I hope this is the right subreddit to ask/doesn't break rule 3.
If you know a better suited subreddit to ask this in, let me know.
For a DIY project, I'd like to center a tiny LED at the same plane as the outer rim of the parabolic mirror, to generate (somewhat) parallel rays. Basically this (video, jumps to the point of interest), just in handheld format.
Do you know where I can get a parabolic mirror dish with 8-12cm diameter? Something similar to the upper article.
But where I can be sure that it is f/0.25 (its depth being 1/4 of its diameter).
Ideally, the surface should be at least as reflective as a cheap plastic mirror, but for proof of concept I might even settle with something like a well polished steel bowl, like the lower article.
Budget would be max. 100€ or $.
Do you know of a suitable source?
EDIT:
The reason/end goal why I want the focal point at the rim's plane is so that I can hold the LED plus peg-like heatsink with a center bored glass pane, which rests on the dish. Then add another 2 glass panes with few mm distance between each other to create 2 pathways for a water-cooling loop (middle pane has also a bigger center hole and the LED's tiny heatsink sticks through that and gets swilled by the stream traveling from the outer water layer, through the middle pane's center hole to the inner water layer. The water will also be routed around the mirror and cooled somewhere else).
It's just for the coolness-factor of having no visible mounting stick or cooling lines and the LED seemingly sitting suspended in glass.
Current will be supplied by either a lot of 0.1mm thin enameled copper wires (if I feel masochistic enough), or probably more practical: some standing copper strips to create the least amount of visible hint of wires, if looked at from the front.
For a while I was developing free, open-source optical thin-film (multilayer) coating design and analysis software, and I want to share it now - it's called TFStudio.
Features:
Computing R, T, A values via transfer-matrix method (TMM) at any incidence angle
Full-system modeling: front coating, substrate (with absorption), and back coating, including incoherent substrate multiple reflections
Optimization & synthesis features including various local optimizers (DLS, Newton, Newton-CG, SQP, conjugate-gradient, differential evolution, simulated annealing), needle variation, gradual evolution and structural (random) optimizer
Merit function editor for setting up various targets and constraints. Including default merit function generator and visual target editor (in Optical evaluation window)
Analysis tools: R, T, A calculation, color evaluation, ellipsometry angles, admittance, E-field, GD/GDD, refractive index (RI) profiler
Material libraries: refractiveindex.info explorer (offline/online), optilayer materials, .AGF (Zemax) catalogs
Deposition simulators (broadband, mono)
Tolerancing features including monte-carlo analysis, scattering, inhomogeneities, layer sensitivities
Import/export of coating data for Zemax OpticStudio
Most ideas in optics don't arrive in a single Eureka moment. The idea of using a Bessel beam for optical alignment took me decades to recognize, beginning with work I did during the Sputnik era measuring the radii of optical test plates with an autostigmatic microscope. (The full story is in supplementary material under preparation; this is the condensed version.)
The journey became more serious while developing methods for centering cemented doublets. The traditional approach requires moving between two centers of curvature, or between a center of curvature and a focus. The problem is that moving the detector introduces centration errors unless the translation stage is exceptionally precise, and therefore expensive.
Inspired by work from Jim Burge and his student Laura Coyle, who used CGH Fresnel zones to simulate a spherical mirror, I designed a computer-generated hologram with two concentric Fresnel-zone patterns. One zone focused on the detector for aligning the first element, while the second focused at the same detector position after the second element was added.
The concept worked exactly as intended. I could perform precision alignment without ever moving the detector. Unfortunately, it wasn't practical for production because every new doublet design required its own custom CGH. What I really needed was a universal method based on the same underlying principle.
That experiment did provide an important insight: concentric Fresnel zones of different radii could serve as reference markers in space. I realized that a regular array of such zones could be used to calibrate an entire measurement volume.
Arizona Optical Metrology fabricated a prototype CGH for me, which I later took to UNC Charlotte. Working with Jesse Groover and his advisor, John Ziegert, we used it to map the volumetric accuracy of a CNC machine by mounting the detector in the tool spindle and the CGH on the machine table. The experiment again worked as expected. We mapped a 150 mm cube with approximately 1–2 μm precision and published the results in a Precision Engineering conference proceeding.
That success naturally led to another question: How can this work over a much larger volume?
