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When photographing a bright light source (stadium floodlights) a lens flare effect presents itself in the image (shot on an iPhone 13 pro). What causes this effect and how can I accomodate with the settings of the camera? enter image description here

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    \$\begingroup\$ Does this answer your question? What causes lens flare? \$\endgroup\$ Nov 10, 2023 at 16:52
  • \$\begingroup\$ On iPhones, part of the flare can often be attributed to lenses being dirty. \$\endgroup\$
    – Hugues
    Nov 12, 2023 at 23:33

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Every light source is slightly scattered by any lens and you see point light source as a point on the photo only if it has normal brightness.

Light sources with extreme brightness reveal that every lens scatters small portion of all light over a wide area. You cannot do anything with that except:

  • using "highlight recovery" if available
  • underexposing your photographs

but that might not work if the projectors are too bright. The safer solution is instead to :

  • overexpose the image so that projectors have less details
  • decrease highlight contrast if your camera program has this parameter

Also, try cleaning your lens.

The uneven "flood" (better called blooming) is caused by the fact that the projectors are facing in different directions. The ones which cause massive blooming are directed almost exactly at you.

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What causes this Effect?

The intensity of the light combined with the properties of the lens. All lenses scatter light to one degree or another. Under more even lighting conditions exposure can be controlled so that most of the scattered light is too dim to rise above the noise floor. But when very intense lights are in the frame, the choice must be made whether to expose for the bright lights or for the rest of the scene.

How can I accommodate with the settings of the camera?

If you want details of anything other than the lights themselves in the result, you can't. With phone cameras there are often "streaky" flares that are caused by skin oil on the outer surface of the lens, but I see no such evidence in your sample image. Cleaning the front surface of the lens properly will get rid of the flare caused by light being scattered by whatever residues are accumulated on the front of the lens, but it won't reduce the light scattered by the lens itself.

If you're willing to sacrifice the dimmer details, then reduce exposure by shortening the exposure time, closing down the aperture (if your camera allows, most phone cameras do not), or reducing the ISO setting in a way that the camera does not adjust another of these parameters to compensate.

Here's a moderately cropped image of the Moon and Jupiter very near each other in the sky:

enter image description here
Canon EOS 7D + Kenko Teleplus Pro 300DGX 2X + EF 70-200mm f/2.8 L IS II. Tripod mounted with wired remote release and mirror lockup. 400mm, ISO 200, f/8, 1/125.

Here's a heavily cropped area of Jupiter in a similar image a few minutes later with the same exposure:

enter image description here

Here's the same area around Jupiter with exposure increased seven stops to bring several of Jupiter's brighter moons out of the noise floor. Notice that any details of Jupiter's bands are now completely blown out:

enter image description here
Same equipment as above. 400mm, ISO 400, f/8, 1/2 sec.

Finally, here's an uncropped view of the same area of the sky (tilted 90° to the right) a few minutes later that was exposed 12 stops brighter than the original image above:

enter image description here
Same equipment as above. 400mm, ISO 1600, f/5.6, 2 sec.

The flare that is obvious in the last image was just as present in the first as light passed through the lens. But the exposure was 12 stops or 4,096 times brighter in the last image than the first. What remained hidden in the darkness of the first image is blatantly obvious in the final one, but the brighter exposure level is needed to show a few stars in the same area of the sky that are not nearly as bright as Jupiter and the Galilean moons, much less Earth's own Moon. Those stars were also present when the original image was taken, but they were too dim to be recorded by the sensor at the initial exposure setting.

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The job of the lens is to project an image of the outside world onto the surface of film or digital sensor. Light from the subject plays on the lens. About 95% traverses the lens and this light energy encompasses the image. About 5% is lost, this is due to unwanted reflection off the highly polished surfaces of the lenses. This is per lens element. Refection light loss can be as high as 50%. Lens makers strive to reduce this light loss. Their countermeasure is to coat the surfaces of each lens with a super thin coat of transparent minerals. Coated lenses reduce this unwanted surface reflection to about 2% (per lens element.

Sorry to report that all lenes continue to be degraded by unwanted surface reflections. Worst, some of this reflected light comingles with the image forming rays and this causes what is called “flare light”. Flare light can be devastating. It caused a loss of image contrast and creates “ghost" images.

What you are seeing is ghost images due to internal reflections inside the optical system. Cameras used by advanced photographers often sport a lens hood. This is a hollow tube mounted so the light from the subject must enter the camera through it. The lens hood helps by reducing unwanted entry of “side light” that might otherwise enter the camera. If this side light is shielded, flare light artifacts are diminished.

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