@@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.
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.
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.
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! ;-)
@@grandmasterautistwizard4291 i'm still inside the drone and e-bike project, but the mirror itself (plate with foil pulled tight over it). I plan on redesigning-a 3d printed one with more accuracy and customizeability
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.
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!
Dan, you make some of the most interesting videos on RUclips! 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.
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.
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.
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.
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 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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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...
@@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.
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.
I am thinking about the same thing. I am trying to find a way how to make the best parabolic mirror for a dobsonioan telescope, and btw yes i am sure you will see jupiter pretty damn good if youre gonna build a telescope with aperture of the size of this mirror
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.
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.
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.
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.
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 :)
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 ?
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.
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 . . .
When the sun comes out, we can cook food with it or boil water. watch?v=wyXsYkumHcw The mylar is less than $5 for a full sheet. Thin mylar is best as it stretches. Cheap mylar will remained stretched for years. They actually make optical reflectors out of them.
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.
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.
Dan, are you going to continue making a telescope out of this? I'm an engineering student, and my dream is to design an inflatable space telescope using a similar pressure differential system. When I suggested an inflatable mirror to one of my professors, he warned me that it might not be parabolic enough to reflect an image properly, but I still want to try this out. Thank you for these educational videos!
Sounds like a great idea! I'm a retired AF officer and a new amateur astronomer. I wish you the best. I'm sure you will figure out how to make your inflatable device!
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.
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?
You can actually do it with human power via mouth (sorry could not find a proper way to put that:-) The silicone needs to set for a few days or you inhale lots of horrible vapors. Did that once. The big mirror video explains it also. After a few days it becomes somewhat inert. A goo set of lungs can almost collapse the can lid as the curved mylar strength trumps the shape of the lid with a vacuum. I used the vacuum pump to see if the mylar would pop. It crushed the lid, mylar was still strong.
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"
Telescope mirrors are precise to within a wavelength of the visual range (less than 1 um), I think, there's no way you'll get a lid that is flat and round enough, mylar that is of consistent enough thickness, you won't be able to tape it down with consistent enough stretching. Besides sound and other sources of pressure waves will move the mirror. So I don't think it's doable, at least not simply. There are good reasons for using a solid thick piece of glass. But trying doesn't hurt.
+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.
Attach tubing (mostly just to get distance to the mylar), insert a coil, then you can control the temperature on the inside electrically, within reasonable margins, of course, without moving parts or pumps. All you need is initial vacuum to be in range, close the valve, start and stop heating as necessary.
You're expert making mirrors&lenses&some of your videos show rather large sized devices.Have you ever gotten hurt,hurt or burned something you did not intend with these things. I remember once I had just a small mirror that I left outside one day. Later in the afternoon I walked by and noticed a weak smokey smell.Even later I walked by and saw a trail of black down my table's leg and plume of smoke coming off it at the end. I damn near started a fire&did burn my table leg.
Dan, first of all, thank you for this video... I am amazed with what you did here! Second, I've actually made a 6" f/7.5 telescope, ground the mirror from borosilicate glass, and I'm currently polishing a 10" f/6 telescope mirror. I'm wondering, I know you used mylar, but is there an actual material that, when stretched via vacuum, can maintain a parabolic shape of optical precision? I presume the trash can lid would have to be a near perfect circle (so the trash can is out of the question), and whatever is used in place of the mylar should have a material thickness tolerance of exceptional quality so it stretches evenly. But if this mylar alternative exists, it would make for an interesting telescope mirror. I can imagine being able to focus by varying the focal length with a vacuum pump, among other crazy alternatives... It sounds like something interesting, but I have doubts there would be an actual benefit compared to polishing and figuring a glass mirror. I hope I'm wrong though... It would also be really interesting doing a Foucault test on the mirrors you made to see the quality of the parabola, just for fun... Any thoughts?
It seems to me that temperature fluctuations would be problematic. You'd need the vacuum pump to operate sporadically to counter the effects of temperature on the expansion and contraction of the membrane or mylar alternative.
Bear in mind that the vacuum does not draw the mirror into a true parabola, it's actually part of a sphere. The difference is not material for a solar power application but it won't make a great telescope if you want a diameter more than about f/10. And, variations in the thickness of the mylar -or in the uniformity of the edge support- would cause small variations in the surface which could be even worse for the optical quality.
