But What IS A Lens Flare?

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A lot of people took pictures of the recent solar eclipse in North America and got photos where there’s a ghostly image of the eclipse floating in the sky nowhere near where the sun is!
REFERENCES:
Lens flare prediction based on measurements with real-time visualization doi.org/10.100...
Physically-Based Real-Time Lens Flare Rendering doi.acm.org/10....
From the Series of Articles on Lens Names: Tessar, by H. H. Nasse. Carl Zeiss Camera Lens Division March 2011
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www.toolfarm.c...
petapixel.com/...
www.maxon.net/...
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Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
Created by Henry Reich

[@Naqaj]

We're so used to seeing lens flares that video game graphics spend considerable resources to recreate them in modern games, even though there's no lens involved there at all and no reason for them to exist.

[@mytube001]

That, and chromatic aberrations, which is insane, as our eyes don't have them. Most games are from meant to be the view out of the player character's eyes, after all.

[@D-Rock420]

Yeah I noticed that about GTA5. It was very realistic driving towards the sun 😆

[@IdoN_Tlikethis]

​@@mytube001I hate that so many games have chromatic aberrations and film grain enabled by default, because these effects are often greatly exaggerated compared to modern cameras

[@onebacon_]

Lens flare are understandable tho, they look cool, and kinda recreate the feeling of really bright lights. Chromatic aberration is just ugly

[@altaccout]

Videogames aren't trying to pretend to be a perfect recreation of someone's eyes, they are creative projects that throw in impressionist elements to look good and make you feel something within the limits of a screen You might see rain drops on a first person view despite rain drops not being possible on human eyes, this is a way to invoke the sense that the character feels rain on their face. You might use chromatic aberration to invoke the feeling that it's hard to look at something, or film grain to give a sense of paranoia of shadows

[@TaranVH]

One thing I like about lens flares is that you can see just how much work the image stabilizer is doing, since the flare can be jumping around quite a lot, while the main image remains quite steady.

[@krakow10]

Same deal with reflections, such as on your phone screen. The movement is amplified so that imperceptible motion becomes perceptible.

[@lensflairphotos]

LensFlair likes you too

[@Hyraethian]

Woh, good catch. That's cool.

[@sadderwhiskeymann]

As far as I know (studied electronics ~20 years ago -didn't practice it😢) the stabilizer steals pixels from the edges as to compensate if you move a bit. I remember having a camera with a stabilizer switch on the menu, and when i would turn it on the resolution would drop.

[@Michael-dx8qz]

@@sadderwhiskeymannfor optical stabilisation, the jumping flares are generally less apparent

[@EpicStrat]

I'm a lens designer. Very happy to see some optical engineering content on this channel. This is a quote from the preface of my go-to Stray Light textbook (E. Fest, Stray Light Analysis and Control). 'In 1741, the great Swiss mathematician Leonhard Euler was asked by King Frederick the Great of Prussia to write a tutorial on natural philosophy and science for his niece, the Princess of Anhalt-Dessau. Euler agreed and began writing the tutorial as a series of letters to the Princess, about one a week, for nearly 250 weeks. These letters were eventually published as a collection and became some of the first popular science writing. In a letter entitled "Precautions to be observed in the Construction of Telescopes" (shown in the second figure), Euler recommends that the Princess ". . . (enclose the telescope) in a tube, that no other rays, except those which are transmitted through the objective, may reach the other lenses. . . If by any accident the tube shall be perforated ever so slightly, the extraneous light would confound the representation of the object." He also suggests that she "[. . . ]blacken, throughout, the inside of the telescope, of the deepest black possible, as it is well known that this colour reflects not the rays of light, be they ever so powerful.'" Amazing that we've been collectively observing this phenomena for hundreds of years, and the mitigation techniques for it are largely unchanged since then.

