Sudden "dirt" on ASI1600c sensor

herwig_p

Dear All,

Today while shooting flats during the daytime I recognized some heavy "oily drop" like splashes or dirt on the sensor. It is definitively inside the chamber and not on the cover glass. I am wondering how that can happen, I have not changed anything on the camera/setup. Last time I opened the camera to replace the dessicant tablets was a couple of months ago. There was never an issue with condensation or frost since then.

Anyone seen something similar, like a sudden spot on the sensor without opening the camera?

I guess I will open the camera and try to clean the sensor. What is the best method to do so?

Thanks for your help!

Best regards

Herwig

Sam@ZWO

can you see something by eye?

s3igell

herwig_p wrote:
What is the best method to do so?

The best 1st effort is to use a Photographer's Bulb Blower to see if you can dislodge the dust and get it out of the Imaging Cavity.

Don't use any kind of Canned Air - they contain Oils and other Liquid Chemicals!!

herwig_p

Yes, I can see it clearly through the front window.... in case it is not dust which could be blown away, shall I swipe the sensor with isopropyl alcohol?

herwig_p

I have opened the camera and cleaned the sensor with sensor swaps and Isopropanol. There were smeared smudges on the sensor as suspected (no loose dirt). I think, the culprit is the dislodged "QC" sticker on the sensor compartment - obviously due to the summer heat in my appartment (was up to 30 deg. Celsius) the glue was "mobilised" and "dropped" on the sensor while the sticker moved. I have no other explanation for the source of the smudges! The dessicant tablets were fine.

see picture

https://photos.app.goo.gl/BTn0tcnuqx654xC12

Anyway - easy fix! The flats are fine again.

Best regards

Herwig

herwig_p

Unfortunately my assumptions were wrong! After cleaning the sensor and changing the desiccant tablets, I took light frames in SGP last night which were fine. When I took flats this morning I discovered very similar smudges again on the sensor which must have occured between the light and flat frames, without me even touching my imaging rig. This sudden appearing marks leaves me puzzled.... anyone any idea?

herwig_p

The problem is solved and has a much simpler explanation - the smudges were clearly coming from remains of frosting on the sensor. For some reason the sensor frosted only slightly over during the flat frame aquisition. I had frost already once, but it did not leave any permanent smudges on the sensor before. The "new" desiccant tablets were obviously saturated already and useless, so I baked all one hour in the oven at 120deg. C to dry them and changed again and cleaned the sensor.

I have now no frost on the sensor and it works fine again.

CS Herwig

Sam@ZWO

herwig_p wrote:
The problem is solved and has a much simpler explanation - the smudges were clearly coming from remains of frosting on the sensor. For some reason the sensor frosted only slightly over during the flat frame aquisition. I had frost already once, but it did not leave any permanent smudges on the sensor before. The "new" desiccant tablets were obviously saturated already and useless, so I baked all one hour in the oven at 120deg. C to dry them and changed again and cleaned the sensor.

I have now no frost on the sensor and it works fine again.

CS Herwig

That's great news!