What causes white halos around bright subjects, and how can I prevent them?
Asked 7/17/2015
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2 answers
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I photographed a high-contrast scene and noticed a white glow/halo around a bright white shirt against a darker background. The image was made with a Canon 6D and EF 24-105mm f/4L. I’d like to understand what causes this effect in-camera and what shooting or equipment changes can help prevent it, rather than relying on retouching afterward.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
2 Answers
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This looks to me like a badly smeared lens, I have taken loads of photos with this much contrast and never seen blooming like this, but dirty lenses (or damaged coatings on my cheaper old film cameras) give exactly this effect.
As Mike Sowsun said in the comments, a cheap or dirty filter could also have this effect.
The effect will in fact be consistent across the image; it's just the case that it will show up more in the brighter areas.
This is how starburst filters work; all light is affected by the filter to the same degree, but only the highlights will have visible stars as they have such high contrast compared to the rest of the scene.
Here is a good read on flare: https://photographylife.com/what-is-ghosting-and-flare (far too long to copy I'm afraid, consider it background reading :)
Re: coatings and flare not related to dirt, I'm no physicist, but as far as I can tell, flare is caused by internal reflections within the lens - causing light to fall on the sensor from unwanted directions. Coatings are designed to be specific thicknesses near the wavelength of light that causes destructive interference that eliminates these.
The light reflected by the coating surface and that reflected by the lens surface have a phase difference of twice the coating thickness. If the thickness of the coating is one quarter of the wavelength of the light to be suppressed, light of that wavelength reflected by the coating surface and light reflected by the lens surface will cancel each other out. This reduces the overall amount of light reflected. In short, coatings make use of light wave interference phenomena to eliminate reflections.
From: http://www.canon.com/technology/s_labo/light/003/03.html
Also: https://en.wikipedia.org/wiki/Anti-reflective_coating
In short, it's likely cheaper lenses/filters have coatings that do not have sufficient tolerances to work effectively at reducing flare.
It might be worth noting that I've only seen flaring this bad on either a very badly smeared lens, a lens with a damaged coating, or a lens with no coating.
Also, any filter will tend to increase flare because the more glass surfaces you add, the more opportunity for internal reflection.
Originally by user38956. Source · Licensed CC BY-SA 4.0
user38956
11y ago
0
Generated from our catalog & community — verify before relying on it.
The halo is most likely caused by one of two things:
- Overexposure/blooming: If the white shirt is heavily overexposed, very bright sensor pixels can spill into neighboring pixels, creating a glow around the highlight.
- Flare/scatter from the optics: A dirty lens, damaged coatings, or a poor/dirty protective filter can scatter light and make bright areas bloom. This is often most visible where bright subjects sit against dark backgrounds.
How to reduce it:
- Lower exposure enough to protect the white shirt highlights.
- If that makes the rest too dark, consider multiple exposures/HDR or change the scene/lighting if possible.
- Clean the front and rear lens elements.
- If you use a filter, remove or clean it and compare results.
- Inspect the lens for internal haze or coating issues if cleaning doesn’t help.
So the effect is usually a combination of clipped highlights and/or light scattering in the lens/filter system, not something unique to that camera body.
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UniqueBot
AI11y ago
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