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Author Topic: Deep blue fringing on OOF objects against the sky  (Read 13402 times)

bobtrlin

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Deep blue fringing on OOF objects against the sky
« on: January 15, 2018, 09:28:20 pm »

What causes the deep blue fringing one gets around out of focus objects against a bright blue sky?  I often get this on fine branches.  Is this a function of lens quality?  I've been unable to remove it using LR's lens correction tools.
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Two23

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Re: Deep blue fringing on OOF objects against the sky
« Reply #1 on: January 15, 2018, 11:29:39 pm »

Most likely it is purple fringing, also known as "chromatic aberration," or "CA."  It is a lens defect. 


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Bart_van_der_Wolf

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Re: Deep blue fringing on OOF objects against the sky
« Reply #2 on: January 16, 2018, 04:11:33 am »

What causes the deep blue fringing one gets around out of focus objects against a bright blue sky?  I often get this on fine branches.  Is this a function of lens quality?  I've been unable to remove it using LR's lens correction tools.

Hi,

Hard to say without an example. May be caused by the lens, by the Raw converter, or by post-processing (sharpening/clarity).

Cheers,
Bart
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Hening Bettermann

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Re: Deep blue fringing on OOF objects against the sky
« Reply #3 on: January 16, 2018, 04:49:47 pm »

Sounds like Purple Fringing, most likely. Caused by longitudinal chromatic aberration, as opposite to lateral CA. A limitation of the lens. Raw Therapee, which is free, has an excellent tool to remove it.

bobtrlin

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Re: Deep blue fringing on OOF objects against the sky
« Reply #4 on: January 17, 2018, 08:13:42 pm »

This is a crop.  It shows the blue fringing around the fine branches against the sky.  There is purple CA in places as well.  I can easily remove the purple with LR's defringing tool but I can't remove the blue.  The fact that it's such a deep blue against a light blue sky, really detracts from the image.
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Hening Bettermann

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Re: Deep blue fringing on OOF objects against the sky
« Reply #5 on: January 17, 2018, 08:27:39 pm »

I think the primary problem with these branches ist that they are out of focus, so they can not be expected to be perfect.

bobtrlin

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Re: Deep blue fringing on OOF objects against the sky
« Reply #6 on: January 17, 2018, 09:20:52 pm »

I appreciate that but why are they a blue blur?  There seems to be more blue in the blurred branches than in the sky behind them.  Maybe the blurred branches are simply darkening the blue background making the blue appear more intense.  It would be interesting to see if the same thing happens with a lens known to have a good bokeh or exceptionally low CA.  I live in a country with deep blue skies and much sun and am often plagues with this effect when trying to blur the background.
« Last Edit: January 18, 2018, 10:17:54 pm by bobtrlin »
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ErikKaffehr

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Re: Deep blue fringing on OOF objects against the sky
« Reply #7 on: January 17, 2018, 09:38:30 pm »

Hi,

It is called longitudinal chromatic aberration also know as axial chroma. It cannot be corrected, really.

Very few lenses are fully corrected for axial chroma. The list essentially consists of the three Otuses, the Coastal Optics 60/4 APO VIR, the Voigtlander APO Lantars, most of the Fuji GFX lens designs Regarding and the Hasselblad Super Achromats. Hasselblad X lenses I don't know.

Best regards
Erik


This is a crop.  It shows the blue fringing around the fine branches against the sky.  There is purple CA in places as well.  I can easily remove the purple with LR's defringing tool but I can't remove the blue.  The fact that it's such a deep blue against a light blue sky, really detracts from the image.
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Erik Kaffehr
 

David Sutton

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Re: Deep blue fringing on OOF objects against the sky
« Reply #8 on: January 18, 2018, 04:12:57 pm »

This is a crop.  It shows the blue fringing around the fine branches against the sky.  There is purple CA in places as well.  I can easily remove the purple with LR's defringing tool but I can't remove the blue.  The fact that it's such a deep blue against a light blue sky, really detracts from the image.
Hi.
This is pretty quick to remove in an image editor like Photoshop. I hope you don't mind my having a go at you photo.
I created a hue/saturation layer and used the target adjustment tool to identify the colour, desaturated it and then brushed in the desaturation. Then used the colour picker to select the original sky colour and brushed that back in on a new layer, blend mode  set to "colour".
Sometimes in really difficult cases you get shifts in luminosity along the edges of branches after desaturation, and have to use a curves layer to deal with it.
David
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Hening Bettermann

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Re: Deep blue fringing on OOF objects against the sky
« Reply #9 on: January 18, 2018, 04:53:26 pm »

David do I understand that right: You manually painted all these branches?

David Sutton

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Re: Deep blue fringing on OOF objects against the sky
« Reply #10 on: January 18, 2018, 06:32:50 pm »

David do I understand that right: You manually painted all these branches?
No  :)
I set the layer mask to black and quickly brushed the entire sky. That left it a sort of off-white, thus the need to restore some blue.
David
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Hening Bettermann

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Re: Deep blue fringing on OOF objects against the sky
« Reply #11 on: January 18, 2018, 09:00:19 pm »

Thank you.

bobtrlin

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Re: Deep blue fringing on OOF objects against the sky
« Reply #12 on: January 18, 2018, 10:10:37 pm »

Hi.
This is pretty quick to remove in an image editor like Photoshop. I hope you don't mind my having a go at you photo.
I created a hue/saturation layer and used the target adjustment tool to identify the colour, desaturated it and then brushed in the desaturation. Then used the colour picker to select the original sky colour and brushed that back in on a new layer, blend mode  set to "colour".
Sometimes in really difficult cases you get shifts in luminosity along the edges of branches after desaturation, and have to use a curves layer to deal with it.
David
Fantastic David!  Thanks for that.
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