Ngc6744 cdk17

[gregbradley]

I had a few hour window of clear weather the other night before cloud came over.

I am planning to do more on this one but I was surprised at how well "only" 3 hours of data turned out. I guess that is the big advantage of aperture - the light gathering power. I am used to requiring more like 10 hours to get this level of signal. This could be handy given the vagaries of clouds and weather.

Planewave CDK 17, FLI Proline 16803 at -39C, Astrodon Gen 11 LRGB filters,
Paramount ME mount. I am continuing to tweak polar alignment using TPoint and it must be pretty close now after several runs through that and drift aligning. TPoint is a cool program and can be used with any mount and camera.

LRGB 90 40 40 40

http://upload.pbase.com/image/128286384

I also suspect there is a largish star tidal stream going from that yellowish bottom galaxy back to the main spiral arms. Longer exposure may prove it to be there or not.

Greg.

[strongmanmike]

Meeeeh.. so, so....:confuse3:be nice to remove those gradients of course but as you say the light gathering capability shows promise for sure! The image scale is showing its advantage too, both this and the NGC 253 show real fine body. I assume that's the full field? If so the correction is perfect and any image tilt is insignificant, nice!

Hmmmm..you look to have just lassood that outer arm and the galaxy and brightened them though, this is always tempting to do but it isn't real. No way of telling what might be a tidal stream and what is just gradient, would be hard to remove the gradients without removing the tidal stream though..?

Overall very promising!

Mike

[gregbradley]

There definitely were some gradients. My home observatory is reasonably dark but not as dark as at Bigga.
Perhaps the larger aperture also picks up the light pollution more as well? Or it probably was there anyway for the APOs
but it takes longer to get the signal? Not sure.

I'll be adding more to this one as its in a good position early in the evening whilst waiting for other targets to rise.

As you say the correction seems perfect which is always a worry with a large chipped camera.

The tidal stream I think may be there (as you say it may not be due to some light pollution) is the bottom right down to the yellowish galaxy.

The tidal stream to the left was enhanced a bit but not by lasso.

Greg.

[renormalised]

I have a feeling that yellowish galaxy is nowhere near NGC6744. That tidal stream is just a matter of juxtaposition. But then again, I maybe wrong as I don't know how far away that small galaxy is.

There is a tidal stream there, though. See the companion above the main spiral (the "bar" running perpendicular to the spiral...it's a Magellanic Class barred irregular), there's a definite trail of stars and (most likely) gas there. As a matter of fact, if you look closely, you can see very faint OB associations in the stream. There's most likely also a degree of very distorted spiral arm from the main galaxy mixed in there as well.

[strongmanmike]

Here is a contrast enhanced view (http://www.pbase.com/strongmanmike2002/image/127365096/original)of 4.5hrs worth - can't see much there other than galactic cirrus :shrug:

[renormalised]

There's a lot of cirrus there....for sure:)

However, there's definitely distortion of the main spiral from its companion and some faint trailers there. Poor little galaxy is getting the life sucked out of it!!!:P

[strongmanmike]

Here (http://www.pbase.com/strongmanmike2002/image/103969838/original) is 3hrs 40min worth and again enhanced but this time taken from pristene dark skies at 1000m elevation, once again lots of faint cirrus everywhere but nothing else really..?

Mike

[Alchemy]

I've been watching with interest how this new scope will perform, the detail within the core is pretty much on a par with mikes much longer exposure certainly at a quick look at a lower res. However being as mike has put up his as a comparison....... The colors in the two are very different, if I had to make a choice I'd say his were on the money, and I cant see that all that extra exposure would make that much difference in the color dept..... Smoother yes, push it harder for faint detail yes but color ........ Hmmmm.
On a positive note I myself haven't done an image which in retrospect couldn't be improved. I get to a point after a couple hours of processing where you've got so many versions Im not sure just what it should look like.

[strongmanmike]

Just to clarify, I wasn't putting mine up as comparison at all, rather just referencing a deep enhanced negative and B&W version to show there was no tidal stream, that was all. I wasn't directly comparing my colour image to Gregs at all and didn't link to that version :).

Mike

[renormalised]

There's no tidal stream to where Greg mentioned...it's the cirrus, but there is one if you look at the NGC6744A and the distorted spiral arm and stream of stars from the main galaxy. It's faint and you have to know what to look for, but it's there:)

[strongmanmike]

Yeeeeeeh.... but, tidal steams are more commonly noticed around more edge on galaxies, they tend to get a bit lost when looking down on a galaxy.

Mike

[gregbradley]

Yes looking at it again I think you are right. But I just saw an R Jay Gabany 20 hour image of M83 which has been imaged to death and it had huge loopy tidal streams. I'd say these streams are pretty common but they just need super dark skies and very long exposure.





It seems there is a very faint longish spiral arm going out the bottom part like the top half has or am I seeing something out of nothing?