Carlos Paris dont know if this would work well on earth but you mite be on to some thing think about the weight that could be saved if something like this could be used in a space telescope design
Thanks for the clarification Herbert! Maybe a Ritchey-Chretien telescope? It uses hyperbolic mirrors... In any case, I'm just speculating, but I wonder if anyone has actually and seriously attempted this.
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.
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!
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.
Maintaining a solid and reliable focal point would be tough since it relies on vacuum and mylar, but if it was first surface, 98% reflective material with a stiff structure and bullet proof seal, it could work. I think this is a possibility, so don't think of me as getting down on you about the idea as I believe there must be cheaper ways to make a kick butt Dobsonian telescope even if it was built in a disposable manner.
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".
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!
If I might make a suggestion: lay out the mylar, and tape it down to a flat surface to stretch it. Then, place the lid on top, run a bead of silicone or even hot glue around to both bond the mylar to the lid AND seal it. Then trim.
Christian Wang yeah, after thinking about it, I figured exactly that would happen with hot glue, as well as possibly heat distort the Mylar too, so I'll bet silicone would be best.
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.
As mylar melts at 500 degrees, after creating the vacuum, carefully using a hairdryer or heatgun should remove all of the remaining wrinkles and give a totally smooth surface.
I didn't watch this, another time. I saw your square wood frame parabola. I hope you get back to me. I am co spidering a project, mirroring light through a small opening in a container, and dispersing the light on the other side, to light it up. I was thinking Sun tracking, to keep the mirror aimed. It would be very dangerous to use a parabola, in case of accident. I was thinking multiple flat mirrors, that send light at multiple angles, so you get more light entering a small opening, like 3 side by side mirrors, entering at different angles, hitting a mosaic of Tony mirrors, think disco ball.
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.
From the sun, it should reach temperatures exceeding 1000 F over a smaller area with a stronger vacuum and shorter focal length. The video below uses our true solar mirrors. The process should be the same. watch?v=aJ22QCAqFCc
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.
I think you'd end up with a spherical surface and that would lead to abberation. Parabolic is the way to go. This is just conjecture and opinion. I don't know for certain...
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?
try filling it with some kind of low hardening expoxy or fluid of some sort that cures and hardens with the mylar or some other more higher quality reflective meterial and then suck the fluid out until the desired shape is formed and maintaining that form via some kinda precise method optically and until it hardens, and there you go and walla the shape is kept, or it could be used as a mold for glass or some other reflective material to be coated, that would be epic my friend, cheap and economical.
Another idea I had was to set up a drill to drive a turntable flat circular mould into which you pour a resin/hardener mix and then gradually accelerate the spin speed to achieve the requited parabolic surface as the resin hardens. Using this method it should produce a very clean smooth finished surface generated by centrifugation. In fact some telescopes use this principle with liquid mercury, though they can only be used in a vertical orientation. Silvered oil or water will also produce this effect. The spin speed will be directly proportional to the finished sagittal of the mirror which will be a perfect parabola shape.
I would imagine if that mirror was used for a telescope it would suffer from Chromatic Aberration, horrifyingly so. The surface of a optical mirror has to be completely smooth. But, that is a cool idea for a solar cooker. I'd like to give that a try.
This might be difficult to focus especially when it's fixed to a cooker because the parabolic mirror is susceptible to changes in atmospheric pressure.
Manouni Mohamed It has nothing to do with air escaping from the contraption, the device is more like a barometer now, unless the cavity inside is filled with an incompressible fluid, I don't think this can be used reliably.
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?
Here's my whacky idea on that: How about placing it in the oven for a few minutes, sealing it off (with tire sealer?), and then letting it cool to obtain a more permanent vacuum?
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
I just saw that when the temperature changes the curve grows or shrinks. It looked to me like the focal ratio was about 2, which is (in my opinion) too low for a worthwhile telescope. The suction also goes away after about an hour but I think the solution would be to cast it so it keeps the shape.
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Cool idea Dan! Where is the easiest place to get one of these mylar blankets?
The internet.
After 7 years and 12.5 million subscribers they’ve probably found 1 by now..........
Here he is starting his youtube career!
@@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.
@@williamwalters3796 wait ur saying THE king of random died??
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.
