Just a hint for people who want to make one for a good telescope: don't use it, unless you have 24/7 the same temperature in- and outside. It will slightly change it's convex shape when temperature changes. So the burnpoint calculation is for nuts... But great thing for other projects! Thanks for sharing Dan! Keep it up! ;-)

@davidd2661

7 ай бұрын

Ooohhh here we go 10 years later-dc 5v pump with outlet. I'm on building one. I'll tell you if I managed

@vigi86

7 ай бұрын

@@davidd2661 nice!

If anyone else was wondering, the deflection of a circular *thin* membrane due to small pressure differences as a function of radius is w(r) = w_0 (1 - r^2/ R_m^2), where w is the deflection from "flat," w_0 is maximum deflection, and R_m is the outer radius of the membrane. Ref. "Introduction to Microsystem Design" WK Schomburg. This also includes formulas for figuring out w_0 from the pressure difference. So yes, *theoretically* its a perfect parabola. For larger pressure differences, thin membranes approach spherical shapes (think bubbles). For a power generation this is brilliant (cheap and adjustable). I wouldn't discard this for telescope mirrors. For example, if you can make 100 of these mirrors for the same price/time of one highly accurate mirror, you might actually get better images from the collection. There would be a host of challenges (sound, temperature variations). I bet there are some simple ways to overcome these challenges (thicker membrane, controlling pressure) without increasing the cost much.

@maxk4324

5 жыл бұрын

you can control it more accurately if it was done hydraulically with a viscous fluid rather than pneumatically as the incompressibility should reduce the magnitude of volume change due to pressure waves (ie sound waves) in the fluid. Additionally this will significantly dampen the mylar film preventing it from acting like a drum skin.

@geovani60624

5 жыл бұрын

yeah, maybe if you hold the format using some kind of resine after you get the perfect parabola it may work

@chanakyasinha8046

4 жыл бұрын

@@maxk4324 gravity will affect the shape

@trollmcclure1884

3 жыл бұрын

@@chanakyasinha8046 Indeed. Even if it's horizontal it will tend to go flat in the center

Cool idea Dan! Where is the easiest place to get one of these mylar blankets?

@maxmustermann5353

3 жыл бұрын

The internet.

@nunyabusiness4026

3 жыл бұрын

After 7 years and 12.5 million subscribers they’ve probably found 1 by now..........

@astrocactus4097

3 жыл бұрын

Here he is starting his youtube career!

@williamwalters3796

3 жыл бұрын

@@astrocactus4097 he died in a paragliding accident. I remember finding his channel as a kid from videos when he turned projector TV fresnel lenses into solar metal melting machines.

@astrocactus4097

3 жыл бұрын

@@williamwalters3796 wait ur saying THE king of random died??

You're an amazingly creative and talented guy, Dan. I've been watching you for a couple of years now, and you CONTINUE to amaze me with almost every new video!

The optical aberration (second surface side) and image distortion occurs on the outer most area of the vacuum lens. The F/stop aperture rings reduce the image distortion dramatically. Oversized and usage of 50% = the center section of the mirror only works My Canon 7d is dead so no video of it right now but with a secondary mirror and focuser, the image quality of the moon is good. Not a full setup yet. There are issues with the vacuum FL changes. Would need more than just a suction tube.

Dan, you make some of the most interesting videos on KZread! Thanks for all the inspiration you give to me and lots of other people. Even if I never make a single thing you are showing, I love to know that I could. Very few people have the talent (or willpower) to show the practical uses of science and technology to the masses. Thank goodness for teachers like you that show us areas of science that we didn't even know we wanted to see.

technical stuff can make better things, but cheap material like this to get things done? man, you're a genius.

I think your videos are some of the best on youtube. I always enjoy your madness!!! thanks

If you can succesfully make a telescope out of this mirror, it will be a monster

@davidd2661

7 ай бұрын

I'm on trying. I had made the mirror, only with a round plate yet.

Thank you for the nice comments:-) Nice wind spinners on your channel.

Working on a larger version

@H8edsinclair

10 жыл бұрын

Ever think about making a fire piston video

@Freekniggers

3 жыл бұрын

Use a big old satellite dish.

