Bone-Shaking Haunted Mirror Uses Stable Diffusion

We once thought that the best houses on Halloween were the ones that gave out full-size candy bars. While that’s still true, these days we’d rather see a cool display of some kind on the porch. Although some might consider this a trick, gaze into [Tim]’s mirror and you’ll be treated to a spooky version of yourself.

Here’s how it works: At the heart of this build is a webcam, OpenCV, and a computer that’s running the Stable Diffusion AI image generator. The image is shown on a monitor that sits behind 2-way mirrored glass.

We really like the frame that [Tim] built for this. Unable to find something both suitable and affordable, they built one out of wood molding and aged it appropriately.

We also like the ping pong ball vanity globe lights and the lighting effect itself. Not only is it spooky, it lets the viewer know that something is happening in the background. All the code and the schematic are available if you’d like to give this a go.

There are many takes on the spooky mirror out there. Here’s one that uses a terrifying 3D print.

Dielectric Mirror Shines Bright

We knew the mirrors in our house were not really very good mirrors, optically speaking. Your mirror eats up 20 to 40 percent of the light that hits it. High-quality first-surface mirrors are better, but [Action Lab] has a video (see below) of something really different: a polymer dielectric mirror with 99.5% reflectivity. In addition, it has no Brewster angle — light that hits it from any angle will reflect.

Turns out something that thin and reflective can be hard to find. It also makes a little flashlight if you roll a tube of the material and pinch the back end together. The light that would have exited the rear of the tube now bounces around until it exits from the front, making it noticeably bright. The film comes from 3M, and apparently, they were surprised about the optical properties, too.

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Toxic Telescope Makes You Mad As A Hatter

[Hank Green] posted an interesting video about the first liquid mirror telescope from back in the 1850s. At the time, scientists were not impressed. But, these days, people are revisiting the idea. The big problem with the early telescope is that it used mercury. Mercury is really bad for people and the environment.

The good thing about a liquid scope is that you can pretty easily make a large mirror. You just need a shallow pool of liquid and a way to spin it. However, there are downsides. You need to isolate the liquid from vibrations and dust. Another downside is that since gravity makes the shape of the mirror, these telescopes only go one way — straight up.

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Magic Mirror Isn’t Transparent Metal

One of the Star Trek movies has a McGuffin called “transparent aluminum.” While magic mirrors aren’t really transparent, it appears that way to a casual observer. If you haven’t seen one of these, they are polished metal mirrors with a pattern embossed on the back. When you shine a point source of light on the mirror, however, the reflection matches what is on the back of the mirror. Is it transparent? No, and the video by [Steve Mould] below explains what’s really going on.

The reality is that very subtle variations of the surface produce the image. You need some understanding of optics and calculus to fully understand what’s going on.

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A Tiny Forest Of Resistors Makes For Quick And Dirty Adaptive Optics

The term “adaptive optics” sounds like something that should be really complicated and really expensive. And in general, the ability to control the properties of optical elements is sufficiently difficult enough that it’s reserved for big-science stuff like billion-dollar space telescopes.

But that doesn’t mean there aren’t quick and dirty adaptive optics that are suitable for the budget-minded experimenter, like this thermally deformable mirror. As [Zachary Tong] explains, this project, which started quite some time ago, is dead simple — a 4 by 4 array of through-hole resistors stand on end, and these are attached to a glass coverslip that has been aluminized on one side. An Arduino and a couple of shift registers make it possible to individually address each of the 16 resistors in the array. Passing a current through a resistor heats it up a bit, leading to thermal expansion and a slight deflection of the mirror sitting on top of the array. Controlling which resistors heat up and by how much should lead to deformation of the mirror surface in a predictable way.

The video below shows some of [Zach]’s experiments with the setup. Unfortunately, he wasn’t able to fully demonstrate its potential — the low-quality mirror didn’t cooperate with his homebrew interferometer. He was, however, able to use a dial indicator to show deflection of the mirror in the 2- to 3-micron range by heating the array. That alone is pretty cool, especially given the dirt cheap nature of the build.

As for practical uses, don’t get too excited. As [Zach] points out, thermal systems like this will probably never be as fast as MEMS or piezoelectric actuators, and many use cases for adaptive optics really don’t react well to added heat. But changing the shape of a mirror with air pressure is another thing.

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Hackaday Links: June 12, 2022

“Don’t worry, that’ll buff right out.” Alarming news this week as the James Webb Space Telescope team announced that a meteoroid had hit the space observatory’s massive primary mirror. While far from unexpected, the strike on mirror segment C3 (the sixth mirror from the top going clockwise, roughly in the “south southeast” position) that occurred back in late May was larger than any of the simulations or test strikes performed on Earth prior to launch. It was also not part of any known meteoroid storm in the telescope’s orbit; if it had been, controllers would have been able to maneuver the spacecraft to protect the gold-plated beryllium segments. The rogue space rock apparently did enough damage to be noticeable in the data coming back from the telescope and to require adjustment to the position of the mirror segment. While it certainly won’t be the last time this happens, it would have been nice to see one picture from Webb before it started accumulating hits.

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All About Dichroic Optical Filters

[IMSAI Guy] presents for your viewing pleasure, a nice video on the topic of optical filters and mirrors. (Video, embedded below) The first optical device is a simple absorption filter, where incoming light is absorbed in a wavelength-selective manner. Much more interesting however is the subject of interference or dichroic filters. These devices are constructed from many thin layers of a partially reflective material, and operate on the principle of interference. This means that photons hitting the filter stack will interfere either constructively or destructively giving the filter a pass or stop response for a particular wavelength.

As [IMSAI Guy] demonstrates, this makes the filters direction-specific, as photons hitting the stack at a different angle will travel slightly further. Longer travel means the interference effect will be different, and so will the filtering response. You can see this by playing around with one in your hands and seeing the color change as your rotate it. Dichroic filter films can also make for some stunning optical effects. Very cool stuff.

By creating a filter stack with a wide enough range of inter-layer thicknesses, it’s possible to construct a mirror that covers the full spectrum with excellent reflectivity.  Since you can tune the layers, you can make it reflect any range of wavelengths you like. One thing we’ve not seen before is a wedge-like optical filter device, where the layer thicknesses progressively increase lengthways, creating a variable optical frequency response along the length. We guess this would be useful for diagnostics in the field, or perhaps for manually tuning a beam path?

We like the applications for dichroic films – here’s an Infinity Mirror ‘Hypercrystal’. If you don’t want to buy off-the-shelf films, perhaps you could sputter yourself something pretty?

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