My Bubble Nebula. What's wrong wi mi' stars?

[kirkster501]

This is a stack of 18 10 minute subs luminance only no processing as yet.  I seem to have lost control of the stars a bit and they seem to have bloomed despite the Atik 460 being an anti-bloom camera.  From TEC140 and using autofocus that was bang on.  The stars are nice and round but brighter ones have bloomed.  I know I can use some scripts to get these a bit smaller.  Any thoughts guys please?  Or am I being picky?  Whaddyareckon?

[ollypenrice]

Thoughts...

- Are you using the TEC flattener? I know you don't need it for flattening with this camera chip size but it has a considerable effect on the colour correction for imaging, even if this is not offically stated by TEC. If the stars in question are on the blue side they might be better controlled through the flattener. (Remember the L filter is fully transparent to blue.)

- Seeing. We've had strong and gusty northerlies here last week (Brexit Britain should keep its weather to itself, not send it our way!!! ) The seeing was dire early in the week, so bad, in fact, that for the first time since I started imaging ten years ago, I could not record a FWHM value in Bin 1 at all. This was in the TEC 140/Atik 460, so the same setup as yours. (Same mount as well.) Only if I went into bin 2 would Artemis Capture recognize a star as a star and give me a FWHM value. I don't remember that value but it was bad enough to make me close the shed and stick to imaging at low resolution in the Taks. (TEC  gives 0.9"PP, Taks 3.5 "PP) I got a perfectly good Bahtinov focus in the TEC but that's the beauty of the B mask. It is unaffected by the seeing - though this means you don't get to see how bad it is! I was so surprised by being unable to get a FWHM value in bin1 that I hauled out the 14 inch Meade to look at some well known targets visually. This confirmed the terrible seeing, a relief in a way. When the sky is like this I tend to take RGB and wait for good seeing for the luminance.

- Blooming. Don't lose the distinction between blooming and bloating. Blooming involves the chip saturating on a bright target and sending a bleed line vertically down from the saturated source. These days hardly anyone uses non blooming-gate cameras for imaging so the effect is hardly ever seen. People used to cut off the bleed line just below the source and ask the software to guess how to fill it as best it could. Bloating tends to be of optical origin, I think. It occurs when the optics fail to bring all wavelengths (notably blue) to the same focus.

Olly

[Uranium235]

Thats not blooming.

Blooming is when you get a large spike on one side of brighter stars, trust me... if your camera was blooming you would know about it!

This image is in Luminance yes? If so you really need to do some star control when processing, otherwise the starfield will run away from you quite quickly. Other things that also contribute to star sizes are seeing conditions and focus.... though if it was the former you would have a "fuzzy" halo around the brighter stars.

[steppenwolf]

I don't think focus is the issue here and as you now already know, the issue isn't 'blooming'. I believe that atmospherics are playing a big part here but I wasn't aware of Olly's note about the colour correction imparted by the TEC flattener - interesting and worth checking out!

[ollypenrice]

9 minutes ago, Uranium235 said:

Thats not blooming.

Blooming is when you get a large spike on one side of brighter stars, trust me... if your camera was blooming you would know about it!

This image is in Luminance yes? If so you really need to do some star control when processing, otherwise the starfield will run away from you quite quickly. Other things that also contribute to star sizes are seeing conditions and focus.... though if it was the former you would have a "fuzzy" halo around the brighter stars.

Agreed.

If you have a target with lots of dusty stuff or faint reflection in the background sky then you need to milk the luminance to pull it out. (IFN, tidal tails, etc.) If the target is emission nebulosity, as in the Bubble, then it's worth asking yourself what you want your luminance to do. If you ask it to pull out faint stuff you're going to be fighting the star sizes because, sure as eggs, it will pull those out as well. Is it worth the hassle? Would it not be easier and more productive to leave the faint gasses to the narrowband filters which will leave you with nice small stars? I tend to process a not-very-deep LRGB with small stars and then add the Ha and OIII, stretched to the nines but with small stars, to the appropriate colour channels.

Olly

[ollypenrice]

6 minutes ago, steppenwolf said:

 I wasn't aware of Olly's note about the colour correction imparted by the TEC flattener - interesting and worth checking out!

Yves and I worked on some TEC data we did together here pre-flattener, in the Atik 4000. He always had reservations about its blue control. I could live with it since it only affected some stars and I could 'fix it' in Ps. When I went to full frame CCD I had to buy the flattener and I gradually forgot about the blue issue since I was never reminded of it. Along came a CN thread about the TEC's colour control for imaging and in that thread the claim was made that the blue control was improved by the flattener. This accorded exactly with my own findings but I'm not blind to the effects of hindsight. I cannot say that I'd spotted this for myself until it was pointed out, but I am pretty much convinced that it's true. Maybe it convinced Yves as well since he subsequently bought a TEC140!

Olly

[kirkster501]

Hi Guys, This is luminance filter only though.  Why would correcting the "blue" with a flattener have any effect? I'm not collecting any blue.....??????

That said, I have heard about blue being corrected better when the flattener is in place too.

[ollypenrice]

7 minutes ago, kirkster501 said:

Hi Guys, This is luminance filter only though.  Why would correcting the "blue" with a flattener have any effect? I'm not collecting any blue.....??????

That said, I have heard about blue being corrected better when the flattener is in place too.

You certainly are collecting blue through your L filter. You're collecting all the colours of the visible spectrum. The only difference between the L and the B filter is that the B excludes the G and R while the L doesn't - but all the blue goes through both and if it isn't well controlled it will bloat.

