Excessive noise?

[DeCosta]

Hi everyone,

I have been trying to capture an HDR HaRGB version of Orion Nebula.  I have captured some reasonable data a couple of weeks ago.  Last night I tried again but from about 9.00 onwards as Orion got below 35° and closer to the moon the images deteriorated.  I noticed dark rings in the nebulosity and graininess as I zoomed in.  I am guessing its noise?  I don't know whether calibration and noise removal will save this data or if I just ditch the 3 hours of data and try again next year?  I've attached a screenshot which you can zoom in to see the problem.

FYI m using an ASI294mm

Any advice would be appreciated

Many Thanks

Keith Gaskin 

[ONIKKINEN]

Is this a single uncalibrated sub? I'll be honest in that i have no idea what im looking at, never seen anything like this. Something looks very wrong here for sure.

Im guessing here, but this looks like a corrupted file and could be some sort of USB gremlin, or some issue with how the files were written on disk, or worst case scenario a faulty camera. Does the camera produce a normal looking image if you try now in daytime or do they look like this?

[Oddsocks]

Looks a bit like condensation/ice on the sensor, has the camera desiccant been recharged recently?

Load the images in PixInsight’s Blink module and step through the series in acquisition time sequence, if this is condensation or ice on the sensor you will see the artefacts initially appear very small and gradually increase in size as the camera series progresses over time.

 Noise would be randomly distributed across successive frames but ice artefacts will appear to be static and not shift position as you view the images in time sequence. Condensation droplets will appear static initially until they grow large enough to roll across the sensor under gravity.

[DeCosta]

Thanks for the reply.  I have to admit I wasn't aware of dessicant in the camera but I have done a little more research and the artefacts in the images definitely point to condensation and ice.and get worse over time.  I keep my set up in Fuerteventura and image from a roof terrace.  The rig is covered with a big weatherproof cover during the day so the camera is getting quite warm.  Then late afternoon I cool to -15° and remove the cover .  So the camera is going from very warm to very cold in about 20 mins.  Looks like I'll be taking the camera back to the UK to try and change the dessicant.

I don't think I'd have found this out without your advice.

 

Many Thanks

Keith Gaskin

 

 

[Oddsocks]

2 hours ago, DeCosta said:

The rig is covered with a big weatherproof cover during the day so the camera is getting quite warm.  Then late afternoon I cool to -15° and remove the cover .  So the camera is going from very warm to very cold in about 20 mins.  Looks like I'll be taking the camera back to the UK to try and change the desiccant.

Keith.

If you are still in Fuerteventura you can recharge the existing desiccant tablets locally, no need to replace the existing desiccant tablets other than for speed of replacement, or the tablets are worn-out etc.

This ZWO document details the steps required to recharge the desiccant tablets using a microwave oven:

https://astronomy-imaging-camera.com/manuals/How_to_clean_ASI_camera_and_redry_the_desiccants_EN_V1.2.pdf

All cooled cameras are subject to "breathing" pressure. As the sensor is cooled the air pressure inside the sensor chamber drops below external air pressure and damp air is drawn inside the chamber through any tiny gaps in the sensor chamber seals. When the camera warms again at the end of the session the air pressure inside the chamber increases above external air pressure and air is forced out of the chamber. The long-established camera manufacturers have designed their camera bodies with better specified sealing systems that are more able to withstand the changes in pressure (but at a higher cost per camera).

You can reduce the air pressure differential by not cooling so low, the difference in image noise between -15c and -5c is so little with these new CMOS sensors that there is no real need to cool down to -15c and if you cool to only -5c the chamber air pressure difference is reduced. Also, the 2-stage TEC cooling is very efficient with these cameras so that you can begin cooling much closer to the time you intend to begin Imaging when the outside air temperature is lower and the pressure differential across the sensor chamber seals is reduced.

HTH

William.

[DeCosta]

William,

Great explanation.   I am returning to the UK on Wednesday so I will be packing everything away now until June.  Considering taking the camera back to the UK and sending it into FLO or somewhere it can get a good look over.  I bought the camera second hand 2 years ago and I guess its 4-5 years old.  Maybe worth getting it cleaned and "serviced" by professionals.

Once again thanks for your advice.

Keith

[alacant]

22 hours ago, DeCosta said:

taking the camera back to the UK

Hi
In Spain, maybe call Luis at str-astrum who may be more knowledgeable as to your climatic conditions.

FWIW, for cooled CMOS here in Alicante, we've standardised on -5º all year round. In summer it's not easy maintaining much below -10º anyway and the benefit it brings is negligible. 
HTH

Edited March 19 by alacant

[DeCosta]

Hi thanks for that.  I think I'm going to start cooling to -5°. 

I spoke to FLO in the UK and they advised that I remove and microwave the dessicant filters myself as it is a straight forward job.  I did that this afternoon successfully.  I noticed a greasy mark right in the centre of the sensor but I haven't got anything to clean it with out here.  I travel back to UK on Weds where I'll get some cleaning swabs and bring them back out here in June.

Thanks for your help.