wlaidlaw Posted March 19, 2015 Share #41 Posted March 19, 2015 Advertisement (gone after registration) Maybe someone who is close to Leica (mods?) could ask Leica if the CMOSIS folk could write an article in LFI on purple fringing. After all they design sensors and presumably take steps to minimise the fringing. In order to minimise it, you would need to know the cause or causes. Mind you it might end up like the infamous article on the 35 ASPH Summilux, which explained why substantial aperture shift was inherent in the design of this lens. The article sadly, wholly failed to explain why a minority of 35 ASPH Luxes did not suffer from it to any noticeable degree but others were so bad as to be unusable. Wilson Link to post Share on other sites More sharing options...
Advertisement Posted March 19, 2015 Posted March 19, 2015 Hi wlaidlaw, Take a look here Is this CA problem on my 50/1.4 ASPH, it's normal or not?. I'm sure you'll find what you were looking for!
CheshireCat Posted March 19, 2015 Share #42 Posted March 19, 2015 You defocused -i.e. widened the contrast transition, which turns this into a less sharp lens, which will not show purple fringing. The two images have the same exact amount of defocus. Nor does this experiment explain why the effect does not occur on film. About film, can you really prove this does not occur ? And even if you could, a film may be less sensitive to high spectral frequencies than digital sensors. Note that it is not easy to examine film at these magnification levels. Link to post Share on other sites More sharing options...
CheshireCat Posted March 19, 2015 Share #43 Posted March 19, 2015 Actually, longitudinal CA is where one color is focused in the wrong plane compared to the other colors, NOT where it is magnified with respect to the rest of the image. If an image is focused on the wrong plane, it will occupy a bigger area in the "right" plane. In this sense it is magnified, although obviously out of focus. Same way as a defocused point light forms a disc (i.e. the circle of confusion is a "magnified" point). About your other speculations, they are very interesting, but my quick test proves that purple fringing is caused by the lens. If you think my test is flawed, please detail. Link to post Share on other sites More sharing options...
pop Posted March 19, 2015 Share #44 Posted March 19, 2015 If the fringing was caused by mis-focusing, everything which is out of focus (or, perhaps, slightly out of focus) ought to show fringes. Clearly, this is not the case as there would be no discussion about bokeh, creamy or otherwise. There is no such thing as purple, anyway. That´s in your eye. Purple is a mixture of violet and red which occupy the opposite ends of the visible spectrum. Hence, no rainbow will contain the color purple. Link to post Share on other sites More sharing options...
Peter Branch Posted March 19, 2015 Share #45 Posted March 19, 2015 A citation is required......... Happy to oblige. Zeiss OTUS 55 versus Leica SX 50 ASPH, part 2 | The TAO of Leica Quote: The purple fringing often seen in pictures as a blue to magenta edge around clipped highlights is not caused by chromatic aberrations, but might be caused by pixel leakage from overexposed pixels into neighboring ones. It is a defect of the sensor and the in-camera processing and much less an optical phenomenon. I do not question that pictures taken at f/2 with the 50mm f/2 Apo will show superior image quality as compared with pictures taken at f/2 with the 50mm f/1.4 Lux. There are many reasons for this of which Apo correction is only one. If Apo correction consisted of simply getting three wavelengths to focus on the same image plane then Apo would on the one hand be very precise but on the other hand it would be virtually useless. As Jaapv has pointed out the definition of Apo does not specify what happens to the images formed by wavelengths other than the 3 chosen by the designer to be coincident. It seems that both Leica and Zeiss have decided that minimising the overall departure across the visible spectrum is a better form of correction and can in practice be achieved with only two wavelengths being precisely in focus on the image plane. This, of course, opens the door to different degrees of "Apo" correction. And that is exactly what seems to be happening. The 50mm f/2 Apo has "Better" Apo correction than the 50mm f/1.4 Lux. Link to post Share on other sites More sharing options...
