weird lines in my photo

[emyliano2000]

Hi guys.

I got some weird liked in my photo and the only thing I can think of is that my camera (full spectrum 600D) was a bit too warm during the imaging session. It was running at 25C.

I tried the vertical banding removal in Ps but it doesn't do anything.

Emil

[MarsG76]

This is why I stopped using dark frames on my DSLR subs... I had this in the past.

No doubt you used darks to remove noise on your subs, problem I found was that the dark frames not only removed the noisy pixels but left black "holes" or pixels where the noise was.... that in each sub stacked where there is slight drifting between the subs results in this effect.

CameraRAW does a very good job in removing the noise and as a last pass through I run a automated script to remove single pixels in all of my subs, TIFFs, after conversion with a pixel size of "2" and a threshold of "30" dust & scratches filter...

I find that running flats and bias is enough after converting the CR2 files to TIFF in PS CameraRAW is enough... and I end up with smooth subs with none of the artifacts you are seeing.

 

[emyliano2000]

5 minutes ago, MarsG76 said:

This is why I stopped using dark frames on my DSLR subs... I had this in the past.

No doubt you used darks to remove noise on your subs, problem I found was that the dark frames not only removed the noisy pixels but left black "holes" or pixels where the noise was.... that in each sub stacked where there is slight drifting between the subs results in this effect.

CameraRAW does a very good job in removing the noise and as a last pass through I run a automated script to remove single pixels in all of my subs, TIFFs, after conversion with a pixel size of "2" and a threshold of "30" dust & scratches filter...

I find that running flats and bias is enough after converting the CR2 files to TIFF in PS CameraRAW is enough... and I end up with smooth subs with none of the artifacts you are seeing.

 

I always dither and never take darks, only flats and bias. I noticed I get these lined when the sensor temperature is quite high. if it's below 15C I don't get them.

[MarsG76]

3 minutes ago, emyliano2000 said:

I always dither and never take darks, only flats and bias. I noticed I get these lined when the sensor temperature is quite high. if it's below 15C I don't get them.

If you stack 20 or so subs, even with thermal noise, the stack should cancel out the thermals noise because it's random.... 

 

 

[MarsG76]

Notice how the lines are all in the same direction... how is your tracking accuracy?

 

[emyliano2000]

1 minute ago, MarsG76 said:

If you stack 20 or so subs, even with thermal noise, the stack should cancel out the thermals noise because it's random.... 

 

 

 

1 minute ago, MarsG76 said:

Notice how the lines are all in the same direction... how is your tracking accuracy?

 

I have stacked 42x600sec. I'm guiding and it's great, subarcsec on a EQ3.

[MarsG76]

36 minutes ago, emyliano2000 said:

 

I have stacked 42x600sec. I'm guiding and it's great, subarcsec on a EQ3.

 

 

 

 

 

Your guiding does look good, but more accurately, how good is you polar alignment?

Autoguiding will correct for the PA inaccuracies, but slight field rotation will be introduced.... is there much movement of your object/stars on the FOV between the first and last subs of the night?

 

[MarsG76]

Also, what software are you using? and whats your procedure to pre-processing the subs? what software are you stacking with?

 

[vlaiv]

It looks like walking noise.

This happens when you have two conditions (you can check for both, but one is already fulfilled). First condition is that there is slight drift between frames, and it is in one direction. Although you say you guide and dither, can you examine frame by frame if they are random indeed or stars move in straight line between first and last frame.

This can happen even if guiding and dithering. If dither is set to low / small - it might be too small and does not move mount / frame enough (a few pixels instead of dozen or so pixels). It can be also due to dither not being random, or dithering in one axis only (like dither RA only). If using guide scope it can happen as well. I had "excellent" guiding for sub duration but had 20-30 pixel drift over course of the night (2-4 hours). This can be due to number of issues - most notably slow differential flex, and sometimes guide scope pointing slightly off compared to main scope optical axis.

Anyway, this is easy to establish - just look what happens between frames without alignment - or better yet stack them (simple stack like average) - without aligning  - if you get star streaks in same direction as lines that it is probably walking noise.

Yes, other condition is that you have some sort of fix pattern noise not being removed from the image - and in this case you are not using darks and sensor is hot. In 600s exposure you are bound to get hot/warm pixels which can't be removed with bias only calibration and odds are that those hot pixels will repeat in the same place in subsequent subs. That + slight offset of frames during the course of the session - produces walking noise.

[emyliano2000]

2 minutes ago, MarsG76 said:

 

 

 

 

 

Your guiding does look good, but more accurately, how good is you polar alignment?

Autoguiding will correct for the PA inaccuracies, but slight field rotation will be introduced.... is there much movement of your object/stars on the FOV between the first and last subs of the night?

 

 

1 minute ago, MarsG76 said:

Also, what software are you using? and whats your procedure to pre-processing the subs? what software are you stacking with?

 

I polar align with a polemaster and Sharpcap.

