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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 02 Feb 2011 (Wednesday) 16:54
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The King of Purple Fringing

 
CheshireCat
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Feb 03, 2011 18:08 |  #31

airfrogusmc wrote in post #11769652 (external link)
One of the very few lenses I've shot with that has virtually no C/A wide open or below 2.8 is the 200 2L and artificial fluorite is a big reason for that. To add that to an 85L the price would probably double but probably fix the problem.

Probably more... real APO lenses are very expensive.

But knowing a few things, we can minimize this issue with "cheaper" achromatic lenses like the 85/1.8 (and 85L/1.2):

- There are two type of fringing, purple and green. Purple being usually the most noticeable for obvious reasons.

- Both purple and green fringing are absent (ZERO) in the focus plane. And they increase linearly with a point's distance from the focus plane.

- Purple fringing affects points before the focus plane.

- Green fringing affects points behind the focus plane.

Now, it is often possible to keep critical subject points (white or specular highlights) in the focus plane. If this is not possible (subject tilted), try keeping them behind the focus plane as green fringing is usually less noticeable.
In the girl example previously posted, focusing on the white headband would have probably solved the problem.
In the train example, waiting for the train light to pass behind the focus plane would have solved the problem.

I must say I am totally happy with my 85L, and i almost always use it wide open. The very few times I see some noticeable fringings, a quick pp session will take care of it ;)
Never tried the 85/1.8 though, so YMMV.


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RDKirk
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Feb 03, 2011 18:18 as a reply to  @ CheshireCat's post |  #32

The very few times I see some noticeable fringings, a quick pp session will take care of it

What this tells me is that in a couple of years this will be something automatically correctable with in-camera processing, along with optical distortion and vignetting. The camera will contain a lens corrections registry and apply corrective processing as the image is written to the card.




  
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CheshireCat
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Feb 03, 2011 18:34 |  #33

RDKirk wrote in post #11772091 (external link)
What this tells me is that in a couple of years this will be something automatically correctable with in-camera processing, along with optical distortion and vignetting. The camera will contain a lens corrections registry and apply corrective processing as the image is written to the card.

This is not so easy, as this kind of CA has a 3D nature, and image depth information is not recorded by current sensors.

This may change though, but I think it will be a bit more than a couple of years ;)


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RDKirk
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Feb 03, 2011 19:24 |  #34

CheshireCat wrote in post #11772177 (external link)
This is not so easy, as this kind of CA has a 3D nature, and image depth information is not recorded by current sensors.

This may change though, but I think it will be a bit more than a couple of years ;)

Post-capture processing is post-capture processing. The fringing aspects of the lens design is a known factor that changes at a calculable rate in ratio to the aperture.

If it can be removed or at least mitigated in post-capture processing in a computer, it can be removed or mitigated with post-capture processing in-camera.




  
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bohdank
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Feb 03, 2011 19:45 |  #35

Bobster wrote in post #11769709 (external link)
have you had your eyes tested lately?

the PF of this lens is the reason why i didn't buy one when i had the chance..

Ok.... :-)

There is a touch near the hair. Imho, acceptable and doesn't show in print.

Here are 100% crops from the original. No PP done, everything turned off. Taken with a 5D2.


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Feb 03, 2011 22:39 |  #36

BrandonSi wrote in post #11765917 (external link)
I promise to give a good home any lenses you'd like to donate because of this terrible CA affliction.. I can send my mailing address over PM... :D

I'll do him one better. I'll give you ten bucks for each lens sent. and will also pay shipping charges!:D


Canon 50D gripped, EF 50/1.8, EF-S 10-22, 17-40L, 24-105L, 70-200 f/2.8L, 100/2.8 macro, 100-400L, 300 2.8L, Canon 500 f8 mirror with chipped EF mount, 580EX, 1.4x and 2x Canon teleconverters, Canon EF Life-Size converter.

  
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airfrogusmc
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Feb 04, 2011 07:46 |  #37

newworld666 wrote in post #11770566 (external link)
85L as got purple fringe at F1.2 in some conditions (Daytime with sunshine) ..

QUOTED IMAGE
IMAGE LINK: http://photos.corbi.eu …et/1171998489_i​WQiQ-O.jpg  (external link)

But from F1.8 .. it's more than controlled and almost absent ...:D 85L is a King

QUOTED IMAGE
IMAGE LINK: http://photos.corbi.eu …et/1171998475_h​DoJt-O.jpg  (external link)

QUOTED IMAGE
IMAGE LINK: http://photos.corbi.eu …61/1176377285_N​TaP6-O.jpg  (external link)

I've found it to not be that bad once you stop down to 1.8 and better at 1.8 than the 85 1.8 at 1.8. And if you use it to shoot candids or portraits indoors in available light and not shooting chrome out in harsh light (which you would probably be shooting at f/8 and smaller anyway0, its really not a problem. But if you are going to shoot car chrome on a bright sunny day at 1/8000 at 1.2 then ya just might get some fringing but how many times in a lifetime of shooting do you really do that. REALLY. I don't find the 85L to be a problem in almost all "real" shooting situations.




