IC 5146 / C19 - Cocoon nebula - quick & dirty snapshot

[vlaiv]

This one I took yesterday evening, after doing a "round" of collimation of primary on my RC8" to check if things have improved.

Indeed, stars look much nicer than my previous shot of M27, but there is still room for improvement (left hand side is still out of focus, probably a bit more at the top), but I'm really pleased with my first attempt on collimation of primary for RC (did not use any fancy equipment, just cam, bahtinov mask, Sharpcap and eyeball mark I).

I messed up flats, well actually it seems that dust particle settled on the filter between shooting and taking flats (which is really amazing since it took me about 2 minutes, to put flat panel on and start taking flats after I finished with lights, but it was probably due to manually rotating OTA to point up from parked position).

This is 120x60s with ASI1600, IDAS LPS P1, excellent seeing (my guess is 1" or less, guiding was good 0.5-0.6" RMS with occasional drop to 0.4" RMS), transparency was really poor, and temperature high (ASI1600 struggled to keep temp -20C, for most of the subs it was -19.7C with cooler on 100%)

Just basic calibration, stretch and a bit of noise reduction. Not a showpiece work, but I thought of posting it never the less, it might be of use as a reference to someone.

Thanks for looking!

[Rodd]

Now that's what I am talking about!  If you look at my luminance on the fist page as well, you get buried in stars--yours seems to have far fewer....ah, maybe its Ha?  That would explain it.  Awesome capture.  Clear as a bell.  The stars do look sharp.

Rodd

[vlaiv]

1 hour ago, Rodd said:

Now that's what I am talking about!  If you look at my luminance on the fist page as well, you get buried in stars--yours seems to have far fewer....ah, maybe its Ha?  That would explain it.  Awesome capture.  Clear as a bell.  The stars do look sharp.

Rodd

No, it's not Ha, it is Lum with IDAS LPS P2 (I wrote in original post P1 by mistake), so it is just light pollution suppression filter.

I think explanation for fewer stars is: my shot is less wide field, focused on central nebulosity (same size chip but at greater focal length - yours is 1000mm with KAF8300, mine ASI 1600 with 1625mm), so there are much more stars visible in surrounding area, and in part that gives off impression of many more stars. Second is of course, I had really good seeing conditions, coupled with decent guiding and bigger aperture - smaller FWHM, so stars look less dense because of that, and third, most important factor is SNR. I think your image has better SNR, since you managed to get 200 mins vs 120 mins of exposure, and my shot was made in not so good conditions (red zone, around 18" mag skies, with rather poor transparency - hot, humid summer night, with temps around 25C, and according to Copernicus AOD of around 0.5). This of course means that you were able to stretch your image more (compare three galaxies next to nebula, yours are clearly visible, mine not so much, just identifiable) and fainter stars look brighter so they pop out.

[Allinthehead]

Very nice. How are you finding the asi 1600?

[vlaiv]

2 hours ago, Allinthehead said:

Very nice. How are you finding the asi 1600?

For me, it's a treat to work with. I'm used to CMOS cameras, have not used any CCD in fact, only CMOS, and it suits my work style. I don't have much trouble with number of subs / amount of data, and processing, so I favor low read noise / shorter subs solution.

I might add that I'm using custom processing stack, from calibration, alignment to stacking. I don't think I would be able to use DSS for this cam.

Only two minor issues so far with it. I had trouble first time I plugged it in - computer did not recognize the hardware, but I suspect it was due to having guider plugged into usb hub on cam, and I guess it just got confused. After I disconnected everything and plugged in only ASI1600 it worked like a charm (and ever since, without a glitch).

Second thing that I noticed is that chip is rather reflective (or it might be the front glass), when using LPR filter I get those ghost reflections of unfocused light on bright stars. This will probably be solved by moving filter down the light path (but it will require 2" filter instead of 1.25" one I'm using so far). Not yet sure how it will behave with RGB and narrow band filters in regard to this, but can hardly wait to find out (next on my purchase list, I'm really a newbie, second year in astronomy and imaging).

