Pacman Nebula Ha

[vlaiv]

Or to be more precise, a piece of Pacman Nebula

After quite a bit of pause I'm out and imaging again, so I after doing some PEC recording and preparation (change of gear), I decided to do quick test of Ha filter (first light).

This is result:

It is 32 x 4 minute for total of 2h and 8 minutes, scope is RC8", camera ASI1600, Baader Ha 7nm - FOV is restricted on such a large object with this focal length.

I'm just amazed by this as I image from red zone (18 mag skies) and narrowband just does not care about this. Seeing was poor and there was quite a bit of wind, so stars are bloated and resolution suffered. This image is binned x3 for effective resolution of 1.5"/pixel.

[MarsG76]

Excellent return from the imaging break... looks tops.

 

[gorann]

Promising re-start Vlaiv!

By the way, I thought binning in CMOS was just a software trick that really does not help much on matching resolution (as the pixels are not binned when detecting the photons)

[gorann]

PS. did you protect the stars while stretching? Or were they of this size also in the un-stretched subs?

[vlaiv]

3 hours ago, gorann said:

Promising re-start Vlaiv!

By the way, I thought binning in CMOS was just a software trick that really does not help much on matching resolution (as the pixels are not binned when detecting the photons)

You can think of it as a trick, but it is "legitimate" thing to do. It differs slightly from hardware bin in that you are binning each pixel with its own read noise, while with CCD binned pixels get only one read noise. So it produces slightly less SNR gain, but it still improves SNR. On the other hand it is not good as resampling, due to pixel size induced blur (which is small compared to seeing / tracking blur at these resolutions), but simple resampling is providing even less SNR gain over software binning. So it's sort of a compromise. But it does "sharpen" up appearance of image and makes stars look smaller (matches sampling resolution to actual level of information in image in this case). I usually bin x2 to get 1"/pixel but sometimes if seeing is bad 1"/pixel is still undersampled and binning more pixels does not result in loss of detail while it provides more SNR.

3 hours ago, gorann said:

PS. did you protect the stars while stretching? Or were they of this size also in the un-stretched subs?

I didn't do any "fancy" processing on this one, no star masks or special attention to not getting blown / swollen stars. Just regular calibration, simple stack method (average) and Level / Curves in Gimp. I did "masked" noise reduction in very faint background regions (I do this by creating copy of initial layer, do noise reduction on this copy, add layer mask on this by using same denoised data and then invert mask - dark areas become light while light areas become dark and masked of, so only darkest parts of image - where there is noticeable noise get denoised - I usually blend in this layer somewhere between 30-50% depending on how much noise I want to mask off).

You can see how much seeing was causing trouble - look at diffraction spikes - they are blurred even at this resolution - they should be very sharp in good seeing.

[Rodd]

Looking good.  How was your focus?  The central star--the big one, is really a multiple system that is hard to reveal but when focus is nailed it shows up.  You have a  bulge, so you are almost there.  Won't take much

Rodd

[vlaiv]

22 minutes ago, Rodd said:

Looking good.  How was your focus?  The central star--the big one, is really a multiple system that is hard to reveal but when focus is nailed it shows up.  You have a  bulge, so you are almost there.  Won't take much

Rodd

Not 100% sure about focus, I focused at 3/4 out in field to try combat edge of field curvature in RC, so center might have not been in perfect focus, but then again, it was really hard to tell due to poor seeing, probably local thermals (heating season starting, and target was slightly due north from my location - that means over houses) and wind.

You are right about central stars, they are "resolved" in stack - this is screen shot of x2 bin, only slight linear stretch:

So all three stars are there, almost fully resolved, but due to variation between seeing in frames - there are substantial "wings" on stars - give it enough stretch and they merge in single "blob"

[tooth_dr]

That’s a wonderful PacMan. I’ve spent a few days staring at my own as I’ve been processing it and I’ve really started to notice lots of little details.  Yours really has a nice depth. 

[Rodd]

4 minutes ago, vlaiv said:

Not 100% sure about focus, I focused at 3/4 out in field to try combat edge of field curvature in RC, so center might have not been in perfect focus, but then again, it was really hard to tell due to poor seeing, probably local thermals (heating season starting, and target was slightly due north from my location - that means over houses) and wind.

You are right about central stars, they are "resolved" in stack - this is screen shot of x2 bin, only slight linear stretch:

So all three stars are there, almost fully resolved, but due to variation between seeing in frames - there are substantial "wings" on stars - give it enough stretch and they merge in single "blob"

Poor seeing will get you every time.  I don't have much experience with thermals as I use refractors mostly, and the C11Edge is a closed system--I guess it could have thermals seeing the volume is much greater.  It does have vents, and I have considered getting a fan for fater equilibration.

Rodd

[vlaiv]

1 minute ago, Rodd said:

Poor seeing will get you every time.  I don't have much experience with thermals as I use refractors mostly, and the C11Edge is a closed system--I guess it could have thermals seeing the volume is much greater.  It does have vents, and I have considered getting a fan for fater equilibration.

Rodd

I was not thinking about tube thermals - RC is open system, and I did spend like 2 hours of PEC capture / training prior to this, so it has cooled properly - I was referring to local thermals from surrounding houses / chimneys. These are worse than regular seeing - stars jump around much more - rather than just blurring. I was guiding with RMS between 1.2" and 0.7" with occasional jumps to even 3" - all due to wind and local thermal turbulence.

[Rodd]

So that's why my FWHM is not as good as it should be when I am shooting toward the north-west, which is the darkest part of my sky--but it is over the house.  That explains it.

Rodd

[peter shah]

love the scale....nice work