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The "No EQ" DSO Challenge!


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I'm still fairly new to imaging, but have had a good start with Planetary and Wide Field images. Obviously, like most of us, it's the Deep Sky stuff I'd like to glimpse, but time, location and more im

Assorted shots with a Nexstar 102SLT and a Canon 1000D. 30sec subs at ISO1600. Total exposures range from 5 mins (M20)  to ~1hr (M31). NigelM

I'll play... these are all early, I've now gone HEQ5 or Astrotrac... but...  These were all shot using a NexStar SLT with an ST80 clone, and an unmodded  Canon 450d. The mount and scope, in total cost

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11 minutes ago, SteveNickolls said:

I use the "Linear, was Bayered, is not white balanced" (the second) option for my Canon camera Nige. You might want to experiment. 

Cheers,
Steve

Thanks Steve,  I have been using the first option till now, so I will see if there's any difference when I redo my last image ☺

Nige.

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I decided to reprocess my images of M56 from the other night too with PixInsight to see if it makes a difference. It's not quite a fair competition as I could stack different exposures and ISO setting in the second attempt and I used calibration. However, it does show that I would over clip the blacks in Photoshop (though I've blown the core of M56 in the second image). I don't know if I'm going mad or have I been throwing a lot of data away by using Photoshop badly or am I just creating a false background by overstretching??

BEFORE (15 x 45s ISO 1600 using Esprit 80 on the Evo mount and the Canon 60D. Bro calibration, stacked in DSS and processed in Photoshop with final tweaks in Lightroom

large.5730e49595535_20160504M56.jpg

AFTER (15 x 45s ISO 1600 plus 1 x 60s ISO 400 and 7 x 90s ISO 400 using Esprit 80 on the Evo mount and the Canon 60D. Bias, darks and flats used for calibration, stacked and processed in PixInsight with final tweaks in Photoshop and Lightroom)

large.M56.jpg

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1 hour ago, Nigel G said:

A quick question.  In StarTools which tab should I open my image with........., linear, was not Bayered or is white balanced ......linear,was Bayered, is not white balanced. ........modified and not linear ........ or .......I'm not sure. 

Nige.

50% of users click 'I'm not sure' the other 50% are liars :-)

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As Ken has busy re processing his images so have I on ngc 7000. 

I have processed these 2 identically, even the masks were the same,  First is 85 x 45 plus 5 x 90s. Second is the 85 x 45s 

There's a big difference in the images. I'm not sure that 10 more 45s would have the same effect as the 5 90s.  What do you think ?

Nige.

PSX_20160509_224440.jpgPSX_20160509_224602.jpg

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The power of the longer sub.

You could stretch the bottom one more but then all the nasties will start to show up.

The top image is showing the various processes that go on in nebulae, they are rarely just red or pink.
You have the blue of Rayleigh scattering or hydrogen+oxygen emission, reds to pinks to magenta of emission.
The varying colours of the emission depends on how much dust is absorbing the light, the more the dust
absorbs the redder the emission.

 

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11 hours ago, Stub Mandrel said:

50% of users click 'I'm not sure' the other 50% are liars :-)

Moi!

I use the X-T1 which isn't a Bayer array, and I don't fiddle with it in DSS, so notwithstanding DSS's hidden activity, I click the first box.

Ian

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9 hours ago, Nigel G said:

As Ken has busy re processing his images so have I on ngc 7000. 

I have processed these 2 identically, even the masks were the same,  First is 85 x 45 plus 5 x 90s. Second is the 85 x 45s 

There's a big difference in the images. I'm not sure that 10 more 45s would have the same effect as the 5 90s.  What do you think ?

Nige.

 

That's a startling difference for a 12% increase in total exposure. Now my foundations are getting a bit shaken up, which I admit are a bit shaky anyway, because I keep coming back to this post, "To stack or not to stack: 30 x 1s = 1 x 30s?" (https://stargazerslounge.com/topic/245183-to-stack-or-not-to-stack-30-x-1s-1-x-30s/#comment-2668145 ). May be it has a lot to do with camera noise. I realise that longer subs do allow one to dig out the fainter objects, but in this case it's not as though you've a lot of longer subs in the mix. Puzzling.

Can I ask a few questions please?

  1.     When you say "85 x 45s plus 5 x 90s", is that the actual number that DSS used for stacking, or what you loaded it with?
  2.     What scores did DSS give to the 90s subs?
  3.     If you were to stretch the bottom image more, do you get nasties showing up?