[@catvamp100]

69 likes... nice

[@catvamp100]

Also, we've been trying better lenses and blacker blacks(paint)

[@vigilantcosmicpenguin8721]

I guess that was the 18th-century equivalent of the six-pointed spikes from the JWST. Some things stay the same.

[@justingould2020]

Unless you're Anish Kapoor@@catvamp100

[@KO47893]

Something that's fascinating to me is that we've become so accustomed to seeing lens flair in video and images that we replicate it in CGI to increase the realism even though removing lens flair would represent a live scene better.

[@a52productions]

Would it? It might just be my eyes, but when I focus on a bright light from far away, there's usually a tiny spiky halo around it. Not as big as a lens flare from a camera, but a lens flare nonetheless.

[@DlyanMatthews]

@@a52productions thats a different effect than lens flaring, but is something minutephysics has a separate video on (from 9 years ago) for the curious: kzbin.info/www/bejne/jIekfHmAbbuJppY

[@KaitouKaiju]

​@@a52productionsYou probably have minor astigmatism

[@Lemony123]

@@KaitouKaiju yeah, I also have it.

[@TheRealSkeletor]

@@a52productionsThat's either astigmatism or you're perceiving the reflections of light off your own eyelashes (I'm not crazy, that's an actual thing).

[@gamebuster800]

fun fact: some lens flares are actually the reflection of the sensor in the rear-most element, so even if lenses are very good at eliminating reflections, some cameras have particularly shiny sensors the lenses weren't designed for.

[@Rwdphotos]

that's one of the reasons why old lenses designed for film cameras don't work very well on digital cameras, because they reflect too much light that comes from the sensor.

[@germansnowman]

That’s also why these look green - it’s the color of the sensor.

[@Skarix]

In animated shows and movies, the animators often add lens flares especially for shots of the sun, despite the fact that they're "not supposed" to happen. This is because people have gotten so used to seeing them in videos that the lack of it feels off. It's such a happy accident that people go out of their way to make it happen as a non-accident.

[@primenumberbuster404]

Man, I missed u so much :)

[@3tree3]

4real

[@vklmao8677]

4real

[@TheCrewExpendable]

Parasocial relationships are not healthy.

[@ThatWhoCares]

4real

[@TwistingStew69]

4real

[@jannegrey593]

It feels like it's been a long time, since I saw Minute Physics video. Great as usual.

[@asailijhijr]

There was a partial eclipse in my area a few years ago and I could see it in the shadows of the trees. The leaves of the tree made several thousand pinhole cameras, which all of them looked like the eclipse (though I couldn't confirm this by looking at the eclipse directly).

[@Bob94390]

I believe you. The curtains in my bedroom once made a pinhole camera. At night I could see a "bright" circle on a cupboard. It was only when this happened again at daytime that I realized that I had seen the moon and the sun.

[@RibusPQR]

So that's what causes that! I was confused because shadows don't look like that.

[@tiaxanderson9725]

I tried to put my hand behind the sun, but to no success. Then suddenly, half a year later, I succeeded even though I wasn't doing anything different :P

[@Bob94390]

Just remember to keep a distance so you don't burn yourself.

[@erikziak1249]

The takeaway from this video is: Always use a hood on your lens, even if there are no visible bright sources in the image that might cause flare. Not only does a hood reduce even indirect light hitting the front element of the lens and causing flare and other problems, it also protects the lens, as it creates a physical barrier between the first lens element and the scene, making touching, hitting or scratching the lens much less likely.

[@brianfunt2619]

Yeah but it has disadvantages, such as sticking out when you want to put the camera away, and making it difficult to rotate polarising filters. So I wouldn't say always use a lens hood.

[@carjac820]

We've been so accustomed to lens flare in digital media that lens manufacturers started to market such defect as a feature. Sometimes even intentionally design the lens to actually have flares

[@josephgrainey5048]

I'm so happy you're still making videos. I used to watch every new video in hs and my early 20s. Nice to know you're still here.