  
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bohdank
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Feb 04, 2011 08:03 |  #38

I would say the same for the 85/1.8

For the few times you might get some PF, it is worth it, imho. Just don't shoot chrome or barcodes.


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newworld666
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Feb 04, 2011 09:24 |  #39

:oops: ... I didn't find to be a problem that @f1.2 there was PF in some circumstances (bright daylight with chrome or ultra white plastics)
I was more or less showing my mistake, and explaining that it was easily corrected even @f1.8, which still gives a nice and acceptable bokeh :D.


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george ­ m ­ w
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Feb 04, 2011 10:29 |  #40

For the few times you might get some PF, it is worth it, imho. Just don't shoot chrome or barcodes.

So true. it's just another tool in the bag, and you need to play to it's strengths. I bought mine mostly to use for portraits, and for the times when shooting in low light situations where that is a good focal length.
The example I showed above of the chrome emblem on my truck was to demonstrate a worst case scenario for a friend that was considering buying one of these lenses.
I still consider this lens to be a bargain in the Canon lineup, and I often recco it to folks who are considering it.


regards, george w

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JeffreyG
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Feb 04, 2011 16:52 |  #41

Snow is generally what gives the most headaches with lenses that are prone to PF. There are lots of legit, non-measurebating test shots that become troublesome in snow with PF.


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John ­ Sheehy
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Feb 04, 2011 17:00 |  #42

Darkwand wrote in post #11765263 (external link)
I was somewhat surprised to get a photo like this, I've never gotten purple fringing headlights before.

The culprit?

Canon 85mm f/1.8 USM, what else? :p

I love this lens, this flaw only gives it character, the image is at f/2.0

The bulbs were probably very heavy in infrared output. At 85mm and f/2, IR is likely to be OOF even if the DOF is fairly deep for the visible spectrum. Lenses just aren't generally designed to focus IR along with visible light.




  
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Enrico84
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Feb 04, 2011 17:11 |  #43

I can easily notice PF on 85L shooting wide open, same was with 85f1.8 when I had it...stopping down helped to reduce it, but almost 2 grands later I realize the problem is still here




  
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newworld666
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Feb 04, 2011 17:15 as a reply to  @ JeffreyG's post |  #44

:confused: .... I don't know for other lenses .. but I didn't noticed with 85L even @F1.2 any PF i snow :oops: ... I just had a quick look but such samples should have been concerned :rolleyes:

IMAGE: http://photos.corbi.eu/Family/2010-03-08-Ski-Valmorel/IMG8061/808961703_PhusU-XL.jpg
IMAGE LINK: http://photos.corbi.eu …061/808961703_P​husU-O.jpg  (external link)


:rolleyes: I think with 85L, we only get PF between F1.2 and F1.4 with bright white/iron small parts surrounded with a rather dark colors :confused: ..

maybe like that one @F1.4 only PF I see is when there is white in middle of black ..
IMAGE: http://photos.corbi.eu/Family/2010-03-08-Ski-Valmorel/IMG8156/808962378_yqjcc-XL.jpg
IMAGE LINK: http://photos.corbi.eu …156/808962378_y​qjcc-O.jpg  (external link)

As soon as we close @f1.8 or less i don't think I get any pictures with 85L with PF ...

I put some samples with dogs in snow I didn't see any PF in them ...
http://photos.corbi.eu …12-01-Edge/14886117_U7ERH (external link)
http://photos.corbi.eu …Easy-Neige/10693949_Hrg9j (external link)

Marc
5DMKII+1Dx 24L1.4II 85L1.2II 180L3.5 300F2.8nonIS TC2XII ..... Sigma14F2.8AFDG, Zuiko 500F/8 Reflex
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CheshireCat
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Feb 04, 2011 17:27 |  #45

RDKirk wrote in post #11772443 (external link)
Post-capture processing is post-capture processing. The fringing aspects of the lens design is a known factor that changes at a calculable rate in ratio to the aperture.

If it can be removed or at least mitigated in post-capture processing in a computer, it can be removed or mitigated with post-capture processing in-camera.

Sure, only problem is computers do not work as well as humans at guessing which pixels are axial CA and which pixels are actual image colors.
I believe computers will be able to surpass humans eventually... it just won't take two years :D
Note that the keyword here is guessing, because information has been lost.


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The King of Purple Fringing
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