Caustic lenses are really weird 

I now have a Discord server: discord.gg/B6uNzAgshy Come and say hi. The sponsor is Henson. Get 100 free blades with your first safety razor: hensonshaving.com/stevemould use code stevemould

the transition from the goofy shaving sequences to the horrible business model of printers to the sponsor was amazing

I love how you can clearly see Steve getting more and more giddy with this shaving bit as the video goes on.

I cannot believe that I didn't see the changes in your facial hair until the half-way point. The strange feeling I got, once I realized it had been happening already and I'd been missing it, will be my main takeaway from this video. And the concept of caustic lenses will probably be floating around there somewhere too... but certainly not as palpably.

That. Is how you make a RU-vid video. Take notes people. This man. This man right here.

Loved how the shaving starts off subtly and gets progressively more. Way to go, all in for a sponsor. Hope they appreciate you.

Caustics are also one of the hardest problems in computer graphics, because light from anywhere in the scene might just end up on one of those bright lines, so you have to simulate a ton of light rays to get a noiseless image.

Bro the gradually shaving your beard throughout the video melted my brain.

A1 video Mould. I’ve been subscribed since at least the 10th grade (im 25 now) and I can tell you that I’ve noticed how your videos have gone from purely informative to informative and genuinely entertaining. Feel like you’ve come into your own shoes in the RU-vid sphere. Can’t wait to see what you got cooking next man. This is one of the best educational channels on this site.

You integrated the sponsorship so well and without interrupting the video that I watched the whole thing at the end out of curiosity and respect. Very well done!

1:11 - that's one of the most beautiful things that exists in my opinion. Since I was a kid I always were mesmerized by those lights under the water.

That subtle smile, you know what you are doing with your beard. Bravo!

4:18 this is so cool, I would love to see something like a scaling medieval landscape with a castle or something but instead of it being thru the thin edge, carve it so if shine light thru it sideways you get a long flat artwork

At EPFL (where the Alan Turing image comes from) there are a few of those acrylic panels under the library so that when sunlight shines on it, faces of famous people show up on the ceiling. Pretty impressive "resolution" too when the light shines just at the right angle

The most impressive part is seeing the black areas, you'd just expect the non-lit sections to be the same as the loght passing through flat glass. Seeing that immense contrast is so cool!

Finally! I've been waiting for this follow-up!

visually encoded shaving transform is a nice touch and proves production & editing skills.

Man.. The gags that Steve has for his first video of the new year always get me. Between his ballerina act last year and the disappearing beard gag this time, it makes me wonder if the family he visits during the holidays are all buttoned down people who don't respond to his humor, and he just has to let it all out afterward?

Noticing half the beard gone at 3:49 really shocked me. Had to go back to make sure it wasn't gone from the beginning!

What a cool idea for an episode and very well done. Very fascinating. Bravo

The way you introduced your sponsor is so awesome!

I absolutely love the creative approach to the ad read. We are so used to skipping over ads because they are just written by a company who is paying the creator to read a script. When a creator spends the extra time and effort to make the ad their own with a creative twist or spin on the ad read it really makes you want to watch the ad! Not because it’s an ad but because now it is content form the creator who you are there to watch in the first place.

I'm curious how they actually make these peices of glass.

Okay but that business card one from the beginning is genius-

Good job on the sponsorship spot! It did make me want to try a safety razor and I like well engineered items. I'd have been willing to pay £30 for the handle, but nearly £60 is too rich for me.

Half beard Steve is not real, it can't hurt you. Half beard Steve: 3:48

Wait a damn second! 5 minutes into the video and I only just now notice that half his face is shaved? Am I missing something? XD Btw great video so far. Edit: okay the shaving is progressing as the video goes on... I am THOROUGHLY confused xD

smooth transition 🙂Also - the pattern made by those lenses when turning, reminded me of video waveform monitors.

Thank you! Your videos always brighten my day. Then in top of that, I learn something new.

3:48 his beard is half gone but it’s all there in the shot before Edit: it gets worse throughout the vid

I can't help but notice how the reflections look just like a video waveform monitor when light reflects from them at a narrow angle, I think it is a good analogy for how they work

The mention of Optimal Transport made me realise that there must presumably be an infinite number of Suboptimal lenses that produce an identical image.

I love that you are holding back laughter in every cut where you're partially shaved.

That must've been so difficult to not laugh during the parts with the beard transitions.

Steve you're missing half your beard

I absolutely stayed and watched the entire sponsor segment because I was super curious. Well played

Love how you carried the sponsor all the way through for a reveal at the end. Just like the light shining through the glass reveals the lion. Brilliant!

