andybarton Posted March 14, 2016 Author Share #21 Posted March 14, 2016 Advertisement (gone after registration) This is not jpg compression. This is from the DNG file. Link to post Share on other sites More sharing options...
Advertisement Posted March 14, 2016 Posted March 14, 2016 Hi andybarton, Take a look here Strange artefact in centre of image (M240). I'm sure you'll find what you were looking for!
david strachan Posted March 14, 2016 Share #22 Posted March 14, 2016 Very nice picture. Link to post Share on other sites More sharing options...
wizard Posted March 14, 2016 Share #23 Posted March 14, 2016 Very nice capture, Andy. And I think jmahto hit the nail with his explanation in #12 above. Best, Andy Link to post Share on other sites More sharing options...
Jared Posted March 14, 2016 Share #24 Posted March 14, 2016 Almost certainly Newton's rings, likely caused by the UV filter since it is the one flat element that is orthogonal to the optical axis. It can happen with any image but is much more likely to be visible with monochromatic light sources since the interference pattern can't be drowned out by other frequencies. The green in most auroras is caused by oxygen emission lines at 558nm--a green yellow. There are often components of nitrogen and molecular nitrogen as well, but those are usually red. I would shoot auroras or any monochromatic light sources such as most street lights without the filter and these interference patterns will likely vanish. In the meanwhile, the same solar filters that can clean up banding in blue skies will likely clean up this image if you feel the need. - Jared Link to post Share on other sites More sharing options...
jaapv Posted March 14, 2016 Share #25 Posted March 14, 2016 Something to try? https://fstoppers.com/post-production/learn-how-fix-color-banding-using-just-one-simple-tool-7946 Link to post Share on other sites More sharing options...
2wk Posted March 14, 2016 Share #26 Posted March 14, 2016 I've seen it before on night shots. Like others have stated.....UV filter. Link to post Share on other sites More sharing options...
CheshireCat Posted March 14, 2016 Share #27 Posted March 14, 2016 Advertisement (gone after registration) Almost certainly Newton's rings, likely caused by the UV filter since it is the one flat element that is orthogonal to the optical axis. It certainly is Newton rings. But the filter is not the only flat element that is orthogonal to the optical axis. The sensor is another one. The sensor is a reflective surface. All digital sensors also have a sensor filter stack with refractive properties. Check chapter 2 here: http://nikon.com/about/technology/life/imaging/nano/index.htm Particularly interesting is the fact that new "optimized for digital" lenses need special coating to reduce bouncing back reflections from the sensor. The filter may definitely play a role in this reflection path,so first thing is removing it and see if the issue is still there. If still there, then try a lens that is "optimized for digital". And if still there, use photoshop As a matter of fact, I can reproduce this issue with my iPhone 5s and a monochromatic orange light source from a street light. Of course, I have no filter on my iPhone camera. Link to post Share on other sites More sharing options...
Jared Posted March 14, 2016 Share #28 Posted March 14, 2016 In theory we could figure out the exact elements involved. Since we know the wavelength of the light involved and could figure out the size of the rings with a little help from the original poster, it's easy enough to determine the radius of curvature of the spherical element involved. Two flat surfaces don't yield rings, so there must be a Plano-convex surface as well. Normally, it is hard to get such perfectly round, concentric rings unless you have physical contact between the flat surface and the plano-convex surface, so I am going to retract my statement of "likely the UV filter" and substitute "likely in the CCD filter stack". Should have thought it through more carefully. Easy enough to check, of course, by simply removing the UV filter. However Photoshop is the only realistic solution if the interference patterns are being generated at the detector. A solar curve and adding spatter would fix it easily enough in Photoshop. - Jared Link to post Share on other sites More sharing options...
jaapv Posted March 14, 2016 Share #29 Posted March 14, 2016 The Summilux 35 FLE has a plano-convex surface as front element AFAIK. Link to post Share on other sites More sharing options...
CheshireCat Posted March 14, 2016 Share #30 Posted March 14, 2016 This is not jpg compression. This is from the DNG file. And even if it was a JPEG file, there is no image compression algorithm that generates Newton rings artifacts. Link to post Share on other sites More sharing options...
