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NGC6888 / Crescent Nebula in Ha (MN190/314L+)


AndyUK
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Last night surprised me - I wasn't expecting it to be clear, but it gave me a chance to have another practice. As I've been having (yet more) issues with focus, I laser collimated with the Hotech at setup and then did a star test, then used a Bhatinov mask and then used the focus aid window in Artemis Capture - Again, I started looking at FWHM and BRI figures but then tried a tip that Coco gave me looking for the REALLY faint stars - If they disappeared as the seeing changed, then that must be about as good as you can get...

Starting at just past 11pm (I considered that the Ha filter might enable me to start just a tad early), I took 30x600s exposures. Sadly I lost 9 of these due to guiding artefacts, almost all at the end of the session :( - When it started to get light, I discovered that some clouds had moved in that didn't cause the guider to lose lock, but obviously did sufficient to cause it not to be quite as good as it should be. Anyway, it was getting fairly light by then anyway.

I also got some flats for the first time (:)) using Virtual Light Box on the laptop and placed the screen flush against the top of the scope... After much faffing around with everything, I finally found that 0.8s gave me an ADU of around 24,000 (a little high perhaps?).

21x600s, 50 bias and 20 flats, DSS and then some minor tweaks in CS5. I'm still not sure about the stars - To my eyes it still looks a tad fuzzy(?), but this object with the scope on this chip certainly fills the frame. (Any critical comments would be very gladly received...!)

andyuk-albums-atik-314l-picture11699-ngc-6888-crescent-nebula-mn190-21x600s-ha-50-bias-20-flats-applied-stacked-dss-post-processing-cs5-6th-june-2011-9-frames-lost-due-poor-guiding-caused-high-level-clouds.jpg

[EDIT - Slightly reworked image from original to tone-down over aggressive stretch]

Edited by AndyUK
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Not bad at all Andy, you can see that outer shell just appearing. The 314L+ gives nice detail to dso's in that focal length, but a much widerfield is really nice for objects like this. Collimation seems to be good as well..

p.s. Downloaded your data, but not had a chance to play with it.

Nadeem.

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You certainly got it there! :) But as you said, yes it looks a bit fuzzy and noisy for some reason. It looks like this usually when theres a bit of high cloud, you can see some of the brighter stars are a bit "soft". Maybe being a little less aggressive with the stretch may help becuause although you have the centre of the nebula, the outer arms are over-stretched (total white-out... lol sounds like a TV game show).

More data should sort all that out though, keep it going!

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Looks good to me Andy.

As for stars was this imaged with the mak newt? All the stars seems to be leaning to one side maybe collimation is a little off, its only very slight though and looks like you are going to be producing some great images very soon :)

Edited by shaunster
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Cheers guys - Thank you very much for the comments!

@ Nadeem

but a much widerfield is really nice for objects like this. Collimation seems to be good as well..
Yes, I must admit, when I looked this up on CCD Calc I actually wondered how easy it would be to frame it (something I always struggled with a little with the 40D as I haven't yet used APT with its focus stacking aid) - This is REALLY easy with a CCD camera, but as you say, this FOV gives no sense of scale. However, I REALLY wanted to test out my collimation / focusing and thought that this would be as good a test as any... On the subject of collimation, this, like dust, is now becoming yet another OCD - Although I used the Hotech (supposedly perfect out of the factory?) AND did a star test, it's possible my eyes still may have missed something... at mega zoom, the stars appear to be ever so slightly triangular? Hopefully it's just me not performing the star test accurately enough as I don't want this to be a possible focuser misalignment :) - I thought I'd ruled that out months ago!

@ Twotter - I think I know what you mean - If you stare at it long enough it begins to move (like one of those fractals from the 90's!)

@ Uranium - I'm glad it's not just my eyes... and there obviously was some cloud up there as it b*ggered up 90 mins of subs :eek:, but of course I couldn't see them until it started getting lighter.

If the weather's kind (which isn't looking likely for the rest of this week :(, I will indeed try and get some more to iron out the noise and (hopefully) sharpen it up a bit. I'll also have a play at reprocessing - I find it even harder with these mono images in the same way that I always found it tricky taking B&W film photos...

@ Shaunster - Yes, it was the MN190... I think it is beginning to come together now, but I reckon I can only give myself a C+ for this one - I obviously need to do better star testing... and hopefully that will prove that this isn't an issue with focuser misalignment.

(To be honest, I'm fairly pleased with this as a deep shot, although my wife's only comment was "why is it not in colour?" :()

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I wasn't going to do a re-work of this, but I just found "Lucy-Richardson Deconvolution" in Maxim... We like that tool!

