Slashdot Mirror
Deformable Liquid Mirrors For Adaptive Optics
eldavojohn writes "Want to make a great concave mirror for your telescope? Put a drop of mercury in a bowl and spin the bowl. The mercury will spread out to a concave reflective surface smoother than anything we can make with plain old glass right now. The key problem in this situation is that the bowl will always have to point straight up. MIT's Technology Review is analyzing a team's success in combating problems with bringing liquid mirrors into the practical applications of astronomy. To fight the gravity requirement, the team used a ferromagnetic liquid coated with a metal-like film and very strong magnetic fields to distort the surface of that liquid as they needed. But this introduces new non-linear problems of control when trying to sync up several of these mirrors similar to how traditional glass telescopes use multiple hexagonal mirrors mounted on actuators. The team has fought past so many of these problems plaguing liquid mirrors that they produced a proof of concept liquid mirror just five centimeters across with 91 actuators cycling at one kilohertz and the ability to linearize the response of the liquid. And with that, liquid mirrors take a giant leap closer to practicality."
Why not just spin it, and while it's spinning, lower the ambient temperature so that it freezes? And if you remember your thermodynamics, you'll remember that raising or lowering *pressure* raises or lowers the temperature of a gas -- seal it up, spin it, then freeze it. Easy peasy.
#fuckbeta #iamslashdot #dicemustdie
Global Vision 2020 is doing something similar to this, creating eyeglasses for people in third-world countries.
They have glasses with special lenses that can be filled with oil. The oil changes the shape of the lens.
The client puts the glasses on and fills the lens with oil until he can see clearly. Then the technician seals the glasses so the amount of oil (and shape of the lenses) won't change any further.
$10 per set of glasses, and no optometrist required to issue them.
If you're looking for a worthwhile charity to donate to, this may be one to consider.
If you're a zombie and you know it, bite your friend!
Laslo: Well what would you use that for?
Ick: Making enormous Swiss cheese?
(Chris laughs.)
Mitch: The applications are unlimited.
Laslo: No. With the fuel you’ve come up with the beam would last for what15 seconds. Well what good is that?
Chris: Oh Laslo. That doesn’t matter. I respect you but I graduated.
Mitch: Yeah, let the engineers figure out a use for it. That’s not our concern.
Laslo: Maybe somebody already has a use for it. One for which it is specifically designed.
PS: I'm serious.
Put a drop of mercury in a bowl and spin the bowl. The mercury will spread out to a concave reflective surface smoother than anything we can make with plain old glass right now..
so our bowl making technology exceeds our bowl shaped mirror technology? seems like we could just hire the bowl makers and fire the current crop of mirror makers, problem solved.
The liquid takes on a shape that minimizes its surface tension. Small imperfections in the bowl don't affect the surface tension and are smoothed over.
My only political goal is to see to it that no political party achieves its goals.
Sounds like something perfect for the next generation Hubble (or the next next one - the next one is getting ready for launch). Why fight gravity, when you can just spin it in space?
Course - making it spin for a long time between maintenance visits (on who knows WHAT vehicle) could be tricky.
Okay, I'm in line for a debate. Now what?
Now tell him he is wrong, and why he is wrong.
Don't know something? Look it up. Still don't know? Then ask.
Ignoring the mischaracterization of glass that you're trying to start a debate about, the answer to your question is: No, becuase mirrors are not made of glass.
Bathroom mirrors have a protective layer of glass, but the reflective layer is silver. At best that would be "partially liquid" if we pretend that glass is a liquid. Many mirrors do not have such a protective layer, though; the mirror I use for backpacking is simply a thin metal sheet. Mirrors for lab optics typically don't include a glass layer because it would serve no purpose and would interfere with the mirror's intended use.
The defining element of a mirror is the reflective part, which is made of metal and is usually solid.
The perfect shape comes from the spinning liquid: the bowl doesn't have to have any particular shape. You can even use a flat-bottomed bowl, you just need more mercury.
"Flat-bottomed bowls, you make the liquid scope go 'round..." -- Freddie Mercury
You are wrong in 4 ways:
I know where you can get a lot of oil, but it might be a bit salty...