Nice shaving transition! I didn't notice until 6:00, lol.

An ad so well executed, I wish the usual sponsor blocks were more like this

Great video and yes Henson razors are awesome. Switched from cartridges a year ago and love the smooth shave and cost savings knowing that blades cost only $0.10. I usually get about 5-7 good clean shaves out of one.

What an ingenious lead in to the sponsorship. the whole video I'm like "okay... he's surreptitiously losing more and more facial hair every time it cuts back to him. wtf is going on?"

Man. This is possibly only time that a sponsorship in a RU-vid video has me sold on the spot.

Imagine having this guy as your physics teacher

Nice plug for the safety razors :) I use one from the 50's, the plating is a bit worn but works just fine.

you can start a fire using water as a lens! you just need pretty clear water and a lot of direct sunlight. there are a few different ways to make it work, but a ziplock bag full of clear water might be the easiest. i've also seen a regular water bottle do it with a lot of patience

I'd love to learn about the deeper maths behind the optimum transport problem!

So weird! I haven’t seen this particular video till now even though I’m subscribed. I didn’t notice the shaving thing till 4:50. I had to rewind and watch it from the beginning to see the progression. This just messed my brain up! How did I not notice? lol

Great video. I am working in a closely related field. If you do X-ray Nano-Imaging you have to solve the exact opposite you problem, you measure one of those smeared-out patterns where you can guess the coarse shape of the object, and your goal is to find the density of the object (your sample in the microscope) that has produced the pattern you observe. Mathematically it is almost identical. The more technical term for this is X-ray Inline Holography.

"Once you know that you want 'hair' from your beard to go there..." Loved the explanation as always! Steve is an amazing teacher who has mastered the art of explaining difficult concepts in a fun n engaging way. You rock man!

This is your best work so far Steve. It could even be the greatest RU-vid video ever made. Theme, explanation, advertising tease, all perfectly executed. You could also have mentioned that the razor blades involve no plastic waste, which was my main reason for buying a similar competitor that I won't mention for obvious reasons.

oo i've actually thought about this tech a few years back, how it could be used in lamps in a room to direct the light to more efficiently (and more prettily) illuminate the room

I've seen a similar thing before concerning images having depth, the Kodak film 'Kodachrome' had layers which were said to improve the image - it was an extremely complex and therefore expensive developing process that was abandoned decades ago.

THANK YOU! FInally! some good explainer on controlling caustics. I really wish The Rayy would make a software that could make these virtually, or even better a depth pattern for cutiong out of metal

I love when people cover new technologies such as this one that I didn't knew existed! Here is another recent technology that may interest people here : Cypris Materials has created polymer pigments, that while colorless when dry, turns to any color of the spectrum once applied as a paint. They work based on structural colors the same way as opals do. They have a few videos on RU-vid, they are worth watching!

IIRC the optimal transport problem prompted a matematichian to make the first nomograph , wich is a printed analog computer composed of lines with numbers on and it's meant to be used with a string or a ruler , I reccomend checking them out because they are pretty awsome

Ohhh, how awesome your channel is, I want this show on tv!

6:48 Everyone pauses to do a web search

You can also make that shape in coffee mugs by rotating a two circles of different diameters connected by a single point on each of their circumferences. The mug version has an exact ratio of 2:1 for the smaller and larger rings respectively. I can post images of several that I created a couple of years ago if you want to see some examples.

Well done integrating the sponsorship. Interestingly safety razors seem to be making a comeback on multiple fronts. As a decades long user of classic safety razors I applaud this an find it amusing at the same time. Feels a bit like being smug and saying „ah, finally… Took you long enough“. I was also fed up with the cost for the cartridges. Their only upside really is that you can usually put cartridges 😅into carry-on luggage if you happen to fly.

This video was smooth in SO MANY WAYS The main topic flow The beard The printer to razor Segway the end

No one noticed his beard disappearing.🤣🤣🤣

I always look forward to these video, thank you Steve!

The video is great as always, but man do i want one of those razors now, what a beauriful integration!

Curious...and alarming! (and EXCELLENT tie-in for Henson!!! Well done!!!)

i was sitting by the pool today and i literally thought about the ripples that are caused and i thought about it and when i figured it out my first thought was "huh, could be a steve mould video" love your videos man!

Never seen such an immersive endorsement of a shaving razor .

I only noticed when he was at half face and had to watch the whole video back from the beginning and couldn't stop laughing ahahahah

FWIW - I tried a ton of safety razors this spring and Henson is the best. Rad to see them sponsoring your video. It's so rare to see a product sponsor a content creator ... and the product is actually great! Go buy a Henson, do it now!