Thanks for the video. This method was used when B.Schmidt made his corrector plates for schmidt cameras, nearly hundred years ago. Using mylar is good idea and results are interesting, esp. very short focal lenghts paraboloids.

I think I might try this with an old glass rice cooker lid. It already has a hole on the top to let the steam out and the edges are smooth. Great demonstration as always.

Ooooo. Thank you! Keep up the good work. I hope it works out for y'all to get a TV show. Y'all make science interesting. Thanks again, Suzie

Amazing. It will be a nice school project I will help my daughter with, Thanks again Dan!!

I read the comments below, Dan. You're inspiring new ways of creating energy from (what could be) waste products from the landfill or local curb. You're inspiring minds along the way. Good job, Man! :D

Very nice! The stretching makes a real nice surface! It is not strictly necessary. The pressure will smooth the material enough. There will be some radial wrinkles, but for cooking it is more than fine. I love your videos. They are entertaining and i always learn something.

definitely one of your better diy videos that ive watched. thank you Dan Rojas

@GREENPOWERSCIENCE

8 жыл бұрын

+BigBrainTheory Jr. Thank you for the great comment. Inspiration for me to make some new videos. Have been in a rut. Not for ideas, just work and got burned out on the new viral/social media requirements now needed to get people to watch.

Dan, I just want to tell you, you are a brilliant popularizer. Thanks !

@meetoptics

2 жыл бұрын

Agreed, so good

might make sense to insert a reversed tyre valve into that vacuum hole then you can withdraw any air at will and would make for a much better seal....

@WereLivingInLP

9 жыл бұрын

Good idea, I was thinking of running a bead of RTV silicone around the rolled edge of the trash can lid to help seal the mylar film to the the metal lid.

what mil or thickness is this that you use here, great video thanks

I have added "Plastidip Spray" to the interior and stretched while wet. Then you give it a spin so all the spray goes to the outer edges, draw the vacuum and it helps. Temperature changes can also make the focal length change.

@maestroamonathan4279

3 жыл бұрын

have you tried making a dubsonian telescope using this ..please make one.

Dude, you're a genius! You just got a sub!! (:

Gorgeous and excellent work I wish you success

Hi, The vacuum is not needed for flat mirrors or the drum effect but for a light gatherer, the vacuum draws the centermost surface deeper creating the curve in the mirror.

Nice job Dan.

Am I correct in suggesting that the greater the vacuum the shorter the focal length as long as the Mylar does not bottom out?

Will do, we are sunless for a few with a front. The acrylic mirrors we have are 2x as strong but this could make some tea or more? I know the big one is a monster.

Awesome work. For other applications, i like stretchy electrical tape to seal stuff airtight. Often makes the result look quite neat too. The stretchiness helps it fit around edges nicely. How fine a focus (mirror side to burn point) does vaccume accomplish? It is close to deal by chance or by laws of nature as good as it gets? Thanks!

Great idea!! A suggestion for hopefully an improvenment: -- After making all the above, construct a strong cylinder around the lid. -- Put water on the mylar, inside the cylinder. -- Hopefully, the weight of the water will bend the mylar into a parabole (I think!). I think that even with just this, you might have a bigger curve, hopefully a better one (!) Further: -- A clear and thick glass disc can be put inside the cylinder, with a rubber on the edge, sealing the water below. There should be a hole on the glass disc for air to escape. -- Then pushing the disc downwards, would push the water even more, and increase the curvature of the mylar. Perhaps (!!) this curvature will be better, or parabolic!! Again, you gave us a great idea!! Exactly the diy ideas for a lens I was looking for.

Good job Dan. Sandia natl lab had done research on a thin film mirror 20yrs ago that is electrostatic. So what they did was first measure the mirror surface with a laser, then use a cathode ray to move the electrostatic film mirror surface to make it perfect.

Maybe, I am testing them. Our mirrors on our site are second surface so while they produce a good image they have optical aberration for telescopes. Not a problem for solar but screws up a good image. The mylar is first surface on one side. We are making some first surface mirrors from acrylic.

