Image artefacts

[VectorQuantity]

For years I've noticed artefacts similar to that in the attached image, a 60 second 300x300ish crop from a single CCD frame. Since these are removed by stacking it's not been an issue but I've always wondered what they are.

I have some ideas but thought I'd put this as an open question.

[vlaiv]

Most likely cosmic ray hits

[inFINNity Deck]

Indeed most likely cosmic rays, the following article may be of interest: https://www.astro.rug.nl/~nobels/Characterising_the_cosmic_rays_in_a_CCD_nobels_and_bremer.pdf

Nicolàs

[VectorQuantity]

1 hour ago, inFINNity Deck said:

Indeed most likely cosmic rays, the following article may be of interest: https://www.astro.rug.nl/~nobels/Characterising_the_cosmic_rays_in_a_CCD_nobels_and_bremer.pdf

Nicolàs

Thanks that's a useful doc. This document characterises this as most likely a 'worm' but without giving much information about how it arises, but it references  'D. Groom. Cosmic rays and other nonsense
in astronomical ccd imagers.' which I've found at https://www.astronomy.ohio-state.edu/MDM/OSMOS/CCD_CosmicRays_groom.pdf.

This one's more detailed and if I'm reading it correctly implies it's the result of a gamma or x-ray hit.

[ONIKKINEN]

Very interesting read both @inFINNity Deck and @VectorQuantity. Seeing as i have nothing better to do i am now taking 3600s darks to see how many on average would hit my sensor. Doubt i will do anything with the information but im just curious how common this is.

[inFINNity Deck]

22 minutes ago, ONIKKINEN said:

Very interesting read both @inFINNity Deck and @VectorQuantity. Seeing as i have nothing better to do i am now taking 3600s darks to see how many on average would hit my sensor. Doubt i will do anything with the information but im just curious how common this is.

That would me quite interesting! Could you please post your findings here?

Nicolàs

[vlaiv]

25 minutes ago, ONIKKINEN said:

Very interesting read both @inFINNity Deck and @VectorQuantity. Seeing as i have nothing better to do i am now taking 3600s darks to see how many on average would hit my sensor. Doubt i will do anything with the information but im just curious how common this is.

I've found that majority of impacts in darks are not in fact cosmic rays but of earthly origin.

Once I created set of darks near some tools used to clean wood stove - bucket and small shovel and since those had some ash residue on them - I got much higher incidence.

Conclusion was that it was due to radioactive decay in ash (wood absorbs radioactive material) - quite possibly from Chernobyl era.

Btw - take any set of darks and stack them with max operator instead of average and you will in one image how many hits you had over whole session of taking darks.

[inFINNity Deck]

1 hour ago, VectorQuantity said:

Thanks that's a useful doc. This document characterises this as most likely a 'worm' but without giving much information about how it arises, but it references  'D. Groom. Cosmic rays and other nonsense
in astronomical ccd imagers.' which I've found at https://www.astronomy.ohio-state.edu/MDM/OSMOS/CCD_CosmicRays_groom.pdf.

This one's more detailed and if I'm reading it correctly implies it's the result of a gamma or x-ray hit.

Good that you found that document as well, thanks for sharing! The first paragraph of the Nobels and Bremer article explains it likewise:

Quote

Particles with extremely high energies (up to 1020 eV) have been detected. It is found that these particles originate from extraterrestrial sources, galactic as well as extra galactic. The bulk of these particles are composed of protons and atomic nuclei and are called cosmic rays. It is known that supernovae and active galactic nuclei are able to accelerate charged particles to extreme energies trough magnetic fields.

Nicolàs

[ONIKKINEN]

26 minutes ago, inFINNity Deck said:

That would me quite interesting! Could you please post your findings here?

Nicolàs

Sure, im going to give it some time to get some sort of meaningful average over some period of time. I am also interested in getting real world data on how much dark current my camera produces so im going to take at least 5 subs to get some meaningful amount to sample from.

22 minutes ago, vlaiv said:

I've found that majority of impacts in darks are not in fact cosmic rays but of earthly origin.

Once I created set of darks near some tools used to clean wood stove - bucket and small shovel and since those had some ash residue on them - I got much higher incidence.

