NGC 4945, dust deserts. Now with 46 hours of exposure
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 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.
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!
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
wow excellent work M&T!
almost looks like you used some Ha with that shot!
Russ
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.
Quote:
Originally Posted by alan meehan
My that's a wonderful shot I love the colours in there well done M&T
thanks ALAN
Cheers, Alan!
Quote:
Originally Posted by 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!
Thanks Colin. Fewer faint fuzzies than say around Grus, but still surprisingly many given that they're being seen through the milky way.
Quote:
Originally Posted by 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.
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.
Quote:
Originally Posted by 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
No animal shapes to really see though huh?
Mike
Thanks, Mike, you're generous and encouraging.
Quote:
Originally Posted by plantnerd
Splendid image I can see the planetary nebula also. What are the random red blotches in the background noise or processing artifacts?
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.
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
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.
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.
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.
That's nice Mike and Trish. Lovely star colours and huge image scale. The galaxy colour is lovely and warm.
Thanks muchly, Paul.
Quote:
Originally Posted by 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
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).
Quote:
Originally Posted by Stevec35
An extremely worthy NGC4945 guys!
Steve
Thanks, Steve!
Quote:
Originally Posted by 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.
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.
Quote:
Originally Posted by multiweb
The oompa loompa galaxy. Very cool shot.
Cheers, Marc!
Quote:
Originally Posted by 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.
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.
Quote:
Originally Posted by PRejto
Wow, beautiful image! I love the richness of colour.
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.
Their scope is only slightly larger. They must be sacrificing something on an altar at midnight. Thanks for showing us. Awesome.
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
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
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.
to create this image is no mean feat. (my last piece of code was in the Jurassic era of Fortran IV...) 