My 6yo, 8yo, and I love your videos!! Thanks so much for sharing fascinating science to all ages!!

Great video, I’ve always been fascinated how you can manipulate projections of transparent 3d objects, seeing all the details magnified on a wall or something. Basic lenses lol.

Amazing explanations, thank you

Best sponsorship bit on youtube period. Awesome vid as always but as a lifelong electric shaver guy I'm genuinely tempted to get one of these just to support the business model

I really thought a Fourier transform was going to be involved. I swear I learnt that at uni, maybe with lasers.

These are beautiful, thanks for shaving Steve!

Best sponsor plug ever. Didn’t notice the hair disappearing until the cut with the half and half shave lol

Your 1/2 Five O' clock shadow hologram is very convincing! Super cool! Great video!

Closest thing to this I've experienced is the Camera Obscure effect caused by my window shades. They're blackout style, but not true blackout, as the edges still let some light by. It's those edges that create the lens... So when my mom is walking outside around the side of the house near my bedroom, I'll see her shadow get projected along the wall where that light is shining through. Or, the vehicle at it drives around the driveway. Obviously, though, everything is upside down.... But it's still every bit recognizable. 😊

Always enjoy Mould's playful approach to STEM.

Interesting , Steve; it reminds me of the moiré fringe effect. I have always thought it would a fine idea if the bridges of motorways have the spacings of their grills altered so that, just at the right time, the moiré fringe spelt out something: 'Drive carefully', for example. The maths is well beyond me, but maybe the two ideas are related?

3:51 I like the Half beard cut, great new style!!!

I normally like your videos, but the way you presented your sponsor was GOLD. I 💯 support Henson already, but that just sold me all over again

I can confirm, safety razors are great. I bought one a few weeks ago for €20, you can get a pack of 100 blades for €0.10 a piece, and they actually shave _better_ than a conventional razor! Although it is also easier to cut yourself if you're not careful. This was actually the first time I cut my legs while shaving. Ouch. But you can also take them apart to get the hair out! So great!

What's wild is those Japanese "magic mirrors" that were crafted by hand hundreds of years ago that do something similar. They were created when Christianity was banned in Japan. It worked like a normal mirror but could also reflect an image of a cross in sunlight.

Safety razors are fantastic! Nice work on the sponsorship!

Interesting video! I’d always thought they’d be similar to diffraction patterns, which are the Fourier transform of the diffraction grating. But it looks like the maths is much more complicated with caustics.

The beard has been a fucking trip

I didn't notice the beard until 4:55.

Like watching The Howling” but in reverse. Clever. Very clever! As always.

Very interesting and clear explanation

I always wanted to use things like this on that Glow In The Dark paper, to "store" the image

0:01 hi timed

Steve be shedding like my long coat German Shepherd when spring hits!!!

Love the creativity of the sponsor implementation

Was waiting for this video, ever since I found the research done at EPFL I am fascinated - love to all the light enthusiasts out there! ✨

If someone out there still hasn't switched to safety razors, you have to give it a go. They really are better once you get used to holding the different shape. They are more environmentally friendly, and the replacement blades are dirt cheap. My favorite part about safety razors is that you can take out the blade and rinse off any hairs that get stuck in gaps.

At 03:50, I noticed the half-shaved look and thought that it was your new look or something. Then I felt like verifying it, so I went back i n the video and saw that what I noticed were the first few frames with this look. Then as I continued watching, I happened to look at the video description, and understood that it was part of the sponsorship message.

As for the printer problem: All printer manufactures today also do sell models where the ink is just in an accessible tank and in fact you can put any ink into that tank you like, there is no way for the printer to check if that is original ink. But of course such a printer costs several hundred dollars, as you are in fact really paying for the printer here to later on save on ink. Yet it turns out that you really must print a lot before that can pay off for you. If you only occasionally need to print a few papers, your printer may need replacement before you were able to print enough to validate its costs, as even if little used, printers do age and they will need replacement (actually just some parts need but those are often not designed to be replaced in the first place and replacing those would cost almost the same price as a new printer, so where would be the point)

Re: printers, a decade or so ago I looked into the numbers and saw it was legitimately cheaper to buy a brand new printer than to buy all new ink cartridges, and I did that a few times, giving away or selling the now inkless printer for extremely cheap. I've now got one that can use third party/refillable ink cartridges that are priced reasonably (there are plenty that will detect the non-brand-name cartridge and refuse to operate!) and it's a good printer that doesn't hassle me, too :) Still hate printers, though.

@6:53 is that a pull back or is he just circumcised?

I love exploring the world with you!