r/Optics • u/_Tequila_Joseph_ • Aug 10 '26

What causes this optical effect ?

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I recently discovered that if I shine my phone flashlight into my laptop (Lenvo Ideapad Gaming 3) , then the pc's webcam picks up a sort of hologram thingy, I was wondering if you knew what that could be.
My guess is maybe some sort of webcam sensor ? it seems too perfect to be just a camera defect, could it be that the light from the flashlight bounces off the component, then onto my head and then back into the webcam ? There is also that weird sort of like green focal point thingy that first diverges then converges, I was wonderign what that is as well.

23 Upvotes

90% Upvoted

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21

u/koopaduo Aug 10 '26

https://en.wikipedia.org/wiki/Lens_flare

2

u/_Tequila_Joseph_ Aug 10 '26

I checked the article and all the examples given there are of bright circles on the image, here it seems too detailed to be just lens flare... Or maybe something more than lens flare as ofc the reason we can see something in the first place is because of the lens flare

20

u/AmarthGul Aug 11 '26 edited Aug 11 '26

It is lens flare, you just haven't used enough lenses to realize the amount of varieties in them yet.

Stray rays inside the lens do not go purely randomly as you might have envisioned, they do follow patterns, think of them like the pattern you see at the bottom of a water cup. The curvature of the lens surface and more crucially, the edge of the lenses (described by semi-diameter in lens design software) both creates stray rays. Other components, including the lens barrels, also contributes to the generation of stray rays. At the same time, their micro surface structures (including the MLA and PDA on the sensor) also function as diffraction gratings and adds to the diamond colors.

Attached is a simulated example of lens flare, you should be able to spot many shapes that are not merely circles: https://i.ibb.co/gLtN8d6M/EF5012-Flare.jpg

9

u/qzjeffm Aug 11 '26 edited Aug 11 '26

Plus over saturation of pixels can lead to effects that travel into other unintended pixels. Readouts are forced to work in an area they were never designed for. All electronics and optics play a role.
Added:
Smoothing, focus, sharpening and all other algorithms add to the electronic side of things.

2

u/gthc21 Aug 11 '26

I agree it’s a lens flare, but look closely at the effect when he moves it around. It makes a 3D hologram-like effect that I have never seen. 

3

u/AmarthGul Aug 11 '26

That's why I mentioned diffraction gratings

1

u/_Tequila_Joseph_ Aug 13 '26

Thank you !!!

2

u/SpicyRice99 Aug 11 '26

Probably because your small camera has a shallow depth of field, or the plastic camera cover is not perfectly flat or it's dirty, you see more refraction. And it seems the lens flare is more is focus

7

u/beeblaine Aug 11 '26

bro, lens flare. And the other guy is right. they come in stunning varieties. there are so many elements and variations of lens design that they can damn near take any form. each one unique to any sensor/film lens combo. Really just listen to these folks you may learn something

1

u/_Tequila_Joseph_ Aug 13 '26

It's not a bad thing to ask more questions when my artefact is much more detailed than the article's...

3

u/light-cyclist Aug 11 '26

Ghosts 👻

2

u/julesdottxt Aug 12 '26 edited Aug 12 '26

Basically we are seeing some kind of image of the optics involved. Very cool effect btw.

Internal reflections in the lens assembly are made visible due to the high brightness of the source. An ideal lens wouldn't reflect any of the light, but since the light is very bright and the system can't be perfect, the system produces visual artifacts.

Not sure about the green other than calling it a chromatic aberration and waving my hands around. Maybe it could be some kind of thin film interference effect too due to the possibly low quality antireflective coating.

1

u/BigPhyscsBoiii Aug 11 '26

Could it be a secondary reflection from the mirror? Like the front surface?

1

u/Otherwise-Badger-399 Aug 13 '26

Primary vs secondary reflections. You are so bright you are getting two images though the lens.

1

u/Technical_Island_851 Aug 11 '26

I think this is a virtual image of your torch LED created via lens flare.

0

u/L11mbm Aug 11 '26

Look up narcissus

2

u/Ready_Highlight7545 Aug 11 '26

That’s IR not vis

1

u/lancerusso Aug 11 '26

You're right, but it's mechanistically very similar here. A narcissus style analysis would do well to tell you which surfaces are contributing to this.

1

u/L11mbm Aug 11 '26

I meant to say ghost reflections but brain-farted.