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DSS processing - vertical lines?


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Hi All,

Finally managed to collect some data on M51 in the recent clear spell.

The subs looks good but when I run them through DSS I get these odd tiny vertical lines.

Also my hot pixels look like they turn into stripes...

I've tried with and without darks.

Have tried just stacking the best 5 subs.

Tried stretching in DSS and tried taking the original TIF from DSS and stretching using external software.

Everything I try I get the same thing - and it isn't evident on any of the individual subs.

Camera is a modded 600d.

Scope is an at8rc with .9 FR/FF.

Subs were 5 mins guided.

Here's an example image:

Into the Whirlpool

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Not sure about the lines but that is an awesome shot of M51. Looks like you've even gotten some brown showing up in the dust lanes which I couldn't manage with any amount of processing. I'm sure someone will be along to help figure out how to address the vertical lines and once that's resolved you will certainly have a "keeper" of M51 :)

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Hi Gareth, they look similar to problems I was having on some of my images as discussed in this thread. I dropped my ISO to 800 (like yours) but also had a fiddle with some of the setting in DSS. I have found that some of my best results come with the following.

LIGHTS - MEDIAN

DARKS/FLATS/BIAS - MEDIA KAPPA SIGMA clipping

Under DARKS I have checked DARK OPTIMISATION and nothing else (I may have to have a fiddle and figure out what some of the others do!)

And in the RAW Settings under OPTIONS I don't have any White Balance boxes checked.

To be honest I don't know what half of this really means, but it seems to help with mine - once I started trying to get clever, the issue got worse! The marks are still there, but to a lesser degree and seem controllable if the processing isn't too aggressive. You can see a slight improvement from my first to the second image (I think)!

I didn't get to try gradient xterminator as I don't have Photoshop.

Good luck!

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Not sure about the lines but that is an awesome shot of M51. Looks like you've even gotten some brown showing up in the dust lanes which I couldn't manage with any amount of processing. I'm sure someone will be along to help figure out how to address the vertical lines and once that's resolved you will certainly have a "keeper" of M51 :)

Thanks very much! Yes, M51 is my #1 target and if I can get a 'keeper' out of this data I'll be well pleased!

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Hi Gareth, they look similar to problems I was having on some of my images as discussed in this thread. I dropped my ISO to 800 (like yours) but also had a fiddle with some of the setting in DSS. I have found that some of my best results come with the following.

LIGHTS - MEDIAN

DARKS/FLATS/BIAS - MEDIA KAPPA SIGMA clipping

Under DARKS I have checked DARK OPTIMISATION and nothing else (I may have to have a fiddle and figure out what some of the others do!)

And in the RAW Settings under OPTIONS I don't have any White Balance boxes checked.

To be honest I don't know what half of this really means, but it seems to help with mine - once I started trying to get clever, the issue got worse! The marks are still there, but to a lesser degree and seem controllable if the processing isn't too aggressive. You can see a slight improvement from my first to the second image (I think)!

I didn't get to try gradient xterminator as I don't have Photoshop.

Good luck!

Thanks a lot for that - I did shoot some darks but adding them or leaving them out seemed to make little difference.

I will certainly try those settings with another DSS run

I have managed to sort it out a bit using various post processing tools to remove the issues. I'd rather fix the original image though!

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What combination  of the various calibration frames are you using?

Which of the four main ones that you use with DSLR images and using the DSS terminology  of  Lights, Darks , Bias and Flats....?

Peter...

I have lights, darks and (now) bias.

I didnt add flats as the image is pretty flat anyway and i dont have any arefacts to remove..

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Having looked carefully at the image the streaks arent "vertical"...  Which would lead me to look at the darks...

That is a very good point!

but if i take out the darks completely I get the same issue.

Is it that I need *better* darks?

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Unless I have a sensor which exhibits significant glow artefacts (mainly the older cameras which I no longer own) I don't use darks...

The combination I use is lights, flats and bias.  With enough subs Statistical stacking (Kappa Sigma)  and a slight misalignment of the PA (natural dithering)  and if needed application of the Cosmetic hot and cold pixel removal option in DSS the results seem to be ok...

Out of interest was there a significant temperature change across the range of subs you took for this image?

I'm not imaging anywhere near as much as I used to be these days but some of my older DSLR images can be seen here...

Peter...

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Hi Gareth

Do you leave a decent gap between subs to allow the sensor to cool a bit? I would imagine that with lots of 5 min subs you'll get increasing exif temperature...

You could try stacking just lights to see if you still see the problem.

Louise

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When I was investigating DSLR sensor temperature issues, I found the gaps needed to allow the sensor to cool at all would be so long that it wouldn't be viable to do astrophotography. I don't think this artifact is sensor temperature related per se.

James

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I used to find badly matched darks were worse than no darks - provided you took other measures to process out the hot pixels - Dithering either "forced"  through the capture software or "natural" by slight misalignment (is used to get around 0.1 pixel drift in 300s subs) and Statistical stacking such as KS (which also removes sat and aircraft trails and even passing  sus frame clouds)  .. this really starts to come into it's own once you have a decent number of subs...

Peter...

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I would also think 5min subs with that scope might be on the low side.

I once had this on M101 even though I had 4hours of data, the crud appeared on hard stretching.

I had matching darks but they did'nt do any good in DSS or Imagesplus.

In the end I accepted the subs were not long enough and only stretched so it did'nt appear.

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When I was investigating DSLR sensor temperature issues, I found the gaps needed to allow the sensor to cool at all would be so long that it wouldn't be viable to do astrophotography. I don't think this artifact is sensor temperature related per se.

James

Hi James

If I'm doing 5 min subs I leave a minute between - it helps to prevent the temp rising too much. Longer subs than that, I leave a longer gap but not more than 120s - though if I do 10 min subs I won't do more than 2 or 3 at a time anyway (but that's one of my particular limitations!). I don't know what the cause of the op's problem is but I thought I'd just share my approach :).

Louise

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Thanks Louise / James that's a good point. I only had 5 seconds between subs so maybe the temp did start to build...

Though I tried just taking the first 5 subs and stacking them and i still got the issue so I'm pretty sure my issue isn't temperature related.

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