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Old 24-09-2015, 07:25 PM
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NGC6334 in Ha super stretch

Its been a while.
In a Guinness fueled sick-of-no-output moment. Here is Cats Paws Neb in 3nm Ha 40min subs total 20hrs.
Big here https://fredsastro.smugmug.com/Photo...-1/i-6B3SnwN/A

Ive got colour, but have had to deal with "modified hubble" processing properly lately. Ive been lazy till now simply by mapping NB filters to RGB. Its just not good enough these days, some in these hallowed pages have progressed way past that simple thinking .

Anyway, Ill post colour soon, but I dont think this amount of stretch will work on the colour version.
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Old 24-09-2015, 07:56 PM
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Looks great Fred, looking forward to the colour version
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Old 24-09-2015, 07:56 PM
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Typical Fred image that ie. POW!

Processing looks a tad rushed and stars have funny shapes but man, you can feel the long exposure! great stuff

Go the Guinness ... actually, we have a boutique brewery in our apartment building called Bentspoke, they make some 18 different beers and cider and my favourite is called Big Nut a really full flavoured dark ale style beer...absolutely magic, I could eat it (actually I have slow cooked lamb shanks in it - maaaw yum!), if you are ever in Canberra please let me know and I would love to shout you a few (7.5% alcohol though so no processing afterwards )

Mike
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Old 24-09-2015, 07:56 PM
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Hi, Fred,

Magnificent.

The 20 hours has produced an extremely smooth, grit-free result. No having to guess about faint detail. Your optical train, guiding, etc are working flawlessly. We had lots of fun exploring the tiniest details, especially in the fainter areas.

Minor: There's a very slight tendency toward posterization or blockiness of some of the brighter detail. Perhaps it's getting too stretched and then you're unstretching it a bit. You might be able to protect the bright stuff.

Hubble palette: I can see why you might want a simple H-alpha OIII blend to look natural colour. You can do that. There's a very plausible mapping that makes sense. But with Hubble tri-colour, there's no way that they can make it look "natural" and still preserve the astrophysical information and meaning in the SII (or NII) channel. H-alpha and SII (and NII) are all almost precisely the same colour!

Best,
Mike and Trish
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Old 24-09-2015, 08:41 PM
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Quote:
Originally Posted by Slawomir View Post
Looks great Fred, looking forward to the colour version
Yeah, I bet you are, punk . You cause me so much grief (and rat156)

Quote:
Originally Posted by strongmanmike View Post
Typical Fred image that ie. POW!

Processing looks a tad rushed and stars have funny shapes but man, you can feel the long exposure! great stuff

Go the Guinness ... actually, we have a boutique brewery in our apartment building called Bentspoke, they make some 18 different beers and cider and my favourite is called Big Nut a really full flavoured dark ale style beer...absolutely magic, I could eat it (actually I have slow cooked lamb shanks in it - maaaw yum!), if you are ever in Canberra please let me know and I would love to shout you a few (7.5% alcohol though so no processing afterwards )

Mike
The funny stars are orthog.... whatever probs I think, minor, PS will fix it. Yes, im up for 18 beers, that would be processing havoc methinks, worth a try.
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Originally Posted by Placidus View Post
Hi, Fred,

Magnificent.

The 20 hours has produced an extremely smooth, grit-free result. No having to guess about faint detail. Your optical train, guiding, etc are working flawlessly. We had lots of fun exploring the tiniest details, especially in the fainter areas.

Minor: There's a very slight tendency toward posterization or blockiness of some of the brighter detail. Perhaps it's getting too stretched and then you're unstretching it a bit. You might be able to protect the bright stuff.

Hubble palette: I can see why you might want a simple H-alpha OIII blend to look natural colour. You can do that. There's a very plausible mapping that makes sense. But with Hubble tri-colour, there's no way that they can make it look "natural" and still preserve the astrophysical information and meaning in the SII (or NII) channel. H-alpha and SII (and NII) are all almost precisely the same colour!

Best,
Mike and Trish
Thanks Mike. The colour will be with SII, Ha and OIII. In this case, "modified hubble" is not bicolour, just that the 3 NB filters are mapped differently. The blockiness is a worry. ahh, haddnt thought of that, overstretching and then unstretching, I do that sometimes, interesting.

Last edited by Bassnut; 25-09-2015 at 07:03 AM.
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Old 24-09-2015, 09:51 PM
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Fix the star shapes and you have a winner, Fred!
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Old 24-09-2015, 10:40 PM
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Nice work Fred. I have one I am working in a similar image scale as well.

Greg.
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Old 25-09-2015, 08:40 AM
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Had another look this morning. Truly stunning.
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Old 25-09-2015, 08:48 AM
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The full res is smooth and with excellent detail. The star though are not great. In the words of Martin "time to move away from traditional guiding mate". You won't regret the move.

