ASI 294MC Pro Colour Blotches

[Darren_S (Darren)]

I often get ugly RGB ‘pixels’ in the centre of my images with the 294MC Pro. The attached image is 20 x 3 minutes stacked with about 30 darks and flats (no dark flats). Camera cooled to -10c. Gain 120. No filter but happens with my Optolong Extreme also. Some minor stretching in Photoshop. They are difficult to remove in processing and ruin the image. Scope is a Redcat51 but also happens with my Esprit 100. Don’t think it is a scope issue.

Does anyone have similar experiences with this camera? I would be grateful for any wisdom!

Cheers.

[Stephane]

Hi Darren, I’m not sure if it would be related or not, but you definitely need bias frames (or flat darks). You can take bias frames any time and keep the master for many months. Try calibrating your light frames again with the bias and see if that fixes the problem.

[Dave882 (David)]

This looks very similar to what I got with my 294mc when I was pushing the cooling fan beyond about 85-90%. It causes issues with the image, and if you do biases in the same way you will INTRODUCE those same patterns over your image as well.

[Darren_S (Darren)]

Originally Posted by Stephane

Hi Darren, I’m not sure if it would be related or not, but you definitely need bias frames (or flat darks). You can take bias frames any time and keep the master for many months. Try calibrating your light frames again with the bias and see if that fixes the problem.

Thanks Stephane. I’ll try this. 🤞

[Darren_S (Darren)]

Originally Posted by Dave882

This looks very similar to what I got with my 294mc when I was pushing the cooling fan beyond about 85-90%. It causes issues with the image, and if you do biases in the same way you will INTRODUCE those same patterns over your image as well.

Thanks David. I do keep an eye on the cooling and even in summer at -10c it rarely goes over 70%. Do you still have this problem or have you fixed it?

[Kuz]

I am with Dave. In hot weather I go to minus 5 and than minus 10. After say 5 minutes. I would dry out the moisture tablets inside the camera as well.or replace
them

[Nikolas (Nik)]

This happened to mine, it is frosting/condensation on the sensor which if not cooled quickly or you recharge the dessicant will resolve itself.

[Darren_S (Darren)]

Originally Posted by Kuz

I am with Dave. In hot weather I go to minus 5 and than minus 10. After say 5 minutes. I would dry out the moisture tablets inside the camera as well.or replace
them

Nailed it Dave & Kuz. Took flats in my store room tonight. Dodgy colour pattern visible at -10, -5 and 0 degrees. No pattern at room temp which is about 25c.

[logandc99 (Logan)]

My ASI294mcPro started producing the central blotchiness after about 6 months of use due to condensation on the sensor and I ended up having to cool it max to about -5 in summer only over about 40mins. I did go through the motions of "drying out" the tablets but it made no difference in the end. I just have to cool super slowly.

[frank777 (Frank)]

I literally had the same problem with the same camera rear its head last week. I found that condensation was forming as soon as the cooling got down to zero degrees (I was routinely getting it down to -10). I've now settled on +5 degrees, just to be on the sade side.

[Darren_S (Darren)]

Originally Posted by frank777

I literally had the same problem with the same camera rear its head last week. I found that condensation was forming as soon as the cooling got down to zero degrees (I was routinely getting it down to -10). I've now settled on +5 degrees, just to be on the sade side.

Thanks Frank. Interesting to know others have the same issue. I recharged the desiccant and tested with flats. Anything 0 degrees & below had condensation, and like you +5 was ok. I might run with that from now on but it kind of defeats the purpose of having a cooled camera. Might be easier to process out the heat noise than the condensation artefacts though. I found that suggestions of others to very slowly cool the camera didn’t work for me.

[Darren_S (Darren)]

Originally Posted by logandc99

My ASI294mcPro started producing the central blotchiness after about 6 months of use due to condensation on the sensor and I ended up having to cool it max to about -5 in summer only over about 40mins. I did go through the motions of "drying out" the tablets but it made no difference in the end. I just have to cool super slowly.

Hi Logan, it’s definitely annoying! I have new desiccant tablets on the way and will do a full clean of the sensor and protective glass. Don’t know if it will work. I tried the very slow cooling after recharging the original desiccant (allowed about 45 mins to get from room temp to -10) but no luck - still condensation.

[logandc99 (Logan)]

Originally Posted by Darren_S

Hi Logan, it’s definitely annoying! I have new desiccant tablets on the way and will do a full clean of the sensor and protective glass. Don’t know if it will work. I tried the very slow cooling after recharging the original desiccant (allowed about 45 mins to get from room temp to -10) but no luck - still condensation.

I'll be interested to hear if the new desiccant tablets solve it. The slow cooling can be tedious, especially if there is an issue with having to restart the imaging software for any reason and you have to cool all over again.

[Darren_S (Darren)]

Originally Posted by logandc99

I'll be interested to hear if the new desiccant tablets solve it. The slow cooling can be tedious, especially if there is an issue with having to restart the imaging software for any reason and you have to cool all over again.

Hi Logan,
New desiccant tablets and a clean of all the glass with the wife’s DSLR sensor cleaner has done the job! There may have been some residue on the sensor glass that contributed to the condensation. I’m sure the issue will surface again but hopefully not too soon, and I now know how to fix it!!

[frank777 (Frank)]

Originally Posted by Darren_S

Hi Logan,
New desiccant tablets and a clean of all the glass with the wife’s DSLR sensor cleaner has done the job! There may have been some residue on the sensor glass that contributed to the condensation. I’m sure the issue will surface again but hopefully not too soon, and I now know how to fix it!!

What sensor cleaner did you use? In trying to solve my condensation problem I've left a smear either on the sensor or the protective glass layer. Flats get rid of it during calibration but I'd still like to get rid of it and I think a proper clean with a sensor cleaner is required.

Frank

[Darren_S (Darren)]

Originally Posted by frank777

What sensor cleaner did you use? In trying to solve my condensation problem I've left a smear either on the sensor or the protective glass layer. Flats get rid of it during calibration but I'd still like to get rid of it and I think a proper clean with a sensor cleaner is required.

Frank

Hi Frank. It doesn’t have a brand name on it but we bought the kit online from a camera store - designed for DSLRs but no different for Astro cams. Just follow instructions - need to wipe the glass several times with applicators provided in the kit. I cleaned all 3 glass surfaces - one external and two internal once cover is removed. The applicators may be just as important as the cleaner to avoid smearing. Good luck!!