jaapv Posted March 23, 2015 Share #121 Posted March 23, 2015 Advertisement (gone after registration) That BS does not match your experience, unless you believe that stopping down the lens magically "fixes the sensor" instead of reducing the lens LoCA No- the image projection on the sensor changes - obviously. Fixing it would entail replacing it by a strip of film. Link to post Share on other sites More sharing options...
Advertisement Posted March 23, 2015 Posted March 23, 2015 Hi jaapv, 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 23, 2015 Share #122 Posted March 23, 2015 Perhaps a bit of both. Stopping down certainly reduces the amount of light striking the sensor, and typically improves lens performance. Stopping down does not reduce the amount of light, provided you compensate the exposure time accordingly. This easy test can show you the sensor has nothing to do with PF: - Camera on a tripod. - Frame tree branches. - Focus so that most branches are in front of the focus field (i.e. focus behind the branches). - Overexpose wide open (e.g. 1/2000s@f/2), - Take the photo, and make sure you see PF. - Do not re-focus. - Stop down 4 stops and set the equivalent overexposure (e.g. 1/125s@f/8). - Take the photo, and verify that PF is gone (or dramatically reduced) even if the amount of light striking the sensor is the same. Link to post Share on other sites More sharing options...
CheshireCat Posted March 23, 2015 Share #123 Posted March 23, 2015 No- the image projection on the sensor changes - obviously. Fixing it would entail replacing it by a strip of film. You were the one saying that blur helps removing PF, therefore having a sharper image projection (because of the stopped down lens) should increase PF by your reasoning. But it is the other way around, therefore you are wrong Link to post Share on other sites More sharing options...
jaapv Posted March 23, 2015 Share #124 Posted March 23, 2015 I have no idea what the aperture will do to the microlens collimation on the sensor, but I suspect there might be a reason there. Link to post Share on other sites More sharing options...
lct Posted March 23, 2015 Share #125 Posted March 23, 2015 Stopping down does not reduce the amount of light, provided you compensate the exposure time accordingly. If you compensate, you still over expose, what is the point of that? As long as you over expose, the risk of blooming will remain as is. Link to post Share on other sites More sharing options...
adan Posted March 23, 2015 Share #126 Posted March 23, 2015 Stopping down does not reduce the amount of light, provided you compensate the exposure time accordingly.This easy test can show you the sensor has nothing to do with PF: - Camera on a tripod. - Frame tree branches. - Focus so that most branches are in front of the focus field (i.e. focus behind the branches). - Overexpose wide open (e.g. 1/2000s@f/2), - Take the photo, and make sure you see PF. - Do not re-focus. - Stop down 4 stops and set the equivalent overexposure (e.g. 1/125s@f/8). - Take the photo, and verify that PF is gone (or dramatically reduced) even if the amount of light striking the sensor is the same. Funny you should mention that...... As you say, stopping down should eliminate PF - IF it is caused by longitudinal/axial CA. (Long. CA being a problem of focusing of different colors, and thus reduced, as with any mis-focus, with increased DoF at smaller apertures). Images below taken with 35 Summicron v.4 (non-ASPH) at a full range of apertures (with shutter speed adjusted to maintain overexposure). A focal length that is unlikely to suffer from much long. CA in any case (short focal length). Leica M9. Purple fringing at all apertures. In fact, purple fringing increases substantially at f/11-f/16 - not sure what that is all about, but f/11-f/16 is theoretically where diffraction starts to kick in with a FF 18Mpixel sensor. Further reading: Glossary: Chromatic Aberration: Digital Photography Review. Note particularly example and discussion of sensor microlens CA. I.E. a sensor effect and "typical digital camera phenomenon." 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=2785632'>More sharing options...
wlaidlaw Posted March 23, 2015 Share #127 Posted March 23, 2015 Advertisement (gone after registration) Andy, Diffraction works like a single lens or prism and therefor different frequencies of light would be diffracted to different amounts (it is why you often use a grating in a spectroscope in place of a prism). Therefore increased diffraction would increase the CA, probably both lateral and longitudinal. Wilson 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=2785648'>More sharing options...
CheshireCat Posted March 23, 2015 Share #128 Posted March 23, 2015 If you compensate, you still over expose, what is the point of that? As long as you over expose, the risk of blooming will remain as is. And this is the point. If the risk of blooming is the same, and the image has no PF, then it cannot be the sensor. I have no idea what the aperture will do to the microlens collimation on the sensor, but I suspect there might be a reason there. I think wrong microlenses collimation causes issues like the "italian flag" we all know about. Purple fringing is a different thing. Besides, this excerpt from the "Canon 1Ds Mark II white paper" may explain why digital sensors show more purple fringing than film: Normally, it’s nearly impossible to provide both high resolution and minimal false color, but the EOS-1Ds Mark II has a 3-layer optical low pass filter that works with the DIGIC II chip to reduce false colors while having minimal impact on resolution. Link to post Share on other sites More sharing options...
jaapv Posted March 23, 2015 Share #129 Posted March 23, 2015 Besides, this excerpt from the "Canon 1Ds Mark II white paper" may explain why digital sensors show more purple fringing than film: That refers to colour aliasing and Moiré, which is something quite different. Link to post Share on other sites More sharing options...
