NGC 4945, dust deserts. Now with 46 hours of exposure

[Placidus]

Over the new moon we photographed NGC 4945 in Centaurus. The unusually warm colour is because we are seeing this dusty galaxy through the dust of our own milky way, and the blues are being partially dispersed. Despite this, there are still some strongly blue regions in the spiral arms where presumanbly hot young stars are forming. The delicate dust lanes are worth exploring out into the halo.

The very bright star in the image is Xi 1 Centauri, of spectral type A0, and therefore very hot and very blue despite the milky way dust. Xi 2 Centauri (or vice versa) is just out of field to the bottom left.

In the original image (www.mikeberthonjones.smugmug.com/Category/Astrophotography-at-Placidus/i-TbJVNHp/0/O/0119%20NGC%204945%20L9%20RGB%202p5% 20each.jpg) you can see detail in a very faint face-on spiral at about 2 o'clock from the main galaxy.

There is also another distant magellanic, irregular galaxy hidden behind a bright star at about 8 o'clock.

Lum: 9hrs, RGB 2.5 hrs each. Aspen CG16M on 20" PlaneWave. Processing GoodLook 64.

Hope you find it interesting.
Mike and Trish

[rustigsmed]

wow excellent work M&T!
almost looks like you used some Ha with that shot!

Russ

[alan meehan]

My that's a wonderful shot I love the colours in there well done M&T
thanks ALAN

[Atmos]

Looks great? It has everything, not quite so fuzzy galaxy in the foreground, mis faint galaxy or two and then a bunch of faint fussies. It even has a star on the RHS that almost hurts to look at!

[Tony_]

Great image Mike and Trish.

There's also a green spot that looks like a PN above the 2 bright orange stars on the right. It's quite faint - I wonder if it's catalogued?

Regards,
Tony.

[strongmanmike]

That's a great result guys, lovely fidelity and colour - a real 20" CDK in self built stainless steel observatory using Berthon-Jones control, worthy shot :thumbsup:

No animal shapes to really see though huh? :question:

Mike

[plantnerd]

Splendid image I can see the planetary nebula also. What are the random red blotches in the background noise or processing artifacts?

[Placidus]

Thanks, Russ. We've experimented successfully with some galaxies like NGC 300 and Barnard's Gx adding H-alpha in as red, but it takes ridiculously long exposures. Very tempting though.



Cheers, Alan!



Thanks Colin. Fewer faint fuzzies than say around Grus, but still surprisingly many given that they're being seen through the milky way.



Thank you Tony. Sadly, the green spot seems to be an artifact. Still tracking it down, but probably to do with flats or darks needing updating.



Thanks, Mike, you're generous and encouraging.



Rats! You guys have sharp eyes! As mentioned, pretty sure that the PN and the random red blotches are artifacts. The Aspen CG16M (or at least ours) occasionally imagines vaguely star-like artifacts that are transiently consistent from sub to sub, either in the lights or (worse) in the darks. If we dither by a huge amount between images, they go away with stacking and data rejection, but I think we're under-dithering. Buying a better camera is another option, but Santa would need serious buttering up.

Many thanks,
Mike and Trish

[Paul Haese]

That's nice Mike and Trish. Lovely star colours and huge image scale. The galaxy colour is lovely and warm.

[ericwbenson]

Hi M&T,
The semi-random red blotches in the light frames could be RBI. A new 16803 camera might not help (or could be worse!). Large dithering steps is really the best approach (i.e. I am using 20 pixels in ACP, sometimes need even more with the Focus Max left over ghost donut).

If you are seeing them in the darks, are you doing darks right after lights?
That would be the worst case for injected RBI into the darks. The camera should be warmed up and then cooled back down (this empties out the RBI sites) before doing darks after lights.

Best,
EB

[Stevec35]

An extremely worthy NGC4945 guys!

Steve

[gregbradley]

A very nice 4945 Mike. One of your best. I couldn't see any red spots but I agree it could be RBI. Your camera has RBI preflash so you try that out.

