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Solar Gravity 2018

Author Topic: Black spots in processed image  (Read 204 times)

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Offline squreshi786

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Black spots in processed image
« on: 14:27:52, 25 February, 2018 »
Hi
Started to use Canon 5D Mark 2 (unmodified) with my Tak 102 with IDAS p2 FILTER for LP. Took 300sec X16 lights of M42 at ISO 1600 (Moon 40%), 60 Flats (Aurora flats, ADU 30000, Flats wizard in SGPro), 7 X darks, and 30 odd bias, run the batch processing and the initial image I got post ABE is attached. The question as you could see from the pic, forget about the vignetting, and some other casts, What the hell are these black spots, are these dead pixels, should calibration have not dealt with this. These are certainly not dust bunnies as I got the sensor cleaned by Canon authorised dealer to canon standards a week before I imaged. I also done the sensor remapping. Cant see much on the individual darks or flats or even on master dark or flats.
Are these dead pixels or what. or is my sensor dying.

PS.none of these spots are on my un processed subs or flats. I have also tried taking the flats by two different methods (1- via IPAD screen, 2-By aurora flat screen) still get these spots on the final image. Don't know where the problem is. A week ago did a 2 min X 12 images with few calibration frames and on the final image I just got 2 black spots, now these are 6 or 7. May be its longer exposure which is multiplying the dead signal pixels in the sensor this time.

Please advise
Losmandy G11, Gemini-1, GEMINI-ASCOM, Pole Master QHY, Takahashi TSA-102 F/8, Altair astro 60mm Guide scope (piggybacked). Loadstar X2 autoguider. PHD2 Autoguiding. Canon 600 T3 (Astronomiser modified). Pixinsight Processing

Offline chris.bailey

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Re: Black spots in processed image
« Reply #1 on: 14:46:05, 25 February, 2018 »
A few observations.

7 Darks is not that many to take compared to 30 bias and 60 flats though you may be better off taking none at all due to poor temperature matching. 30,000 ADU is quite 'hot' for a DSLR flat and they look to me not to have done a great job. As well as the black spots there is an anomaly in the top left corner and the uneven illumination in general.

They are not cold pixels as they would be a streak rather than a blob. I would say they are sensor dust and that may well be within Canons standards. You could get that much just by changing a lens and they would not show in daytime images. Properly exposed flats should sort them out.

Chris
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Offline squreshi786

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Re: Black spots in processed image
« Reply #2 on: 16:10:25, 25 February, 2018 »
Thanks Chris
I have tried testing sets of flats from 25000 to 40000 ADU, 30-40 in a set. I have tried taking the flats from two sources, 1-from an iPad screen and 2- Aurora flats (http://www.gerdneumann.net/english/astrofotografie-parts-astrophotography/aurora-flatfield-panels/uebersicht-aurora-flatfield-panels-overview.html), and nothing worked.
Interestingly I imaged m42 with 2 min exposures X 15 with equal darks, 30 odd bias and flats 2 weeks ago and at that time the issues with illumination and vignetting weren't that awful and only had a few black spots (Attached pic), it was only then when I realised that I was getting the black spots I took it to Canon to clean. So why would the situation worsen, well the only difference I can glaringly see is that the length of my exposures has gone up (i.e. 5 min subs) and I do take you point about the darks, and i will run the script without darks to see if I get any different response.

I am really stuck with WHAT SHOULD THE CORRECT ADU FOR MY FLATS BE----I HAVE NO ANSWER. But is it just a matter of flats or is there something underlying very simple or very complex that I am too ignorant to have not noticed.

Let me know what you think.
Losmandy G11, Gemini-1, GEMINI-ASCOM, Pole Master QHY, Takahashi TSA-102 F/8, Altair astro 60mm Guide scope (piggybacked). Loadstar X2 autoguider. PHD2 Autoguiding. Canon 600 T3 (Astronomiser modified). Pixinsight Processing

Offline chris.bailey

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Re: Black spots in processed image
« Reply #3 on: 22:09:58, 25 February, 2018 »
The issue is down to your DSLR being a 14bit device. 25,000 at 16 bit is likely to lead to clipping at 14 bits. I don't image with a DSLR but I would recommend Flats with a peak of 10-12,000 at 16 bits to have a hope of them not being clipped at 14 bits.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

 

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