Image artefacts question

[SB]

Hi All,
Help appreciated with this question of image spots appearing in subs ASI183MC Pro (see attached).

* The same pattern of spots appears when filter is changed ( so not filter related)
* Spots do not appear when cooling is turned off
* Cleaning the AR cover makes no difference.

Is this a dew problem inside the AR cover?

Many thanks

Chris

[iborg]

Hi Chris


I don't have an answer for you, but, a possible test.


During the day, set up the equipment and do dark exposures for the same length of time, with and without the cooler.


Dew should not not be an issue under these conditions, and if no spots are visible, I would put your current spots down to dew.



Good luck


Philip

[multiweb]

Is this a sharpened subs or just unprocessed raw? If the latter. could be droplets on your sensor. Other wise hot pixels.

[SB]

Hi Marc and Philip,
Thanks for your reply.

This was an unprocessed 600Sec Fit file.

I have now cleaned the AR protect window and the sensor cover. It has not made a difference. I have heated the desiccator tablets also.

I have been taking test shots 0.02 sec on white background and these spots only appear once the temp is below zero. The spots get larger as the temperature drops. Don't think they are hot pixels.

SB

[multiweb]

That's very odd then. :question: No idea what could cause this.

[SB]

… well, who would have thought! I switched to Bin4 and then back to Bin1 and the artefacts went away. So I rebooted AsiAir and the spots returned! So went to Bin4 then back to Bin1 no difference, but when I increased the exposure in Bin4 and then went back to Bin1 the artefacts had gone!!

Must be something to do with software rather than ice crystals between the sensor glass. Bit of a loss to explain this.

SB

[iborg]

Does indeed sound confusing.

Are the camera or AsiAir new? Is new firmware available for either?

New or old, I suggest contacting ZWO.

Good luck!

Philip

[SB]

… the Bin settings turn out to be a red herring! In summary:

*The artefacts appear once the camera cools below Zero Deg C
* The artefacts always appear in the same position.
* They disappear once the camera has been powered on for 5 to 10 minutes.

SB

[multiweb]

It has to be some dirt on the sensor and/or the window. :shrug:

[SB]

… looks like others have had this problem, see:

https://www.cloudynights.com/topic/787338-unusual-artifacts-on-images-upon-cooling/

SB

[multiweb]

There you go. I rest my case. :lol: