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Old 27-11-2023, 03:28 PM
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Peter Ward
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Spider Season.

I must admit not to be a fan of weirdly coloured Tarantulas...

The colours of Nature already does some more than interesting things with them,
particularly the glowing variety.

Like subtle dust and tints of ionized oxygen.

With that in mind, here's my take
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  #2  
Old 27-11-2023, 06:20 PM
John W (John Wilkinson)
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Really nice image Peter with bright colours and depth. What was the exposure time?

Cheers, John W
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Old 27-11-2023, 06:49 PM
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Really nice image Peter with bright colours and depth. What was the exposure time?

Cheers, John W
Ta. There's around 2 hours of Ha and 1 hour per RG&B channel.

The Tarantula is quite red, hence the temptation is to let the h-alpha component swamp the image.

But there are some really blue stars and OIII in the mix. The area is hardly monochrome but certainly NOT Teal, Yellow, Brown or Olive.

I think I've got the colour about right....but like so many deep sky objects with a large dynamic range there could be small but valid variations that are more pleasing to the eye.
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Old 28-11-2023, 09:56 AM
keller60 (Bill)
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Wow!


This one reminds me of your NASA APOD a while back...but this field is wider
and looks more finely resolved. I think you've taken it up a notch.



A benchmark image for sure.


Thanks for posting
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Old 28-11-2023, 10:07 AM
Dave882 (David)
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Thatís a beauty Peter. Youíve handled the dynamic range expertly and the detail in the super bright areas is brilliant. I love this colour rendition, although I also donít mind seeing the green/blue hues. Interestingly, through the eyepiece, probably because of my natural ocular deficiencies, it looks entirely blue/green to me!
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Old 28-11-2023, 10:24 AM
TrevorW
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Nice one Peter
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Old 28-11-2023, 10:48 AM
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Looks good Peter. Is this a recent image? I thought you were selling the Alluna at one stage.

Greg.
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Old 28-11-2023, 11:09 AM
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Quote:
Originally Posted by gregbradley View Post
Looks good Peter. Is this a recent image? I thought you were selling the Alluna at one stage.

Greg.
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Originally Posted by TrevorW View Post
Nice one Peter
Quote:
Originally Posted by Dave882 View Post
That’s a beauty Peter. You’ve handled the dynamic range expertly and the detail in the super bright areas is brilliant. I love this colour rendition, although I also don’t mind seeing the green/blue hues. Interestingly, through the eyepiece, probably because of my natural ocular deficiencies, it looks entirely blue/green to me!
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Originally Posted by keller60 View Post
Wow!...........
Thanks Gents. The Ha is archive data...the RGB is new.

As for selling the Alluna...well, while the images it has produced has won some major prizes (e.g. Royal Greenwich)
it really doesn't get used much anymore...hence I should probably sell it.

...but.... the market in OZ is such that I'd have to sell it for a fraction of its replacement cost.

They are silly money now. A new one with Zerodur optics etc. will run $AUD90k.

I'd accept a bit over half price, but to quote from The Castle. Probably Dreamin'

Plus this is still a faint possibility of getting a property on the NSW south coast...
A dark sky and RC16 running at F6.0 ...... hummmm!

Last edited by Peter Ward; 28-11-2023 at 11:40 AM. Reason: typo
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Old 28-11-2023, 11:45 AM
Startrek (Martin)
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As always, itís a pleasure to look at your work
Lovely natural image and the stars are magnificent
Iíve gotta get off NB ( Ha ) fever and start putting those RGB filters to good use ( obviously when the moons not around )
Regarding the NSW south coast , I wouldnít wait too much longer , prices are going off the Richter scale. Developers are pushing further south as well ( our place is only 2.5 hrs drive to Sydney which is ideal as we have a bunch of kids and grandkids)
I bought my place in 2016 and itís nearly tripled in price ( I have a small ocean view through the trees located 120m from the beach. Places near the beach with water views have tripled in price or more. Itís ridiculous

Cheers
Martin
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Old 28-11-2023, 02:12 PM
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As always, itís a pleasure to look at your work
Lovely natural image and the stars are magnificent
Iíve gotta get off NB ( Ha ) fever and start putting those RGB filters to good use ( obviously when the moons not around )
Regarding the NSW south coast , I wouldnít wait too much longer , prices are going off the Richter scale. Developers are pushing further south as well ( our place is only 2.5 hrs drive to Sydney which is ideal as we have a bunch of kids and grandkids)
I bought my place in 2016 and itís nearly tripled in price ( I have a small ocean view through the trees located 120m from the beach. Places near the beach with water views have tripled in price or more. Itís ridiculous

Cheers
Martin
Thanks Martin. Hey, narrow band has its place, particularly if you are in the urban imaging space. RGB is always a challenge from the 'burbs whereas NB can be got most nights and certainly can be fun.

Though I am somewhat over the urban camo palettes that come and go like last year's catwalk fashions.

As for the south coast....yep...would be much cheaper to go bush....but chief financial advisor and one that must be obeyed, will have none of that, hence I keep looking.
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Old 28-11-2023, 06:59 PM
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Details and structure look great Peter, a pleasing result.

Last edited by Andy01; 28-11-2023 at 10:11 PM.
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Old 28-11-2023, 08:46 PM
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Details and structure look the great Peter, a pleasing result.
Thanks for the tip o' the hat. I think the framing is about right...but
the seeing (something larger apertures reveal quite well) was not
so good for the Red channel.

Always room for improvement in the inevitable re-shoot
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Old 02-12-2023, 03:59 PM
matlud (Mathew)
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Very nice Peter, I like the palette which works very well here.
CS, Mat
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  #14  
Old 03-12-2023, 08:45 AM
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Very nice Peter, I like the palette which works very well here.
CS, Mat
Ta mat. But no palette used here. it's essentially RGB i.e. natural colour.

Gosh, now there's a concept!
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  #15  
Old 03-12-2023, 07:47 PM
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Once upon a time in a galaxy far, far away, there was this fellow called
Dr David Malin who revealed the universe to the world in real and natural colour.

While there has been some opinion, masquerading as fact, about the real colour of the Tarantula nebula is being "dealers choice". This is simply false.

Work done...sometime ago...by Helmholtz pretty much established the colour theory of how a warm human eye perceives the world.

Film, sensor and camera manufacturers like Kodak, Ilford, Nikon, Canon etc. then went to some effort to deliver technology that faithfully reproduced colour
on print, digital screens and other media. Wedding photographers who constantly make the bride's face look green generally don't last long hence colour fidelity was paramount.

The problem for astrophotographers is most astronomical objects are really dim
and simple observation doesn't work on them.

Ever wonder why the backyard looks like shades of grey under moonlight?
The photopic cells in you retina (cones that sense red, green and blue light) become dormant and the scoptic cells (rods) which don't register colour, do all the sensing. The point?

When looking at the sky, we don't have vision sensitive enough to perceive the real colour of deep sky objects. Yet this colour is just as real and consistent as your
green (or maybe yellow ) lawn or favourite flower when seen under the light of day.

Seems the lost art, that Malin laid the foundations to, is to take calibrated deep exposures in Red Green and Blue light, then combine them to create a full and *accurate* colour image.

Pointing your imaging rig at a colour test chart, then taking red, green, blue exposures....or simply adjusting the RGB gain on a *OSC camera will get you close. (*full spectrum OSC...daylight cameras filter out H-alpha light)

And guess what? The Tarantula nebula really is shades of red.

If it isn't, then some other part of the spectrum has been added to the mix.
There are no rules that forbid this. Only colour fidelity is lost.

Last edited by Peter Ward; 03-12-2023 at 08:00 PM.
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Old 03-12-2023, 08:25 PM
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Quote:
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And guess what? The Tarantula nebula really is shades of red.

If it isn't, then some other part of the spectrum has been added to the mix.
There are no rules that forbid this. Only colour fidelity is lost.

Hi Peter,
I just checked the stacked results of RGB for my Tarantula data from 2014
and there is clearly a strong signal in all RGB channels
not just the Red channel -
so I don't know why your picture is mostly Red
even though it's a superb picture?

cheers
Allan
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Old 03-12-2023, 08:32 PM
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Hi Peter,
I just checked the stacked results of RGB for my Tarantula data from 2014
and there is clearly a strong signal in all RGB channels
not just the Red channel -
so I don't know why your picture is mostly Red
even though it's a superb picture?

cheers
Allan
Did you calibrate for the sensor's spectral sensitivity and filter transmission?

BTW Malin's AAO renditions, while lacking some of the dynamic range of current tech, are also red.
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Old 03-12-2023, 08:51 PM
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Did you calibrate for the sensor's spectral sensitivity and filter transmission?

BTW Malin's AAO renditions, while lacking some of the dynamic range of current tech, are also red.

Hi Peter,
no -
I put each of all 5 stacked and registered frames into NASA FITS Liberator
to do the stretching for me.
I suppose that normalises the output due to high compression?

Did you allow for the sensor's spectral sensitivity and filter transmission?
Most sensors drop away from the peak quantum efficiency for Blue and Red.
So anyway -
I am now looking at 5 pictures of LRGB Ha
and they all have strong signal.
I think I would know if the output was wrong as
the White balance would be out?
Bright stars come out as White - usually - although
that can be from exceeding the well depth.

cheers
Allan
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Old 03-12-2023, 09:13 PM
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Hi Peter,
no -
I put each of all 5 stacked and registered frames into NASA FITS Liberator
to do the stretching for me.
I suppose that normalises the output due to high compression?

Did you allow for the sensor's spectral sensitivity and filter transmission?
Most sensors drop away from the peak quantum efficiency for Blue and Red.
So anyway -
I am now looking at 5 pictures of LRGB Ha
and they all have strong signal.
I think I would know if the output was wrong as
the White balance would be out?
Bright stars come out as White - usually - although
that can be from exceeding the well depth.

cheers
Allan
I didn't invent the physics. It was tried and tested long ago.

You've already noted that blue and red ends of a sensor have lower QE...hence you need exposures to account for this get a correctly balanced colour exposure.

As I mentioned, shoot and process a colour test chart and get a handle on both filter curves and sensor QE. You may be surprised how colours don't match the chart when its held next to a monitor.
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Old 03-12-2023, 09:20 PM
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Quote:
Originally Posted by Peter Ward View Post
I didn't invent the physics. It was tried and tested long ago.

You've already noted that blue and red ends of a sensor have lower QE...hence you need longer exposures to get a balanced exposure.

As I mentioned, shoot and process a colour test chart and get a handle on both filter curves and sensor QE. You may be surprised how colours don't match the chart when its held next to a monitor.
That's true,
in the end we're just having fun -
we're not trying to be scientists and in fact
even the Hubble and JWST pictures take liberties with absolute values
of brightness from different filters for their published pictures.

Look at the Hubble pics for Ha, S2 & O3 filters.
Ha is much brighter than the other 2 but they normalise it
to make an interesting picture and it shows which elements are shining
and where they are and their relevant structures.
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