I look forward to your final image. Always an interesting outcome on any of your images.
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Old 25-09-2015, 01:03 PM
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Quote:
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The funny stars are orthog.... whatever probs I think, minor, PS will fix it. Yes, im up for 18 beers, that would be processing havoc methinks, worth a try.
Just remember that the stars and nebula are not independent. If the stars have funny shapes, then you are losing detail in the neb. No software fix is going to recover that detail.
Great pic by the way.
Geoff
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Old 25-09-2015, 04:25 PM
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The star problem is not guiding its your camera is tilting to the left or right.
The stars on the right are much better. The stars on the left have an odd pear shaped bump that looks like a tracking error but isn't. Tracking errors are over the whole image not part of it. Tilt issues typically are one side only or one or two dodgy corners and the others are fine.

There are some slight autoguiding tracking issues but not severe. A good TPoint and activate Protrack tracking corrections may help, plus another Tpoint model and accurate polar alignment to tweak the PA a tad.
You're earlier images have shown this tilt issue before but being a remote setup its not a simple fix being a hardware adjustment that is required. Perhaps some brass shim sheet from a steel supplier

CCDinspector can help show the tilt. But to correct you need to establish which side of the camera looking at it from the back corresponds to which side of the image. It may be reversed like it is on my Honders setup.
My Honders is reversed top and bottom and left and right compared to the image. So to correct the left side of the image you need to pack out the right side of the camera looking at it from the back (assuming it needs to be packed out which is most likely what it needs).

Ideally though you refocus until the left side improves and notice if you had to move the focus in or out. If it is out then you simply pack out the corresponding camera side. If it is in then you need to work out the corresponding camera side and pack out the other side. Complex but once you work on it kind of simple. Where it goes south is if you don't work out which side of the image corresponds to which side of the camera looking at it from the back (where you will be standing to adjust it).

Its like drift aligning.

From my recent experience with this I would say the problem is not minor its major and the packing required may be as much as 1mm+.

Greg.

Last edited by gregbradley; 25-09-2015 at 04:36 PM.
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Old 25-09-2015, 04:39 PM
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Greg the issue is not all tilt. Certainly an element on the left hand side but the stars on the right are not tight circles either. Those are triangular. Check the high res. In any event I am sure Fred is aware of the issue. I suspect that getting up to Siding Springs is a little hard.
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Old 25-09-2015, 05:41 PM
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Quote:
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Had another look this morning. Truly stunning.
Thanks Mike, on rereading your post I think you mean the blockiness on the bright bits is just clipping, thats lazy on my part, ill fix that in the colour version. I too thought natural looking tricolour NB wasnt always viable, but I have now fiddled with channel colorizing that allows adjustable hue. I suspect many find this obvious and I knew about it but haddnt realised its potential until forced to. There are several ways to do this, some seem obvious (even with elaberate tutes) but create artifacts. It took a while for me to work out what works best.
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Old 25-09-2015, 05:56 PM
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Thanks for the input on the screwy stars guys. Yes, it means the left side must also be blurred somewhat unforch.

Guiding is OA and is pretty good, 2 arc sec P/P and way less than 1 arc sec RMS. High P/P can cause stars to distort, but not cause too much trouble for long exposure extended neb, which is affected more by RMS.

PA has drifted a bit over 2 yrs, hasnt been touched since installation and has settled down over a year, that could cause a problem. Im pretty sure the squareness of the cam is the problem. I have protrack on but not PEC, on installation testing that gave the best result. I havent done a Tpoint model for over a year because plate solve just stopped working (a long time ago) despite every setting being perfect. I got it working once, did the map, and that was it.

Its far away, one day ill go there and do PA, clean up, do a model, fix the cam alignment, but in the mean time its all working well enough. Mega data hides a lot of problems :-).
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Old 25-09-2015, 06:14 PM
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Thanks for the input on the screwy stars guys. Yes, it means the left side must also be blurred somewhat unforch.

Guiding is OA and is pretty good, 2 arc sec P/P and way less than 1 arc sec RMS. High P/P can cause stars to distort, but not cause too much trouble for long exposure extended neb, which is affected more by RMS.
.........
Sorry Fred, I see you already are using the force. I incorrectly thought you were not. My mistake.
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Old 25-09-2015, 07:31 PM
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That's got Fred written all over it. 40 minute subs... Haha. The stuff of dreams.
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Old 25-09-2015, 11:47 PM
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PA has drifted a bit over 2 yrs, hasnt been touched since installation and has settled down over a year, that could cause a problem. Im pretty sure the squareness of the cam is the problem. I have protrack on but not PEC, on installation testing that gave the best result. I havent done a Tpoint model for over a year because plate solve just stopped working (a long time ago) despite every setting being perfect. I got it working once, did the map, and that was it.

I find plate solving can be touchy. It works easily on the Proline 16803 with 2x2 binning but often does not work well on the Trius due to lack of stars. That is also 6.3mp. You have to make sure the image scale is accurate and best to know the north position angle as well. CCDInspector or CCDcalculator will tell you the image scale.

PA is very likely to be off after 2 years. So the tilt and some PA should tighten things up nicely. Paul's right there is some tracking error showing in the best parts of the right side but in the left corners the fainter stars (these show up the tilt errors the most) are horizontal streaks. It must be off by quite a bit, not a small amount to be like that. That's my recent experience at F3.8 (which exaggerates this type of thing). F8 is somewhat forgiving so the error must be large.

Greg.
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