I'm using DSS and sometimes Pixinsight (following the Light Vortex tutorial) for stacking and I get the same lines in the photo for both methods of stacking.

[emyliano2000]

5 minutes ago, vlaiv said:

If dither is set to low / small

I use APT to control the exposures and dithering and the Max possible distance in APT when choosing PHD for guiding is 5. with my lacerta I can choose a much higher distance. Don't know why I can't do it when guiding with PHD2

 

[Thalestris24]

Hi

Are you using Kappa-Sigma stacking? In my (limited) experience it's the best algorithm to use with dithered subs. Also, you seem to have a mono image??

Louise

[MarsG76]

1 hour ago, emyliano2000 said:

I polar align with a polemaster and Sharpcap.

If you turn off DEC guiding, how quickly does your star drift north or south?

 

[emyliano2000]

6 hours ago, Thalestris24 said:

Hi

Are you using Kappa-Sigma stacking? In my (limited) experience it's the best algorithm to use with dithered subs. Also, you seem to have a mono image??

Louise

Yes, I did use the Kappa-Sigma. The image is mono because I used a Ha filter and I extracted the red cannel from the rgb image.

5 hours ago, MarsG76 said:

If you turn off DEC guiding, how quickly does your star drift north or south?

 

I don't think it's the polar alignment. I always try not to have an error larger than 4-5" and there's not gonna be much drift.

[Thalestris24]

Hmm... What are individual subs like? I take you didn't enable hot pixel removal in DSS? Have you tried stacking in another application?

[emyliano2000]

7 minutes ago, Thalestris24 said:

Hmm... What are individual subs like? I take you didn't enable hot pixel removal in DSS? Have you tried stacking in another application?

The lines are there but you can barely notice them in each of the subs. Stacking all of them brings it out a lot. Hot pixel removal is disabled in DSS. I stacked in pixinsight too and got the same result so I deleted that stack. ☹

The only thing I can think of is the sensor being too hot at 25°C because I don't get them when the sensor is colder.

Maybe I should change the dithering from uniform to square.

[vlaiv]

1 minute ago, emyliano2000 said:

The lines are there but you can barely notice them in each of the subs. Stacking all of them brings it out a lot. Hot pixel removal is disabled in DSS. I stacked in pixinsight too and got the same result so I deleted that stack. ☹

Streaks being present in each sub excludes walking noise.

Second suspect on my part would be read noise. What sort of ISO did you use for this capture and was it any different than usual?

[emyliano2000]

 

6 minutes ago, vlaiv said:

Streaks being present in each sub excludes walking noise.

Second suspect on my part would be read noise. What sort of ISO did you use for this capture and was it any different than usual?

ISO1600 the same as I use every time for Ha shots. Have a look at this one. Exactly the same settings.

9

[Thalestris24]

Just to check - are you sure you are actually dithering i.e. you see the pointing position move relative to the guide star? Are you using a clip Ha filter? Any possibility that streaks are on the filter as a consequence of cleaning, for example. If it was due to high temperature then obviously keeping exposure times down would help or, better, add a cooling mod. Or , of course, better still, save up for a cooled mono camera!

Louise

[emyliano2000]

2 minutes ago, Thalestris24 said:

Just to check - are you sure you are actually dithering i.e. you see the pointing position move relative to the guide star? Are you using a clip Ha filter? Any possibility that streaks are on the filter as a consequence of cleaning, for example. If it was due to high temperature then obviously keeping exposure times down would help or, better, add a cooling mod. Or , of course, better still, save up for a cooled mono camera!

Louise

I am definitely dithering. APT is telling me when the dithering starts and I can notice it in the PHD graph. I never cleaned the filter as I take good care of it.

I don't wanna go mono for now, no time or money. I only do Ha occasionally when the moon is up, not HaRGB.

Hopefully I will get a cooled OSC soon.

Thanks.

[Stub Mandrel]

21 hours ago, emyliano2000 said:

I tried the vertical banding removal in Ps but it doesn't do anything.

Did you try horizontal banding removal ?

Yes, almost certainly made worse by the temperature, it was long exposures last summer that convinced me to cool my DSLR.

[david_taurus83]

19 hours ago, emyliano2000 said:

I use APT to control the exposures and dithering and the Max possible distance in APT when choosing PHD for guiding is 5. with my lacerta I can choose a much higher distance. Don't know why I can't do it when guiding with PHD2

 

There is a setting in global tab in PHD2 where you can change the dither distance. I changed mine from the default 1, to 3 and left the APT setting at 5. It makes a very noticeable improvement in the distance moved. Takes longer for tracking to restart though.

[emyliano2000]

23 minutes ago, david_taurus83 said:

There is a setting in global tab in PHD2 where you can change the dither distance. I changed mine from the default 1, to 3 and left the APT setting at 5. It makes a very noticeable improvement in the distance moved. Takes longer for tracking to restart though.

Thanks, I'll give that a go.