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.
yeah, maybe if you hold the format using some kind of resine after you get the perfect parabola it may work
@@maxk4324 gravity will affect the shape
@@chanakyasinha8046 Indeed. Even if it's horizontal it will tend to go flat in the center
The only perfect circles in the world come from fluid pressure
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! ;-)
Ooohhh here we go 10 years later-dc 5v pump with outlet. I'm on building one. I'll tell you if I managed
@@davidd2661 nice!
Thx
@@davidd2661 Update?
@@grandmasterautistwizard4291 i'm still inside the drone and e-bike project, but the mirror itself (plate with foil pulled tight over it). I plan on redesigning-a 3d printed one with more accuracy and customizeability
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.
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!
technical stuff can make better things, but cheap material like this to get things done?
man, you're a genius.
Dan, you make some of the most interesting videos on RUclips! 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.
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.
have you tried making a dubsonian telescope using this ..please make one.
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.
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.
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 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.
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.
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.
Working on a larger version
Ever think about making a fire piston video
Use a big old satellite dish.
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.
Thank you for the nice comments:-) Nice wind spinners on your channel.
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.
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.
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....
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.
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?
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.
Love the video. But question, will this work for the base mirror of a telescope ?
I'm searching for the same, it's been a while, did u try it ? Did it work then?
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
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.
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.
I dont think the figure is the greatest problem for optical performance.
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...
@@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.
@@h.n.4060 The surface thickness of the mylar?
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.
amazing mirror. can i dry it for my diy reflecting telescope mirror. will i be able to see Jupiter and saturn with this parabolic mirror ?
I am thinking about the same thing. I am trying to find a way how to make the best parabolic mirror for a dobsonioan telescope, and btw yes i am sure you will see jupiter pretty damn good if youre gonna build a telescope with aperture of the size of this mirror
@@jannovak6987 it would certainly be a hell of a lot cheaper
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.
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.
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.
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?
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.
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 :)
Maybe at the edge would give a deeper drum like sound?
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 ?
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.
I think your videos are some of the best on youtube. I always enjoy your madness!!!
thanks
Dan,
I just want to tell you, you are a brilliant popularizer.
Thanks !
Agreed, so good
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 . . .
he might have used a valve
When the sun comes out, we can cook food with it or boil water.
watch?v=wyXsYkumHcw
The mylar is less than $5 for a full sheet. Thin mylar is best as it stretches. Cheap mylar will remained stretched for years. They actually make optical reflectors out of them.
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.
Epoxy resin is my thought....
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.
Dan, are you going to continue making a telescope out of this?
I'm an engineering student, and my dream is to design an inflatable space telescope using a similar pressure differential system. When I suggested an inflatable mirror to one of my professors, he warned me that it might not be parabolic enough to reflect an image properly, but I still want to try this out. Thank you for these educational videos!
Sounds like a great idea! I'm a retired AF officer and a new amateur astronomer. I wish you the best. I'm sure you will figure out how to make your inflatable device!
If you can succesfully make a telescope out of this mirror, it will be a monster
I'm on trying. I had made the mirror, only with a round plate yet.
@@davidd2661have your telescope ?
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.
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?
nighhawklight made that just search it, i want to make one but iam not entirely sure how to determine focal point by his method
what mil or thickness is this that you use here, great video thanks
You can actually do it with human power via mouth (sorry could not find a proper way to put that:-) The silicone needs to set for a few days or you inhale lots of horrible vapors. Did that once. The big mirror video explains it also. After a few days it becomes somewhat inert. A goo set of lungs can almost collapse the can lid as the curved mylar strength trumps the shape of the lid with a vacuum. I used the vacuum pump to see if the mylar would pop. It crushed the lid, mylar was still strong.
Really smart never used mylar sheet before. Will make a nice solar cooker. What is the specifications of the mylar sheet?
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"
Telescope mirrors are precise to within a wavelength of the visual range (less than 1 um), I think, there's no way you'll get a lid that is flat and round enough, mylar that is of consistent enough thickness, you won't be able to tape it down with consistent enough stretching. Besides sound and other sources of pressure waves will move the mirror. So I don't think it's doable, at least not simply. There are good reasons for using a solid thick piece of glass. But trying doesn't hurt.
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.
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
definitely one of your better diy videos that ive watched. thank you Dan Rojas
+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.