[@xizar0rg]

I wasn't able to photograph the eclipse so much as I was able to capture a very nice lens flare of the eclipse.

[@FHBStudio]

Time and Date has great eclipse calendars, and you can also use Stellarium to view the solar system (and stars etc) and advance/rewind time. I couldn't catch the last eclipse, but I could view it in Stellarium afterwards. Wasn't as impressive, but still fun to do.

[@Bob94390]

Thank you for a very informative video. Some others could have made a one hour video with the same information; you managed to compress it down to 5 minutes. Impressive!

[@Rwdphotos]

You wondered if the flares were the shape of the lens element or the aperture, and you could actually see the shape of the aperture in the flare as it moved across the frame. There's a perspective shift that happens relative to the position of the light source that causes the aperture to take "cat's-eye" shapes towards the edges of the field of view (similarly how your own pupil would look if viewed from a side angle, you're essentially viewing a circle from the side, causing it to become more oval in shape).

[@6Twisted]

I hope game devs who feel the need to add lens flare and chromatic aberration to their first person games see this.

[@SioxerNikita]

Why? Most game devs that add lens flare and chromatic aberration is aware that it is a "fictitious" effect. They are adding it for theme and vibe, giving a more cinematic look.

[@jean-huguesbouchard1045]

0:00 Did not know you were from Canada. Hi fellow Canadian from Montréal (QC)

[@CorpCoCEO]

I got a few photos like this with my phone, what an awesome accidental science lesson on top of the already extremely cool science moment, the eclipse itself

[@roeesi-personal]

You can also get flares inside your own eyes (or at least I can), when you look at a strong light projector you can see a rainbow around it (and probably other circles as well) which is a diffraction flare of the human eye.

[@Zaborav]

I just remembered what these videos remind me of. Blue's Clues, when drawing the clue. With the low bass in the background and the drawings, etc. fun stuff.

[@TK_Brainslug]

didn't JJ Abrams perfect the lens flair? :D great video as usual Henry. I hope the rest of the family is doing well

[@lensflairphotos]

I cant say anything about Henry but I'm doing great thanks for mentioning me! haha

[@Lynxdom]

I was hoping someone would bring this up :) Makes me wonder if there are lenses engineered for dramatic flairs :)

[@smurfyday]

Honest Trailers!

[@hanniffydinn6019]

JJ Abrams & 80s films love lens flare! 😎😎😎😎😎😎😎😎😎👍👍👍👍👍👍👍👍

[@DomyTheMad420]

i genuinely got an amazing laugh out of everyone going: "AHA SEE?! this is proof of

[@KnowArt]

great video as always

[@PhysicsPolice]

Great video, entertaining script, especially at the end!

[@MeeKtheOWL]

If I look at a bright led and just squint, it recreates an interference pattern in the flares.... neat!

[@__-pl3jg]

This seems like what we see in all those military UFO videos. Except I think it's the parallax reticle being out of focus we're seeing in those UFO videos.

[@goyhlandstar]

I am actually surprised U're still alive and actively uploaded on Utube. Thanks for Excellent Works!!

[@sisi7304]

sometimes lens flares add depth and make for really cool shots intentionally, but having it work on eclipses is even cooler!!

[@the-vuk]

We are so used to flares in images that video games program them into their rendering when it shouldn't even be there. They make extra effort to make it look realistic.

[@FactsRandomizer]

Best teacher on youtube

[@coin777]

1:40 Human visual system response is logarithmic. So 1% light passing is just 25% less bright than 99%. Not 1% as bright...

[@SioxerNikita]

Yeah, but it is still only 1% as absolute bright, in terms of luminance.

[@Rwdphotos]

sensors are not logarithmic in response. A log curve needs to be applied to give a resemblance to human vision. Also, the 1% figure had nothing to do with relation to vision; 1% transmittance is a measured valued in relation to the strength of the source. It would be improper to curve it in relation to human vision with respect to lens design. The closest relationship you get would instead be a "t-stop" value.