Great video, great technique. What did u use for the vacuum?

Oh my god, I am SOO going to create a reflector telescope with this method! GENIUS!

@Hunter-jj3ud

4 жыл бұрын

Have you attempted this yet?

This has my head tingling about using a bicycle rim. Sure it has all them spoke holes, and would need a solid backing, but it's an option for anyone that doesn't have a garbage can lid. Love the telescope idea, but would seem a tougher mylar material would be needed for a solid focal point. On the other hand, that could be adjusted on the fly if it did change and have a sensitive vacuum gauge to dial in the parabolic aspect of it. Keep up with the kick butt vids you two!

I have a 4' diameter Andrews microwave parabolic dish. What would you suggest as a reflective coating? Aluminium foil crinkles when applied to the curved surface and disperses too much of the light.

The mylar stays firm over time. The vacuum does not seem to stretch it to a week point. Once the vacuum is released the mylar remains like a drum. Not sure how many years/months it will do. I have a 5 year old stretch mirror that is still firm, it is not exposed to vacuum, just stretching.

Awesome video again! Thanks. Hey dan, if i used silicone glue to seal it, would the vacuum last longer? i'm going yo try it and use tape to hold it in place until it dries out and maybe put a tube in the back.

I love your instructional videos! Very helpful. I'm wondering if this system would work for making large rectangular mirrors for an art installation. Provided the mylar is taught, does the surface provide a clear reflection?

Here's an idea! Try bridging a speaker magnet from the edge at four points, then silicone glue a speaker coil to the center of of the mylar. I wonder how that would sound? I'd use it with my piano sound board and strings that I have hanging with homemade pickup coils. I hammer, scratch and pluck at the strings for a really freaky sound. I'll bet the sound and feedback ability would be just incredible. Peace :)

@ColettaHughes

7 жыл бұрын

Maybe at the edge would give a deeper drum like sound?

Can you use this technique to throw fiberglass resin on that Parabolic shape

The profile of that mirror isn't parabolic; it is a segment of a sphere. As air pressure pushes in on it, the mylar will behave like a bubble membrane. Since air pressure pushes perpendicular to the surface at all points, it cannot form a parabola, only a sphere. If all the air pressure were parallel to the axis, then you would get a parabola. Because it isn't a parabola, the light focus will have some spherical aberation to it, making it unsuitable for precision optics. But it is definitely more than good enough for solar concentration.

@kevinmartin7760

7 жыл бұрын

Probably not quite a sphere either. A soap bubble keeps the same tension as it is stretched. This membrane is elastic and the tension increases as it is stretched. Furthermore, if the stretching is anisotropic, the tension will be too. Near the edge the stretching is almost completely radial and so is the resulting tension. At the center the tension is isotropic.

@springbloom5940

7 жыл бұрын

I dont think the figure is the greatest problem for optical performance.

@kalebbruwer

6 жыл бұрын

Really good point, but this won't work for optics anyway. Good luck calibrating a telescope where the mirror is constantly changing shape because of some tiny leak...

@76Eliam

5 жыл бұрын

@@kalebbruwer I found an academic paper that calculated the profile of such "pumped film" concave surface few months ago. If I remember well the profile is actually surprisingly close from a perfect paraboloid, excepted at the borders. Sadly I can't find this paper anymore.

@fpowerm

5 жыл бұрын

@@h.n.4060 The surface thickness of the mylar?

at first I thought there was a washing machine running in the background :D that's really a neat method to make a parabolic mirror!

Excellent project .... really inexpensive and simple way to construct a sophisticated bit of kit. ....I'm going to make one. My only reservation is that the parabolic Mylar surface looks a bit vulnerable ? Would it be possible to load the trash can lid with a slow setting gel, the excess of which you could remove when you evacuate the lid/mylar space so that the mylar would settle down onto the gel surface as it attains its parabola ?

Hi MUDDy, Seaming 6 pieces together this week with tape. looking to use 16 footers for the square design. Unless I get time to bend some wood strips. Looking for a 16 foot solar ray:-) Round would look so much better. HAPPY NEW YEAR!

rescued a couple satellite dishes from the trash a while back with no idea what to use them for ...i wonder if i can use the for this?