Peter Branch Posted March 19, 2015 Share #46 Posted March 19, 2015 Those with an 18mm f/3.8 Super-Elmar-M ASPH might like to confirm my experience that the fringing that occurs on very high contrast edges towards the edge of an image is always magenta on an M (Typ 240). The "Correct for CA" function in ACR 8.7 removes it completely. But that does not mean it is CA! I've tried to post an example but it does not show at all clearly using a file processed to be suitable to be posted on the forum. Link to post Share on other sites More sharing options...
wlaidlaw Posted March 19, 2015 Share #47 Posted March 19, 2015 Advertisement (gone after registration) Those with an 18mm f/3.8 Super-Elmar-M ASPH might like to confirm my experience that the fringing that occurs on very high contrast edges towards the edge of an image is always magenta on an M (Typ 240). The "Correct for CA" function in ACR 8.7 removes it completely. But that does not mean it is CA! I've tried to post an example but it does not show at all clearly using a file processed to be suitable to be posted on the forum. Peter, I will give that a try with my 18 SEM on both M240 and M9 to compare CMOS and CCD, if the sun comes out today. I have found that thin bare tree branches against a bright sky brings out the worst in purple/magenta fringing. Capture One Pro V8.1 has a specific purple fringe reduction tool which you can either use globally or locally with a brush, that works very well. Wilson Link to post Share on other sites More sharing options...
jaapv Posted March 19, 2015 Share #48 Posted March 19, 2015 If the fringing was caused by mis-focusing, everything which is out of focus (or, perhaps, slightly out of focus) ought to show fringes. Clearly, this is not the case as there would be no discussion about bokeh, creamy or otherwise. There is no such thing as purple, anyway. That´s in your eye. Purple is a mixture of violet and red which occupy the opposite ends of the visible spectrum. Hence, no rainbow will contain the color purple. Indeed this is magenta fringing. Link to post Share on other sites More sharing options...
jaapv Posted March 19, 2015 Share #49 Posted March 19, 2015 If you think my test is flawed, please detail.I did; it does not occur on film. If you disagree, please provide an example.Flaws: Trees at near-infinity. Lenses do not focus precisely on infinity * . You pulled back. How much? How can you determine the amount for both settings. Was there wind inducing motion blur? Was a tripod used? Was there hot air blurring? The only thing this test shows that magenta fringing occurs or does not occur depending on a host of circumstances. * We can make the calculation complicated or simple, but a usual value is inf=500x focal length. I bet the trees in the first shot were focused spot-on. Link to post Share on other sites More sharing options...
thighslapper Posted March 19, 2015 Share #50 Posted March 19, 2015 Mr Cat ....... explain this with reference to chromatic aberration alone ....... Noctilux at 0.95 Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/242349-is-this-ca-problem-on-my-5014-asph-its-normal-or-not/?do=findComment&comment=2783383'>More sharing options...
wlaidlaw Posted March 19, 2015 Share #51 Posted March 19, 2015 I think that is a classic case of local over-exposure swamping nearby pixels and producing a false result. It might (not saying it is) be a different phenomenon to purple (or magenta) edge fringing. Wilson Link to post Share on other sites More sharing options...
jaapv Posted March 19, 2015 Share #52 Posted March 19, 2015 Mr Cat ....... explain this with reference to chromatic aberration alone ....... Noctilux at 0.95 That is a nice one: both magenta "fringing" in front of the window and green/red chromatic aberration in other parts Link to post Share on other sites More sharing options...
lct Posted March 19, 2015 Share #53 Posted March 19, 2015 All that has been beaten to death folks. Anything new since this thread ? http://www.l-camera-forum.com/leica-forum/leica-m-lenses/119433-noctilux-0-95-purple-fringe.html Link to post Share on other sites More sharing options...
jaapv Posted March 19, 2015 Share #54 Posted March 19, 2015 New faces - old misconceptions http://www.l-camera-forum.com/leica-forum/digital-post-processing-forum/115965-fringing-technical-problem.html http://www.l-camera-forum.com/leica-forum/leica-m9-forum/107052-m9-50-lux-asph-too-much-4.html Link to post Share on other sites More sharing options...
CheshireCat Posted March 19, 2015 Share #55 Posted March 19, 2015 If the fringing was caused by mis-focusing, everything which is out of focus (or, perhaps, slightly out of focus) ought to show fringes. No. Everything that is enough in front of the focus field and contains enough high-frequency highlights and contrast for you to notice. There is no such thing as purple, anyway. That´s in your eye. Purple is a mixture of violet and red which occupy the opposite ends of the visible spectrum. Hence, no rainbow will contain the color purple. You probably meant "magenta". The rainbow contains the color "purple", as clearly explained here: 16 million persons can't be wrong Link to post Share on other sites More sharing options...
