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Learning what's normal for an astro camera?

Astrophotography Beginner CMOS DSO Equipment Filters
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#1 cray0n

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Posted 25 February 2024 - 10:09 PM

I'm relatively new and still trying to understand what's normal and what's not with regard to images. 

 

The setup I'm posting about: sharp star 61EDPHIII + asiair plus + am5 + zwo 7 slot 2" filter wheel + asi183MC pro

 

I know amp glow is a problem with the 183, so I'm not surprised I've been seeing that in my images. But after I noticed some obvious electric defects in a stack I did earlier, I changed the usb cable between the camera and askari (still using a cable that came with the camera, so not third party). I didn't run into those problems the next time I imaged the same DSO (NGC 2244), but I am seeing pretty strong vertical bands in the bias and darks:

bias: https://www.dropbox.....21 PM.png?dl=0

 

dark: https://www.dropbox.....41 PM.png?dl=0

 

And they seem somewhat visible in this stacked image that I made quickly in ASIdeepstack:

https://www.dropbox....ck8h4pcdz8&dl=0

 

I haven't had a chance to do flats, which is why I am not sharing any.

 

This is only my second night using filters, and as mentioned above, I'm using a filter wheel. The images in this stack came from an Ha filter and also an optolong moon glow filter and I think my skies are probably Bortle 6-ish, though the seeing was less than ideal this evening. 

 

With all of my narrowband images (including an Optolong L-eXtreme duo band) during the live stack I was finding that there was a very visible dark bar down the center of the image. That's less visible in the final stacked image above, but I wonder if it might still be there. 

 

So my question is: are these normal things that will go away with more careful processing? Should I be concerned about such strong electrical effects in the camera? How do you know when you have successfully subtracted off these kinds of effects?

EDIT: gain of 68 on lights/dark/bias

 


Edited by cray0n, 25 February 2024 - 11:32 PM.


#2 imtl

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Posted 25 February 2024 - 10:28 PM

What gain did you use?



#3 cray0n

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Posted 25 February 2024 - 11:31 PM

Oh right I should edit to include — 68. Pretty low.

#4 Tapio

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Posted 26 February 2024 - 01:14 AM

If your images look normal after calibration process then there's nothing to worry about how bias or dark frames look like.

Only if there's problems with final stack then it's time to find out where's the problem.



#5 cray0n

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Posted 26 February 2024 - 08:17 AM

When I play with the colors a bit, I see strong vertical bars both to the left and right of the nebula, so I think there probably is an issue?

https://www.dropbox....92hl5jdebi&dl=0



#6 Tapio

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Posted 26 February 2024 - 08:42 AM

Hm, I see that. Maybe you could test with another USB cable.

 

Also, I'm not sure if asi183MC pro was one of those cameras which benefits using flat darks (and longer exposure flats).



#7 unimatrix0

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Posted 26 February 2024 - 09:10 AM

It doesn't look too bad. You mentioned you use a Ha filter. That doesn't really work well with a color camera. You need a duo band filter like opt -extreme or similar.  Your vertical banding could be from just the sensor not receiving enough light. Also your camera has a UV/IR filter window so you could try shooting a galaxy or star cluster without any filters and see what you get. The 183 chip is a bit older and needs a lot of light, also google search what the unity gain for the asi183 camera and use that and adjust the exposure length accordingly and you have to shoot plenty of subs. 

 

I reposted your image after resizing it under 500kb. 

 

edit: You also didn't take flats and biases. Those are not optional if you want clean images.  There is a good chance the vertical banding disappear with the bias, but it will also need the flats. Bias, flats don't work without each other, both needs to be present. 

Attached Thumbnails

  • 76C1WvUg.jpg

Edited by unimatrix0, 26 February 2024 - 09:17 AM.


#8 imtl

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Posted 26 February 2024 - 09:15 AM

Hm, I see that. Maybe you could test with another USB cable.

 

Also, I'm not sure if asi183MC pro was one of those cameras which benefits using flat darks (and longer exposure flats).

If he is using gain 68 than I suggest like you that he should check the USB cable.

 

No need for flat darks with this camera. It works with bias as well.




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