Love your videos! If you could, could make a video demonstrating how well this design cooks food or boils water? I think some of us would be interested in seeing that. Thank you again and keep on making great videos! :D

Awesome!! We are so doing this! Seriously cool idea and it looked great! Thannnnnnk-you

I have deleted most of the optical aberrations causing image distortion. I will have a video soon explaining the simple process. Very effective for low cost reflectors as they can be designed very large and any surface area loss for optical corrections is not an issue as compared to a real mirror that each sq cm of surface costs lots of money.

interesting...I hope you make a video explaining this in more detail sometime. I LOVE your channel man.

@meetoptics

2 жыл бұрын

The explanation is amazing!!!

It looked like a forming black hole distorting space-time when you pulled the vacuum!

That's brilliant! I am going to have to try that.

If you put the tape down with a thin sliver of foil or some such over the hole, you can pull a vacuum (those little food saver/jar vaccuum pumps work pretty good), it will actually lift the tape up a bit and suck the air out from under it, and when you lift the canning seal head up the foil flaps down over the hole keepinf more air from rushing in.

Can this be used to melt snow on driveway during winter as the sun rays does not fall our side. The sun rays are on the opposite side of our house?

Hi, I was thinking of using your idea to make a small concave/parabolic mirror in order to create a schieleren setup. Can I know how do you close the hole of the trash lid after vacuuming without outside air entering due to high pressure? the size of the mirror that we plan is from 3" to 8" of diameter. Can we control the focal length?

Thanks Dan

Did you try looking at the parabolic mirror with an eyepiece to see if it is accurate enough to use as a telescope mirror?

Really smart never used mylar sheet before. Will make a nice solar cooker. What is the specifications of the mylar sheet?

How would you get a negative pressure in space for something like this? Or are you thinking of positive pressure in front of the mirror, like a sealed telescope tube? Also, the environment in space has very large temperature changes: you have to consider the stability of the mirror surface.

Do you think if you put expanding foam (the stuff you fill big gaps with that goes hard), you wouldn't need to worry about keeping the vacuum. Or what about sticking the edge of a round piece of mylar to a flat surface and inflating it, and then put expanding foam on top.

@marktotman848

5 жыл бұрын

Epoxy resin is my thought....

If I wanted a small pocket sized parabolic mirror you think this same thing would work with a pickle jar lid?

Is we are able to get parabolic mirror will the reflectiveness be enough for astronomical use

Could you use heat to create the vacuum? heat it under a burner and then seal the hole and as it cools watch is tighten?

@maxk4324

5 жыл бұрын

yes, and mylar is well suited for this as it melts at around 500F. Won't be as effective as mechanical suction, but the two in conjunction can achieve a deeper curved surface than your lungs on their own.

This might also be useful if you do the opposite and pump air into it to make a convex surface. then you could use it as a convex mirror to see around corners, such as if your house is parked on a busy road and it's hard to see traffic coming because of walls or trees etc.

Technically it's a catenary but their shapes both tend to focus light. The only technical important difference is that a parabola focuses to a point and a catenary focuses to a general region.

MORE TELESCOPE MIRROR PLEASE... can you do a complete one ? lol your Genius ...

I wonder if you could use a hoop made of PVC backed by a wood disk to create a larger mirror?

Highly impressive. Thank you

@meetoptics

2 жыл бұрын

Yeah, thank you so much, it is insightful

That's cool. do you get sheets of mylar online? Do you have a video showing how to cook food with that? Can that itself provide heat?

After you draw a vacuum how do maintain it during that brief moment your resealing the hole with tape without losing the vacuum? Seems to me you'd lose the vacuum before you could get the tape back over the hole . . .

@Arujr0938

5 жыл бұрын

he might have used a valve

Love the video. But question, will this work for the base mirror of a telescope ?

@qzerzae4032

4 жыл бұрын

I'm searching for the same, it's been a while, did u try it ? Did it work then?