[@mrapistevist]

Good episode. 👍

[@kocajj]

So cool that you can see sun spots at 3:08 without a proper solar filter to see them. I was expecting them to be drown out on the flare.

[@therealdefoma]

I personally really like how lens flares look. Also, most 3D games with light scattering implement it even though there's no reason to... aside from looking good.

[@griffinschreiber6867]

It's so funny how camera people try to make lens flare go away, and computer graphics people try to add it.

[@AlexanderTzalumen]

I recently got a really clean photo of an eclipse through juuuust enough cloud cover. The blue halo around it is a very interesting visual effect.

[@jdos2]

Nicely diagramed Tessar!

[@PhilipMurphyExtra]

A video of information, This is great

[@davidhayward1426]

The explanation of why the flair is green in your examples is really interesting. (Hint: the sensor of cameras that use Bayer patterns looks green)

[@Heavenira]

AMAZING video on the subject, "What is bloom? (And how is it simulated?)" (2021), talks about how to simulate real artifacts like glare in cameras.

[@mahxylim7983]

So cool, i never question those

[@natures_guardians]

Please. I need more uploads!

[@JuanWonOne]

A toonie!? I think thats the second coolest part of this video!

[@ginnyjollykidd]

One of those lens flares-as you moved it across the sun-seemed to indicate a bowl-shaped flare cupping another flare. It's that caused by the camera? I've seen during one eclipse decades ago that light shining through the trees hit the ground in "C" - shaped crescents, just like on my pinhole cards. The edges of these tree leaf aperture were also made up of crescent-shaped lights, even though the light on the ground seemed to mirror the shape of the aperture it came through. I could put my hand between the light and the ground and block it. I'm assuming even the camera obscura I made as well as the leaves caused the little crescents on the ground even as waves were bent at the edges of the aperture. To see the flares, I assume you have to look back through the aperture to see the light bounced off the aperture.

[@mikegale9757]

Well, that was fun. Good job.

[@overestimatedforesight]

Hello old friend, welcome back

[@Kang_The_Creator]

*As someone who Got into Indie Filmmaking & VFX/Compositing back when the First JJ Abrahams Star Trek came Out i feel called out as would my entire group of friends at the time probably upon seeing this* 😅 *We went ham on the Flares and i had to kick my Lens Flare Addiction JJ Abrams Gave My Indie Film Making Circle.* *Now as a Designer I'm Addicted to Bloom & A Level of Saturation that would make Doctor Who Throw Up.* *To be fair its inspired by that 2000s Era of Games like Oblivion back in that "Bloom & Color" way.* *Amazing Work & Super Informative Video!* ✨ *I will actually be using this video to try and test doing some more realistic shots jus because i wanna see the difference now that i know* *Truly I feel quite dumb for never realizing this although I've never even handled a camera with an adjustable lens due to budget constraints* *Wouldn't have gotten good at VFX & Compositing if i could afford to do anything* 😂 *You Rock* *Please Take my Like & Sub!* 💕 🙏 Edit : *Apparently I Was Already Subscribed...* *They All Blur Together after a While*

[@adityaadit2004]

can you please explain how aperture affects depth of field in camera in terms of mechanical?

[@iissamiam]

The brightest thing is why cinematographers use lens flare. The flare emphasizes and illustrates the brightness of a light source, because movie screen can only get so bright.

[@wynchesster]

I loved how you used a toonie :)

[@turkysanwtch]

Do we know if our eyes lens flare? Is it something our brain just filters out? If there's no such thing as a perfect lens our eyes have to have some kind of defect like that, right?

[@logitech4873]

Our eyes have pretty minimal flaring because they consist of 2 lenses, meaning it's a very simple optical formula with less chance of flaring. The downside is that our eyes only provide a sharp image in the very middle of our vision. Our peripheral vision is pretty terrible. Cameras are expected to provide a sharp image all across the frame.

