Eagle, with millstone

[Placidus]

Fifteen hours of the Eagle. Two crystal clear nights in a row, and no technological slip-ups.

Original image here (http://www.mikeberthonjones.smugmug.com/Category/Star-Forming-Regions/i-rcKGQ2j/0/O/Eagle%20Ha%203%20OIII%206%20SII%206 hrs.jpg)

Unusually for us, a bit of PhotoShop finger-painting to bring out some of the ultra-faint stuff, and to increase the central contrast, but I don't think we've put in anything that isn't really there.

To our chagrin, this year's Eagle, though wider field, isn't really showing anything more sharply than our old STL-11000M shot. The main improvement is the inclusion of 6 hrs of [SII].

If we imagine that the dark wedge-shape top centre is the Eagle's head and razor sharp beak, looking down hungrily on the Pillars of Creation (one thinks of Prometheus), then there is either a giant pineapple ring, or more mythologically, a Sisyphean millstone, emerging above and to the right of the head. This structure and its surrounds is really fainter than shown here.

As always, we direct your attention to the tiny "Reluctant Parachutist", seen in profile, whose equipment has let him down, saying his prayers. The Parachutist is to be found to the right of the Pillars.

To the right of the Parachutist is some magnificent, swirly, wispy material strongly glowing deep blue in [OIII] which we haven't really noticed before.

To our left of the Eagle's beak is one standard magnificent dragon, facing to the right. It seems to have caught something to eat.

At the right of the base of the pillars is an H-alpha shock front forming a plateau, or ledge. This ledge is populated with various crouching hell-hounds, which luckily could be viewed as a distant city, with mysterious towers.

Finally, and marginally more scientifically, we note the strong OIII emission on streaming, steaming material evaporating from the "head" of the tallest pillar.

We've stretched the red and blue channels until the image is overall colour neutral. At 16 bits, the final image darks are not burned out, but reduction to 8 bits has clipped the very blackest bits.

3 nM filters. Green: H-alpha 3hrs; Red [SII] 6hrs; Blue [OIII] 6hrs. Aspen CG16M on 20" PlaneWave on MI-750 fork. Field 36'arc, 0.55 sec arc/pixel.

[multiweb]

:eyepop: You're cranking them up lately. Gorgeous field. I really like the top part coming down on the central bok swith the cluster in the middle, all those filaments look great. Very 3D. :thumbsup::thumbsup::thumbsup:

[Atmos]

Amazing job there, you certainly look like you're going after ESO :P

[Paul Haese]

Cool 3D feel. Just down the base of the pillars looks very 3D. Huge image too. Nice work.

[strongmanmike]

Another lovely colour palette Mike and Trish, well done :thumbsup:

Very grand

Mike

[gregbradley]

Boom, there is the detail in the pillar and great contrast. Nice.

Greg.

[Placidus]

Thanks, Marc. Touching wood about the cranking. The gear seems to have settled down, excepting for needing a dew-heater on the secondary on some really wet nights.



Thanks, Colin. They're safe for a bit longer.



Cheers, Paul! It's not as sharp as we'd like, and I think I've done the unspeakable and over-sharpened it a bit in an attempt to compensate. Pleased with the relatively clean [SII] though.

Best,
Mike

[Stevec35]

That's a nice Eagle Mike and Trish. Plenty of good detail.

Cheers

Steve

[DJScotty]

Truly magnificent you pair.
Thanks for your imaginative description. I had never been able to see an eagle in this nebula until you described. Now I can see nothing but!
Awe inspiring :thumbsup:

[Placidus]

Thanks heaps, Mike!



Thanks again, Greg. Oh, I wish I could adjust the altimeter and make the observatory a couple kilometers higher.



Thanks, Steve.



Thanks muchly, Scotty. We reckon that finding little dragons and gremlins helps one remember the image, and makes it easier to compare mentally with others. Also lots of fun.

Best,
Mike & Trish

[jase]

Marvelous rendition M&T! Narrowband has always suited M16 and you've certainly done it justice. The details are exquisite. Well done.

[Placidus]

Thanks, Jason. Agree that NB works well here.
Best, M n T.

[topheart]

Love the detail. Love the colour. I still have trouble with NB images with red star colouring and wonder what techniques people use to try and minimise that if they wish to deal with it?? ...??Layer some short sub RGB data to the stars only??
Just looking at what different people do .....

Very nice image indeed!!
Well done!!

Thanks,
Tim

[Placidus]

Thanks, Tim.

The cause of the magenta or red rings is the much greater stretching of [SII] and (to a lesser extent) [OIII] compared with the ubiquitous H-alpha.

