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Archive 2012 · Is this purple fringing on 35L?
  
 
fahadm
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p.1 #1 · p.1 #1 · Is this purple fringing on 35L?


Just got back from Barcelona and noticed these purple lines in high contrast areas of photo below:

Bareclona Crepe

Is this normal, or do I have a faulty lens. Maybe these B&W UV filters make things worse?

Gear:

1. Canon 5D mkii
2. 35L shot at f/2.0 and 1/200
3. B&W UV filter

Thanks a million for your time/feedback



Oct 05, 2012 at 12:13 PM
Monito
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p.1 #2 · p.1 #2 · Is this purple fringing on 35L?


Nope, not birefringence.

That's ordinary chromatic aberration. Notice how it is magenta on one side of a bright object and green on the other; I'm looking at a shoe lace at the bottom left and Nike logo bottom center. With dark objects against light tones it would also be green on one side and magenta on the other, but on the outsides.

Notice also how it shifts to the other way on the other side (white paper, white shoes, right edge middle) There the green and magenta swap sides from the left side of the photo.

Birefringence is magenta all around and occurs prominently with things like sparkling backlit water.



Oct 05, 2012 at 12:33 PM
fahadm
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p.1 #3 · p.1 #3 · Is this purple fringing on 35L?


Monito: thank you very much for your informative response. Much obliged.


Oct 05, 2012 at 01:12 PM
thedigitalbean
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p.1 #4 · p.1 #4 · Is this purple fringing on 35L?


Monito is largely correct but the terms are not.

What you see in that image is lateral (or transverse) chromatic aberration, rather than axial (or longitudinal) chromatic aberration which is what Monito is referring to as birefringence.

More about CA:

http://en.wikipedia.org/wiki/Chromatic_aberration

More about birefringence:

http://en.wikipedia.org/wiki/Birefringence

More about purple fringing:

http://en.wikipedia.org/wiki/Purple_fringing



Oct 05, 2012 at 02:53 PM
Monito
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p.1 #5 · p.1 #5 · Is this purple fringing on 35L?


Canon calls it birefringence, especially in reference to the 85 mm f/1.8.

[on edit:] I'm not finding references from Canon to birefringency, so perhaps they have changed their tune. I'll stop using the term and defer to the previous poster.



Oct 05, 2012 at 02:56 PM
Bacalhau
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p.1 #6 · p.1 #6 · Is this purple fringing on 35L?


I would have to look at shots with my Canon 35L again, because I don't recall to see so much CA. Only lens I ever seen so much, was on a ef 8-15mm loaner from CPS


Oct 05, 2012 at 04:15 PM
jeraldcook
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p.1 #7 · p.1 #7 · Is this purple fringing on 35L?


Bacalhau wrote:
I would have to look at shots with my Canon 35L again, because I don't recall to see so much CA.


I don't recall seeing that much CA on my 35L either and I'm pretty sure I would have noticed.



Oct 05, 2012 at 04:20 PM
 

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Monito
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p.1 #8 · p.1 #8 · Is this purple fringing on 35L?


Chromatic aberration is stronger in out of focus areas, because lenses are optimized for best performance at the plane of focus (no surprise).

In the example photo, the focus is on the wall in the back, and the kids near the wall are relatively in focus but not quite that sharp, and their feet and leaning forward heads and hands are not as sharp. Those are precisely the areas in the photograph with the CA.

It was shot at f/2, which even at 35mm would have shallow Depth of Field that close and that large.

Thus it is not surprising that others would have the impression of less CA with that lens.



Oct 05, 2012 at 05:12 PM
fahadm
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p.1 #9 · p.1 #9 · Is this purple fringing on 35L?


In order to have a fair assessment, I've uploaded the untouched file, conversion from RAW by LR3.6. The version on the first post had a LR filter applied (A-GAME2).

Also note that I did not use a tripod and had the B&W UV filter on.

Unedited Photo

Is above CA normal for a 35L?

P.S. I've never dropped my camera/lens, but who knows what happened during shipping or when not around!



Oct 05, 2012 at 05:37 PM
Monito
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p.1 #10 · p.1 #10 · Is this purple fringing on 35L?


fahadm wrote:
Is above CA normal for a 35L?


It's normal for any lens in out of focus areas. The wall behind the kids is the plane of focus. Their shoes and the paper where you see the CA are out of the Depth of Field.



Oct 05, 2012 at 05:55 PM
fahadm
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p.1 #11 · p.1 #11 · Is this purple fringing on 35L?


Monito: just saw your earlier post. Thanks again for your response. The autofocus decided to shoot the back-wall (i.e. blame shifting ).

Witnessing how difficult it is to shoot the unexpected, I have even more appreciation for photojournalists and street photographers. How can they do so much in such little time?



Oct 05, 2012 at 06:01 PM
Ralph Conway
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p.1 #12 · p.1 #12 · Is this purple fringing on 35L?


fahadm wrote:
Monito: just saw your earlier post. Thanks again for your response. The autofocus decided to shoot the back-wall (i.e. blame shifting ).

Witnessing how difficult it is to shoot the unexpected, I have even more appreciation for photojournalists and street photographers. How can they do so much in such little time?


They know how to use their gear. :-) And they are trained in things like this. This is why they prefere lenses which allow to focus manual even if they are set to AF. One can correct the cameras decision. If you are well used to do this it is a matter af few 1/100th seconds.

Ralph



Oct 05, 2012 at 06:12 PM
Monito
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p.1 #13 · p.1 #13 · Is this purple fringing on 35L?


The photo was made at ISO 100. When you move into shade, increase the ISO to 400 and the lens will be shooting at f/4 instead of f/2. On the 5D2, you could easily make a photo like that at ISO 800. I'd probably go to 1250 if I needed to.

That way you get more Depth of Field. The old master photojournalists loved to shoot 35 mm lenses and pre-focus and use small apertures (larger numbers) to get lots of DoF.

Also, the shot was at 1/200. There is not a lot of movement there, but even so, 1/200 is probably a good choice. However, you could drop down more with a 35 mm lens to, say, 1/125 and gain some depth of field there.



Oct 05, 2012 at 06:21 PM
PasiM
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p.1 #14 · p.1 #14 · Is this purple fringing on 35L?


I say that is normal with 35. Wait to see how bad it can be with 85 1.2 II
It sure will go away after 2.8->



Oct 05, 2012 at 07:12 PM





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