That's cool. do you get sheets of mylar online? Do you have a video showing how to cook food with that?

where did you know from, the vacuum is creating a parabolic surface? (not spheric or anything else) Has someone a link to the physics? Thank you!

I liked it. What about a one way valve in the hole ? Be good if you could press down on the handle, to draw out air.

Oh that’s awesome, thanks for showing me how to do that.

@meetoptics

2 жыл бұрын

The explanation is amazing!!!

Would you stiffen it with epoxy?

Dan does the Mylar retain its elasticity over time or will it memory if you keep a vacuum on it after time?

Dan, how well does Mylar reflect UV light. I am working on my exposure box and mirrors are ok but but low uv reflectivity due to the glass. Is Mylar better than a mirror to reflect UV light?

so i can used this in building a Newtonian or.dubsonian telescope... i have a new project

Nice work !

So is the vacuum just to make it more parabolic? How do you think it would do without the vacuum?

Great idea, excellent project, lightweight, good for cooking but not good for telescopes. Remember that a good telescope mirror will require an 1/4 lambda precision of the parabola, and anything below 1 lambda won't work even for very low magnification light bucket telescopes. And the focal length will change with the time as the vacuum degrades, so it will be close to impossible to put this in an arrangement with any type of secondary mirror.

I got my vacuum to hold for about 30 minutes what have yall done to elongate that time?

The image quality is good from the center 50% of the mirror, the outer 50% screws it up. For solar cooking it does not matter as light is light so long as it covers the cooking vessel but, I have shrouded part of the mirror and it helps dramatically while also reducing the collection area. Since we are using cheap materials, I am thinking a 40" mirror could make a working 20" mirror 50" = 25" and so on. CPF bulb images very good.

is that the only way? It is kind of already assembled I have to constantly pull the vacuum.

To create a vacuum could you just push on the drum face while air hole is open, seal the hole with the tape tab and then stop pushing on? It seems like it would be easier to do than using a pump and tubing. I don't know if the mylar could take the abuse, though.

excellent idea and working proof!

@meetoptics

2 жыл бұрын

It is so good, definitely!

Thanks Dan! Looking forward to it!

@meetoptics

2 жыл бұрын

It is so good, definitely!

I didn't had any Mylar lying around in my house so I used the inside of a bag of chips, which seems to work as well as a mirror (haven't tried making a parabolic mirror using a vaccum though). However it did not seem as clear as the Mylar, and its size is much smaller.

Absolutely Brilliant

Another awesome project I can't wait to put on my list lol. One of these days.

@meetoptics

2 жыл бұрын

It is so good, definitely!

Is this a parabola or a catenary shape? In space you are going to have to draw a better vacuum better than that of space. I once inquired into just venting a mass spectrometer to space and I found out that the vacuum of space is rather "dirty".

Did you come up with a way of having these hold their parabolic shape permanently in this handy Mylar + bin lid configuration? Maybe pressurise from the outside and introduce some resin through the hole in the back and swirl that around to coat the inner surface and set in that distorted shape? Or use the vacuum as shown here and then spread resin on the shiny concave face?

@dogodogo5891

3 жыл бұрын

nighhawklight made that just search it, i want to make one but iam not entirely sure how to determine focal point by his method

you are one cool cat! thank you for sharing

Couldn't you use a hair dryer to relax the creases and make the surface smother?

THANK YOU VERY, VERY MUCH!!!

you're my man guy, thanks for the idea

@meetoptics

2 жыл бұрын

It is so good, definitely!

Wonderful!

I grabbed a steel pan that was unexposed for 2 minutes. I assumed it had cooled. Nasty blister. We keep all the lenses out of the sun when not in use or they are tracking and in a safe area. I avoid the focal point with my hands. The shower mirrors with x enlarging have caused me issues. I had one set on a table outside and it almost burned up the seat in our old van. Water bowls of clear glass for pets outside have started fires too. Google search "windows melt siding"

The silicone can get messy with the stretching. If it gets on the first surface side in the form of a smear, it will not come off. If you do it, just light coat. I think it will work. The design is for human powered vacuum suction. If you use silicone do not do that for a few days. Vapors are :-0 Use a shopvac or other pump.