4 ms·

Fresnel lens are everywhere now... I most recently came across them embedded as a planar lens in a semiconductor part used for DNA sequencing: http://41j.com/b

by new299 7y ago

Fresnel lens are everywhere now... I most recently came across them embedded as a planar lens in a semiconductor part used for DNA sequencing: http://41j.com/blog/2018/12/quantumsi/ http://41j.com/blog/2018/12/quantumsi/

a3n 7y ago
The "meatball" https://en.wikipedia.org/wiki/Optical_landing_system https://en.wikipedia.org/wiki/Optical_landing_system The system described is for aircraft carriers. I know about it because I maintained a smaller version on a fast frigate in the seventies. It was slaved to the ship's gyrocompass, which provided a stable horizontal reference. (Besides navigation, the gyrocompass also provided that stable reference to the ship's gun.)
Theodores 7y ago
They aren't! Years ago they used to be common on the backs of cars, so you could look where you were parking. Vans and estate cars invariably had them. But now? Backup cameras. Same with the original lighthouse application. They don't use Fresnel lenses any more. The lighting tech used for aircraft has superceded the Fresnel tech of old. So lighthouses are done differently now. Even in home applications Fresnel lenses don't last the distance, You don't have hacky Fresnel lenses in products to make up for them having a naff CRT for the image. But then again, Fresnel lenses do live on, but in better ways. There are many compound lenses for lights that are not a classic Fresnel lens but work nicely.
- rangibaby 7y ago
  Nikon makes fresnel telephoto lenses, and they save size + weight vs their classic counterparts
  - Theodores 7y ago
    In practice though most lenses and applications move away from being Fresnel. The lights get better or a camera or other screen technology replaces it. Fresnel lenses are like motorbike sidecars, they are a cheap hack. But if I was to post 'you don't see motorbike sidecars these days' then some nitpicker on HN would Google search a new Kickstarter project of a motorbike sidecar and - two seconds later - mod me down for being generally but not universally correct. As I understand it the Nikon lenses are not 'Fresnel' as we know it. The idea is to combine a regular lens with a Fresnel lens to remove chromatic aberration. The weight saving isn't what it is about since there is still a regular lens that the Fresnel lens works with.
    - i_am_proteus 7y ago
      > In practice though most lenses and applications move away from being Fresnel. Tungsten fresnel lights (and now LED fresnel lights) are very common in videography. The lens provides a simple spot/flood mechanism.
    - rangibaby 7y ago
      The fresnel element version of the 300mm f/4 lens reduces the weight by half and the size by one third compares to the non-fresnel version
    - hug 7y ago
      > But if I was to post 'you don't see motorbike sidecars these days' then some nitpicker on HN would Google search a new Kickstarter project of a motorbike sidecar and - two seconds later - mod me down for being generally but not universally correct. I'm of course not going to downvote you, but just to help you out with your point IMZ-Ural still manufacture motorcycles with sidecars to this day, and in fact are working on a fully electric model.
  - maxxxxx 7y ago
    True! "Proprietary Phase Fresnel technology" on the 500 PF. It looks very different though.
  - ISL 7y ago
    Canon makes them too -- look for the DO lenses.
    - buserror 7y ago
      For many years now I've owned a 70-300 DO very very compact zoom lens and always been happy with it. There are some rare optical artifacts, in some lights, on some subjects, but it's never been a problem in real life.
- pmyteh 7y ago
