Strange horizontal lines.

[oOChrisOo]

Hello everyone. 
 

I’m very new to astronomy, and even more of a novice when it comes to astrophotography. So, I’ve been taking images of deep space for a couple of months now. I’m using a very basic DSLR, just one I had in the house. (Canon 4000d) and an William optics Z61 telescope. I recently bought an optolong l-extreme dual band filter. Since using this filter I seem to be getting strange horizontal lines through my images. I’m not sure if this is anything to do with the filter, as I haven’t removed the filter from the telescope since I attached it. But the frames are stacked in DSS, and I’m trying my hand at Adobe photoshop for post processing. And the slightest curve stretch and these strange lines appear! 
 

any info on what they are and how I could fix them would be a massive help. 
 

I’ve attached an image of the North America nebula with a quick process to show you the problem. 

[Clarkey]

I will watch this with interest. I have a ASI 1600mm pro that is my 'normal' imaging camera. However, so I could potentially run two rigs simultaneously I recently got my 600D modified. Unfortunately, I am getting horizontal banding too. Not as bad as this, but certainly noticeable. I checked my previous non-modified camera results from some time ago and it is not as bad - but still there. I have looked at the calibration frames and it does appear on the darks and bias frames, as well as the lights. Nothing on the flats. Even with the calibration it is on the final images. I have tried darks only, without bias and bias only but neither seem to solve the problem. Obviously using a DSLR the temperature cannot be controlled for the calibration frames which does not help. However, APP which I use for stacking is supposed to compensate for variations in temperature from the calibration frames to the lights. Despite this I still have two clear horizontal strips about 1/3 and 2/3 of the way down the frame. 

I have partly managed to remove them in processing, but to me at least, they are still clearly visible.

[newbie alert]

Horizontal banding, quite usual on canon 450, 550....

In ps and within carbonie tools there's a horizontal band tool, not sure if it fixes the issue but worth a try

[Budgie1]

3 hours ago, oOChrisOo said:

Hello everyone. 
 

 I’m using a very basic DSLR, just one I had in the house. (Canon 4000d) and an William optics Z61 telescope. I recently bought an optolong l-extreme dual band filter.
 

Is your EOS 4000D standard or has it been astro modified? I ask because the L-eXtreme filter is designed to only let Ha & OIII light through, but a standard DSLR has a filter on the sensor which will block most of the Ha wavelength of light and this may be part of the issue, if the camera is standard.

I had banding with my Astro Modified EOS 1300D, although the banding I had was wider and less visible.

There's a set of tools (scripts) for Photoshop which are aimed a astrophotography called AstronomyTools. You have to buy them, but it's only about £20 and there are some very handy tools in the download, including a Horizontal Banding Noise Reduction tool. 

The PixInsight software also has a built-in script for removing the banding from Canon cameras in the Scripts/Utilities menu.   

[Whirlwind]

I believe this is a function of the architecture of the DSLR.  This DSLR uses CMOS so each each row is read out using a different set of electronics.  As such each row has a slightly different read noise associated with it.  This is generally not a problem when you have plenty of signal.  In day time use it won't be noticed and you probably didn't notice it when it was unfiltered because of general background noise (light pollution etc).  Now you have a narrowband filter most of the background is removed so this underlying pattern is exposed.  It is much better controlled on CMOS astronomy cameras because they are cooled and have been designed to control this as much as possible - something that DSLR camera manufacturers give less consideration to (as they aren't designed for only astro work).  

The solution is to dither by several pixels (slightly move the cameras pointing) each time you image.  This will mean that the location of the bands will be different on each image of the object.  If you take enough and then average/median combine the images the effect will be removed as you have averaged out across the final image.  Most imagers regardless of camera dither as it allows you to remove stubborn artefacts that processing can sometimes struggle to remove.

[oOChrisOo]

18 hours ago, Budgie1 said:

Is your EOS 4000D standard or has it been astro modified? I ask because the L-eXtreme filter is designed to only let Ha & OIII light through, but a standard DSLR has a filter on the sensor which will block most of the Ha wavelength of light and this may be part of the issue, if the camera is standard.

I had banding with my Astro Modified EOS 1300D, although the banding I had was wider and less visible.

There's a set of tools (scripts) for Photoshop which are aimed a astrophotography called AstronomyTools. You have to buy them, but it's only about £20 and there are some very handy tools in the download, including a Horizontal Banding Noise Reduction tool. 

The PixInsight software also has a built-in script for removing the banding from Canon cameras in the Scripts/Utilities menu.   

This was a big help.  I downloaded AstronomyTools and it helped massively. I can still see a small amount of banding but the overall image is much better. 
 

thanks a lot, greatly appreciated. 

[kirkster501]

It is also why darks are so important with this issue.  I can also get it with my QHY268C if I use incorrect darks.

[Omeganon]

On 07/02/2021 at 14:16, kirkster501 said:

It is also why darks are so important with this issue.  I can also get it with my QHY268C if I use incorrect darks.

What do you mean by ‘incorrect darks’? I’ve started seeing this on my QHY268c as well when using the l-extreme. My darks are at the same gain, offset, time, and temperature as my images. I even redid my dark library thinking that there was something wrong there as well. Were you able to narrow down what was wrong?

Edited September 11, 2022 by Omeganon

[kirkster501]

The darks, flat darks and the flats (all three file types) must be at the same *everything* as the lights or else you will get these lines.  I have also found the USB3 cable is crucial as well.  Use a high quality one.