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Tried capturing M42 and horsehead nebula last night with my new Astro-modified EOS Rebel XT. During post processing I noticed these weird spots and lines across the image. Would you happen to know if this was because of the mirrors of the telescope (i.e. dirty mirrors) or is something wrong with the camera? What's weird is that this 2 images were taken with the same exact camera at the same exact position but some artifacts visible on M42 did not show up on the horsehead nebula.

Btw I checked the mirrors of the telescope but I cant find the weird long spots

M42rebelxt.thumb.png.a7b99dfa0aeeb5478c902bebb9e404cb.png

Horseheadrebelxt.thumb.png.c10b814ad6cd7045be2bfa396f752e33.png

Edited by lalou

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This effect is caused by the heat up of you sensor (thermal noise) and  the reason why it stretches toward one direction, is because the image was slightly shifting between subs. When the stars/nebula were aligned but the noise was being moved in the opposite direction of the image drift, hence creating the "lines" or "streaks".  

The orion nebula looks much smoother than the horsehead due to the noise reduction used.

There is also a hint of something that might be sitting on your sensor.

Edited by MarsG76

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I agree with @MarsG76 regarding the streaks. It's sometimes called walking noise. The only sure way to avoid it is to dither between exposures.

 

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Keep in mind that M42 has a huge amount of reddish dust surrounding it--in deep images of this target you will see that it is actually embedded in a dust filled region.  Some of what you point out in that image looks like it might be the dust.

Rodd

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Thanks for all your comments. I think I'm not used to the modded version yet since I think it is more susceptible to absorbing thermal noise compared to unmodded cameras. The video helped a lot!

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13 minutes ago, Rodd said:

Keep in mind that M42 has a huge amount of reddish dust surrounding it--in deep images of this target you will see that it is actually embedded in a dust filled region.  Some of what you point out in that image looks like it might be the dust.

Rodd

M42rebelxtArtifacts.thumb.png.19b8d303decbbbfebc9c3b62f407c125.png

Actually I'm weirded out by the black lines from the image. I'm not sure if that is also because of the thermal noise or something on the lens of the camera or the mirrors

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1 minute ago, lalou said:

Actually I'm weirded out by the black lines from the image. I'm not sure if that is also because of the thermal noise or something on the lens of the camera or the mirrors

Look at the dust lane right near the trapezium region (the main one separating the nebula from the little horn to the left).  Follow it down and it seems to just extend down into your circle you drew.  Some of this stuff is really there I think.  maybe you have stretched to aggressivly

Rodd

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12 minutes ago, Rodd said:

Look at the dust lane right near the trapezium region (the main one separating the nebula from the little horn to the left).  Follow it down and it seems to just extend down into your circle you drew.  Some of this stuff is really there I think.  maybe you have stretched to aggressivly

Rodd

It looks weird already when I overstretch it  tho.

M42RebelXTTrial2.thumb.png.f962578544c570ef8a24b4188c6cea90.png

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BTW do you guys have any recommended software for fixing or post processing these types of image which has a lot of thermal noise? Or do I just have to take better shots with less thermal noise?

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