Olly

[steppenwolf]

2 hours ago, ollypenrice said:

You certainly are collecting blue through your L filter. You're collecting all the colours of the visible spectrum. The only difference between the L and the B filter is that the B excludes the G and R while the L doesn't - but all the blue goes through both and if it isn't well controlled it will bloat.

Good answer!

[kirkster501]

OK Olly thanks, I will check into the flattener, they are not that expensive.  Do you need to start messing around with spacers etc with the TEC flattener? 

[kirkster501]

17 hours ago, ollypenrice said:

You certainly are collecting blue through your L filter. You're collecting all the colours of the visible spectrum. The only difference between the L and the B filter is that the B excludes the G and R while the L doesn't - but all the blue goes through both and if it isn't well controlled it will bloat.

Olly

I never thought of it like that!!!!!!!!  Yes of course, L is letting the whole shebang through.  Great stuff, thanks!

[r3i]

Hi Steve,

Can you categorically rule out poor seeing conditions?  It doesn't take much of a drop in atmospheric clarity to have an effect on the image quality.  If recent conditions have caused poor seeing in southern France, the effect is going to be much worse under our leaden skies.  I had to write off a night of images on Friday due to poor seeing.

CCD Inspector is great for keeping any eye on such things whilst you're imaging, as it analyses each exposure as they are saved to disk - it becomes quickly apparent when the conditions are going downhill as data such as the background ADU start getting crummy, and the image viewer (which gives a highly stretched preview) readily confirms this.

 

[johnrt]

Steve!

I always keep a bottle of "Stars Away" by my prosessing computer, get the image loaded up, then a couple of squirts on the monitor screen, wipe anti clockwise with the enclosed "magic cloth" 7 times and; "Bang, the Stars Are Gone!" It's available from all good Snake Oil re-sellers & outlets!

Here's what it did for your jpeg!

 

 

In all seriousness some dust & scratches filters in photoshop on a duplicated layer, the healing brush to tidy up the left over craters, use select colour range & expand & feather selection by a couple of pixels, copy to a new layer and then a minimum filter works wonders. Didn't get your bigger stars in my 60 sec process on the jpeg, but they can be controlled with careful stretching and a later minimum filter. There isn't anything there I wouldn't really expect to see on a fairly deep Lum image.

[ollypenrice]

1 hour ago, kirkster501 said:

I never thought of it like that!!!!!!!!  Yes of course, L is letting the whole shebang through.  Great stuff, thanks!

Not that expensive!?!?!?  You must be earning more than I do! 

There is a chip distance to be respected. You buy the flattener from TEC and an Astro Physics adapter (TEC tell you which one) and then you need to order a spacer of the right length. Not wanting to get this wrong I ordered the lot from Optec in the states and then seriously considered murdering the postman when he gave me the customs bill.

To be honest, for the 460 chip I'd wait and see if you found that the blue issue troubled you. I only found it on a few stars (not in every image) and fixed it in Ps when I saw it.

Olly

[Andyb90]

Could dew be a factor or can that be ruled out?

Andy.

[kirkster501]

4 hours ago, r3i said:

Hi Steve,

Can you categorically rule out poor seeing conditions?  It doesn't take much of a drop in atmospheric clarity to have an effect on the image quality.  If recent conditions have caused poor seeing in southern France, the effect is going to be much worse under our leaden skies.  I had to write off a night of images on Friday due to poor seeing.

CCD Inspector is great for keeping any eye on such things whilst you're imaging, as it analyses each exposure as they are saved to disk - it becomes quickly apparent when the conditions are going downhill as data such as the background ADU start getting crummy, and the image viewer (which gives a highly stretched preview) readily confirms this.

 

Hi Mike, no, I cannot rule that out.  And, silly me, it could be dew because my dew heater controller is blowing a fuse in my power distribution box and i need to work out why [and it was a cold night].  So dew is a possibility.  Also, I have not had this issue before either on my other images (that are half complete due to incessant cloud).

No Olly, I wont be investing in the flattener just yet mate; I'm not a millionaire like you yet with a global mega-business called Les Granges that you just floated on the NASDAQ.... if I used a bigger chip on this scope at some point I will do so though. Yuri categorically tells me that a flattener is not required for the smallish chip in the Atik 460 and he refutes that the blue channel is not controlled as much as the others.

Thanks John @johnrtfor the work on that image.  Does it pass your demanding eye? I am not fishing for compliments I just want to know if those stars are "acceptable".  It won't win any prizes but i am trying to gauge it....

[ollypenrice]

Well, I think I've seen improved blue stars since fitting the flattener. There was a particular and distinctive kind of blue halo which I no longer get, rather like the pupil of a blue eye, but these things can be caused by microlensing on the chip and other sources. Who knows. 

Like John I don't think your stars are particularly bad from a dense starfield. You could try a star-masked stretch as well. I'd come back to the question, what exactly are you wanting from a deep luminance shoot on this target? You're getting a little evidence of dark dusty stuff in a few places but if you want to chase the gasses it is easier to do so in Ha and OIII because these filters will give you more gas and smaller stars - just what you want. My plan of attack on these targets is to get reasonable LRGB but not to stretch it too hard (because that would pile on the starfield while not doing much for the nebulosity) and then add the NB layers to the appropriate colours. You'll also find far more small scale detail in the NB, particularly in Ha for the Bubble itself. If your L layer is too strong it will be hard for this fine detail to make itself seen.

Olly