Although I thought RBI fades out after several subs. High cooling slows down its fade out. But you would need new darks with RBI on as well as the noise will be different. Its worth a try to see if this helps it.

Greg.

[multiweb]

The oompa loompa galaxy. Very cool shot. :thumbsup:

[RickS]

Very nice work on this strangely coloured galaxy, M&T. You've made it quite a bit more interesting than some of the drab versions I've seen. Some little gems in the FOV too.

Cheers,
Rick.

[PRejto]

Wow, beautiful image! I love the richness of colour.

Peter

[alpal]

Hi Mike & Trish,
what a beautiful image.
It made me have a look at the Chart32 image:
http://www.chart32.de/component/k2/6-galaxies/ngc-4945

cheers
Allan

[Placidus]

Thanks muchly, Paul.



Thanks muchly for the thoughts, Eric. I understand the ghosting issue, having carefully read through the physics and also spoken with the manufacturers. I try to focus on a pretty faint star (eg mag 10 for Lum). An original synch shot is also a great way of getting a nice after-image. At -30 deg, takes about 3 1hr subs to disappear. But quite independently of ghost images, the camera can also "imagine" little blobs which come and go in quite a different manner to ghosting. I've chosen not to go down the infrared pre-flash route. NASA advises that unless you cool the camera to something like -70C, the pre-flash hugely increases the noise. I found that to be true. Consequently pre-flash is only the go if you need it for quantitative astrophotometry and you can go very very cold. So, as you rightly point out, the best defence is strong dithering. I've been lazily relying on a not-so-perfect re-centre after focusing to do the dithering for me. Trouble is, either with winter or with wearing in of gears, the re-centering has been getting annoyingly better! I'm going to have to write in an explicit dither. (I do all my own scope control electronics, firmware, and software).



Thanks, Steve!



Thanks muchly, Greg. As I mentioned to Eric, I'm not keen on infrared pre-flash. I think stronger dithering is the way to go.

Elsewhere you gently and kindly drew my attention to a green gradient. Had a go at fixing that, and it does improve the image. Many thanks. In addition, I think we need to get some more RGB (well dithered !!!) at next new moon.



Cheers, Marc!



Thanks, Rick. I'm feeling anxious now. Had a few goes at reprocessing the image, adding in another 4 hrs of Lum, and am struggling to reliably reproduce this version. Coming out more contrasty and less warm. That will learn me to keep good notes.



Thanks, Peter.



Oh, wow! That image is astonishing. Their scope is only slightly larger. They must be sacrificing something on an altar at midnight. Thanks for showing us. Awesome.

Thanks again to all,
Mike and Trish

[strongmanmike]

Weeeell actually.. The CHART 32" scope has 2.5X your light grasp, almost 2X better resolution (according to Dawes) and enjoys sub arc sec seeing at almost 3X your altitude above sea level in dry desert like conditions... and is some 50km (in a straight line) from the nearest major city of only about 200,000 pop :)

[alpal]

Thanks Mike ,
it's a sad fact that we here at Ice in Space can never hope to
image as well as the CHART32 beast.
For a start we can never get the sub arc second seeing.
However - we can use it as a reference for our images.

cheers
Allan

[Peter Ward]

I am in awe of "M&T imaging Inc."

Your own code :eyepop: to create this image is no mean feat. (my last piece of code was in the Jurassic era of Fortran IV...)

What an impressive result. :thumbsup:

P.S Dare I say....it also rather looks like a fish swimming towards me. :)

[DJT]

Beautiful image, MnT. The colour is great and the stars are a-popping.

Nicely done.:thumbsup:

[Placidus]

Thanks very muchly Peter. This one doesn't remind me of any particular life form, though I expect there is life there somewhere.



Cheers, David!

[Placidus]

We now have a total of 13 hrs Lum (in 1hr subs) plus 11 hrs each RGB (in 30 min subs).

