Stars in my lens
June 9, 2009 7:11 AM Subscribe
When a camera is focused on a bright light, there is a "star" flare around that light. I've noticed that in different situations, that flare has a varying number of points... What decides how many point the lens flare has? BONUS QUESTION: I've only ever seen even point counts... Can odd happen?
Best answer: Yep, aperture blades. And there's always an even number because each blade's midpoint makes a point, and the corners between two blades makes a point.
posted by notsnot at 7:21 AM on June 9, 2009
posted by notsnot at 7:21 AM on June 9, 2009
There are in fact lenses with odd numbers of aperture blades. Some SLR lenses have 7- or 9-blade apertures.
posted by kindall at 7:58 AM on June 9, 2009
posted by kindall at 7:58 AM on June 9, 2009
Yes, but as notsnot points out, each blade creates two points. So there can only be an even number of points.
posted by HFSH at 8:37 AM on June 9, 2009
posted by HFSH at 8:37 AM on June 9, 2009
Each blade creates two points? Huh? Bokeh can be any shape. Check out the Lensbabygallery under the creative aperture kit.
I'd deep link to the 5 point star orchid picture but web 2.0 doesn't like that.
posted by chairface at 11:47 AM on June 9, 2009
I'd deep link to the 5 point star orchid picture but web 2.0 doesn't like that.
posted by chairface at 11:47 AM on June 9, 2009
Yep, aperture blades. And there's always an even number because each blade's midpoint makes a point, and the corners between two blades makes a point.
notsnot, close, but no cigar. The blades are the cause, but the doubling effect is not due to "corners + midpoints". Rather, the stars are diffraction effects from the symmetry of the blades, and diffraction causes the doubling.
There's a +1 diffraction order, and a -1 diffraction order, for every blade. The two are indistinguishable (the polarity is arbitrary, essentially), so the apparent effect is a doubling of the diffraction source "number of features".
Sorry if my techno-speak is kinda stilted today...
posted by IAmBroom at 12:05 PM on June 9, 2009
notsnot, close, but no cigar. The blades are the cause, but the doubling effect is not due to "corners + midpoints". Rather, the stars are diffraction effects from the symmetry of the blades, and diffraction causes the doubling.
There's a +1 diffraction order, and a -1 diffraction order, for every blade. The two are indistinguishable (the polarity is arbitrary, essentially), so the apparent effect is a doubling of the diffraction source "number of features".
Sorry if my techno-speak is kinda stilted today...
posted by IAmBroom at 12:05 PM on June 9, 2009
This thread is closed to new comments.
posted by sanka at 7:11 AM on June 9, 2009