Why do out-of-focus highlights look doubled in shallow depth-of-field photos?
Asked 8/29/2019
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When shooting with a Canon EOS 600D at wide apertures and longer focal lengths, some out-of-focus areas show what looks like ghosting or doubled shapes instead of smooth blur. Bright edges and reflective objects in the background appear multiple times within the blur. Is this a lens defect, or is it a known optical effect related to bokeh?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
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This appears to be caused by ring-shaped / bubble / donut bokeh produced by your lens, which has soft or nearly transparent central areas and a strongly defined outer ring.
So rather than a soft Gaussian-like blur you might get from more pleasing smooth bokeh, long edges of high contrast (such as the outlines of leaves, branches, etc.) in the background appear almost as slightly blurred double images.
See also:
- Besides mirror lenses, what can cause ring-shaped bokeh?
- A link from that question (Markus Keinath - Soap Bubble Bokeh Lenses) in particular demonstrates images with apparent doubling due to the bokeh.
- Russell McMahon's answer to How do I find a camera specifically for bokeh / a very shallow depth of field? in particular shows good examples of the apparent doubling effect of the ring bokeh caused by a mirror lens, especially the photo of the kid drinking, with a silver car in the background.
Originally by user11924. Source · Licensed CC BY-SA 4.0
user11924
6y ago
0
Generated from our catalog & community — verify before relying on it.
This is most likely not sensor ghosting or a camera fault. It’s a bokeh characteristic of the lens: ring-shaped, “bubble,” or “donut” bokeh.
With some lenses, out-of-focus highlights are rendered with a bright outer edge and a weaker or more transparent center, rather than as a smooth soft blur. When the background contains high-contrast edges—like leaves, branches, or reflective details—those bright-edged blur circles can overlap in a way that looks like doubled or repeated outlines.
So the effect is usually caused by the lens’s optical rendering of defocused areas, not by rays landing in the wrong place on the sensor. It tends to be more noticeable at wide apertures and in scenes with small bright highlights or strong contrast in the background.
In short: this is a known bokeh behavior, not necessarily a defect. If you want smoother out-of-focus rendering, a different lens design will usually make more difference than changing the camera body.
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