Q289_20110606NGC6888HaAppliedREWORKDeconvolved1PshiftJPG.jpg

I lked it so much, I then tried to have a go at a couple of "old" DSLR images... Sadly it was too much for my 4Gb memory laptop :). I'll have to ask work to buy me a new one (and make it ruggedised so I can take it outside without worrying!)

[EDIT: Now with 1 pixel shift]

Edited by AndyUK
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Cheers Peter - I was really impressed with deconvolution, although the "default" settings I found didn't work on any of the 3 other Atik images - Perhaps it's something that needs to be done prior to combining(?)

If we can get another clear night or two soon (please?) I quite fancy taking some OIII frames and seeing what an HOH or OHO image will look like... With a lot of luck I'll end up with a result like Uranium's (?)

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Can't see the original but the deconvolved one (love that word!!!) is a blinder. Wow, it really is tight and contrasty...and BIG. Time for a celebration! An on-form MN190 takes some beating.

I think your ADU value is fine for the flats. I used to go for that and then too much cloudy night reading made me go for 30,000 instead. Makes little difference that I can see but I have stuck with 30,000.

Great result.

The O111, if you do it, contains some surprises, things that look like artefacts but aren't. JCJC is the expert on this. Recommended.

Olly

Edited by ollypenrice
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Thanks Olly - I'm not sure why you can't see the first image as it's on my screen (can anyone else not see it?) but I can tell you that it's nowhere near as sharp as this LRD version... :(.

When shooting with the DSLR, I read somewhere that I should try to aim for flats between 1/3 to 1/2 saturation, so as you say I guess anywhere in the region of 22K-32K is within bounds.

However, using VLB and having to flip the laptop over the top of OTA whilst it was still controlling the camera via Artemis was helluva palaver, and having looked at the flats, I'm not really convinced that the laptop screen covers the whole area of the OTA... The longer I think about it the more I'm wondering why I haven't pressed the trigger on one of those EL panels yet :)

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Cheers Guy... and thanks for the focusing tip :). It wasn't half as "stressful" as trying to watch the FWHM/BRI values!

I definitely want to have a crack at taking some OIII on this - Olly's comments about them showing surprises has me very intrigued(!) and also Uranium's ED80 image has really set the bar... Mind you, if the OIII come out as well as the Ha, then I'll be well chuffed!

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How on earth did you get deconvolution to work? Whenever I use it, it just makes things look like a pigs breakfast :)

I see youve been less aggressive with the stretch too, much, much better. The detail has returned to the outer edges.

Edited by Uranium235
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How on earth did you get deconvolution to work? Whenever I use it, it just makes things look like a pigs breakfast :)
Pure luck I think - Everything else I've tried it on has ended up with a completely different result! I just followed the recommended defaults on the Arizona Maxim section

I've just made a note of your exposure settings actually (hope you don't mind?), as further to suggestions in this thread, apparently I NEED to get some OIII to go with it (I just hope I can get LRD to work with that one too!)

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Great image, it could be made a little sharper by processing to remove the very slight right to left drift in the stars (ie using the paintshop method of subtracting an offset a layer copy).

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Yep, have a go at adding ome OIII to make it come alive. Though you may have a bit more difficulty framing it in OIII becuase the signal is a lot weaker than Ha (even at 5x bin). I got round that by placing the central star in the middle of the reticule of artemis capture, you cant miss then :)

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Cheers Nick... You're right, there is something not quite 100% with the stars - I'll try an offset layer and see if I can tweak it just a tad....

@ Uranium Thanks again! I'm sure I would have been out there swearing my head off not being able to frame the blasted thing! With the weather forecast not looking too great, I'm not sure when I'll be able to take them mind, but at least I won't have to worry about the moon getting in the way again.

(I hadn't noticed that star close to the centre - If I'd thought about it more, I'd have centred that in the first place... :))

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Nice and sharp Andy! Good image scale too.

As Olly says, OIII is really interesting. Needs lots of time and careful processing I think. It's hard to tell artefacts from reality sometimes.

Jordan.

P.s. here's a image from Les Granges showing the OIII

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Good grief....!!! :icon_eek:. What an amazing image... :)

(I'm not sure I like the idea of it needing careful processing as I seem to be a bit clumsy and naive at the moment... :rolleyes:)

Still, if I'm able to get some good OIII subs, then I can play with them at will. I don't think I've ever seen a HOO image blended in with RGB before... On the subject of HOO, I'm assuming it's okay to use the same OIII subs for both G and B channels...?

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