Attach tubing (mostly just to get distance to the mylar), insert a coil, then you can control the temperature on the inside electrically, within reasonable margins, of course, without moving parts or pumps. All you need is initial vacuum to be in range, close the valve, start and stop heating as necessary.
You're expert making mirrors&lenses&some of your videos show rather large sized devices.Have you ever gotten hurt,hurt or burned something you did not intend with these things. I remember once I had just a small mirror that I left outside one day. Later in the afternoon I walked by and noticed a weak smokey smell.Even later I walked by and saw a trail of black down my table's leg and plume of smoke coming off it at the end. I damn near started a fire&did burn my table leg.
Dan, first of all, thank you for this video... I am amazed with what you did here!
Second, I've actually made a 6" f/7.5 telescope, ground the mirror from borosilicate glass, and I'm currently polishing a 10" f/6 telescope mirror. I'm wondering, I know you used mylar, but is there an actual material that, when stretched via vacuum, can maintain a parabolic shape of optical precision?
I presume the trash can lid would have to be a near perfect circle (so the trash can is out of the question), and whatever is used in place of the mylar should have a material thickness tolerance of exceptional quality so it stretches evenly. But if this mylar alternative exists, it would make for an interesting telescope mirror.
I can imagine being able to focus by varying the focal length with a vacuum pump, among other crazy alternatives...
It sounds like something interesting, but I have doubts there would be an actual benefit compared to polishing and figuring a glass mirror. I hope I'm wrong though...
It would also be really interesting doing a Foucault test on the mirrors you made to see the quality of the parabola, just for fun...
Any thoughts?
It seems to me that temperature fluctuations would be problematic. You'd need the vacuum pump to operate sporadically to counter the effects of temperature on the expansion and contraction of the membrane or mylar alternative.
Bear in mind that the vacuum does not draw the mirror into a true parabola, it's actually part of a sphere. The difference is not material for a solar power application but it won't make a great telescope if you want a diameter more than about f/10. And, variations in the thickness of the mylar -or in the uniformity of the edge support- would cause small variations in the surface which could be even worse for the optical quality.
Carlos Paris dont know if this would work well on earth but you mite be on to some thing think about the weight that could be saved if something like this could be used in a space telescope design
Carlos Paris The vacuum/mylar trick doesn't form a parabola, it forms a hyperbola
Thanks for the clarification Herbert! Maybe a Ritchey-Chretien telescope? It uses hyperbolic mirrors... In any case, I'm just speculating, but I wonder if anyone has actually and seriously attempted this.
Pour enough resin in to coat the inside, then draw the vacuum. It should stick to the Mylar and maintain its shape when depressurized.
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.
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!
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.
Oh my god, I am SOO going to create a reflector telescope with this method! GENIUS!
Have you attempted this yet?
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!
Maintaining a solid and reliable focal point would be tough since it relies on vacuum and mylar, but if it was first surface, 98% reflective material with a stiff structure and bullet proof seal, it could work. I think this is a possibility, so don't think of me as getting down on you about the idea as I believe there must be cheaper ways to make a kick butt Dobsonian telescope even if it was built in a disposable manner.
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".
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!
i wander if it possible to use as telescope mirror?
+Dara rin Yes, watch this:
ruclips.net/video/bBXKbfqI49E/видео.html
+Dara rin no
+GREENPOWERSCIENCE That's not the same mirror!
It is, you have to watch the whole video.
If I might make a suggestion:
lay out the mylar, and tape it down to a flat surface to stretch it. Then, place the lid on top, run a bead of silicone or even hot glue around to both bond the mylar to the lid AND seal it. Then trim.
have you tested this?
No, I certainly haven't but I can't see why it would not work well.
J0llyR0ger I tried exactly this but then I ughhh used hot glue and t cooled too quickly
Christian Wang yeah, after thinking about it, I figured exactly that would happen with hot glue, as well as possibly heat distort the Mylar too, so I'll bet silicone would be best.
Nighthawk in light made a video on that ruclips.net/video/8CLRTa_ocmo/видео.html
Am I correct in suggesting that the greater the vacuum the shorter the focal length as long as the Mylar does not bottom out?
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.
As mylar melts at 500 degrees, after creating the vacuum, carefully using a hairdryer or heatgun should remove all of the remaining wrinkles and give a totally smooth surface.
