Leicakillen Posted March 4, 2011 Share #1 Posted March 4, 2011 Advertisement (gone after registration) Dear experts, When I take my night photos I often get star shapes around light sources - this is not very ugly but I would like to understand why. Sometimes I don´t get this effect - the lights are round light sources. See below - the first image is with my Summicron 35 v4 and you can see this effect clearly on the right hand side. Second image - same evening in Gamla Stan Stockholm but without this effect - Summilux 50 ASPH. Any comment apreciated. Tack /Anders 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/145587-star-shaped-light-sources-why/?do=findComment&comment=1606449'>More sharing options...
Advertisement Posted March 4, 2011 Posted March 4, 2011 Hi Leicakillen, Take a look here Star shaped light sources - why?. I'm sure you'll find what you were looking for!
Washington Posted March 4, 2011 Share #2 Posted March 4, 2011 Gosh, I remember when they sold filters to do just that. Maybe they still do. Link to post Share on other sites More sharing options...
Leicakillen Posted March 4, 2011 Author Share #3 Posted March 4, 2011 ...I did NOT use these filters Washington.... /Anders Link to post Share on other sites More sharing options...
bill Posted March 4, 2011 Share #4 Posted March 4, 2011 Keeping your front element scrupulously free from grease will help, as will avoiding any microscratches on the lens or any filter. What does this have to do with M9s? Regards, Bill Link to post Share on other sites More sharing options...
ho_co Posted March 4, 2011 Share #5 Posted March 4, 2011 Those are sometimes called 'diaphragm spikes' and are caused by diffraction by the diaphragm blades. Different diaphragms have different numbers of blades, and the actual shape of the diaphragm opening varies with aperture. A round opening doesn't generate spikes. A diaphragm with an even number of blades generates an even number of spikes. One with an odd number of blades will generate twice the number of spikes as there are blades. (Recently learned that bit from Michael Hußmann at http://www.l-camera-forum.com/leica-forum/leica-m9-forum/164242-inordinate-amount-ca-2.html#post1600294.) Link to post Share on other sites More sharing options...
Lindolfi Posted March 4, 2011 Share #6 Posted March 4, 2011 Here some more explanation, for which I've drawn some figures: This phenomenon can be explained by "diffraction". That is a process by which light rays come through the aperture and are dispersed by the straight sides of the aperture and only amplify themselves where the waves match. This figure shows what is going on A number of light spots emerge on a straight line at right angles to the straight sides of the aperture. The brightness becomes less at increasing distance from the primary light spot and so points of a star emerge. When there is an odd number of aperture blades, there is a star shape with twice the number of arms as there are aperture blades, since the diffraction happens to both sides. This figure illustrates that effect With an even number of aperture blades you get the same number of arms of the star shape because each time two arms coincide. Like in this figure: Link to post Share on other sites More sharing options...
Washington Posted March 4, 2011 Share #7 Posted March 4, 2011 Advertisement (gone after registration) Leicakillen, Sorry for the misunderstanding as I did not mean to imply you did use a filter. It was just a memory that once this effect was in vogue and people did use filters to achieve such. I really didn't know why this happens but I was sure you would be hearing from folks that do: and then we'd both learn something. Cheers! Link to post Share on other sites More sharing options...
Mikep996 Posted March 4, 2011 Share #8 Posted March 4, 2011 Yes, that "effect" has always existed and, as noted, is based on the number of diaphragm blades, the lens opening, the relative brightness of the light, and the position of the light point in the frame. Shoot the same light source/exposure with different lens openings and you will see the amount of "starring" change. Smaller apertures exhibit more starring than wider apertures. Further - different focal length lenses exhibit different levels of "starring" at the same settings. If you move the light source "point" around in the frame it will also change. That's why you see it on some lights in your first frame and not others. Diaphragm lenses have always done this; As explained by Lindolfi, it's just a physical effect caused by the light/diaphragm. Some people love the effect in night/sun shots and use smaller lens openings to get it. Link to post Share on other sites More sharing options...
earleygallery Posted March 5, 2011 Share #9 Posted March 5, 2011 You need to use a star filter for a more pronounced result Link to post Share on other sites More sharing options...