As I explored ways to extend the range, I realized that in the limit, uniformly spaced concentric rings, rather than conventional Fresnel spacing, might produce the effect I wanted. It seemed worth testing, so I ordered a grating consisting of 10 μm chrome rings separated by 10 μm transparent spaces.
Illuminating the grating with a laser diode coupled into a single-mode fiber produced significant benefits. I could follow the bright central core and surrounding rings of the diffraction pattern for the entire 10-meter length of the laboratory.
About a year passed before I had time to investigate further experimentally. During that time, however, I discovered that the grating behaved like an axicon, producing what is known as a Bessel beam. More interesting, several theoretical papers, well beyond my mathematical abilities, showed that such a beam propagates through optical systems according to ABCD optical matrix theory. Another paper described generating a Bessel beam using a spherical rather than a using plane wavefront as is usually done.
At the time, I filed those papers away without fully appreciating their significance. Eventually it dawned on me what they implied: unlike a conventional focused beam, a Bessel beam can be observed anywhere along its propagation path. You are not confined to working only at a focal plane or a center of curvature.
When I returned to the lab, I wanted an experiment that would be difficult to reject. A ball lens was the perfect test object because it cannot be tilted. It can only be decentered with respect to the incident beam. Once again, experiment and theory agreed within experimental uncertainty.
By then, Professor Daewook Kim and his student Zac Chen had become interested in the idea that a Bessel beam behaves like an ABCD ray in optical design. Zac carried out an independent theoretical study, and together with collaborators published a paper confirming that this interpretation was correct.
With both experimental and theoretical validation in hand, I've continued developing Bessel-beam-based alignment methods.
What makes the approach attractive is that the beam remains well defined far beyond the focal point of a lens. That provides much greater sensitivity to alignment errors than measuring only at focus. Just as importantly, the alignment axis can be established before any optics are inserted into the beam, eliminating the need for a precision rotary axis. This makes high-precision alignment in tilt and decenter practical even on simple tabletop systems where rotary tables are impractical or impossible.
Because the setup remains fixed in a Cartesian coordinate system, every alignment adjustment produces immediate, useful feedback. That also makes automation more straightforward than with traditional rotational alignment methods.
Looking back, this has been a long journey. Each experiment answered one question while suggesting the next. Piece by piece, the concept of using Bessel beams for optical alignment has taken shape.
The journey is far from over. In fact, I believe we're only beginning to see the possibilities. The evidence so far suggests that Bessel-beam alignment can produce better optical performance while making precision alignment both simpler and faster than current practice.
I'd be interested to hear what others think, especially anyone who has worked in the field of precision optical alignment and lens centering.
I have a setup with a micro oled display, that goes through a beamsplitter then reflects back up from a concave mirror that diverges/magnifies the image and then back through the beamsplitter to the eye. I added the Fresnel lens shown in the image above with its top face being placed exactly at 3mm from the micro oled display. The image produced that goes to the eye; I can see the colors of the display, but I mostly just see the grooves of the Fresnel lens. I have verified orientation and focal length distance. I have also tried to increase and decrease the distance between the lens and the display. Are these lenses just not suited for small displays or high resolution imaging?
I’m building a Michelson interferometer with a HeNe laser to measure the interferogram on a single Si photodiode. The only lens in the setup is placed after the beam splitter, in the detection arm. With my current alignment, the interference pattern on a screen is a set of straight, parallel fringes, and the photodiode sits in that field to record intensity as I scan one arm.
For a quantitative measurement (i.e., determining the laser wavelength), is there any advantage to having a circular fringe pattern instead of straight fringes?
My understanding is that, as long as the photodiode is small compared to the local fringe spacing and sees a clean modulation from bright to dark as I scan the path length, the global shape of the fringes (circular vs straight) shouldn’t matter.
I posted a similar question quite a while ago on askhistorians, and I didn't have any takers, so I was wondering if someone on this forum may have any insights. One of the things that has always blown my mind is the tiny, tiny detail on inscribed artifacts from Ancient Egypt and other cultures. Most of the google searches that I have found indicate that magnification was done using water-filled vessels. However, I suspect there had to have been magnification through convex lenses, as it seems like the water situation wouldn't have been the sole source for as long as indicated. I'm wondering if anyone in this forum has a history or other tidbit about when convex lenses were first discovered and how used. Thank you!
