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Old 13-04-2021, 02:32 PM
RugbyRene (Rene)
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Images have a blue/salmon cast I can't get rid of

Hi all,

Hope someone can help me. Last night I had a fairly successful night of imaging. I managed to capture NGC3324, M83 and NGC6188 (2 panel mosaic). I stacked M83 in PI using the exact same workflow as always and when I opened the master and did a stretch I noticed a blue cast across the image. No worries, I thought, I'll use DBE and that will sort it out. Ran a DBE as I always do, re-stretched the image and the blue cast was still there.

I then stacked NGC6188 and got the same result. I stacked NGC3324 and this time I got a horrible salmon cast when I stretched it. The colours of the nebula look nothing like I got from the previous few nights. I imaged the previous 3 nights and the blue/red cast was removed as expected.

I'm running an Esprit 100, with an ASI294MC and IDAS P1 LPR filter. Nothing has changed in my set-up. No settings have changed in my capture or processing software.

The only thing I did, probably stupidly, was leave the scope out all day yesterday. It was covered by a scope cover and a towel so it was protected from the direct sun. It was only 21 degrees in Sydney but it was in the direct sun all day.

Oh the only other thing I did (again probably stupidly) is I had shone a flashlight down the OTA as it was taking an image as I wanted to see if there was dew forming on the lens.

So the question I have is has the sun fried my sensor? Is there a way I can test it to see if it is faulty?

I've attached a single sub that has been stretched. These were taken a couple of weeks apart. The first was taken last night for 180sec, the second was taken a couple of weeks earlier for 120 sec. The first image is not normal, The second is what I expect.

Rene
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Last edited by RugbyRene; 13-04-2021 at 02:57 PM.
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Old 13-04-2021, 03:50 PM
JA
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Originally Posted by RugbyRene View Post
...

So the question I have is has the sun fried my sensor? Is there a way I can test it to see if it is faulty?
Hi Rene,

There are a few possibilities to try to nail down, but before making any conclusion I would use the camera in daytime to image or video a terrestrial object as close as possible to you, within the confines of your scope (to avoid UV haze effects with distant objects). Do this without the light pollution filter fitted AND THEN compare this to what you can see by naked eye or through binoculars.

That would help nail down if the colour cast is in the camera or somehow occurring via software or other changes you were not aware of at the time of image capture. A couple of other thoughts: Are you 100% certain you used the same filter for both images? Did you perhaps also use an additional UV/IR filter on one image but not the other?

Best
JA

Last edited by JA; 13-04-2021 at 04:04 PM.
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Old 13-04-2021, 08:01 PM
RugbyRene (Rene)
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Originally Posted by JA View Post
Hi Rene,

There are a few possibilities to try to nail down, but before making any conclusion I would use the camera in daytime to image or video a terrestrial object as close as possible to you, within the confines of your scope (to avoid UV haze effects with distant objects). Do this without the light pollution filter fitted AND THEN compare this to what you can see by naked eye or through binoculars.

That would help nail down if the colour cast is in the camera or somehow occurring via software or other changes you were not aware of at the time of image capture. A couple of other thoughts: Are you 100% certain you used the same filter for both images? Did you perhaps also use an additional UV/IR filter on one image but not the other?

Best
JA
Hi,

Nothing has changed on the software side and I only own 1 filter which hasnít left my rig since I bought it.

I go through a checklist to ensure I donít miss anything which is why my suspicion lies with the camera.
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Old 13-04-2021, 11:31 PM
JA
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Originally Posted by RugbyRene View Post
l go through a checklist to ensure I don’t miss anything which is why my suspicion lies with the camera.
OK then: test it as discussed without filter in daylight at varying light levels from low-light upwards on terrestrial targets and look for any obvious colour cast in images versus what you observe un-aided via naked eye, via binoculars or via the eyepiece . This may or may not show a colour cast difference and therefore help point you towards a conclusion on whether there is a camera issue

Good luck.

Best
JA

Last edited by JA; 14-04-2021 at 06:15 AM.
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Old 14-04-2021, 07:09 AM
JA
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Originally Posted by RugbyRene View Post
l go through a checklist to ensure I don’t miss anything which is why my suspicion lies with the camera.
OK then: test it as discussed without filter in daylight at varying light levels from low-light upwards on terrestrial targets and look for any obvious colour cast in images versus what you observe un-aided via naked eye, via binoculars or via the eyepiece . This may or may not show a colour cast difference and therefore help point you towards a conclusion on whether there is a camera issue

Possible camera issues aside: your most recent exposures are 50% longer in duration (180 Vs 120s), perhaps the stacking or other stretching/processing is sensitive to that. I can imagine it might be as the signal to noise ratio, all else being equal, would be greater in the longer exposure. Maybe you should also do a back to back comparison on the same night of say 60s Vs 120s Vs 180s Vs 240s exposures and see if there is any change in the colour cast experienced either before or after any processing with varying exposure duration. Good luck.

Best
JA
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Old 14-04-2021, 08:18 AM
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gregbradley
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Your sensor is fine.

Maybe try one of those Ha/O111 filters that are around.

Add yellow and magenta to the reds using the selective colour tool in Photoshop.

Greg.
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