Slashdot Mirror

Depends on what the mirror was made of. Some would absorb the heat activated by infrared "excitement" of their molecules.

Regular lens glass isn't great for IR.

Many of the best IR lens materials can't stand humidity.

http://www.edmundoptics.com/re...

This was a software issue. The camera 'saw' the truck, but the edges didn't have high enough contrast.

Fundamentally though, this was an autopilot induced crash. If the driver had continued to pay attention, he could have avoided it. Airplanes had the same problem, driver assists are dangerous if they allow the driver to feel safe when not focused on driving.

You've just described an IR pass-through filter, used in millions of television remote controls...

Something like this, I think, that took all of 20s of web searching to find.

It's more like a lensing effect. Same principle as a fiber optic coupling sphere - it's all EM, just the wavelength is different.

http://www.edmundoptics.com/re...

Hold the key a few inches behind your head and look at the car you want to lock/unlock.

That trick has worked for me for years.

"equip planes with a return-fire laser?"

They could start with mounting retroreflectors on the cockpit windows.

http://www.edmundoptics.com/op...

Bad side effect: it will help the bad guy to aim better.

http://www.edmundoptics.com/te... "Huge opaque disk" seems a lot more confusing then calling it a massive lightweight lens.

Sapphire is pretty cheap.
http://www.edmundoptics.com/optics/windows-diffusers/ultraviolet-uv-infrared-ir-windows/sapphire-windows/1904

"Sunglasses wouldn't help," he says - in fact, wearing them would only exacerbate the effect. That's because the glasses would not affect the green laser light - chosen because that colour is particularly irritating - but the laser would appear even brighter contrasted against the darkened background.

So they'd just have to wear glasses with optical notch filters to defeat thus?

The "frictionless" magnetic gear shown will still have friction in the bearing. The magnetic "teeth" will introduce a huge amount of backlash into the gear system. And you would run into problems if you tried to stack gears beside each other in a gearbox. The high pull-off force/low twist-and-pull force application is neat though. One limitation is that rare earth magnets tend to be brittle, and make a mess when they break.

To be clear though, magnets have been made with multiple poles for a long time, for example those flexible fridge magnets will often have alternating poles across their surface. Also, the pull off application is in many ways similar to the "switchable magnetic bases" . In these devices, the orientation of the magnetic is changed to force the field lines to go through the surface underneath, or to be contained within the base. The innovation in the present work is the use of coding theory to design the patterns.

Here's some light control grating material, if they don't make a panel in your size. Two of these rotated at 90 deg. to each other would leave a very narrow viewable window. Not cheap, but not VR-goggley either.

The best way to think of it is to ignore spot size and all that. A beam with a 0.07 degree width needs to be pointed with an accuracy of 0.07 degrees or better.

Sorry, but 60% is not the world record. The world-record in efficiency is currently about 42.8%, held by the University of Delaware. Here's their press release.

However, the most efficient cells in production for commercial use are from Spectrolab, a Boeing subsidiary. They claim 40.7% as of December 2006 - which was the world's record until UD broke it 23 July 2007.

According to Spectrolab's web site, the cells they're producing for distribution include their Ultra Triple Junction cells, with a minimum efficiency of 28.3% and a typical terrestrial efficiency of 31% claimed.

In their FAQ, they claim that a concentration of 500 suns is typically optimal. On the earth, you then have to deal with the fact that 2/3 of the energy is not turned into electricity - which means a significant amount of heat to deal with. You would want to cool the cell with something, lest it burn up. Their FAQ mentions that using a 1 cm^2 cell, at 500 suns and 25C will produce about 17.5W - so you'd be "spending" at least 500 cm^2 of real estate to prodcue the 17.5W : 500 cm^2 for a Fresnel lens to focus it down to 1 cm^2 on the cell.

I think they'll sell to anyone as long as you're a U.S. citizen and agree to the export limitations. However, they have a minimum purchase of $5,000 - but you must spend more to get optimal pricing.

Well. My point is this: 60% is not what anyone's achieved. Most companies are just trying to get their $/Watt price as low as possible in order to get widespread acceptance - instead of attempting a new world-record.

I wish that someone had gotten to 60% - it's 2/3 of the way to the Carnot limit of 95% If you're referring to these guys and their "quantum dot cells", from their web site you'll see that it's still all theoretical.