The new beastie is here. (www.mikeberthonjones.smugmug.com/Category/Astrophotography-at-Placidus/i-F7d2QnC/0/O/NGC%204945%20L%2013%20Hrs%20RGB%201 1%20hrs%20each.jpg)

We offset the new data by a couple minutes of arc so that artifacts would not line up. Seems to have helped.

We hoped that the extra colour data might make the colour of the main galaxy more definite. Almost nothing happened. Main thing that happened with the extra data is the background is less gritty, with less artifact, and there are more faint fuzzies visible.

In processing, we fixed the green gradient that Greg noticed. That removal of the green gradient produced the expected very slight change in the colour of the galaxy.

Cheated a tiny bit and did some local brightening round the little face-on spiral that's at about 2 o'clock from the main one.

Overall, we're pleased to have put in the extra work. Thanks to everyone for the suggestions.

Best,
Mike and Trish

[Atmos]

The galaxy appears a bit more defined now, the extra data has certainly helped, especially with some of the stars along the right side of the image. The background is a lot nicer, especially around the brighter areas and the background galaxies are showing by better and pop out more.

What I do prefer from the original is the stars. They are a lot softer, have a far gentler fall off. They are more distracting in the newer one, sharpening? I have given up sharpening my images because it tends to leave the stars with a bright core and then a hard fall off.

The extra data has helped :)

Edit: On review, not sharpening, they're just a fair bit brighter over the original :)

[Placidus]

Thanks for your close and accurate inspection, Colin. I agree with your sentiments. I'm finding a global sharpening can produce nasty sequin-like stars, and am trying to avoid that. My goal was to just brighten the numerous extremely distant galaxies which were too gritty to see before, but are now plausibly there.

I produced two versions of the image. The first was optimized for the main galaxy details, strongly sharpened, which showed the details of the main galaxy nicely but had very ugly stars. The second version was optimized for the background and extremely distant galaxies: wavelet filtered, brightened, but not sharpened.

I then combined the two images according to the 150 pixel low pass filtered regional brightness, thus getting the sharp version in the galaxy core, the bright smooth version in the background, and pro rata in between. (This is analogous to using two layers and a mask in PhotoShop).

The vast majority of stars got brightened a lot and sharpened a tiny bit.

Agreed that the stars do look a tad intrusive now, but attempts to use a more conventional star mask produced nasty transition zones, and I was reasonably happy with the current version, which I think achieved the goal of showing the distant fuzzies better than before.

Perhaps one could mount an argument that distant galaxies are not the point of the image, and should be sacrificed, but my motivation was that I was really rather surprised to see any at all, given that we're in full-on Milky Way here, and so I wanted to show them.

Thanks again for looking so closely, and again, you are right, and I broadly agree with you.

Very best,
Mike

[Shiraz]

that really is an exceptional image, with lots of interesting detail glowing through the dust and stars - and very careful management of the colour. This has to be one of your best, bravo :thumbsup::thumbsup:.

thanks for the insight into your processing technique.

[Atmos]

That is the beauty of image processing, every time we do it it is different! Taking the new one on its own, I wouldn't fault it, I do have your previous one to compare against though :P

As a whole it is a better image and the stars are not bad, just preferred the softness they once had :) I do like that you have brought out the fainter stuff, I wasn't sure if that was on purpose or if it was a consequence of extra luminance (better signal to noise).

What I do like about PixInsights PixelMath is that the expression:
iif($T<0.1, sh, $T)

What this would do is any pixel on the target ($T) image that has a value less than 10% will be replaced by the sharpened (sh) image. This will allow you to increase the background without effecting the stars.

I've never actually tried it but I have tried something similar to increase the background... Just hasn't worked very well. Increases the background but doesn't graduate as it goes.

[Placidus]

Thanks again, Ray and Colin.

In a fit of madness we did yet another 8 hours of luminance, and tried hard to do something along the lines discussed above. The large faint spiral came out even better, but the stars remain big and fat. After our success with H-alpha on NGC 300 and Barnard's, Trish is keen for us to add some H-alpha in to 4945 as red, but we've headed off to some galaxies in Hydra for the new moon. No more fiddling with this one for a while.

Very best,
M & T