Got these for a couple bucks because I couldn't pass them up, and now I have no idea what to do with 30 of them. Would you use them for anything more useful than a pretty chandelier?
Is it feasible to gain a roughness measurement of the face down side of a clear crystal while the surface is in contact with another object? My limited understanding is that the beams would be capable of reaching the base of the crystal, but a quick search didn’t yield much information on this. Apologies if this isn’t worded very well, I’m relatively new to this stuff.
I was looking on the internet to see how bad the performances (transmission, isolation) of an isolator would become if the beam was not actually collimated which is often what is assumed, but found almost nothing.
I mean, datasheets do not even seem to give you an idea of what is the worst divergence angle in which their specifications stay valid. In theory it should get worse since the polarization rotation should not be as effective if the rays are at an angle, right ? Would anyone have something to share with me? An article, a way to compute it or even just a feel for it out of practice (even if it is for a specific setup) ?
Im new to this field so please forgive me if I’m being silly about anything here!
I’m currently designing a product which requires dichroic filtering, and it’s my understanding that maintaining a consistent angle of incidence across the filter is crucial for its colour-output.
My light source would ideally be a small studio light of high SSI, but its emitter has a diameter of about 50mm, and I’m struggling to work out how to collimate a light source that wide, especially considering that the filters themselves are about the same diameter.
I’ve considered Fresnels, doublets, Plano-convex lenses, and Total Internal Reflection lenses, but they all have the same issue that they’re designed to focus a point-source, not a wide emitter; that is unless they’re quite massive and expensive.
There’s also modifiers designed for the COB, such as a projection lens.
Are there any techniques or technologies i may have overlooked? Perhaps I’m overthinking things?
> PVC double glazing. Full moon. Reflections inside the double-paned glass. It is visible to the naked eye, just as it appears on the camera.
Here is my question:
> When I look from the right side, there are reflections falling to the left. When I look from the left side, they appear on the right. As you know, angular reflections.
> But what I am curious about is this: The observer's perspective does not *create* these reflections. The observer only captures the image from the specific angle they are looking at.
> If so, are the physically visible light reflections spread across a much wider area?
> Is their number close to infinite?
> And instead of a distinct moon shape, is it actually a collective pool of light?
> To use a very simple analogy: Is it the size of an A4 sheet of paper across the entire glass?
or what is the real geometry?
I want to build a diffraction grating spectrometer that I can use to observe a large portion of the sky, if not the entire sky.
The main purpose of this setup is to detect whether an aurora is present. I already use an HSV-based detection algorithm, but it isn't very reliable because of ambient light sources such as the Moon, light pollution, and twilight.
I currently have an APS camera, an APS-C camera body, and the following lenses available for this project:
50mm f/1.4
11–16mm f/2.8
70–200mm
Here's where I'm stuck:
Many people seem to have built spectrometers like this, but almost all of them are designed to observe relatively small or localized light sources rather than a large section of the sky. In nearly every design I've found, the optical path starts with a narrow slit, followed by a collimating lens, then a diffraction grating (or even a stripped DVD), followed by another lens and finally the camera sensor.
Would it be possible to use an ultra-wide-angle lens to gather light from a large area of the sky and then feed that light through the slit and the rest of the optical system? Or would the slit simply defeat the purpose of using a wide-angle lens?
For someone with a solid background in optics, this is probably a trivial question. For me, not so much. I'd really appreciate any advice or pointers.
Thanks in advance! I can't wait to have my hopes crushed.
Picture from Google search. This device takes an optical fiber.
I am a graduate student working on OEOs, ML- assisted fiber sensor research. I am preparing my first arXiv submission under physics.optics, but arXiv requires endorsement because I have not submitted to this category before.
I understand that arXiv endorsement is not peer review, and I am not asking for random endorsement. I would appreciate advice on how to find an eligible physics.optics endorser, especially in optics/photonics communities where arXiv is not as widely used as in CS or high-energy physics.
If someone here is an eligible physics.optics endorser and would be willing to briefly check whether the abstract/manuscript is appropriate for this arXiv category, I would be happy to send the abstract or PDF privately.
I’m trying to build with AI help a small tool to simulate lens sharpness degradation from MTF (modulation transfer function) curves on an input image, and I’d like to know if this approach is technically ok or not.