BTW - you can buy a plastic Fresnel lens here, unless they've changed the web page. Be careful and wear a welding helmet (or equivalent) so that the intense concentration of sunlight on something won't be able to cause a light bright enough to burn your retina.

If you're doing this often enough, as you say, why don't you buy a linear polarizer? Here is a relatively cheap one. Much better ones can be had for more money. You can also use circular polarizing films to block reflected glares.

Edmund optical sells some good IR bandpass filters I've used in the past: here

I wasn't going to get into the whole "is 25 years appropriate" arguement, but since you asked ...

I don't think FPMITA prison is appropriate for this doofus. Take away his lasers. He's a fiber optic tech (or something related?) Take away his access to lasers. Force a career change on him. Tatoo "asshat" on his forehead. House arrest with a tracking collar would probably do fine. A year of intense scrutiny will alter his outlook, and that's the point, right? This guy's probably more ignorant than fundamentally evil. A prison sentence makes you and me pay (financially) for his transgression. I'm not interested in that. Prison should be reserved for truely violent and dangerous folks.

If he does it *again* after all that, then it's definitely malicious. Toss him in the clink if he even *looks* at an Edmund Scientific catalog ...

Using plain glass it'll be real hard to read. Beamsplitter glass is what's needed, even paying the $300 for the 60/40 glass is a lot cheaper than buying a teleprompter.

If you are having heat problems you need to put a 45 deg cold mirror between the light source and the LCD panel. They are expensive but they allow you to greatly increase the lumens which you can thow out because there is less infrared heating of the LCD panel. http://www.edmundoptics.com/onlinecatalog/displayp roduct.cfm?productid=1900&CFID=3282620&CFTOKEN=dcc c6c4571313046-39113206-3048-41AD-84BFA8B603869B78

Stupid link didn't make it in:

IR Cutoff Filters.

Serves me right for not previewing.

Edmund Industrial Optics.

You looked in the wrong places :> here's multiple variations of mounted sharp cutoff IR filters virtually extinguishing above 780nm and still transmitting 80-90% in optical, they are optical quality and pre-mounted on threaded mounts - Edmunds

A bit pricey, but not outrageous, about half of your price for most.

Though there will be some transmission obviously so if you up the brightness enough you might be able to swamp the camera.

No idea what the characteristics of the Tiffen Hot Mirror filter is though, can't find specs for it anywhere.

The folks at the venerable Edmund Industrial Optical probably have what you seek.

Edmund...ah...what a catalog.

I think I better post a few mirrors:

Mirror #1

Mirror #2

Mirror #3

The last one is pretty fast. Try and use one of these instead of the main site!

"Transparent Alumina" in the form of Optical Sapphire has been widely available for years. See, for example, Edmund Optics. It's also used in high-end wristwatches.

Here's a blue laser. Only $7271.20. There's also violet.

Here's a blue laser. Only $7271.20. There's also violet.

get a length of copper tube from home depot, the thicker the better. I got a length of tube and then some repair coupling to put over it, to make the tube thicker. then drop a strong magnet down the tube. It will float slowly down instead of falling at a normal rate. here's a page describing a simmilar experiment.. you can get great magnets from wondermagnet. (the spherical ones work best.)

Another fun thing: get two linear polarizers and then show that they are transparent when lined up but opaque when crossed. This is pretty cool if you haven't seen it before. You can get nice big ones from edmund optics.

Also you can get 1/2 wave retarder film from this same place; put the retarder film between the crossed polarizers, and it opens up a little "window" which allows you to see through the otherwise opaque polarizers.

Other stuff you can do with polarizers: look at a window and observe that the glare on the window is dimmer when you turn the polarizer the right way. Also cross two polarizers and put a piece of clear plastic (like a CD case) between them, and you can see all sorts of pretty colors. Also you can take a clear plastic bag and stretch it and put it between the two polarizers, and the colors will indicate the stresses in the bag.

Edmund Optics will sell you sapphire windows, along with tons of other cool stuff. Ball lenses are pretty neat, too.

Edmund Optics will sell you sapphire windows, along with tons of other cool stuff. Ball lenses are pretty neat, too.

As I've pointed out, look through a pane of (clean) glass, then through some plexiglass.

I'm not saying that its relevant for audio, sicne I have no clue what more THD a TOSLink cable adds.

You took it that I recommend glass, or think its stupid to use plastic... on the contrary, I pointed out the irony of using a cheap plastic part in an expensive stereo.