Ian

 

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4 minutes ago, The Admiral said:

That's a startling difference for a 12% increase in total exposure. Now my foundations are getting a bit shaken up, which I admit are a bit shaky anyway, because I keep coming back to this post, "To stack or not to stack: 30 x 1s = 1 x 30s?" (https://stargazerslounge.com/topic/245183-to-stack-or-not-to-stack-30-x-1s-1-x-30s/#comment-2668145 ). May be it has a lot to do with camera noise. I realise that longer subs do allow one to dig out the fainter objects, but in this case it's not as though you've a lot of longer subs in the mix. Puzzling.

Can I ask a few questions please?

  1.     When you say "85 x 45s plus 5 x 90s", is that the actual number that DSS used for stacking, or what you loaded it with?
  2.     What scores did DSS give to the 90s subs?
  3.     If you were to stretch the bottom image more, do you get nasties showing up?

Ian

 

DSS  did stack all 5 90s and dropped only 2 45s  all the frames were spot on though.

I will check the 90 scores against the 45s and get back to you.

As in the first post of these I can bring out much more detail in the second image,  but not get the same colours  This was purely a test to process them identically and see what happened. 

Nige

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I'm going to try an experiment today, what do you think the result will be

I'm going to take the 3 best 90second exposures and copy them several times to get about 60 frames, I will have to rename them all different I think. Then stack them.

Will it work ?

Nige.

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10 minutes ago, Nigel G said:

I'm going to try an experiment today, what do you think the result will be

I'm going to take the 3 best 90second exposures and copy them several times to get about 60 frames, I will have to rename them all different I think. Then stack them.

Will it work ?

Nige.

That won't do much. Stacking is able to remove noise because noise is random, so over the period of many pictures it can figure out what's random and what isn't. If you stacked the same picture 100x the randomness of the noise wouldn't be there. 

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4 hours ago, Nigel G said:

Scores are as follows 

90s highest score 2348 lowest score 1300. 3 are over 2000.

45 highest score 2000 average score about 1000 

They are very good scores Nige. I usually find the top score is between 1000 and 2000, with a tail that goes down to single figures, and a handful with no score. Varies of course.

Ian

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Result.

You all know the result, an absolute wash of mixed colour with stars thrown in, incredible noise ?. I knew it wouldn't work otherwise people would have cottoned on a while ago ?but I had to find out.

I'm not going to post it here it might spoil our reputation hehehe.

Nige.

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3 hours ago, Nigel G said:

but I had to find out.

I'm not going to post it here it might spoil our reputation hehehe.

I do like a good experiment, well done Nige ! Awwww go on, heheee.

Actually I am going to propose another experiment, Ian and me and no doubt many others were surprised at how those 5x90 made such a difference, so one wonders if the other 85x45 were needed ! perish the thought !! So, experimentally, what do the 5x90 look like by themselves stacked alone ?

So many variables so many foundations to wobble :)

 

Edited by SilverAstro
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I thought I'd try and show what I meant about light pollution gradients with a graphic as I can't explain it well in words. One of the main issues we face as AltAz imagers is field rotation. Our images rotate over time as we track across the sky. The top three "photos" show the same group of 5 stars taken, lets say, 20 minutes apart and show considerable rotation. I've shown an even light pollution rising from the bottom that impacts the bottom part of each photo. So the stars rotate but the light pollution does not.

When you stack these images, the software registers the locations of the five stars and aligns the photos so they stack over each other. However, now the gradient is in a different location. The lower stacked image shows how the program de-rotates the images to align the stars but this now causes the gradient in each image to be rotated the exact opposite angle in each image and this is stacked - pollution being an additive.

It's much easier to remove the simple linear gradient from each image (but very time consuming) than remove the more complex, bow tie, gradient in the stacked image. I wonder how much this impacts on the final quality of our images. 

Gradients.jpg

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5 hours ago, The Admiral said:

They are very good scores Nige. I usually find the top score is between 1000 and 2000, with a tail that goes down to single figures, and a handful with no score. Varies of course.

Ian

I never know how much stock to put in the scores other than as a relative measure between subs. For different targets I get very different scores - where there are few stars, the scores are much lower. It's not something I really understand within DSS and only use it as a guide. I've noticed one of the modules in PixInsight that I've used when following the tutorials provides a range of different quality measurements of an image including the size and elongation of stars, and how you can combine these to provide a weighting when stacking the images. My most recent attempt, processing M56, included 5 subs which I'd assessed as only "maybe" quality but I stacked them anyway and PixInsight used them but placed a lower weight against them. I probably should have excluded them but its a balance between what each additional 45 second exposure adds compared to how much it reduces sharpness of the overall stacked image.

