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Purple fringing with Samyang 8mm
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PostPosted: Thu Apr 28, 2011 10:08 pm    Post subject: Purple fringing with Samyang 8mm Reply with quote
Hello.
I have a little problem with purple fringing with my Samyang 8mm (labeled as "Walimex Pro 8mm 3.5")

Especially on HDR-pictures it's very strong (look at the bikes in the right corner)

Kiel@Night von Chloressigsäureethylester on Flickr
(The picture is taken at F8. The little fog-spot near the middle is a finger-print, the small spots is sticky dust on my sensor)

Is that normal? Is it removable? With which software?

Thx

Last edited by ForenSeil on Thu Apr 28, 2011 11:49 pm; edited 2 times in total


PostPosted: Thu Apr 28, 2011 10:16 pm    Post subject: Reply with quote
Wow Surprised

That is an INCREDIBLE shot! Shocked

Purple fringing can sometimes be removed in RAW, I use Adobe Camera RAW. However, in many cases it's not that straight forward and you end up needing to lower the purple saturation.


PostPosted: Thu Apr 28, 2011 10:23 pm    Post subject: Reply with quote
In an 8mm fisheye lens, chromatic aberrations are nearly unavoidable.
However your picture is so artifact by post processing, that I don't see why it should be really a problem: just use "replace colour" in photoshop, click with eyedropper on the purple and replace it with one of the shades of orange of your picture. Nobody will ever detect or question the replacement, in that context.
I actually personally think that the purple fringing in this picture provides a nice change from the yellow-orange tint of the rest of the photo, the purple being almost the complementary colour.
It would have been a more nasty problem if your photo was realistic. Then to remove a purple fringing would have been harder. One technique (which may work well or not so well, depending on the single image) is to open the hue-saturation tab, select "magenta" as colour, then click eyedropped on the purple fringed area, and then lower saturation until it goes away (hopefully not influencing other nearby colours).


PostPosted: Fri Apr 29, 2011 5:04 am    Post subject: Re: Purple fringing with Samyang 8mm Reply with quote
ForenSeil wrote:

I have a little problem with purple fringing with my Samyang 8mm (labeled as "Walimex Pro 8mm 3.5")


That is lateral chromatic aberration, not purple fringing. Notice it's red and green towards the edges, no purple.

I got this too in some scenes with the Samyang fisheye. I'm pretty sure you can fix it with software. My Pentax camera software (based on Silkypix) includes correction for aberrations and it managed to reduce these quite a bit.


PostPosted: Fri Apr 29, 2011 1:04 pm    Post subject: Reply with quote
I think one can create lens profiles for Lightroom 3, which should be able to remove the CA quite reliably. Not sure how much effort it is to create one -- apparently you have to print out charts and photograph them --, but there might be a profile available on the web already.

That is of course, if you use Lightroom. Smile

PS. Very nice capture.


PostPosted: Fri Apr 29, 2011 4:42 pm    Post subject: Reply with quote
You don't need to create a color profile to correct CA, it's enough to save the settings and you can choose to have them applied automatically on images at import time (although I would not recommend that if you use other lenses also in the same day). Another possiblity also very fast, you select one image of 8mm lens, correct the CA, then by use of Ctrl or Shift you select the other images of the 8mm lens, then "Sync Settings".


PostPosted: Fri Apr 29, 2011 6:44 pm    Post subject: Re: Purple fringing with Samyang 8mm Reply with quote
Laurentiu Cristofor wrote:
That is lateral chromatic aberration, not purple fringing. Notice it's red and green towards the edges, no purple.


Lateral CA isn't red/green by definition. It can also be blue/yellow or a combination of both. It all depends on how well corrected the lens is.


PostPosted: Fri Apr 29, 2011 7:39 pm    Post subject: Reply with quote
Orio wrote:
You don't need to create a color profile to correct CA, it's enough to save the settings and you can choose to have them applied automatically on images at import time (although I would not recommend that if you use other lenses also in the same day). Another possiblity also very fast, you select one image of 8mm lens, correct the CA, then by use of Ctrl or Shift you select the other images of the 8mm lens, then "Sync Settings".
Yes, of course. I always have troubles with doing manually, so I thought an actual lens profile might be the easier way.


PostPosted: Sat Apr 30, 2011 12:15 am    Post subject: Reply with quote
Thank you all very much for the answers Smile


PostPosted: Sat Apr 30, 2011 6:46 am    Post subject: Re: Purple fringing with Samyang 8mm Reply with quote
AhamB wrote:
Laurentiu Cristofor wrote:
That is lateral chromatic aberration, not purple fringing. Notice it's red and green towards the edges, no purple.


Lateral CA isn't red/green by definition. It can also be blue/yellow or a combination of both. It all depends on how well corrected the lens is.


Right, I didn't say it has to always be red/green. It's not purple and occurs towards the margins only, while purple fringing isn't limited to the edges of the frame and doesn't have an opposite color fringing showing up.
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