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04-30-2011, 02:03 AM   #1
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Purple strokes

Okey i was out to the local park and took some pictures.

almost most of the pictures was like the ones attached

I used k-5 + 100mm 2,8 pentax macro lens

As i remember the pictures i tok with my k-7 was not like this.

is there something i can do about this ?
the pictures are cropped

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04-30-2011, 08:27 AM   #2
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I did this by de-saturating the purple in PS.
(Would be better done with the raw file)
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04-30-2011, 11:08 AM   #3
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I have been playing with old lenses (M42) and all of these do this fringing plus green on the other side. I used old Porst 55/1,2 on my K10D and it had this too under f2 but now with K-5 I can use this Porst just for psychedelic pictures. It is so extreme that i can not correct it any more.
So to various degree all my manual lenses do this - Takumar 50/1,4; Rikenon 55/1,4; all 7 versions of Helios 44. Single coated ones less though.
So I wonder is it due to K-5 great sensor or something else. Contemporary lenses are normal.
04-30-2011, 01:38 PM   #4
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The mystery of purple fringing (PF) is seriously deep. There are a number of theories and explanations on the Web (none from the camera/lens makers ). Some say that it is simple longitudinal chromatic aberration (CA). Others claim that it is related to incident light angle against the micro-lens array of the camera sensor. I take the empirical approach and simply state that it appears to be an interaction of certain lens designs with the digital sensor technology. I get PF with some of my lenses (77/1.8 Limited (mild) and Zenitar 16/2.8 (not so mild) for example) on the K10D, but not with others. Those same lenses NEVER behave that way on color film.

In fact, I have only seen one example, in over 40 years of photography, of anything that even remotely resembled PF on film and that was with my Olympus XA near the frame margins. I believe that case to be very nasty CA related to the XA's unique lens design.

So regardless of the cause, it is pretty much a fact of life with current digital sensors. When I tested the DA 15/3.5 Limited, it had mild PF. My 18-55 Kit has it at times as well (so much for digital-optimized lenses). With the exception of the lenses mentioned above, the rest of my kit is relatively PF-free.


Steve


Last edited by stevebrot; 04-30-2011 at 01:43 PM.
04-30-2011, 01:42 PM   #5
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QuoteOriginally posted by vanakaru Quote
I have been playing with old lenses (M42) and all of these do this fringing plus green
That is CA. The clue is the green. True PF is purple/deep blue only and often "spreads" or "blooms" to adjacent areas.


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04-30-2011, 01:45 PM   #6
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QuoteOriginally posted by Wheatfield Quote
As an aside, any lens and any camera can be made to do this.
Pretty much true...it is generally only a matter of degree. The guy (Steve, I guess) at Steve's Digicams used to include a PF test image (cellophane-wrapped candies under strong direct light) as part of his test suite to show whether a particular camera model was resistant to PF.


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05-01-2011, 03:25 AM   #7
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ok thanks for replyes

i got theese tips

Commonly advocated methods of avoiding purple fringing include:

Avoid shooting with a wide-open lens in high contrast scenes.
Avoid overexposing highlights (e.g. specular reflections and bright sky behind dark objects).
Shoot with a Haze-2A or other strong UV-cut filter.[2]
05-01-2011, 03:33 AM   #8
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Shooting at maximum aperture can exhibit PF on a lot of cameras although some lenses seem to be worse than others. My DA 10-17mm fish-eye seems to be really bad for PF even when stopped down, my Sigma 10-20mm never has a problem with PF (my Canon copy and my Pentax copy).

My Canon EF 50mm f/1.4 exhibits horrific PF when shooting at f/1.4 in sunny conditions with high contrast (think black text on a white board), but stop down to f/2.0 and it's removed completely.

05-03-2011, 07:49 AM   #9
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In my experience coming from Nikons, the Pentax lenses are more prone to purple/green fringing than the Nikons.

FWIW I sent back my first K5 because it did this quite badly. The second unit doesn't exhibit the issue to nearly the same level. Common sense (and experienced photographers) say this is a lens issue only, but I thought I'd share my experience. Additionally, some Pentax users say that the K5 is more prone to the issue than K7 or K20d. Either way, it should be controllable. As the above user stated, de-saturating the purple channel in Photoshop has worked for me on the rare occasion that I still see strong fringing.
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