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Random color shift between frames from the same night - settings - with UHC filter

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#1 theabsurdist8

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Posted 18 June 2021 - 07:12 PM

Capture.JPG

 

Hi. I was imaging Elephant Trunk Nebula a few days ago and I realized that some of my frames had a purple hue and then suddenly, the color shifted to greenish hue. I had the exact same settings (did not change anything) and same region of the sky and same day. I am posting two frames to show what I mean. Usually my images with the filter have green hue which is expected but the purple one makes no sense. The images I am posting here were taken a minute apart. I am thinking maybe the filter was loose and it suddenly went into the right spot but the color change is not gradual.


Edited by theabsurdist8, 18 June 2021 - 07:24 PM.


#2 KLWalsh

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Posted 18 June 2021 - 07:36 PM

Is there any possibility that some other light source (car headlights? Heat lightening from over the horizon? Or…?) caused some momentary sky glow?

#3 Dynan

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Posted 18 June 2021 - 07:48 PM

The difference is small enough that it should calibrate out. Take a good look next time you're imaging and see which color you get.



#4 james7ca

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Posted 18 June 2021 - 08:49 PM

You don't say what camera you were using but since you're posting in the DSLR forum I assume that you were using a DSLR. Okay, so when using my Sony NEX-5 APS-C cameras I've seen something similar now and then and I think it is probably a bug in the camera's firmware or a glitch with the sensor. It doesn't happen that often but every once in a while a frame will have a very different color balance (for lack of a better term). I suppose it could even be a glitch in the way the Bayer pattern is being recorded in the frame (throwing off the debayering).

 

I've also seen frame instability in one of my dedicated astro cameras (an ASI174MM) and in those cases I think it is a bug in the driver. In this case it's not like a change in the color balance but a gross change in the amount of amp glow, such that the frames are almost unusable. The common fix in this case is to do a power cycle on the camera. Fortunately, this latter issue doesn't come and go so I can usually catch it before I start my imaging for the night.

 

In both cases I think it is caused by a random bug somewhere in the firmware/driver or a simple glitch in the sensor itself. My solution, since it happens so infrequently is to ignore the issue. This is one reason why it's always a good idea to do a blink inspection of your files (both lights and darks and bias if you use the latter). Either that or run a quality selection tool like PixInsight's SubframeSelector. Practically speaking, however, if you don't notice any problems in your finished master then it may not be something that you should even check for (assuming that it happens very infrequently -- like a few frames once in a while on different nights).


Edited by james7ca, 18 June 2021 - 10:44 PM.

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#5 theabsurdist8

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Posted 18 June 2021 - 09:20 PM

Is there any possibility that some other light source (car headlights? Heat lightening from over the horizon? Or…?) caused some momentary sky glow?


To me it seems like something more permanent since the colors purple for about an hour or more

Edited by theabsurdist8, 18 June 2021 - 09:21 PM.

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#6 theabsurdist8

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Posted 18 June 2021 - 09:23 PM

You don't say what camera you were using but since you're posting in the DSLR forum I assume that you were using a DSLR. Okay, so when using my Sony NEX-5 APS-C cameras I've seen something similar now and then and I think it is probably a bug in the camera's firmware or a glitch with the sensor. It doesn't happen that often but every once in a while a frame will have a very different color balance (for lack of a better term). I suppose it could even be a glitch in the way the Bayer pattern is being recorded in the frame (throwing off the debayering).

I've also seen frame instability in one of my dedicated astro cameras (an ASI174MM) and in those cases I think it is a bug in the driver. In this case it's not like a change in the color balance but a gross change in the amount of amp glow, such that the frames are almost unusable. The common fix in this case is to do a power cycle on the camera. Fortunately, this latter issue doesn't come and go so I can usually catch it before I start my imaging for the night.

In both cases I think it is caused by a random bug somewhere in the firmware/driver or a simple glitch in the sensor itself. My solution, since it happens for infrequently, is to ignore the issue. This is one reason why it's always a good idea to do a blink inspection of your files (both lights and darks and bias if you use the latter). Either that or run a quality selection tool like PixInsight's SubframeSelector. Practically speaking, however, if you don't notice any problems in your finished master then it may not be something that you should even check for (assuming that it happens very infrequently -- like a few frames once in a while on different nights).



I think you're right. It seems like a glitch to me too. I'm using Canon 70D but I've never had this issue before. I will keep an eye on it though. I didn't start stacking yet cuz of this but I will now and let's hope it doesn't impact the image much. I have 15 hrs worth of data so I think this wouldn't affect it much.

#7 AgilityGuy

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Posted 18 June 2021 - 10:16 PM

My Nikon D800e does the similar thing periodically but no idea what causes it.



#8 asanmax

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Posted 20 June 2021 - 11:08 PM

That's an interesting phenomenon. 

I see this behavior rarely but it does make me wonder what could be causing it.

Here is a couple of images taken one after another. Same conditions, no changes in the settings or around the imaging rig. No occasional clouds or fog.

654654.jpg



#9 galacticinsomnia

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Posted 21 June 2021 - 01:29 AM

There is always some weirdness with enviromental lighting.  My neighbors were using a red light, and it bled into my images even from 3 houses away.  Red brake lights are also an issue, as well as IR Remotes,  and motion detectors.  My advice would be to use a dew shield or long lens hood and see if it continues.

Clear Skies !!


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#10 Tapio

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Posted 21 June 2021 - 01:31 AM

Could it be a passing cloud ?



#11 james7ca

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Posted 21 June 2021 - 06:27 AM

On my Sony NEX-5 cameras I saw shifts even in the darks, so it wasn't being caused by extraneous light sources or clouds.


Edited by james7ca, 21 June 2021 - 06:27 AM.



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