Who would win this election: Andrew Weiner vs Andrew Weiner's weiner.
MIT's Technology Review is 'nalyzin a team's success in combating problems with a-bringin' liquid mirrors into the practical applications of astronomy.
FTFY
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Prisencolinensinainciusol. Ol Rait!
Adding to parent comment..
I am pretty sure that most large "glass" mirrors used in astronomy actually use a very thin top layer of aluminium as the reflective layer, perhaps only 3 atoms thick... And I recall reading somewhere that this layer is cleaned off and applied every couple of years because of corrosion.
No sig. Move along - nothing to see here.
Seems to me that liquid mirrors would be orders of magnitude more sensitive to vibrations than solid ones. (Experiement: fill a glass with water; tap the glass; which has a greater amplitude, the ripples on the surface of the water, or the ripples on the surface of the glass?)
And rotating something large and heavy with a motor, moreso while simultaneously manipulating its surface with several dozen actuators, is a huge source of vibrations.
I thought one of the points was that you don't want to fix the shape permanently. Adaptive optics lets you adjust the mirror to account for atmospheric distortion. Think of it like being able to change the prescription of your glasses. A liquid mirror would allow for near-infinite possibilities to adjust how the light is reflected, with greater precision than current adaptive optics systems.
Oh please. You need a good dose, and constant exposure. Otherwise your body will purge it. Don't drink it, but don't drink motor oil either.
Just be careful. You average hobbyist has no problems with it.
The Kruger Dunning explains most post on
Actually, most telescope mirrors are made from glass (some are made of special glasses, that have low thermal expansion and so on, but nevertheless glass), glass being the important "ingredient" of the mirror. The reason is that glass has no crystal structure and can be polished to very high degree of accuracy and achieve the required figure (a paraboloid) with very high precision. Glass is also a very stable medium if prepared (annealed) properly.
Since the purpose of an astronomical mirror is to collect light in a precise way, the figure of the mirror is of most importance. The role of the metal layer on the surface is only to increase the reflectivity of the glass. There were (and, for some specialized uses probably are) some metal astronomical mirrors (made of speculum metal, mostly before glass got into wide use) but they allow a figure that is no better than the glass ones, and are difficult to polish and maintain.
In fact, metal coating isn't even necessary to use a glass mirror. When you make a telescope mirror, before you send it off for coating you'd perform what is known as "star tests". You'd set up your telescope, put in the uncoated mirror in it, and look at stars to see if the mirror shape is good. I could easily see a lot of planetary detail with my last (40") mirror while I was testing it without coating. Looking at the Moon was blinding.
In a front surface mirror such as in a telescope, the surface of the glass is in fact the mirror because the important part is the shape and smoothness of the surface. You do not need to coat it with a reflective material because the glass itself is somewhat reflective. A large noncoated mirror is good for viewing the moon, which has a lot of detail but is very bright.
After countless hours grinding and polishing or thousands of dollars spent on an optician with a good reputation or even tens of thousands spent on ion milling of the glass, you might want to have your mirror tested with an interferometer. That is done before the mirror is coated. That's because the glass is the mirror. The coating simply makes it more efficient.
It is true that some mirrors are made with non-glass materials such as quartz or zero expansion ceramic. ...or Mercury.
How about spinning the bowl of mercury facing up, then swinging the bowl around a horizontal axis? Like a bucket of water swung at arm's length over one's head then back down, then back up, in a cycle, the way kids show each other "centripetal force"? The momentum would keep the concave surface intact as the whole contraption spun and swung around. Then the contraption could be rotated on the other horizontal axis, pointing the concave mirror at whichever direction was desired.
The mirror would point in that direction only intermittently, as the mirror swung past that point in its arc. But the image sensor could be sampled only at that moment, as the position synced with the desired direction.
All of that swinging would have to be calibrated to compensate for the interaction of the various axes of spin. But that all sounds like a set of DSPs could do it, with a laser interferometer keeping the cycles synced and sampling at the right timeslot.
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make install -not war