We've got a lot to learn, but we're aware of six approaches to dealing with the resultant red or magenta stars.

(0) Ignore them. As that famous Caribbean astrophotographer Bob Marley so aptly put it, in his textbook Confrontation, "Dey say it's just a part of it.". On close inspection, many Hubble and ESO shots have magenta stars. This approach works best if you have a space telescope and tiny stars to start with.

(1) Remove the stars entirely. This involves trying to guess what is "under" the star. A bit like trying to repair an inkblot on a tablecloth by examining the pattern of the cloth and replicating it. Fred (BassNut) and others are good at this. Identify the star mathematically, then use multiple linear regression or the like to interpolate what would have been there. It works really well on smooth nebulosity, but very badly if the star concerned is right over some complex HH jet or shock front that is important to you.

(2) Identifying the stars and desaturating them to white. This is like bleaching a beetroot stain on a tablecloth. It's what we tend to do. It's just a cosmetic fix, but it doesn't require one to pretend to know what is under the star. The first limitation (not so bad) is that one's star-finding algorithm has to be able to find at least 20,000 stars, and to not imagine any, or you'll be left with all the faint ones, or have holes punched in your nebulosity. We try to avoid conspicuous grey rings by just partially bleaching, so the magenta is still there, but no so visually distracting.
The second limitation is that very bright stars take up a huge amount of real estate once they've been stretched to show [SII], and ultimately there's some overlap with the nebulosity. One can then choose between either (a) grey rings in the nebulosity, or (b) choosing to put up with red rings around the brightest stars. We think that's a good scientific solution, but they do stand out like sore thumbs.

(3) Taking RGB exposures of sufficient length that the star in its natural colour will be at least as big and fat and bright as the [SII] after stretching. One then registers the RGB shot to the narrowband shot, and takes the brighter of the two images. That's fair enough, and honest, but for something like say the Norma Supernova Remnant, where the SNR is incredibly faint, it's actually good-bye nebula. The stars overwhelm. It's also a lot of hard work for what is basically a cosmetic fix.

(4) A combination of (1) and (3). One guesses what is under the star and replaces it with a fake guessed background. One then puts smaller, less stretched, RGB stars more or less as place-holders, or eye-distracters, so that you don't see quite so badly how the star removal went.

(5) The final method (which again Fred mentioned to me) is to identify and remove the stars in the red and blue channels only. This works especially well in [OIII] because there tends to be less sharp detail in [OIII] and one doesn't have to guess so hard what to put there instead. One now re-identifies the (now much smaller) star, and bleaches it to white. That method should have the advantages of all and the disadvantages of none. We're yet to master it.

Best,
Mike

[strongmanmike]

Nicely summarised :thumbsup:...lastly (6) you can't make everyone happy so do what you like :D

[topheart]

Thanks very much Mike (Placidus) for adding so much to the discussion. I appreciate the time and effort and thoughtful response!!
Cheers,
Tim

And you too Strong Mike!!

[Geoff45]

Very sharp and crisp M&T. Nice colour too.
Geoff

[Placidus]

Thanks Geoff.

[rustigsmed]

very nice M&T I still remember your last shot of this posted, love that parachuter!

Cheers

Russ

[Placidus]

Thanks Russ. We had a look at combining the two images. That produced a small reduction in grittiness in the blackest recesses, but of course no increase in bright detail, as that wasn't photon limited. And the old data has a smaller field, and no [SII].

[SpaceNoob]

Top image M&T, my only criticism is the weird effects from whatever you used to sharpen? Looks like good data was present, even if you had some trouble with SII? Plenty of detail is presented, the fainter stuff looks really cool too.

I think I just fiddled with mixes and effectively produced synthetic H-beta from the Ha and Oiii for mine. Which brings it in-line with the emission spectrums and the stars go fairly neutral without having to add RGB stars. That said, I don't really stick to any palette like hubble or whatever else exists as I can't really get them to work out right.

Cheers,
Chris

[RickS]

Great image, M&T, and I always enjoy the descriptions. The "reluctant parachutist" made me chuckle :thumbsup:

[Placidus]

Thanks muchly Chris. The weird effects are probably not from sharpening so much as trying to remove red-magenta haloes.

I struggle with "synthetic" channels. No objection whatsoever to the fuzzy extent that what we are doing is digital art. (I also paint and sculpt). But part of the thrill of astrophotography for me is showing that what the textbooks say is up there is really up there. As opposed to what politicians tell us for example. Showing what the textbooks say is up there is easier if I stick to a conventional mapping.



Thanks, Rick. :)

Best,
Mike