  Very common in theatrical lighting, where a somewhat-focused beam is wanted but the not-quite-crisp edges characteristic of a Fresnel lens are an asset rather than a liability. For example: https://www.strandlighting.com/global/products/rama-led-fresnel-mkii https://www.strandlighting.com/global/products/rama-led-fres...
- djmips 7y ago
  Vive (SteamVR) headsets use fresnel lenses. (vive vs vive pro comparision) https://i.imgur.com/SvxVRUL.jpg https://i.imgur.com/SvxVRUL.jpg
tropo 7y ago
It could be a zone plate. They look similar, but focus based on diffraction instead of refraction. https://en.wikipedia.org/wiki/Zone_plate https://en.wikipedia.org/wiki/Zone_plate The diagram could be either, but isn't a perfect match for either. Perhaps a hybrid is possible. The 4-level right-angle construction (stair step) is weird.
- new299 7y ago
  The Zone plates are very cool. Thanks for the link.
- dreamcompiler 7y ago
  Zone plates work great for radio waves. I don't know why they aren't used more than parabolic dishes, since they're easier to manufacture and mount. Perhaps the gain is smaller for a given diameter?
  - burfog 7y ago
    A third choice is the phased array. There are two dimensions to focus, and they don't have to be done the same way. For example, the trough antenna is parabolic in one direction but uses something else in the other direction. Viewed from along the resulting beam, it is a rectangle. Manufacture the reflector involves a simple 1-dimensional bend of the metal.
  - consp 7y ago
    My guess would be twofold: adding delay if the source is not straight though enough to screw communication or diffusing the image too much if your focal point is not a point but a sensor.
  - dTal 7y ago
    Zone plate focal length is wavelength dependent, unlike parabolic dishes.
neetdeth 7y ago
Very common example: Focusing lenses in front of smartphone camera flash LEDs.
dreamcompiler 7y ago
Here's one from Amazon for $8 that's A4-sized and probably weighs a few grams. Great for magnifying or building a solar oven. If you can find one a meter square, you could probably weld with it in full sun. [0] https://www.amazon.com/11-75-Fresnel-Magnifier-Projection-PREMIUM/dp/B00IITFX02/ref=mp_s_a_1_6 https://www.amazon.com/11-75-Fresnel-Magnifier-Projection-PR...
- dmix 7y ago
  > I had one of these for years and somehow lost it. I recently replaced it. One of the uses I put it to was starting fires. It will ignite a pine board in seconds. Don't get your hand at the focal point with the sun shining through it or you will burn the peewadden out of your hand. It's not as good as a magnifying glass for reading. I have taken pictures through one to blow a small picture up into a larger one. You’ve got to love Amazon reviews sometimes. Googling “peewadden” also has an interesting story from the American civil war.
- ljf 7y ago
  I used to run a site that showed people how use these to create a projection tv (a bad one!) from a fresnel lens and a CRT tv. Was a fun and simple project for kids.
  - PhasmaFelis 7y ago
    Anyone remember AcidWarp? It was a DOS program from the early '90s, distributed through BBSes, that generated lovely flowing color patterns. It came zipped with a text file with instructions for building a Fresnel-based projector for your PC monitor. Looks like it's still online: http://www.noah.org/acidwarp/ http://www.noah.org/acidwarp/
jcl 7y ago
"Big Face Box" was a fun project I saw at a Makers Faire: https://makezine.com/2017/05/25/bigfacebox-a-simple-way-to-gigantify-your-head/ https://makezine.com/2017/05/25/bigfacebox-a-simple-way-to-g... I'm not sure where they got the plastic sheet lenses from... I know old rear-projection TVs used to have giant ones. (They had a warning on the booth: "Do not take outside". I'd hate to learn that lesson the hard way.)