Conclusion was that it was due to radioactive decay in ash (wood absorbs radioactive material) - quite possibly from Chernobyl era.

Btw - take any set of darks and stack them with max operator instead of average and you will in one image how many hits you had over whole session of taking darks.

The ash thing sounds perfectly plausible to me. Mushrooms for example are still quite high in Cesium-137 from Chernobyl fallout and there are regions here where its not recommended to forage wild mushrooms and eat all that many of them.

[VectorQuantity]

21 minutes ago, vlaiv said:

I've found that majority of impacts in darks are not in fact cosmic rays but of earthly origin.

Once I created set of darks near some tools used to clean wood stove - bucket and small shovel and since those had some ash residue on them - I got much higher incidence.

Conclusion was that it was due to radioactive decay in ash (wood absorbs radioactive material) - quite possibly from Chernobyl era.

Btw - take any set of darks and stack them with max operator instead of average and you will in one image how many hits you had over whole session of taking darks.

The second doc (D.Groom) mentions something interesting in that there's an exception to gamma/X-ray generating these 'worms' and that's a beta particle orginating from Potassium decay in BK7 glass i.e. Crown glass which of course can be used in APO's even if some lenses are FPL51/53. I have however seen this effect when imaging with numerous scopes which may point to it being an external source and not 'scope glass' related.

[VectorQuantity]

1 hour ago, vlaiv said:

I've found that majority of impacts in darks are not in fact cosmic rays but of earthly origin.

Once I created set of darks near some tools used to clean wood stove - bucket and small shovel and since those had some ash residue on them - I got much higher incidence.

Conclusion was that it was due to radioactive decay in ash (wood absorbs radioactive material) - quite possibly from Chernobyl era.

Btw - take any set of darks and stack them with max operator instead of average and you will in one image how many hits you had over whole session of taking darks.

This is a max stack of 179off 600 second darks at minus 20. KAF8300. It's covered with the things. Seems to have an average distibution across the frame. Also the track angles are random, I assume this means it's a not a point source.

[inFINNity Deck]

2 minutes ago, VectorQuantity said:

This is a max stack of 179off 600 second darks at minus 20.

 

Do I understand this right: this is 30 hours worth of darks?

Nicolàs

[VectorQuantity]

Just now, inFINNity Deck said:

Do I understand this right: this is 30 hours worth of darks?

Nicolàs

Yep. 

[vlaiv]

3 minutes ago, VectorQuantity said:

This is a max stack of 179off 600 second darks at minus 20. KAF8300. It's covered with the things. Seems to have an average distibution across the frame. Also the track angles are random, I assume this means it's a not a point source.

Another thing that made a difference for number of hits was where I was shooting darks.

If I shoot in basement of my house - number that I get is significantly smaller. I guess that house itself and surrounding earth (since basement is below surface level) provides some shielding from background radiation. It also points to me not having Radon issues in my basement

 

[Rodd]

18 minutes ago, vlaiv said:

It also points to me not having Radon issues in my basement

Ha!  You can upend the radon testing industry.  You can certify buildings by creating master darks (with no rejection algorythym) in peoples basements!  

[VectorQuantity]

1 hour ago, vlaiv said:

Btw - take any set of darks and stack them with max operator instead of average and you will in one image how many hits you had over whole session of taking darks.

From a second camera for comparison. Kaf16200 139off 600seconds at minus 20. same effect is visible. Rescaled to 50%.

 

[ONIKKINEN]

I left the camera running overnight, but it looks like my mini-pc shut down after 9 subs, so here is 9 hours of darks with 1h subs at -10c with my rising cam IMX571 OSC camera. I did not debayer the subs and stacked with pixel maximum in Siril. To my eye it looks like there are far fewer hits than with the previously posted shots, even considering differences in exposure times. The linked paper mentions pixel height as well as pixel pitch, so maybe a modern CMOS sensor has a very shallow pixel as well as a smaller pixel pitch so there are fewer hits?

Also answered my own question about the dark current of the camera, at -10c there is 1 electron per roughly 30 minutes of exposure of dark signal.

[inFINNity Deck]

Another read: https://sci-hub.se/10.1109/JSEN.2017.2732499

Nicolàs