Why do I get purple fringes ?

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Phil Wheeler wrote:
[]
> Do I care? No .. just trying to provide what I think is useful info.
> Paul can go read it or remain ignorant.
>
> Phil

You may not care, but I do. Whilst purple-fringing has a similar
appearance to chromatic aberration in lenses, it does not have the same
underlying cause, and to describe it as "lens chromatic aberration" is
quite simply misleading.

Cheers,
David
 
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On Wed, 8 Dec 2004 10:19:29 -0000, "David J Taylor"
<david-taylor@invalid.com> wrote:

>Phil Wheeler wrote:
>[]
>> Do I care? No .. just trying to provide what I think is useful info.
>> Paul can go read it or remain ignorant.
>>
>> Phil
>
>You may not care, but I do. Whilst purple-fringing has a similar
>appearance to chromatic aberration in lenses, it does not have the same
>underlying cause, and to describe it as "lens chromatic aberration" is
>quite simply misleading.

... not "misleading" .. just plainly wrong period. :)
 
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First go read the book, David -- then we can communicate.

David J Taylor wrote:

> Phil Wheeler wrote:
> []
>
>>Do I care? No .. just trying to provide what I think is useful info.
>>Paul can go read it or remain ignorant.
>>
>>Phil
>
>
> You may not care, but I do. Whilst purple-fringing has a similar
> appearance to chromatic aberration in lenses, it does not have the same
> underlying cause, and to describe it as "lens chromatic aberration" is
> quite simply misleading.
>
> Cheers,
> David
>
>
 
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Read the book, pal .. then tell me if *it* is misleading.

Messages here tell little.

imbsysop wrote:
> On Wed, 8 Dec 2004 10:19:29 -0000, "David J Taylor"
> <david-taylor@invalid.com> wrote:
>
>
>>Phil Wheeler wrote:
>>[]
>>
>>>Do I care? No .. just trying to provide what I think is useful info.
>>>Paul can go read it or remain ignorant.
>>>
>>>Phil
>>
>>You may not care, but I do. Whilst purple-fringing has a similar
>>appearance to chromatic aberration in lenses, it does not have the same
>>underlying cause, and to describe it as "lens chromatic aberration" is
>>quite simply misleading.
>
>
> .. not "misleading" .. just plainly wrong period. :)
>
 
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Phil Wheeler wrote:
> First go read the book, David -- then we can communicate.
>
> David J Taylor wrote:

What's that supposed to mean? I point out that PF and CA don't have the
same underlying cause. Don't you agree with that?

David
 
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On Wed, 08 Dec 2004 21:05:33 GMT, Phil Wheeler <w6tuh-ng5@yahoo.com>
wrote:

>Read the book, pal .. then tell me if *it* is misleading.
>
>Messages here tell little.
>

pal .. if the author is not able to differentiate CA and PF in origin
he should not be writing books in the first place .. that's what
messages here may tell you .. :)
 
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On Tue, 07 Dec 2004 18:11:51 GMT, "Jeremy" <jeremy@nospam.com> wrote:



>It is Chromatic Aberration, and it results from the optical property of
>light of different colors tending to focus at slightly different planes from
>the exact point of the film (or sensor) plane.
>
>It is typically at its worst on long zoom lenses. Some manufacturers (Nikon
>especially) use extra low dispersion glass elements in some of their long
>lenses to minimize this problem. Previously, some manufacturers used
>fluorite elements, rather than glass ones, but fluorite elements tended to
>be expensive and were easily shattered.
>
>If your lens exhibits this fault, I am unaware of anything you can do to
>minimize it (you might see if the effect is less pronounced if you don't
>rack out the zoom as much). There is no filter that will correct this
>problem.
>
>I purchased a camera with a 3x zoom as my way of steering clear of this
>problem. Some manufacturers use better lenses than others. If your camera
>does not have interchangeable lenses, the only way to get rid of the problem
>is to replace the camera with a better model.
>
>There is more to the quality of the image than simply the number of
>megapixels . . .
>
>


Two comments - first I hope I'm answering the proper poster. And
second I don't feel qualified to get into the argument whether it's
the lens or something else, but I have been closely involved in the
"low dispersion lens" field. Several years ago I did a lot of
searching for a really good spotting scope to attach to my digital
cameras. After trying MANY that were not up to the task, I tried a
Kowa that did NOT have the fluorite lenses, and it was also not
adequate. I considered the Kowa models with the fluorite lens, but
about then I was pointed to the Swarovski scopes with H.D. glass, and
bought one of those. It was the most expensive then available, but
I've never regretted it. NO fringing, NO chromatic aberration that
I've ever detected. ALL these tests with the same cameras, thus I
conclude that for MY purposes it was not the camera, but the long
range lenses!!! Take this for what you wish. (And I still do not
really know if the Swarovski uses fluorite lens or not, but it's the
best I found.)

Olin McDaniel
 
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In message <PtidnWFVbvFUiivcRVn-vg@comcast.com>,
"Paul H." <xxpaulhtck@zzcomcast.yycom> wrote:

>"Drifter" <zespectre@askme.com> wrote in message
>news:d9ubr012v45hp0k6hlklf9vcn6bffpoiu5@4ax.com...

