Artifacts

Giuseppe Passera

Hi Adam

I'm processing an image of M51 made with a cmos camera.

I did darks last night, flats and darlflats. The luminance image has artifacts that I can't explain. In reality I had seen a video of yours in which you talked about the salt and pepper effect but I can't find it anymore in the amount of videos you have on the site.

I did everything with WBPP, I activated the cosmetic correction, I checked if there were pixels at 0 but everything seems ok. 

Some idea?

thanks and refards

Giuseppe

BlockHead

Without diving into the data and looking at all of the calibration data, the raw data, the calibrated data... etc it is hard to say exactly. 

However, this has the appearance of a rejection issue (usually when using Winsorized Sigma Clipping). That is what it looks like to me. It also means there are a large variance in some of your subframes if I am correct.

-the Blockhead

Giuseppe Passera

Adam actually I used winsorized sigma clipping. I'll try sigma clipping.I don't think there is a great variability, the frames examining them with blinking seem pretty homogeneous. To a lesser extent the problem also occurs on the rgb channels. Thanks for now as always.
Giuseppe

BlockHead

You should try GESD. The result should be different in this case.

(if it is what I think it is)

-the Blockhead

Giuseppe Passera

Adam
I will try also GESD. I’ve already done but the darks was pretty old so I got the same artifacts ansd I thought “old darks, not enoug frame so letr’s go with winsorized”. Now i will do a second try for GESD
Thank you as usual
Giuseppe

Giuseppe Passera

Ok.

The problem is in the master flat.

But why?

I've done all in the right way, I suppose.

All the dark flats are of the same amount of time of the relative flats and the flats are aroud 40% of the histogram.

Can I ask you for a help?

Here there are all the files involved :"https://1drv.ms/f/s!AvSe4qE-a_kToaIj7BEICxS0b8kc-w?e=J4J0tA"

Thank you 

BlockHead

Did the individual flats show anything?

That is pretty bizzarre.

-the Blockhead

BlockHead

I looked at the files. This appears like something is wrong with your camera.

Perhaps the TEC or cold finger is causing an issue.

-the Blockhead

Giuseppe Passera

Gosh...

I will inverstigate...

Probably some cmos settings.

Thank you very much.

Giuseppe

Giuseppe Passera

Adam

...probably some ice on the sensor...

The issue is present only on the flat and flat and lum were done in separate days...

I wil try to do a slower cooling.

Thanks and regards

Giuseppe

Giuseppe Passera

It was certainly ice. 

By cooling the camera in two steps of 10 celsius each , the artifact disappeared. It's time to change the desiccant.

Thank you and regards

Giuseppe

BlockHead

Yeah..the cold finger would do that.. but in your case the nearly perfect ellipse was remarkable.

-the Blockhead

Giuseppe Passera

:)

Giuseppe