NGC 6744 in Pavo: 24 hrs

[Placidus]

Wikipedia describes NGC 6744 in Pavo as the most Milky-Way-Like in our immediate neighbourhood.

We've had two goes at this galaxy before, back in 2012 and 2013. It is big, very big, but of notoriously low surface brightness, and being gentle, kind, and milky rather than a star-burst for example, somewhat vanilla, so a challenge to make it really sparkle without distorting the truth.

Here is attempt three. (https://photos.smugmug.com/Category/Astrophotography-at-Placidus/i-pdm3f2h/0/367b3ebb/O/Z%20NGC%206744%20Pavo%20L%2016p5%20 RGB%202p5%20each.jpg) We have 16.5 hours of Lum, mostly during very good seeing, and 2.5 hours per channel of R, G, and B, all in half-hour subs.

Perhaps the thing the 20" PlaneWave does best is to photograph the very faintest detail, for example the tiny blue dots in the outermost spiral arms, and the squillions and squillions of distant background galaxies.

Aspen CG16M on 20" PlaneWave on MI-750 fork. Most processing in GoodLook 64, but with some final tweaking by Trish using LightRoom, to selectively dehaze the core.

[atalas]

:eyepop:Hey guys what a tremendous shot......sooooo deep!I could study this field for months.

Fine work on NGC 6744 but, the deep field steals the show for me!

Awesome guys :thumbsup::thumbsup::thumbsup:

[strongmanmike]

Wow...very cool....

Overall a great field, loved looking all around it :thumbsup: and no worms or dots :P:P

Strange :question:... and I may be wrong, but.. there are several strange blobs throughout the field, including some red ones, that don't seem to be actual galaxies...? :shrug: is that RBI..?

Mike

[Placidus]

Thanks muchly Louie. The deep field is often like those last tiny crunchy bits at the bottom of a bag of chips. Worth the forage.



Thanks, Mike, thrilled that you like it. Yes, the blobs are indeed RBI from the focussing stars. We need to dither much more between subs. Then they would disappear with automatic outlier rejection.

The scope control software is written in hideously ancient Borland C++, and the Borland compiler won't run under anything after Windows 7. That means that to increase the dithering I have to put on lots of warm clothes, grab sandwiches and a thermos, and go up there and do quite a bit of programming. Spring is just around the corner. Why put off today what I can put off tomorrow?

Best,
Mike

[cometcatcher]

Wow! This thing is faint but one would never know going by the image.

[jwoody]

Wow, very nice. Such detail.
As you said all those background galaxies....

Cheers
Jeremy

[alocky]

Lovely treatment of a tricky target, even under the wonderfully dark skies you must have. This is definitely an image where the compressed version does it no justice at all, the original full-resolution file at the end of the link kept me amused for a long time, just crawling about the galaxy and looking at all the nicely resolved HII regions.
regards,
Andrew.

[gregbradley]

A very nice deep version of NGC6744. I have imaged this one a few times and its quite faint. It also seems a bit harder to get good autoguiding that far south as well. Plus its quite low even at its high point so seeing can be considerably worse down there.

A couple of points. There is a tinge of excess green in the image throwing off the colour balance a little. HLVG free plug in for Photoshop cleans it up as does SCNR in Pixinsight. I think green is a common issue even at dark sites as that is the common colour of airglow in our neck of the planet. Doing a lot of nightcapes has revealed to me just how much nightglow is commonly around. I see it quite a lot at my dark site and sometimes its really strong. I often wondered why I would get excess green at my dark site despite virtually no light pollution. Doing nightscapes showed me why.

The other is the black point. The background on my monitor seems very close to clipped. Its not but there is no room for the usual charcoal background sky.

Its a processing choice but there is also a bit of room left to lift the galaxy in this image. It holds up well to processing which shows how strong your signal is from all those hours and 20 inches of exposure. But that's your processing choices and to my mind neither right nor wrong but there is more left on the processing table should you wish to accentuate it more.

Do you think there is a gain from 30 minute subs? Some of the stars seem overexposed yet they are not super bright stars. But then you have gotten very deep. Would 10-15 minute exposures have worked better though? What's your take on that?

RBI on a focus star? Is that an Apogee issue? Are the focus stars too bright/saturated? I don't see RBI on my 16803 unless its something super bright like the lights on a passing low jet. Perhaps that is something adjustable like the gain?? (a driver improvement perhaps). As you say a large enough dither would do it but will that unsettle your autoguiding?

Anyway just my thoughts on an already excellent image.

I wonder if our Milky Way has an arm that swings up to the LMC like that?

Greg.

[Atmos]

Having attempted this with a 5" one night, wow yours is deep! Lovely shot Mike and Trish :)

[billdan]

That's excellent M&T, so much detail, and heaps of background galaxies. A just reward for a great effort.

Cheers
Bill

[alpal]

Hi Mike & Trish,
that's a top image & well done to bring out the faint arms.
There are so many other galaxys too.

cheers
Allan

[Placidus]

Thanks, Kevin!



Ta, Jeremy.



Thanks Andrew! The sky is quite dark. We park the Polaris Ranger ATV about 30 metres from the observatory and a bit downhill, so that when we turn the headlights on it doesn't wreck the photo. Trying to find the vehicle in the dark usually means walking around until we bump into it. One can see the lights of Orange, Bathurst, and Dubbo in the distance, but incredibly, it is still Sydney, some 312 Km away, that is the brightest. We'd guess we're closer to Bortle 3 than 4.