CheshireCat Posted March 19, 2015 Share #56 Posted March 19, 2015 Quote [E.Puts]: The purple fringing often seen in pictures as a blue to magenta edge around clipped highlights is not caused by chromatic aberrations, but might be caused by pixel leakage from overexposed pixels into neighboring ones. It is a defect of the sensor and the in-camera processing and much less an optical phenomenon. In your citation, Erwin is speculating about what might be the cause. He is probably thinking about CCD sensor bloom (although that would not explain the "purple" color), and in my opinion he is wrong. It is also interesting to note that in the article I have previously cited he says: Quote [E.Puts]: Because of the relative insensitivity of silver-halide emulsions for the blue region, most designers in the past assumed that one sdid have to pay attention to this part. This attitude has been referred to as the 'cursed 435 wavelength'. Even a talented designer as Dr. Mandler evaded this wavelength. In the diagram below one can see the strongly under corrected blue part of the spectral graph. The modern approach is to pay much attention to this wavelength as it is responsable for the blue color fringing, so visible in digital photography. Note how he also explains why on film the issue is not much visible. It seems that both Leica and Zeiss have decided that minimising the overall departure across the visible spectrum is a better form of correction and can in practice be achieved with only two wavelengths being precisely in focus on the image plane. An APO lens is doing exactly that. If you have 3 zeros on the LoCA graph then you have a better form of correction than achromatic lenses (2 zeros). Of course there are different levels of APO correction, but the most important problem here is the correction at high frequencies and UV, which have been neglected for years and cause the blue/purple/indigo/whatever_your_name_is_for_this_color fringing. Link to post Share on other sites More sharing options...
CheshireCat Posted March 19, 2015 Share #57 Posted March 19, 2015 The "Correct for CA" function in ACR 8.7 removes it completely. But that does not mean it is CA! There is a possiblity that "CA" stands for "California". The sun here causes too many specular highlights, many of them purple-ish ! But more likely, it actually means Chromatic Aberration Link to post Share on other sites More sharing options...
BerndReini Posted March 19, 2015 Share #58 Posted March 19, 2015 Keep in mind also that even a very light UV/IR filter in from of the sensor will separate light from different wavelengths and focus it on slightly different planes, probably enough to contribute to the problem. The 50 Apo is better corrected for chromatic aberration than the 50lux and more so the Noctilux, but you will never see purple fringing this exaggerated on even very fine slide or negative film. I would also love a full scientific explanation, but I am one completely sure that purple fringing is caused by a combination of the lens and the sensor and not just one or the other. Link to post Share on other sites More sharing options...
CheshireCat Posted March 19, 2015 Share #59 Posted March 19, 2015 Mr Cat ....... explain this with reference to chromatic aberration alone ....... I have already explained it. Did you expect to have purple fringing also in parts of the image where there aren't any purple frequencies (including UV) ? By the way, why don't you shoot the same scene correctly focusing on the wire, or just stop down a couple stops ? If the sensor theories are correct, you will have much more purple fringing. If I am correct, much less. Link to post Share on other sites More sharing options...
CheshireCat Posted March 20, 2015 Share #60 Posted March 20, 2015 I did; it does not occur on film. If you disagree, please provide an example. Erwin Puts seems to disagree with you. Flaws: Trees at near-infinity. Lenses do not focus precisely on infinity * . You pulled back. How much? How can you determine the amount for both settings. What for ? I made sure one was front focused and the other back focused. If you check the second image more carefully, you could notice that the fringing is green instead of purple. But most people won't notice it, as green does not stand out as purple, and because a tree is green. Was there wind inducing motion blur? Was a tripod used? Was there hot air blurring? The only thing this test shows that magenta fringing occurs or does not occur depending on a host of circumstances. You are kidding, right ? Or do you really think a tripod could make the difference for magenta fringing ? * We can make the calculation complicated or simple, but a usual value is inf=500x focal length. I bet the trees in the first shot were focused spot-on. It wasn't. I made sure to focus past the trees (I had also a shot of the trees in focus). You also ignore the fact that most lenses go a little beyond "infinity". Link to post Share on other sites More sharing options...
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