[@turkysanwtch]

@@logitech4873 That makes sense, thanks for the explanation!

[@Bob94390]

That is a very good question. The eye lens has lens flare. But usually we don't notice it since we get used to it, a little bit like we usually don't notice that we see our nose. Lens flare may produce fake images outside of the tiny area where we have sharp vision; then it will be very difficult to notice them. Laser surgery on eyes can produce lens flare, e.g. as halos around street lights at night. I suspect that this may perhaps be caused by quantization of the laser light; it comes as a discrete number of pulses at each location, and between areas with different number of pulses there will be a lens defect.

[@Rwdphotos]

@@logitech4873 we have sharp vision across our entire field of view, but the density of cones in the retina are packed in the center, with mostly rods existing in the periphery. Rods aren't color-sensitive, but are much more light-sensitive, so it's better to have them on the periphery rather than in the center. The retina is bowl-shaped, which actually helps to increase resolving power and reduce things like spherical aberration (related- way easier to have acceptable field curvature, for example). If camera sensors were spherical, we wouldn't need nearly as many corrective elements in lenses, but they would also likely be relatively limited in functionality and need geometric corrections.

[@logitech4873]

@@Rwdphotos I assumed the retinal resolution dropoff also implied lower lens resolution towards the edges. Usually lenses with 1 or 2 elements are only sharp in the middle, and horribly soft everywhere else. I guess there spherical "sensor" area can improve things quite a bit.

[@ScytheNoire]

Don't stare at the sun unless you are a stable genius.

[@1.4142]

I didn't want to buy a solar filter for my camera, so I just stacked 4 layers of car window filter, and it worked.

[@thirdpedalnirvana]

You can point a manual film camera towards the sun. Just don't try to use the light meter. Assume you need max shutter speed and minimum aperture.

[@Felipe-eb4zm]

The phrasing in the script sometimes is funny. I know it’s supposed to mean “unintended” or “undesired”, but when Henry says that light "incorrectly reflected or difracted”, it sounds as if he’s saying “the light didn’t obey the laws of physics” 😄

[@TheOtherSteel]

A minutephysics video! Yes! Ah, for those days of eld when many such videos were published. Perhaps they will be again, one day.

[@PPedroFernandes]

"which, with the sound at least, is kinda of hard" Me: is that a challenge?

[@cuteraptor42]

1:45 1% is a non insignificant amount when we talk about light you will definitely see it

[@christianadam2907]

at 3:10 you can see a sunspot in the projected image of the sun. Nice

[@minecat1839]

I'm JJ Abrams and I approve this message.

[@thefantom12]

What about the eye of the observer? How would that play in lens flares?

[@KerrikkiLurgan]

I think it is really weird how when playing a computer game, you often see in-game suns with lensflare

[@alphaapple1375]

At 2:00: I love how there is a rainbow-color🌈 in the lens flare.

[@MrViii31]

welcome back!

[@AntoniNowak69]

no, that's just a windows loading cursor. someones pc is lagging

[@KeshenMac]

1:45 So brighter = more disadvantaged for privacy

[@durdleduc8520]

here's a question: how come during a partial eclipse, shadows are also cast in the shape of the eclipse?

[@hal2dal]

nice twoonie!

[@olegshevchenko5869]

The last few seconds is how I tell apart the original image and astigmatism 😅

[@Brennen666CA]

A toonie! The coin of my people! Top notch.

[@QuantumHistorian]

Ok but why is the lens flare a resolved image of the bright light source? I'd expect it to be wildly out of focus and blurry if it's caused by incidentally scattering inside the camera lens, because there's no reason why the lens creator would design it to have that effect. Clearly the eclipse photo proves that it is in focus, but why is it in focus?

[@Bob94390]

How could the systematic lens flares described in the video get out of focus? Lens flare is not there by design choice.

[@MikeOrkid]

I'm surprised you didn't talk about anamorphic lenses/filters to amplify the lens flaring. JJ Abrams style.