It looked like a forming black hole distorting space-time when you pulled the vacuum!
Did you try looking at the parabolic mirror with an eyepiece to see if it is accurate enough to use as a telescope mirror?
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?
I wonder if you could use a hoop made of PVC backed by a wood disk to create a larger mirror?
This is definitely correct in theory at least. This is why stopping down the mirror with the cardboard shroud decreases the aberrations.
I didn't watch this, another time. I saw your square wood frame parabola. I hope you get back to me. I am co spidering a project, mirroring light through a small opening in a container, and dispersing the light on the other side, to light it up. I was thinking Sun tracking, to keep the mirror aimed. It would be very dangerous to use a parabola, in case of accident. I was thinking multiple flat mirrors, that send light at multiple angles, so you get more light entering a small opening, like 3 side by side mirrors, entering at different angles, hitting a mosaic of Tony mirrors, think disco ball.
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.
That's cool. do you get sheets of mylar online? Do you have a video showing how to cook food with that?
Great video, great technique.
What did u use for the vacuum?
From the sun, it should reach temperatures exceeding 1000 F over a smaller area with a stronger vacuum and shorter focal length. The video below uses our true solar mirrors. The process should be the same.
watch?v=aJ22QCAqFCc
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.
Amazing. It will be a nice school project I will help my daughter with, Thanks again Dan!!
The first surface side of the mylar is very good. About 80 - 90% aluminum.
watch?v=FyCLOXF1188
@ 6 MINUTES 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?
Couldn't you use a hair dryer to relax the creases and make the surface smother?
I think you'd end up with a spherical surface and that would lead to abberation. Parabolic is the way to go. This is just conjecture and opinion. I don't know for certain...
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?
try filling it with some kind of low hardening expoxy or fluid of some sort that cures and hardens with the mylar or some other more higher quality reflective meterial and then suck the fluid out until the desired shape is formed and maintaining that form via some kinda precise method optically and until it hardens, and there you go and walla the shape is kept, or it could be used as a mold for glass or some other reflective material to be coated, that would be epic my friend, cheap and economical.
Another idea I had was to set up a drill to drive a turntable flat circular mould into which you pour a resin/hardener mix and then gradually accelerate the spin speed to achieve the requited parabolic surface as the resin hardens. Using this method it should produce a very clean smooth finished surface generated by centrifugation. In fact some telescopes use this principle with liquid mercury, though they can only be used in a vertical orientation. Silvered oil or water will also produce this effect. The spin speed will be directly proportional to the finished sagittal of the mirror which will be a perfect parabola shape.
Would the epoxy stick to the mylar? I like this idea and if it does stick to mylar it is definitely worth trying.
hmmm maybe lol sounds sound to me
I would imagine if that mirror was used for a telescope it would suffer from Chromatic Aberration, horrifyingly so. The surface of a optical mirror has to be completely smooth. But, that is a cool idea for a solar cooker. I'd like to give that a try.
This might be difficult to focus especially when it's fixed to a cooker because the parabolic mirror is susceptible to changes in atmospheric pressure.
Manouni Mohamed It has nothing to do with air escaping from the contraption, the device is more like a barometer now, unless the cavity inside is filled with an incompressible fluid, I don't think this can be used reliably.
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?
Dan does the Mylar retain its elasticity over time or will it memory if you keep a vacuum on it after time?
MORE TELESCOPE MIRROR PLEASE... can you do a complete one ? lol your Genius ...
Can you use this technique to throw fiberglass resin on that Parabolic shape
Here's my whacky idea on that: How about placing it in the oven for a few minutes, sealing it off (with tire sealer?), and then letting it cool to obtain a more permanent vacuum?
Dude, you're a genius! You just got a sub!! (:
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
Dumb question: Why do you need the vaccum? Does it make the mylar tighter/more reflective.
Thank you,
Suzie
What would be focal length if we use it for Newtanian telescope?, Also will it work for perfect reflection?
I just saw that when the temperature changes the curve grows or shrinks. It looked to me like the focal ratio was about 2, which is (in my opinion) too low for a worthwhile telescope. The suction also goes away after about an hour but I think the solution would be to cast it so it keeps the shape.
He's a legend
Is we are able to get parabolic mirror will the reflectiveness be enough for astronomical use