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02-09-2008, 04:49 PM   #1
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Red and green outlines in photos

I have had my K10D for about 2 months now, and have been enjoying it. However I have been noticing some annoying issues with some photos. In a lot of pictures, mostly taken outdoors, I can see green and red lines around objects. This usually occurs around tree branches against the sky. I have attached an extreme closeup to demonstrate what I mean. Does anyone know what is causing this? Could the camera be damaged, because it was accidentally dropped a few weeks ago and hit the ground pretty hard. I don't really have any pictures to compare before and after it was dropped, so I don't know if this could be damage caused by that. Any help would be appreciated.



02-09-2008, 05:02 PM   #2
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It's a common issue with older lenses and some third party lenses. The issue is that they have poor coating for the digital sensors. These lenses cause more internal reflections and colour bleeding. New "for Digital" lenses have different coatings to reduce this from happening.

It's not the camera but the lens. My guess is you are using an older lens and most likely a zoom. This will only happen when there is a high contrast situation like the example posted. Bright background light against a dark subject. It does happen in newer glass as well but to a much lesser extent.

Technically the lens is causing Chromatic aberrations (CA) and it's because the lens can not focus different parts of the light spectrum to a common point. IE. different wavelengths of light focus on different image planes. So in other words the lens creates a sort of double/triple image of the various colours in the light spectrum. The other factor is that the sensor of the camera (all of them) are more sensitive to this situation and will record the incoming light incorrectly. The focus of the light rays to the sensor is slightly imperfect and just off enough that the result is this somewhat blurred "purple fringing" around the subject.

Last edited by Peter Zack; 02-09-2008 at 05:18 PM.
02-09-2008, 07:19 PM   #3
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Wow, thanks for the educated reply! This really explains my problem. Is this common with the kit lens that comes with the K10D as well or just with the older lens. The lens I have is the 18-55mm kit lens. Thanks.
02-09-2008, 07:36 PM   #4
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Nice work Peter great explanation

02-09-2008, 07:52 PM   #5
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Chromatic Aberration (CA)

See here:

Chromatic aberrations
02-09-2008, 07:55 PM   #6
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QuoteOriginally posted by ADKphoto Quote
Wow, thanks for the educated reply! This really explains my problem. Is this common with the kit lens that comes with the K10D as well or just with the older lens. The lens I have is the 18-55mm kit lens. Thanks.
Actually it occurs in new and old lenses. There are a few types of fringing. The kit lens does this a lot at wide angles... Even the newest "fast" zoom has this characteristic (though reduced (arguable)). Almost all commmercial lenses have design tradeoffs to make them competitive..
Her's a lens review re: this. Think Klaus's copy was a better one then mine (at least at 18mm), or yours
Lateral chromatic aberrations (color shadows at harsh contrast transitions) surprisingly well controlled with an average pixel width around 1px at the image borders at 18mm and less so beyond. Very few standard zooms show such a moderate CA characteristic.
Pentax SMC-DA 18-55mm f/3.5-5.6 AL - Review / Test Report
Really good "old" lens....
Lateral chromatic aberrations (color shadows at harsh contrast transitions) are very low for a lens designed in the film era. At around 0.2px on the average at the image borders the issue isn't field relevant.
Pentax SMC-FA 77mm f/1.8 Limited Review / Test Report
Not so good new lens:
Lateral CAs (color shadows at harsh contrast transitions) are already an issue for conventional standard zoom lenses so it doesn't come as a surprise that the Pentax 18-250mm has its fair share of problems here. That said the results are comparatively well controlled for most of the range with an average CA pixel width between 1-1.5px at the image borders. The worst spot is reached at 250mm and about 1.75px of CAs which is fairly hefty for this setting.
Pentax SMC DA 18-250mm f/3.5-6.3 ED AL [IF] - Lab Test R
eport / Review
02-09-2008, 09:00 PM   #7
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QuoteOriginally posted by ADKphoto Quote
Wow, thanks for the educated reply! This really explains my problem. Is this common with the kit lens that comes with the K10D as well or just with the older lens. The lens I have is the 18-55mm kit lens. Thanks.
I have this problem with my kit lens. In fact it is the worst lens I have as far as CA's go. I have several early eighties zooms, primes, and some old screwmount lenses. None of them have CA's as bad as the kit lens. Knowing this, when I use my kit lens I just try to avoid the type of situations that produce the CA's, or use a different lens. If I get CA's in my pictures, it can usually be corrected in PP.
02-09-2008, 10:31 PM   #8
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I don't have this problem with my kit lens and it seems to react like Klaus's version (about 1 pixel) I should have been more clear earlier and as jeffkrol stated. It can happen on any lens. But it does tend to be more noticable on zooms and older lenses. That why we see these DG or DL designations on some lenses and of course the DA versions. These all have coatings to try and correct some of this. It's much less common (at least better controlled) on a prime as there are fewer moving elements to cause the issues with focusing the various wavelengths of the light spectrum.

Nice thing is that much of this can be corrected in software as long as the lens doesn't do it too badly. Shooting technique also helps as Fritz suggested.

02-10-2008, 02:36 AM   #9
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QuoteOriginally posted by Peter Zack Quote
I don't have this problem with my kit lens and it seems to react like Klaus's version (about 1 pixel) I should have been more clear earlier and as jeffkrol stated. It can happen on any lens. But it does tend to be more noticable on zooms and older lenses. That why we see these DG or DL designations on some lenses and of course the DA versions. These all have coatings to try and correct some of this. It's much less common (at least better controlled) on a prime as there are fewer moving elements to cause the issues with focusing the various wavelengths of the light spectrum.
Coatings actually have no direct effect on CA, they only impact the contrast with which the errors are rendered at the plane of focus. CAs are inherent to the optical design and are fixed for a particular lens, FL, aperture and focus distance, it's just that they tend to be most visible at high contrast junctures.

Chromatic aberration - Wikipedia, the free encyclopedia
02-10-2008, 07:49 AM   #10
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Distudio, Thanks for that. I stand corrected. I did some further reading and although coatings do increase contrast and help to take care of ghosting of the colour wavelength that each coating layer is tuned to, they don't directly address colour fringes. They do however reduce the ghosting that can make this effect more pronounced.
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