How can I avoid starburst effects on lights in long-exposure photos?
Asked 8/13/2012
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When I shoot long exposures, bright light sources sometimes turn into starburst patterns. In one example I used a Canon 18-55mm kit lens with an ND8 filter, ISO 100, f/32, and a 60-second exposure. I did not use a star filter. What causes this effect, and how can I reduce or avoid it while still getting a long exposure?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
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Its probably due to a narrow aperture. On professional grade lenses, you can usually stop down a bit and still maintain a rounded aperture, however on cheaper lenses, or on all lenses at very narrow apertures, the opening becomes polygonal. That causes the diffraction of light as it passes through the aperture to produce a star pattern (the exact nature of which depends on the number of sides/points in the polygonal opening.) Use a stronger ND filter or and/or a lower ISO setting to reduce the effect.
Given that you are using the kit 18-55mm lens, its unlikely the diaphragm uses rounded blades. Star patterns will start to exhibit pretty early, and get stronger the more you stop down. If you have the cash, you could try getting a higher quality lens. Most of the L-series lenses have rounded aperture blades, which eliminates the effect at the wider stops, and mitigates it in the middle stops (not much you can do once you get down to f/11, f/16, f/22 though.)
Originally by user124. Source · Licensed CC BY-SA 4.0
user124
14y ago
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Generated from our catalog & community — verify before relying on it.
The starburst effect is mainly caused by using a very small aperture, especially around f/22–f/32. At those settings, diffraction increases and the shape of the lens diaphragm becomes more visible, which creates the rays around bright light sources. This is often more noticeable on kit lenses, whose aperture blades may be less rounded.
To reduce it, avoid stopping down so far. Use a wider aperture instead and get your long exposure by:
- using a stronger ND filter
- keeping ISO as low as possible
- possibly using a higher-quality lens with more rounded aperture blades
A filter will not remove the effect once it’s being caused by the aperture; the practical fix is changing exposure settings so you don’t need f/32. A physical circular mask could reduce the polygon-shaped aperture effect, but that’s a workaround and not the usual solution.
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