CheshireCat Posted March 14, 2016 Share #31 Posted March 14, 2016 The Summilux 35 FLE has a plano-convex surface as front element AFAIK. That is actually plano-concave. Link to post Share on other sites More sharing options...
lct Posted March 14, 2016 Share #32 Posted March 14, 2016 [...] The filter may definitely play a role in this reflection path,so first thing is removing it and see if the issue is still there.[...] Yes or removing the darned filter and keeping it in its box all the night. The best place it can be in if you ask me. Great pic Andy Link to post Share on other sites More sharing options...
Peter Kilmister Posted March 14, 2016 Share #33 Posted March 14, 2016 My advice is to use a filter only when necessary. Others will disagree. If you are prone to sticking your fingers on the lens then use one all the time. I keep fingers away from the lens glass. I also carry a microfibre cloth. Link to post Share on other sites More sharing options...
jaapv Posted March 15, 2016 Share #34 Posted March 15, 2016 That is actually plano-concave. Depends which side you are looking at Thanks for the correction. Link to post Share on other sites More sharing options...
andybarton Posted March 15, 2016 Author Share #35 Posted March 15, 2016 I am afraid that going back to take the shot again without a filter really is not an option. I didn't notice this affect on any of the other 300 or so shots of the aurora I took a couple of nights later. I have to say that it does look like the Airy Disk pattern that Pop referred to back at the top of this thread. Newton's Rings need a curved and a flat surface to be touching (like when mounting slides in glass mounts). There are no flat and curved surfaces touching in this set up. Learning something new every day. Link to post Share on other sites More sharing options...
bocaburger Posted March 15, 2016 Share #36 Posted March 15, 2016 Newton's Rings need a curved and a flat surface to be touching (like when mounting slides in glass mounts). There are no flat and curved surfaces touching in this set up. Exactly. And I remember Newton rings with slide mounts and old Leitz Valoy condenser enlargers and they were never perfectly concentric. It also has nothing to do with a UV filter, because the rings are in perfect sharp focus and that is not possible any more than a scratch on a front element can be in perfect sharp focus, so no reason to start up the ridiculous "real photographers don't use no stinkin protective filters" argument again. Because it is in sharp focus there are only two places it could occur optically, the focus plane (or within very conservative DOF parameters) or the focal plane. The only other possiblity an eletronic (digital) artefact. Link to post Share on other sites More sharing options...
lct Posted March 15, 2016 Share #37 Posted March 15, 2016 I rely on you on this but i do confirm that, indeed, "no stinkin protective filters" should be used in night photography when there is any risk of reflections or ghost images. Now YMMV as usual . Link to post Share on other sites More sharing options...
CheshireCat Posted March 16, 2016 Share #38 Posted March 16, 2016 Newton's Rings need a curved and a flat surface to be touching (like when mounting slides in glass mounts). There are no flat and curved surfaces touching in this set up. No, it is not required that the surfaces are touching, also because the surfaces would be touching only on one point. All that is needed is that the surfaces are close enough and the effect magnified enough. Link to post Share on other sites More sharing options...
CheshireCat Posted March 16, 2016 Share #39 Posted March 16, 2016 It also has nothing to do with a UV filter, because the rings are in perfect sharp focus and that is not possible any more than a scratch on a front element can be in perfect sharp focus The lens is focused at infinity, and the light rays coming from infinity are cancelling or amplifying each other depending on the distance between the two surfaces (odd or even multiple of lambda/2). There is no scratch or ring object painted on the filter, this is a virtual object painted by light. If light hits your front element, then bounces on the front UV filter and back into the lens, it might produce Newton rings. Rings are "perfect" in shape because the filter is "perfectly" flat and the lens elements are "perfectly" symmetrical. As a matter of fact, I think this phenomenon can be used to perfectly center lens elements. no reason to start up the ridiculous "real photographers don't use no stinkin protective filters" argument again. Sorry, but your "digital artifact" explanation (or lack thereof) is the only ridiculous thing here. Real photographers don't use no stinkin' protective filters at night ! Not only in this very particular case (monochrome light) but generically to avoid ghosts and other nasty reflections. Link to post Share on other sites More sharing options...
jaapv Posted March 16, 2016 Share #40 Posted March 16, 2016 Actually Leica does use Laser interference measuring to check curvature when polishing lenses. The patterns look very similar to this. Link to post Share on other sites More sharing options...
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