A DIY Fourier Transform Spectrometer

Typical spectrometers use prisms or diffraction gratings to spread light over a viewing window or digital sensor as a function of frequency. While both prisms and gratings work very well, there are a couple of downsides to each. Diffraction gratings produce good results for a wide range of wavelengths, but a very small diffraction grating is needed to get high-resolution data. Smaller gratings let much less light through, which limits the size of the grating. Prisms have their own set of issues, such as a limited wavelength range. To get around these issues, [iliasam] built a Fourier transform spectrometer (translated), which operates on the principle of interference to capture high-resolution spectral data.

[iliasam]’s design is built with an assortment of parts including a camera lens, several mirrors, a micrometer, laser diode, and a bunch of mechanical odds and ends. The core of the design is a Michelson interferometer which splits and recombines the beam, forming an interference pattern. One mirror of the interferometer is movable, while the other is fixed. [iliasam]’s design uses a reference laser and photodiode as a baseline for his measurement, which also allows him to measure the position of the moving mirror. He has a second photodiode which measures the interference pattern of the actual sample that’s being tested.

Despite its name, the Fourier transform spectrometer doesn’t directly put out a FFT. Instead, the signal from both the reference and measurement photodiodes is passed into the sound card of a computer. [iliasam] wrote some software that processes the sampled data and, after quite a bit of math, spits out the spectrum. The software isn’t as simple as you might think – it has to measure the reference signal and calculate the velocity of the mirror’s oscillations, count the number of oscillations, frequency-correct the signal, and much more. After doing all this, his software calculates an interferogram, performs an inverse Fourier transform, and the spectrum is finally revealed. Check out [iliasam]’s writeup for all the theory and details behind his design.

Lumographic Images Created With Lens Only

Lumographic images are those patterns you see at the bottom of swimming pools. When water works as a lens, the light patterns of bright and dark are random and wandering based on the waves above. [Matthew] figured out a way to create fixed images from lens shape alone. The images only morph into view clearly when light shines at the proper angle. At near angles an eerie fun-house mirror effect appears, but too far off and it scatters unrecognisably.

The exact method for designing the optics is not explained, though we are sure someone in our readership could figure it out. The artist claims it to be a hundred year old million-variable math problem. The lenses are often quite thick and do not resemble much of anything. The effect however, is sharp, clear and detailed.

At first he suspected he needed astronomically-expensive military-grade 50 nanometer (0.000002″) precision machining for the lenses, but some friends in the autobody industry gave him a few tips to squeeze good enough accuracy from more affordable industrial machines. The technique also allows for images to appear from mirrors and internal reflections. It is probably not something you can 3D print or machine yourself, but it would be interesting to see someone try.

[Matthew]’s work is on display in the “Composite” gallery at the National Museum of Math in New York (MoMath). See the video after the break for a peak at the machinery he uses to manipulate the lenses to enhance the visuals in the exhibit.

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One Small Step For Magnification, One Giant Leap For Home Lens Manufacturing

DIY Optic Lens

There are some types of projects that we see quite often here on Hackaday; 3D Printers, Development Boards and Video Game Hardware to name a few. Once in a while we see an optics-based project but those use pre-made lenses. [Peter] felt it was time to give home lens manufacturing a shot and sent in a tip about his experience.

The typical lens manufacturing process starts off by taking a piece of glass and manipulating it into a rough lens shape, either by removing material or heating the glass and forming it in a mold. These lens blanks are then lapped using progressively finer grits of abrasives until the final lens shape and surface finish are achieved. The tool used to lap the lens is very specialized and specific to one lens contour shape. This lapping process can be very time consuming (and therefore expensive) depending on the quality and size of the lens being made.

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InfinitEye HMD Brings 210 Degree FOV to the Party


Head mounted displays are coming in hot and heavy this year. InfinitEye doesn’t have an official web page yet, so we’re linking to a review done by TheRoadToVR. Note that this is the second version of the display. InfinitEye released plans for their V1 HMD back in February. The InfinitEye prototype looks strikingly like the early Oculus Rift prototypes. Gaffers tape and what appears to be the frame from a face shield hold together the optical system. It’s this optical system which is interesting. InfinitEye has decided to go with head mounted LCD screens, similar to the rift, and unlike castAR’s projection system.

The InfinitEye team decided to go with two screens, giving them a whopping 1280×800 resolution per eye. The optics are also simple – fresnel lenses. This is all similar to the first version of the goggles, however the InfinitEye team claims that this new edition provides a 210 degree field of view. What we don’t know is exactly what they changed. We’re curious if the wider field of view will reduce the Sim Sickness some of us have felt with the rift – though to be fair, almost any head mounted display requires some time to adjust. What we are sure of is that the future is bright for virtual (and augmented) reality.

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Building an oak telescope

You might not think about the finish of your homemade telescope but if it’s build from solid oak you probably should. [Gregory Strike] built this 8″ telescope a few years back but just posted about it a few days ago. The optics are quite expensive but the rest of the build was done dirt cheap and he did a great job of it.That includes taking care to finish the oak boards that make up the octagonal body of the instrument.

This is much more approachable for the average hacker than something like the 22″ binocular build (or going way too far and building your own observatory). [Gregory] developed his design after looking at a couple of others. If you need a bit of a push to get started check out the telescope resource we ran across in our days of Internet infancy.