Thanks Greg for a very thoughtful reply. The green tinge to some of the background stars worried us. We recalibrated the monitor. Because I'm colourblind, I tend to go by the RGB values more than the look. Yes, some of those stars do have a green tinge. But if we made that go away, by any trick or twist we could think of, the core of the galaxy and many of the tiny background galaxies would start to look implausibly pink rather than orange.

Luckily with the mount sitting on 2.5 tonnes of steel reinforced concrete going down 1.8 metres into the ground, polar alignment says pretty steady year on year, and we don't have problems with guiding. Our home-grown software uses multiple guide stars - here say 20 of them - and two guide cameras, one free-standing taking 1 sec subs and one taking 10 sec subs through the main scope. Seems to work.

Your comment about the black point is an interesting one. We set the black point as accurately as possible, very close to, but not at, the point of clipping, rather than having a grey sky. No astronomical data are lost. Just personal preference.

The old STL-11000M didn't have the residual imaging problem. The Apogee certainly does, and has other problems besides, including little drippy smudges on the stars in long NB exposures, but it is a much better camera otherwise. Oh for the day when someone brings out something like a 16 megapixel CMOS astro-imaging chip with an affordable price-tag.

We'll get stuck into increasing the dithering.

Dimly aware that as well as the faint bridge between LMC and SMC, there is a faint tidal tail between LMC and us, but since it's coming straight at us, it's not for mortals to photograph.

Once again, thanks for your thoughtful comments, especially the effect of airglow on the color of objects low in the sky.



Thanks, Colin! Glad you like it.



Thanks, Bill. We tried combining with data from our two previous attempts, same scope but with an STL-11000M, and us on our L-plates. Tossed it all out.

Very best,
M & T

[willik]

Very nice Galaxy top shot guys
Martin

[marc4darkskies]

That's superb M&T :thumbsup: and crammed with faint fuzzies! Nice dark background too and it's certainly not clipped. This is not an easy galaxy to get right but I dare say this is a benchmark rendition!

[SimmoW]

Ditto for me M&T, fantastically deep! The black level looks ok to me.

My last version of this compares pretty well i think, well relatively anyway! Its a great target in a lovely field.

Very impressed by your custom software and multi star guiding! Not many APers doing this in the world

[topheart]

Hi M+T,
Well this image is a beauty!

Very well done. Wonderful background galaxies in the full resolution image.


Cheers,
Tim

[DJT]

Great image, MnT.

The galaxy is excellent and zooming around with the touch screen and fuzzy spotting was great fun.

Thanks!

[Placidus]

:)



Thanks muchly, Marcus. We're greatly encouraged.



Thanks, Simon! Your version is almost identical, except for a slightly wider field :D



Thanks muchly, Tim.



Thank you David, glad you enjoyed looking.

Very best,
MnT

[RickS]

An excellent NGC6744, M&T! And a wonderful & interesting field as always.

I have seen RBI on my Apogee U16M and also the FLI PL16803 we use at SRO. It's definitely an issue with the sensor and not a specific camera brand (but the sensor temp makes a big difference.) We use RBI preflash at SRO and that fixes the RBI but adds noise and requires more subs. TANSTAAFL :(

[Placidus]

Thanks muchly Rick. So our RBI problems might be generic to the 16803 rather than Apogee. Perhaps others avoid it by using pre-flash. We found that at -30C pre-flash increased the noise so much we chose not to do it. In winter we can easily get -40C, but we lazily decided to stick to -30 because we can do that even in high summer. I think on balance, we'll stick to no pre-flash, and routinely do mini-mosaics, so we can reject the residual images statistically.

Cheers,
Mike

[multiweb]

Terrific shot Mike. I had a go at this one (https://8vy1za-dm2305.files.1drv.com/y4mpzN9zJia15LnZPaPW4k0-Z1fX0tAt0O9Zv_MgQ3fdKP8CyQM5Eyjyumr Ckjc2LTJ1Je_1lCZZDabMrLKx6Juhz8Rp0t W5i0TCHPIFO59rWXgP925h5CDwhhurALEIl RHjVL90hQprbP_HsmmMg3V_tXglM84RR38d 8UAC-05kHS_yao3zLjjxjEkFHxvTB76N_CDhl5aR iZqkuuigbWHgA/NGC6744_placidus_HD.jpg?psid=1) from your place on the northern side of the house with the ED80 a while back but did lack focal length. :lol: Great to see it close up and personal. :thumbsup::thumbsup::thumbsup:

[Placidus]

Thanks muchly Marc. Had a brief look at your image and it looked superb, but now we're back home the link no longer seems to work.

[oernulfs]

That's just beautiful! Wow.

[Placidus]

Thank you Oernulf! Nice to hear from you.

Best,
MnT

[Stevec35]

Very nice MnT! This is a difficult one and I've never been able to do it well from my light polluted backyard. Love the smooth background and the subtle colours.

Cheers

Steve

[Placidus]

Thanks muchly Steve. On light pollution, we've watched Orange (45 km away) grow very rapidly with the mining boom and a commensurate housing boom. Somewhere around 30,000 folk now. But curiously, the light pollution from Sydney, 312 km away, is still the worst.

[Slawomir]

Splendid image M&T :thumbsup:

Currently I'm using the very same target for testing RGB imaging with my modest rig from near Brisbane's CBD. Your inspiring image will serve as a benchmark :)

[Placidus]

Thanks Suavi, we are honoured. Looking forward to seeing your rendition.

Best,
MnT