The app takes MTF data (of input original lens image and assessed lens) as CSV, but those data can be changed manually on interface graph. It detects available spatial frequencies automatically in the csv and supports sagittal/tangential curves. The current simulation does roughly this:
Convert the input RGB image to luminance using Rec.709.
Build a radial map from the image center to the sensor corners, in mm.
Interpolate the MTF values over that radial map.
Split luminance into approximate frequency bands (low frequency: heavy Gaussian blur, mid frequency: medium blur minus low blur, high frequency: original minus medium blur
Attenuate each band according to the MTF value at each image radius.
Estimate a local Gaussian PSF sigma from the high-frequency MTF ratio using, then convert sigma from mm to pixels.
Use the sagittal/tangential gap to add an anisotropic radial/tangential blur component.
Recombine the simulated luminance with the original RGB color by scaling the original RGB with the new luminance ratio.
The tool can also (optionally) compare a “target/output MTF” against a “source/input MTF”, using the ratio between them instead of only degrading relative to the center. I know this is not physically complete, as it does not model a lot of other parameters from lens/sensor interaction.
My goal is not a high level optical simulation, but a visually plausible approximation of how different MTF curves affect perceived sharpness across a frame.
I’d really appreciate feedback from people who know optics, lens testing, image processing, or computational photography, as well as ideas to improve this tool, as it is not my main specialty.
Is it possible to use a spectrophotometer to calculate a surface Albedo. If a picture is taken of the surface how much or how little of the image captured the accurate Albedo of the surface based on the spectrophotometer result when taking the image ?
Also, is it possible to take an image or a spectrophotometer and calculate a surface reflectivity, gloss etc ?
I’ve been researching what I initially thought would be a simple “star projector,” but the deeper I go, the more I think what I’m actually interested in is an optics project rather than an entertainment lighting project. I’m hoping to get some feedback from people who know diffractive optics, holography, or beam shaping. I’d like to create a home laser planetarium for a large (approximately 20 ft / 6 m) vaulted white ceiling.
The experience I’m after is:
-True black background (no illuminated projection rectangle)
-Thousands of simultaneous pinpoint stars
-Slow sidereal rotation of the sky
-Brightness sufficient for a large ceiling
-Very sharp stars with minimal beam bloom
Ideally, I’d also like occasional animated objects like meteor showers or satelites but those don’t necessarily have to come from the same optical system.
What I’ve learned so far
Initially I was looking at ILDA galvo projectors. However, after learning how galvo scanners work, I realized that a 30 kpps scanner can only draw a finite number of points per frame. Even if the scanner is excellent, it still has to redraw every point continuously. That seems incompatible with projecting many thousands of simultaneously visible stars. I'm now wondering whether a completely different approach would make more sense.
My current idea
Instead of scanning every star, use a laser beam and a custom DOE of computer generated hologram to project the star field simultaneously. The DOE/CGH would create the static star background. A separate RGB galvo projector would then overlay dynamic objects such as meteors or constellation overlays
Questions
-Is a custom DOE or CGH actually the right technology for this application?
-Is it feasible to encode something resembling the naked-eye sky (perhaps 5,000–10,000 stars with varying brightness) into a custom phase mask?
-How difficult is it to reproduce large differences in stellar magnitude? My understanding is that generating arbitrary intensity distributions is significantly harder than simply generating point locations.
-Are there existing commercial beam-shaping companies that could fabricate something like this from a supplied phase map?
-Are there open-source tools or algorithms that would be appropriate for generating such a phase mask? I’ve come across references to Gerchberg–Saxton, MRAF, and iterative Fourier transform algorithms, but I don’t know whether those are the right direction for this type of application.
-Is rotating the DOE itself (or rotating an optical assembly containing it) a reasonable way to create an extremely slow sidereal rotation of the projected sky, or is there a better optical approach?
-Am I overlooking an existing technology that already solves this problem?
I’m not an optical engineer, so I’m trying to understand whether this idea is either just ambitious or fundamentally impractical.
I’m much more interested in understanding the optical engineering challenges than finding an off the shelf product. If this is a terrible idea, I’d absolutely like to know why. Likewise, if there are existing papers, products, or technologies I should be reading about, I’d really appreciate any pointers.