jaapv Posted March 23, 2015 Share #130 Posted March 23, 2015 According to the link that Howard posted here, everybody is right in this thread. :D.The PF is allegedly caused by chromatic aberration of the microlenses on the sensor.... I don't quite believe that. If that were the case, where did the other aberrations go, like lateral CA, astigmatism etc.? And how can a single sensel detect lens aberrations? Glossary: Chromatic Aberration: Digital Photography Review Link to post Share on other sites More sharing options...
wlaidlaw Posted March 23, 2015 Share #131 Posted March 23, 2015 Me neither, as each pixel pit only reads a single colour other than Sigma type Foveon multi layer sensors (do they get purple fringing?). It might (?????) be due to light scattering by the micro lenses. Wilson Link to post Share on other sites More sharing options...
Luke_Miller Posted March 23, 2015 Share #132 Posted March 23, 2015 Stopping down does not reduce the amount of light, provided you compensate the exposure time accordingly. It does not reduce the total amount of light (number of photons) striking the sensor, but it does reduce the rate at which they strike it. If sensor blooming is the result of sensor wells overflowing, then reducing the rate at which photons arrive should help. Link to post Share on other sites More sharing options...
CheshireCat Posted March 23, 2015 Share #133 Posted March 23, 2015 Purple fringing at all apertures. In fact, purple fringing increases substantially at f/11-f/16 - not sure what that is all about, but f/11-f/16 is theoretically where diffraction starts to kick in with a FF 18Mpixel sensor. Compare f/2 to f/8, and you will agree with me that CA is dramatically reduced (you will need a better lens for it not to be visible at all), therefore you just proved my point [thanks ]. Wilson has explained what happens when diffraction kicks in. Further reading: Glossary: Chromatic Aberration: Digital Photography Review. Note particularly example and discussion of sensor microlens CA. I.E. a sensor effect and "typical digital camera phenomenon." I am afraid that this "reliable" source is laughably wrong. If you open the full image, you will see that the purple fringing image is a magnified version of the white highlights (i.e. sky behind the trees). Microlenses affect single sensels, they cannot "magnify" an image and project it dozens of pixels outside of their domain, let alone prefer to do that only with the purple color, and only in the sky portion of the image (where UV are most probably present). It is also interesting to note that the camera used is also affected by lateral CA, a different issue especially visible in the tree trunks at the bottom of the image (red/cyan fringes). Besides, that image has been shot with a Canon PowerShot G1, which uses an old low-end CCD sensor, therefore I am not even sure it actually has microlenses Link to post Share on other sites More sharing options...
CheshireCat Posted March 23, 2015 Share #134 Posted March 23, 2015 It does not reduce the total amount of light (number of photons) striking the sensor, but it does reduce the rate at which they strike it. If sensor blooming is the result of sensor wells overflowing, then reducing the rate at which photons arrive should help. Think about a sensor element (sensel) as an empty glass. Overflow does not depend on how slow you pour the water. It only depends on how much water you pour between the start and the end of the "exposure". Sensor blooming is water overflowing a sensel and filling the nearby sensels. And this is what it looks like: http://en.wikipedia.org/wiki/Active_pixel_sensor#/media/File:Blooming_ccd.jpg Look ma, no purple fringing ! Link to post Share on other sites More sharing options...
jaapv Posted March 24, 2015 Share #135 Posted March 24, 2015 That is not really what we are discussing here...You don’t need Wikipedia - there are far better examples on the Forum. Have a look at the FAQ.... Link to post Share on other sites More sharing options...
CheshireCat Posted March 24, 2015 Share #136 Posted March 24, 2015 That is not really what we are discussing here...You don’t need Wikipedia - there are far better examples on the Forum. Have a look at the FAQ.... Actually, some users are discussing sensor blooming as the cause of the OP issue. If we all agree that sensor blooming has nothing to do with the OP image, then we can proceed... P.S. Which FAQ ? Link to post Share on other sites More sharing options...
CheshireCat Posted March 24, 2015 Share #137 Posted March 24, 2015 Me neither, as each pixel pit only reads a single colour other than Sigma type Foveon multi layer sensors (do they get purple fringing?). Of course they do, as purple fringing is caused by the lens. Example: http://www.photoxels.com/images/Sigma/dp2q/image%20samples/DP2Q0037_CA_1024.jpg Link to post Share on other sites More sharing options...
lct Posted March 24, 2015 Share #138 Posted March 24, 2015 I don't see any significant red nor magenta fringing in this image. Same +100% red saturation + 100% magenta saturation: 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=2786033'>More sharing options...
jaapv Posted March 24, 2015 Share #139 Posted March 24, 2015 Actually, some users are discussing sensor blooming as the cause of the OP issue.If we all agree that sensor blooming has nothing to do with the OP image, then we can proceed... P.S. Which FAQ ? Just direct your view upwards in M9 forum (or M240) Link to post Share on other sites More sharing options...
CheshireCat Posted March 24, 2015 Share #140 Posted March 24, 2015 I don't see any significant red nor magenta fringing in this image.Same +100% red saturation + 100% magenta saturation: CA here is more on blue. Check this enlarged crop. 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=2786290'>More sharing options...
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