Iris 3 Panel Mosaic

[Allinthehead]

Hi all, what a great few nights over the Easter weekend. 3 clear nights in 4 days allowed me to complete what would sometimes take weeks or months.

Each panel consists of about 4 hours in 150 second subs. 

Shot with an Asi2600mc through a Tak Epsilon 160ed, mounted on an AzEq6.

Captured with sequence generator pro

Processed in APP, PI and PS.

Hope you like it,

Richard.

Ps, there's actually a flaw in the mosaic. Top of the class to anyone who spots it.😀

[Adreneline]

An inspiring image - brilliant job - flaw or no flaw - I'm for the big picture.

Adrian

[Xiga]

Gorgeous stuff Richard! Nice and bright, to bring out all that lovely dust, yet still with good stars. No easy task! Ghost is looking great too at top-left. 

It appears that to bring out dust like this, one needs 3 things. Aperture, Fast Optics, and a Very skilled hand. 👏

[vlaiv]

43 minutes ago, Allinthehead said:

Ps, there's actually a flaw in the mosaic. Top of the class to anyone who spots it.

You do understand that this sounds like a proper challenge for a pixel peeper like myself?

Such large FOVs start to suffer geometric distortion and stitching software needs to account for this by transforming from 2d into spherical coordinates - stitching in spherical coordinates and then again transforming back to 2d using one of projection techniques.

Depending on projection technique used - angles might not be preserved - angular magnification distortion.

This leads to "split hair" diffraction spikes in stars.

Did I get it, did I get it?

 

[Allinthehead]

26 minutes ago, Adreneline said:

An inspiring image - brilliant job - flaw or no flaw - I'm for the big picture.

Adrian

Thanks Adrian, much appreciated.

16 minutes ago, Xiga said:

Gorgeous stuff Richard! Nice and bright, to bring out all that lovely dust, yet still with good stars. No easy task! Ghost is looking great too at top-left. 

It appears that to bring out dust like this, one needs 3 things. Aperture, Fast Optics, and a Very skilled hand. 👏

Thanks Ciarán, fast optics and aperture certainly help also I think dark skies are very important too. Patience in processing is key too, small incremental adjustments letting the data guide where you go next.

[Allinthehead]

12 minutes ago, vlaiv said:

You do understand that this sounds like a proper challenge for a pixel peeper like myself?

Such large FOVs start to suffer geometric distortion and stitching software needs to account for this by transforming from 2d into spherical coordinates - stitching in spherical coordinates and then again transforming back to 2d using one of projection techniques.

Depending on projection technique used - angles might not be preserved - angular magnification distortion.

This leads to "split hair" diffraction spikes in stars.

Did I get it, did I get it?

 

Here's a gold star for you⭐ now go to the top of the class😆

This shows the more extreme part of the flaw. I'm assuming poor polar alignment also plays a role.

Top left of image

Bottom right

[vlaiv]

10 minutes ago, Allinthehead said:

This shows the more extreme part of the flaw. I'm assuming poor polar alignment also plays a role.

Indeed - it shows rotation well. Spikes change orientation.

You could be right - I think that polar alignment can also cause this. Not sure which was dominant cause here.

 

[Allinthehead]

On 08/04/2021 at 19:39, vlaiv said:

Indeed - it shows rotation well. Spikes change orientation.

You could be right - I think that polar alignment can also cause this. Not sure which was dominant cause here.

 

I'm assuming polar alignment is the dominant factor here as I had a fair amount of rotation between the three panels, I was forced to crop more than I would have liked as a result.

[clarkpm4242]

Beautiful image!  Very nice touch on the processing.

Something to aspire to.

Paul

[vlaiv]

17 minutes ago, Allinthehead said:

I'm assuming polar alignment is the dominant factor here as I had a fair amount of rotation between the three panels, I was forced to crop more than I would have liked as a result.

Similar thing happens when doing wide field shots. Here is example from Stellarium. When I put in Canon 750d (APS-C) and 85mm lens:

I took group of stars - two of them in particular - when I align them to the left edge - line connecting them is angled one way with respect to vertical (top star is right of vertical and bottom is left). When I align same pair of stars to the right edge - angle changes - now top star is left and bottom is right. Whole frame "rotated". In fact - both frames are 0° - aligned with RA - but RA is not straight line it is circle on celestial sphere and as you track RA / circle - your frame rotates.

This is with perfect polar align. This effect can also lead to panels being rotated one with respect to another - and they always are - it is the FOV that dictates if this will be seen or not (small FOV - very small angle of rotation).

[Allinthehead]

3 minutes ago, vlaiv said:

Similar thing happens when doing wide field shots. Here is example from Stellarium. When I put in Canon 750d (APS-C) and 85mm lens:

I took group of stars - two of them in particular - when I align them to the left edge - line connecting them is angled one way with respect to vertical (top star is right of vertical and bottom is left). When I align same pair of stars to the right edge - angle changes - now top star is left and bottom is right. Whole frame "rotated". In fact - both frames are 0° - aligned with RA - but RA is not straight line it is circle on celestial sphere and as you track RA / circle - your frame rotates.

This is with perfect polar align. This effect can also lead to panels being rotated one with respect to another - and they always are - it is the FOV that dictates if this will be seen or not (small FOV - very small angle of rotation).

Nicely demonstrated, would I be correct in assuming that the effect is greater when imaging closer to the celestial poles?

[Allinthehead]

17 minutes ago, clarkpm4242 said:

Beautiful image!  Very nice touch on the processing.

Something to aspire to.

Paul

Thanks Paul, glad you like it.

[vlaiv]

Just now, Allinthehead said:

Nicely demonstrated, would I be correct in assuming that the effect is greater when imaging closer to the celestial poles?

Indeed - mosaic that contains celestial pole will be "180° rotated"