Hmm, very hard to say at this early point. So far the CDK picks up more detail compared to other images I have taken of the same thing. Looking at my image again it really does need the extra hours. Tonight is shaping up pretty well. I'll take some more exposure and see how it works out. Also my southern skies could be a tad darker here. I am picking up a bit of light pollution also. I did fight against a green bias in the colour and that usually means light pollution. Perhaps there was some high cloud as well. Tonight seems very clear so far.

I mainly put it up as a work in progress. I was happy to get that much out of 3 hours on this rather faint galaxy.



yep I realised that.



Also it seems to extend a bit past that irregular companion galaxy.

[strongmanmike]

Just wondering Greg, why -39C specifically? Nothing wrong with it, just seems an odd temp to run at :question:

Mike

[Bassnut]

What were the sub exposure times Greg?

[gregbradley]

I had it set to -40C and sometimes it doesn't quite make it and other times when the ambient drops it does. 39.875 for some reason.

Greg.

[gregbradley]

I've been using 10 minutes Fred. I think now I am getting nice round stars with the Paramount perhaps going back to 15 minutes may be better.

I went with 10 mins on the NJP mount because I was getting flexure with the guide scope beyond that. Its not an issue with the MMOAG.

Greg.

[strongmanmike]

Here is David Malins enhanced Schmidt plate for a comparison

[Bassnut]

OK, well it looks good generally, but the noise is a bit high. More than 10mins on LRGB is mute, given skyglow, more subs is better than longer.

Ha will shine with longer subs with the PME, on nebs.

Luckily Mike has no clue on NF, which shows on the odd inverted B/W crap he posted, thats typical, dont listen to him.

The cam temp IMO is not critical.

[Alchemy]

Sorry, the image I looked at was the 1 Meg when i looked at other versions of the same image, And yes poor choice of words on my part.
Perhaps I should have just said, the color doesn't quite seem there.

[strongmanmike]

Fred it's FNINF :P

[Bassnut]

? :shrug:

[Bassnut]

Ahh, I get it, thats a stock tip for North Rescources, nice, might invest :thumbsup:

[gregbradley]

Aah that is interesting. I see 2 faint spiral arms above and 2 faint spiral arms below. Most images do not show the bottom 2. They usually show 1 of the top 2.

I wonder how many hours of exposure that will take.

Greg.

[gregbradley]

Yes the light shades of blue are a tad off. Although the scope may be picking up the dust more prominently. I saw similar when I imaged it with an RCOS 12.5 inch. I think I'll switch to 2x2 binning for the rest of the colour. I've been using 1x1 and that gives better resolution but loses some potential signal.

Greg.

[RobF]

Impressive start Greg. There's going to be so much to learn and your colour balance and processing will no doubt take a while to get a feel for too. We all want to get going quickly, but in the end its half the fun that's nothing is easy in this hobby of course. Will be watching with great interest, and thanks for showing this early effort and describing the voyage for the rest of us.

[gregbradley]

Thanks Rob.

Learning the gear is part of the fun, I find it enjoyable finding out the best way to handle it. Nice and clear tonight although very windy. I should pickup another 5 hours on this one tonight. Fortunately my observatory is very well placed and wind is far less of a problem than it could be.

Greg.

[strongmanmike]

Fits Nothing In Narrow Field ;)

[Bassnut]

Nothing that doesnt fit NF is worth imaging. Period. :poke:

[strongmanmike]

This doesn't fit narrow field, but it was deffinitely worth imaging! :rofl:

[rally]

Thanks Greg,

Always good to read about other experiences and opinions.
Any example piccies

I am not sure that having 1:1:1 filters is really all that big an issue given that the QE spectral response of every CCD is so significantly different.
Yes - It makes life "easier" if you are doing it quick and dirty, but . . .

Some CCDs peak in the Red others in the green and some even in the blue the variation within the visible range can be up around 30% on some CCDs.
Funnily enough a friend just sent me a compiled graph of all the popular chips yesterday in relation to an asteroid we missed and why we might have missed it !!!

All OTAs introduce some degree of cast anyway - even if its miniscule - there will be variance.

Then there is up to say 10% variation (reduction) in the ADU count for the Blue end of the spectrum compared to Red just by atmospheric extinction dependent upon your imaging Alt (angle).

At the end of the day you really need to do a G2V white balance if you want reliable and consistent results - an image session across a few hours from say 40°alt to Zenith is going to skew your results considerably for the same exposure times.
If you are going lower then maybe there is a 20% difference to deal with !

If you are ignoring that then you won't be colour balanced anyway !

So the issue of 1:1:1 filters becomes moot - to a degree since these other things over whoch you have control of are going to effect things to a far greater degree.

The order in which you shoot your RGB subs is probably going to influence the result to a much greater extent !

Worth noting that some of your image scheduling and capture software can automatically provide the relevant compensation factors for all your subs for this.

Cheers