>> No it isn't. CA is a function of the lens. On some Canon products
>> you can get CA from the sensor, but that is only because the sensor
>> uses "microlenses" over each receptor.

>If it were true chromatic aberration, there would be a spectrum of colors,
>not just a tight band centered about purple. If it were true chromatic
>aberration, then the effect would be present regardless of contrast, whereas
>purple fringing seems to occur solely the transitions between very dark and
>very light areas.

The OP did claim, however, that the effect was directional, implying
possible CA. Without seeing the image, however, all speculations are
weak.

>Blooming caused by electron spill-over from the
>quantum-well photosites on the sensor seems the more likely culprit,
>exacerbated by in-camera sharpening software, perhaps.

Another test would be to shoot at different ISOs. ISO should not affect
CA, but it will affect sensor saturation, as the saturation level of the
sensor is more stops away from average exposure at higher ISOs.
--

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John P Sheehy <JPS@no.komm>
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In message <6Wotd.3951$Ew6.1269@twister.socal.rr.com>,
Phil Wheeler <w6tuh-ng5@yahoo.com> wrote:

>To quote:
>
>""Purple fringing" is the most common type of chromatic aberration in
>digital cameras."
>
>Source is:
>
>http://www.dpreview.com/learn/?/Glossary/Optical/Chromatic_Aberrations_01.htm

DPReview is wrong.

"Purple fringing" originally referred to sensor issues, and then people
later mis-applied it to CA.

Purple fringing from the sensor has nothing to do with chromatic issues;
it is an artifact of the Bayer CFA and the demosaicing process. On most
of the earlier cameras, the green channel was the most sensitive, so it
clipped first and bled over into the red and blue cells (which were not
saturated because of stronger color filters), increasing the balance of
red and blue (purple).
--

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John P Sheehy <JPS@no.komm>
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<JPS@no.komm> a écrit dans le message de
news:gs83t050ldupacgp0229v5v3erblq49sg1@4ax.com...
> In message <6Wotd.3951$Ew6.1269@twister.socal.rr.com>,
> Phil Wheeler <w6tuh-ng5@yahoo.com> wrote:
>
> >To quote:
> >
> >""Purple fringing" is the most common type of chromatic aberration in
> >digital cameras."
> >
> >Source is:
> >
>
>http://www.dpreview.com/learn/?/Glossary/Optical/Chromatic_Aberrations_01.h
tm
>
> DPReview is wrong.
>
> "Purple fringing" originally referred to sensor issues, and then people
> later mis-applied it to CA.
>
> Purple fringing from the sensor has nothing to do with chromatic issues;

Take one second to look at the dpreview example before teaching ex cathedra.
When cyan fringes are on only one side of the subject, or red fringes on the
opposite side, this is a true optical issue.

Produced mainly on long range cheap miracle zooms.

mb
 
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In message <mMCdnRs_-7vHuivcRVn-3A@comcast.com>,
"Paul H." <xxpaulhtck@zzcomcast.yycom> wrote:

>And who appointed dpreview to tbe the official and final arbiter of
>physics/optics/camera terminology, anyway? You cite an authority which has
>been authorized by no one, except perhaps yourself. To quote:

Amen. DPReview is run by humans. DPReview is big, but big does not
equal correct. I get tired of people asking "can Phil Askey verify
that?", when he is clearly a mortal who has bitten off more than he can
chew.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
 
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In message <eOttd.3969$Ew6.3044@twister.socal.rr.com>,
Phil Wheeler <w6tuh-ng5@yahoo.com> wrote:

>I suspect he knows more about the subject than
>most here.

No; it means that he is more inclined to write a book.

Guess what? Publishers are not omniscient gods who know more than the
writers, and only allow people who really know what they're talking
about write. All books should be taken with a pound of salt, and
considered food for thought; not scripture.
--

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><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
 
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In message <10rbrie8qtpcm41@corp.supernews.com>,
"Marvin Margoshes" <physnospamchem@cloud9.net> wrote:

>There isn't a simple, straightforward answer that I know of. I had an Oly
>3030, a camera that many people complained had a purple fringe problem. I
>looked carefully at images that were likely to show the effect, and couldn't
>find it. Perhaps there was some difference in the lens, the sensor, or the
>software in my camera.

Did you use the lowest ISO on most pictures, or shoot images with
extreme contrast? That is where sesnor-related purple fringing is most
likely to happen.

--

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In message <Xns95B8D5F2E23B6klotjohan@130.133.1.4>,
Roland Karlsson <roland_dot_karlsson@bonetmail.com> wrote:

>You have got some different answers regarding the cause,
>as always when this topic comes up :)
>
>The easiest cure (if you cant avoid large contrast in
>the picture, particularly in the corners) is to desaturate
>purple. It is more efficient than one can imagine.
>
>Depending on your photo editor you can select purple
>using several methods. No matter how you do it, just
>desaturate the selection.

It would take more time, but it might be better to visually inspect the
mask and subtract true purple objects from it, or only select purple
areas manually.
--

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In message <96iAd.13392$%k.1424985@weber.videotron.net>,
"m.b." <spamkiller@moon.net> wrote:

>When cyan fringes are on only one side of the subject, or red fringes on the
>opposite side, this is a true optical issue.

That's not purple fringing.
--

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John P Sheehy <JPS@no.komm>
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