that the dew formed on the lens before the dew heaters had time to get things up to temperature. I can test this easily enough by making sure to check out the front objective before kicking off my imaging session. If the lens is clear and I get the same thing then clearly I need to go down the desiccant path.
What do others think? Theory one or theory two? Other thoughts?
Clear skies,
Rodney