Washington Posted March 5, 2011 Share #10 Posted March 5, 2011 Then they still make them I assume, I just haven't thought about those for years. Link to post Share on other sites More sharing options...
Leicakillen Posted March 5, 2011 Author Share #11 Posted March 5, 2011 Thanks - does it mean that I get different effects at different apertures? I guess "more" stars at smaller apertures than bigger?? I just would like to understand if I can control this in any way. regards /Anders Here some more explanation, for which I've drawn some figures: This phenomenon can be explained by "diffraction". That is a process by which light rays come through the aperture and are dispersed by the straight sides of the aperture and only amplify themselves where the waves match. This figure shows what is going on A number of light spots emerge on a straight line at right angles to the straight sides of the aperture. The brightness becomes less at increasing distance from the primary light spot and so points of a star emerge. When there is an odd number of aperture blades, there is a star shape with twice the number of arms as there are aperture blades, since the diffraction happens to both sides. This figure illustrates that effect With an even number of aperture blades you get the same number of arms of the star shape because each time two arms coincide. Like in this figure: Link to post Share on other sites More sharing options...
stunsworth Posted March 5, 2011 Share #12 Posted March 5, 2011 The smaller the aperture - i.e. the higher the number - the more pronounced the stars will be. Open up the lens if you don't want to see them. Link to post Share on other sites More sharing options...
Nicoleica Posted March 5, 2011 Share #13 Posted March 5, 2011 Then they still make them I assume, I just haven't thought about those for years. They are still available. B+W list several in their catalogue. http://www.schneideroptics.com/info/handbook/pdf/B+WHandbook_Full.pdf (Page 43) Link to post Share on other sites More sharing options...
Washington Posted March 5, 2011 Share #14 Posted March 5, 2011 Anders, Just a wonderment because from what I learned here the diaphragm blades cause the effect. So, would fully opening the aperture to withdraw the leaves for a round light path eliminate the cross flair? Naturally this creates other problems such as depth of field….. but a slow lens and perhaps neutral density filters would allow exposure with shutter speed and/or iso adjustment. Do you usually use a tripod? cheers. Just a thought any corrections welcome! Link to post Share on other sites More sharing options...
ho_co Posted March 5, 2011 Share #15 Posted March 5, 2011 Thanks - does it mean that I get different effects at different apertures? ... Anders-- Yes, different effects at different apertures because the blades tend to form a more nearly circular opening at some apertures than at others. With digital cameras, you have the ability to see the result immediately on the review screen. That's an advantage not offered by film. Even though they don't have diaphragms, you'll often see such spikes from optical telescopes as well, usually due to the supports for the secondary mirror. As suggested above, go try a lens at various apertures on the same subject to see how the effect changes; and try additional lenses as well. See also Diaphragm (optics) - Wikipedia, the free encyclopedia. Remember also that diaphragm spikes arise from overexposed sources. I think that at wider apertures therefore, the highlights will tend to be less overexposed with respect to the overall image, and the spikes will be less noticeable. That is, a 16-sec exposure at f/11 gives more time for the spikes to appear than 1/2 sec at f/2. (Someone else can word that better. Obviously, these highlights are blown out in all cases, but with shorter exposures fewer of the photons that cause the effect will reach the sensor.) Link to post Share on other sites More sharing options...
jaapv Posted March 5, 2011 Share #16 Posted March 5, 2011 Not only that, Howard, but diffraction effects increase as the aperture gets smaller. Link to post Share on other sites More sharing options...
ho_co Posted March 6, 2011 Share #17 Posted March 6, 2011 Good point, Jaap. I take it that's because the ratio of circumference to area is greater with as the aperture is reduced? Come to think about it, that would have much more impact on the spikes than my time explanation. Thanks! Link to post Share on other sites More sharing options...
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