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Vignetting help!

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19 replies to this topic

#1 stars n planets

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Posted 26 March 2020 - 09:14 PM

Ive been getting vignetting on my images. The more i stretch the more visible it gets.

I have a asi183mc followed by 5 position filter then a altair 1.0x field flattener at the correct spacing on a Altair lightwave 60mm 420mm F7 triplet.

I can crop some out when imaging somethings and flats do some good. But how can i avoid it to start with or minimise it?

Thanks

#2 stars n planets

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Posted 26 March 2020 - 09:15 PM

Vignetting https://imgur.com/gallery/lOkYd7b

Image of setup

#3 BQ Octantis

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Posted 27 March 2020 - 05:45 AM

That's some very asymmetric vignetting! Are those pics before or after application of flats?

 

BQ



#4 stars n planets

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Posted 27 March 2020 - 06:17 AM

That's some very asymmetric vignetting! Are those pics before or after application of flats?

BQ


After application of flats. I only took one image before i added the filter wheel. Thats why i suspect its that.see picture link.

Vignetting https://imgur.com/gallery/setZgJh

It would be a shame to get rid of it. And not sure why it would nt work correctly. Everything seems aligned correctly and spaced.

Not sure what to do. It seems like the top right is the most effected. I may try turning the camera 180 to see if it move with it???

????

#5 BQ Octantis

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Posted 27 March 2020 - 06:27 AM

Should certainly try rotating; also try some shots of the same target with and without the filter wheel. But I'm shocked that the flats didn't remove it…it doesn't seem like it took a lot of stretching to bring out the offset.



#6 Alex McConahay

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Posted 27 March 2020 - 07:09 AM

If you use PixINsight, try ABE or DBE....Your problem does not look so severe. 

 

Alex



#7 einarin

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Posted 27 March 2020 - 07:50 AM

Looks not too bad to me (easily fixed post processing - like PI or Photoshop etc).

Did you use bias or flat darks ?



#8 stars n planets

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Posted 27 March 2020 - 10:28 AM

I think my flats are no good. How should they look is it opposite to vignetting? With dark bits around the edges?

#9 stars n planets

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Posted 27 March 2020 - 10:31 AM

Should Calibration frames be done with my CLS/duo band filter or not?

#10 nimitz69

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Posted 27 March 2020 - 10:34 AM

 Did you use bias frames? Flats don’t work properly without bias .... it’s math dalek12.gif


Edited by nimitz69, 27 March 2020 - 10:34 AM.


#11 stars n planets

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Posted 27 March 2020 - 10:46 AM

Did you use bias frames? Flats don’t work properly without bias .... it’s math dalek12.gif


I did but i suspect my flats are no good as they are single tone in colour all the way across

#12 stars n planets

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Posted 27 March 2020 - 10:48 AM

Im going to scrub what i have and setup a new lot of Calibration files, for tonights session. 20x of each? I know more is better

#13 Tapio

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Posted 27 March 2020 - 11:02 AM

Yes, flats should look like dark corners.
And you shouldn't move camera between taking lights and flats.

#14 Noobulosity

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Posted 27 March 2020 - 11:08 AM

Looking at your images, I do see a bit of vignetting, but that typically should come out with proper flats.

 

How are you taking your flats?  E.g. sky flats, white monitor, bright tablet screen, LED light panel, EL light panel, etc.

 

Edit to add for clarity to the above post:  by "move the camera", that would mean don't change focus or rotation between lights and flats.  Flats also cancel out dust motes, and if you move the camera around the dust particles won't line up between lights and flats anymore.


Edited by Noobulosity, 27 March 2020 - 11:09 AM.


#15 stars n planets

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Posted 27 March 2020 - 11:43 AM

Can anyone tell me if these are ok.

So i did flats, bias and dark flats

Flats https://imgur.com/gallery/icRBf9h

#16 Noobulosity

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Posted 27 March 2020 - 12:01 PM

The flat looks weird to me. It should be even in color, typically white or gray, and you might notice vignetting around the corners. But your flat has a gradient of color to it.

How did you take your flats? What was your light source?

#17 stars n planets

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Posted 27 March 2020 - 12:07 PM

The flat looks weird to me. It should be even in color, typically white or gray, and you might notice vignetting around the corners. But your flat has a gradient of color to it.

How did you take your flats? What was your light source?


My kitchen wall is white, and has a bright even light on it. I put a white shirt over the front.

My Cls filter is also on.

#18 Noobulosity

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Posted 27 March 2020 - 12:54 PM

Try using a white screen instead, if possible. Also, check the histogram of your flats and try to shoot for 1/3-1/2 way across from the dark side. The flat looked a bit dark to me.

#19 Alex McConahay

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Posted 27 March 2020 - 03:02 PM

Should Calibration frames be done with my CLS/duo band filter or not?

 

Flats must be done with the same imaging train, including the filters. Darks, biases, and flatdarks should be done with the scope covered, and in the dark if possible. For those last three calibration frames there should be no light coming to the sensor, and therefore, it is immaterial if any filters are in the light path. 

 

 

Alex



#20 Noobulosity

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Posted 27 March 2020 - 03:04 PM

Yes, any filters should still be in place for flats to make sure dust on the filter is calibrated out properly.




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