[@eurogryphon]

Lens flares are very noticeable in any J.J. Abrams movie, as they are one of the key visual elements to said films.

[@AntonMadness]

Fist time I watch this movie, I only listen to the bass. Then I have to watch it again and force myselfs watching the darn movie x-D

[@BharatRajagopalan]

Welcome back

[@citratune7830]

what is that thing where lights get stretched out at night when i wear glasses? is this it?

[@eklhaft4531]

this is why it's really easy to see inside house at night ... **checks blinds**

[@Astute-Brute]

Reminds me of astigmatism

[@XBananD]

What is the speed of light from its perspective

[@SuperBlackReality]

I don't get it, if it's a defect or light scattering around inside the aperture, how does the flare produce an "image" like in the example the eclipse, and not just some random noise?

[@Bob94390]

If almost-parallel light rays remain almost-parallel through the lenses, then you will see an image rather than random noise. The lens flares described in this video have this property.

[@chillsahoy2640]

J.J. Abrams I hope you're paying attention and taking notes!

[@TheMarcusGomez]

Noticed lens flairs on night time rocket launches.

[@brachypelmasmith]

why is flare in focus if it is a product of "random" aberrations and reflections inside the lens elements?

[@oophyte]

A toonie? After all these years never knew you were Canadian!

[@tedarcher9120]

Why does the flare appears as a correct image instead of an out of focus blob though?

[@SMunro]

Use a pinhole, and photograph the image projected from the pinhole.

[@Bob94390]

That is a good solution for case where there are enormous amounts of input light available. It is useful for taking pictures of the Sun, but not the Moon :-)

[@rupen42]

I've been using glasses for decades and only now realized the lights I used to play with as a kid are the same as lens flare.

[@coreymeh8335]

i know that not all lenses are perfect but the way the lenses of my mirrorless camera reduce flare to something more tasteful (unless im using a subpar filter on the front of the lens). i loath taking night photography shots with my iPhone, the worst flairing ever especially with city lights, so many tiny little greenish ghosting reflections of the point source of light.

[@juliane__]

Or how most of the airforce UFO videos are made with addional filters, rotating the camera on spot etc..

[@djones02]

Thank you so much. I just wish my dad was around to see this. He was going a bit off the rails in his later years. Not dementia just jaded and disbelieving everything. He was obsessed with conspiracies, especially flat earth and covid. I'm not sure if he thought eclipses were fake but he showed me a picture he took of a partial eclipse and was pointing out how the eclipse was in the wrong place. I told him this was actually really cool efrect of the lense but he did not understand. Unfortunately the covid conspiracy theories got him killed.

[@srgkzy1294]

OMG 😊 ❤ i did this during the eclipse hehehe It was fun ^^

[@DaellusKnights]

Does that apply to "sunbows" too? Not the ones you can see with your eyes in the sky, but the ones that show up in a picture when there isn't one you can see with your head-orbs? On occasion I've had pictures of the sky turn out with really intense multicolor halos around the sun, even though there wasn't one to be seen, or anythign in the sky like clouds to cause one...

[@vibaj16]

maybe those are somehow caused by bloom

[@twang5446]

But why iPhone seems to have much worse flare than other phones? Anything to do with the "sapphire" lens?

[@Laba2Wajile5Dhintay]

great video

[@James2210]

I wonder, do fresnel lenses have the same problem?

[@Bob94390]

There is a reason why fresnel lenses are not used in cameras :-)

[@richardcastelo9587]

Today I learned that you're Canadian like me!!!❤ Oh, and stuff about lens flares, blah, blah, blah, who cares? One of my favorite channels is Canadian!🥳🥳🥳 Behold the glory that is the twonie!

[@Mike__B]

A triumphant return? Or another tease with a half year absence?

[@Nixplaystrombone]

Wake up babe, MinutePhysics just posted!