[Allinthehead]

12 hours ago, vlaiv said:

I might add that I'm using custom processing stack, from calibration, alignment to stacking. I don't think I would be able to use DSS for this cam.

That's interesting, what's the issue with dss, as i use it for Asi1600?

12 hours ago, vlaiv said:

I'm really a newbie, second year in astronomy and imaging

Same here. As regards the reflections, i was getting them with my 80 ed. They disappeared when i changed to Star 71, and samyang 135.

Richard.

[vlaiv]

39 minutes ago, Allinthehead said:

That's interesting, what's the issue with dss, as i use it for Asi1600?

Main issue that I found with DSS is that it is memory limited, it often crashes on large files, and lots of them. Second thing is, and this is my assumption, not really sure about it, but when experimenting I found that it might be true, DSS uses 16bit arithmetic for calibration (not sure for rest of the stack, it does produce 32bit output). My reasoning / calculation show that when using lots of frames, and I tend to really use lots of frames, because exposure is short, and download is fast, and it helps with controlling the noise, one really needs to use 32bit precision from the start, both in calibration and in stacking.

I do have couple of algorithms "in the pipeline" (meaning in my head, I just can't find the time to put it in the code, hopefully soon) that I think are going to further improve results (like frame equalization with gradient removal - for LP, supersampling alignment, variable resolution stacking - again with supersampling, auto deconvolution in stacking - to minimize FWHM and enhance image, etc ...)

That is why I use ImageJ to do data reduction - it gives me flexibility to choose operations and write custom plugins for processing.

[Rodd]

I had a look at mine compared to yours and I notice a ring structure at top in yours that is not in mine.  What is that?  Strange that mine has better SNR and many more stars but not that feature.  BTW I do see the galaxies--3 of them! I had never seen Thanks.  Looking forward to seeing more of your image!

 

Rodd

[vlaiv]

1 minute ago, Rodd said:

I had a look at mine compared to yours and I notice a ring structure at top in yours that is not in mine.  What is that?  Strange that mine has better SNR and many more stars but not that feature.  BTW I do see the galaxies--3 of them! I had never seen Thanks.  Looking forward to seeing more of your image!

 

Rodd

It is calibration artifact

It seems that dust particle managed to settle down either by the end of imaging session, thus not being on all light frames, or I reckon more probable, between lights and flats. Although it took me like 2 minutes to fetch flat panel and mount it on scope and start taking flats, I did move scope manually to point it up (so that flat panel can rest on top) after parking - and it might be that this procedure caused very loose particle to fall of something in imaging train and land on filter.

Funny enough, I did not think of it that much since I've seen it in flats, until a member on the other board asked me "What is that planetary nebula on the top, can't seem to find it elsewhere on images"

[Allinthehead]

34 minutes ago, vlaiv said:

Main issue that I found with DSS is that it is memory limited, it often crashes on large files, and lots of them

Yes i found the same problem when i tried to stack over 800 frames. I've decided to go to 120 second minimum exposure length to reduce number of frames.

[Rodd]

7 hours ago, vlaiv said:

It is calibration artifact

It seems that dust particle managed to settle down either by the end of imaging session, thus not being on all light frames, or I reckon more probable, between lights and flats. Although it took me like 2 minutes to fetch flat panel and mount it on scope and start taking flats, I did move scope manually to point it up (so that flat panel can rest on top) after parking - and it might be that this procedure caused very loose particle to fall of something in imaging train and land on filter.

Funny enough, I did not think of it that much since I've seen it in flats, until a member on the other board asked me "What is that planetary nebula on the top, can't seem to find it elsewhere on images"

WOW---That is a strange donut for sure--it really looks like a nebula.  Most dust motes or other things that flats take care of look like dust motes or donuts or specs or smudges.  Not this one.  By the way--nice presentation.

Rodd