There is so much to learn!

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8 minutes ago, Filroden said:

I thought I'd try and show what I meant about light pollution gradients with a graphic as I can't explain it well in words. One of the main issues we face as AltAz imagers is field rotation. Our images rotate over time as we track across the sky. The top three "photos" show the same group of 5 stars taken, lets say, 20 minutes apart and show considerable rotation. I've shown an even light pollution rising from the bottom that impacts the bottom part of each photo. So the stars rotate but the light pollution does not.

When you stack these images, the software registers the locations of the five stars and aligns the photos so they stack over each other. However, now the gradient is in a different location. The lower stacked image shows how the program de-rotates the images to align the stars but this now causes the gradient in each image to be rotated the exact opposite angle in each image and this is stacked - pollution being an additive.

It's much easier to remove the simple linear gradient from each image (but very time consuming) than remove the more complex, bow tie, gradient in the stacked image. I wonder how much this impacts on the final quality of our images. 

 

you are right, the gradient will 'spread' across the bottom of the image and up the sides due to field rotation.

But... how many hours of subs in a single sitting are people taking here? Look at the overall angular rotation of something like Leo over 2 hours by watching it move in stellarium in fast forward... few degrees maybe?

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7 minutes ago, Filroden said:

I never know how much stock to put in the scores other than as a relative measure between subs. For different targets I get very different scores - where there are few stars, the scores are much lower. It's not something I really understand within DSS and only use it as a guide. I've noticed one of the modules in PixInsight that I've used when following the tutorials provides a range of different quality measurements of an image including the size and elongation of stars, and how you can combine these to provide a weighting when stacking the images. My most recent attempt, processing M56, included 5 subs which I'd assessed as only "maybe" quality but I stacked them anyway and PixInsight used them but placed a lower weight against them. I probably should have excluded them but its a balance between what each additional 45 second exposure adds compared to how much it reduces sharpness of the overall stacked image.

There is so much to learn!

I had a higher star threshold on the second attempt first score was 2380 second was 660 so it seems it's using star numbers.

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28 minutes ago, SilverAstro said:

I do like a good experiment, well done Nige ! Awwww go on, heheee.

Actually I am going to propose another experiment, Ian and me and no doubt many others were surprised at how those 5x90 made such a difference, so one wonders if the other 85x45 were needed ! perish the thought !! So, experimentally, what do the 5x90 look like by themselves stacked alone ?

So many variables so many foundations to wobble :)

 

I'll give it ago ☺. 

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7 minutes ago, nicks90 said:

you are right, the gradient will 'spread' across the bottom of the image and up the sides due to field rotation.

But... how many hours of subs in a single sitting are people taking here? Look at the overall angular rotation of something like Leo over 2 hours by watching it move in stellarium in fast forward... few degrees maybe?

Maybe its my tracking but I notice it frame to frame, i.e. noticeable in minutes, not hours. Thinking about it, I'm exposure limited to 45 seconds for NGC7000 when it was at about 20deg above the horizon and roughly NE (so should show less rotation than something closer to zenith or near the meridian). After somewhere between 60 and 90 seconds I see trails. So I can't imagine how much there is over an hour or two's imaging session.

A quick eyeballing of Hercules between 5pm today and 10pm shows it rotates about 45 degrees in 5 hours.

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25 minutes ago, Filroden said:

A quick eyeballing of Hercules between 5pm and 10pm shows it rotates about 45

That's a neat trick in Somerset :):) today given the wet stuff that is current !

28 minutes ago, nicks90 said:

 Look at the overall angular rotation of something like Leo over 2 hours by watching it move in stellarium in fast forward... few degrees maybe?

But but , a quick point of order ( as it is raining and nowt else to do ! ) the angular rotation in Stellarium is not the same as the field rotation between tracked frames to be stacked.

and the bow-tie effect is somewhat reduced when you superimpose the outline of the final, crop, frame.

and both a linear gradient and a stacked bow-tie, or even a round vignetting, can be quickly reduced (to greater or lesser degree) with a high-pass filter, or failing one of them in your image proc. of choice (eg. freewares !), a high-pass can be made in a layer with a gaussian blur of large-ish radius + an inversion + 50% opacity then a black level clamp. It is quite interesting to play with on a rainy day :)

 

 

Edited by SilverAstro
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