by new299 7y ago

a3n 7y ago

The "meatball" https://en.wikipedia.org/wiki/Optical_landing_system https://en.wikipedia.org/wiki/Optical_landing_system The system described is for aircraft carriers. I know about it because I maintained a smaller version on a fast frigate in the seventies. It was slaved to the ship's gyrocompass, which provided a stable horizontal reference. (Besides navigation, the gyrocompass also provided that stable reference to the ship's gun.)

Theodores 7y ago

They aren't! Years ago they used to be common on the backs of cars, so you could look where you were parking. Vans and estate cars invariably had them. But now? Backup cameras. Same with the original lighthouse application. They don't use Fresnel lenses any more. The lighting tech used for aircraft has superceded the Fresnel tech of old. So lighthouses are done differently now. Even in home applications Fresnel lenses don't last the distance, You don't have hacky Fresnel lenses in products to make up for them having a naff CRT for the image. But then again, Fresnel lenses do live on, but in better ways. There are many compound lenses for lights that are not a classic Fresnel lens but work nicely.

rangibaby 7y ago
Nikon makes fresnel telephoto lenses, and they save size + weight vs their classic counterparts
- Theodores 7y ago
  In practice though most lenses and applications move away from being Fresnel. The lights get better or a camera or other screen technology replaces it. Fresnel lenses are like motorbike sidecars, they are a cheap hack. But if I was to post 'you don't see motorbike sidecars these days' then some nitpicker on HN would Google search a new Kickstarter project of a motorbike sidecar and - two seconds later - mod me down for being generally but not universally correct. As I understand it the Nikon lenses are not 'Fresnel' as we know it. The idea is to combine a regular lens with a Fresnel lens to remove chromatic aberration. The weight saving isn't what it is about since there is still a regular lens that the Fresnel lens works with.
  - i_am_proteus 7y ago
    > In practice though most lenses and applications move away from being Fresnel. Tungsten fresnel lights (and now LED fresnel lights) are very common in videography. The lens provides a simple spot/flood mechanism.
  - rangibaby 7y ago
    The fresnel element version of the 300mm f/4 lens reduces the weight by half and the size by one third compares to the non-fresnel version
  - hug 7y ago
    > But if I was to post 'you don't see motorbike sidecars these days' then some nitpicker on HN would Google search a new Kickstarter project of a motorbike sidecar and - two seconds later - mod me down for being generally but not universally correct. I'm of course not going to downvote you, but just to help you out with your point IMZ-Ural still manufacture motorcycles with sidecars to this day, and in fact are working on a fully electric model.
- maxxxxx 7y ago
  True! "Proprietary Phase Fresnel technology" on the 500 PF. It looks very different though.
- ISL 7y ago
  Canon makes them too -- look for the DO lenses.
  - buserror 7y ago
    For many years now I've owned a 70-300 DO very very compact zoom lens and always been happy with it. There are some rare optical artifacts, in some lights, on some subjects, but it's never been a problem in real life.
pmyteh 7y ago
Very common in theatrical lighting, where a somewhat-focused beam is wanted but the not-quite-crisp edges characteristic of a Fresnel lens are an asset rather than a liability. For example: https://www.strandlighting.com/global/products/rama-led-fresnel-mkii https://www.strandlighting.com/global/products/rama-led-fres...
djmips 7y ago
Vive (SteamVR) headsets use fresnel lenses. (vive vs vive pro comparision) https://i.imgur.com/SvxVRUL.jpg https://i.imgur.com/SvxVRUL.jpg

tropo 7y ago

It could be a zone plate. They look similar, but focus based on diffraction instead of refraction. https://en.wikipedia.org/wiki/Zone_plate https://en.wikipedia.org/wiki/Zone_plate The diagram could be either, but isn't a perfect match for either. Perhaps a hybrid is possible. The 4-level right-angle construction (stair step) is weird.

new299 7y ago
The Zone plates are very cool. Thanks for the link.
dreamcompiler 7y ago
Zone plates work great for radio waves. I don't know why they aren't used more than parabolic dishes, since they're easier to manufacture and mount. Perhaps the gain is smaller for a given diameter?
- burfog 7y ago
  A third choice is the phased array. There are two dimensions to focus, and they don't have to be done the same way. For example, the trough antenna is parabolic in one direction but uses something else in the other direction. Viewed from along the resulting beam, it is a rectangle. Manufacture the reflector involves a simple 1-dimensional bend of the metal.
- consp 7y ago
  My guess would be twofold: adding delay if the source is not straight though enough to screw communication or diffusing the image too much if your focal point is not a point but a sensor.
- dTal 7y ago
  Zone plate focal length is wavelength dependent, unlike parabolic dishes.

neetdeth 7y ago

Very common example: Focusing lenses in front of smartphone camera flash LEDs.

dreamcompiler 7y ago

Here's one from Amazon for $8 that's A4-sized and probably weighs a few grams. Great for magnifying or building a solar oven. If you can find one a meter square, you could probably weld with it in full sun. [0] https://www.amazon.com/11-75-Fresnel-Magnifier-Projection-PREMIUM/dp/B00IITFX02/ref=mp_s_a_1_6 https://www.amazon.com/11-75-Fresnel-Magnifier-Projection-PR...

dmix 7y ago
> I had one of these for years and somehow lost it. I recently replaced it. One of the uses I put it to was starting fires. It will ignite a pine board in seconds. Don't get your hand at the focal point with the sun shining through it or you will burn the peewadden out of your hand. It's not as good as a magnifying glass for reading. I have taken pictures through one to blow a small picture up into a larger one. You’ve got to love Amazon reviews sometimes. Googling “peewadden” also has an interesting story from the American civil war.
ljf 7y ago
I used to run a site that showed people how use these to create a projection tv (a bad one!) from a fresnel lens and a CRT tv. Was a fun and simple project for kids.
- PhasmaFelis 7y ago
  Anyone remember AcidWarp? It was a DOS program from the early '90s, distributed through BBSes, that generated lovely flowing color patterns. It came zipped with a text file with instructions for building a Fresnel-based projector for your PC monitor. Looks like it's still online: http://www.noah.org/acidwarp/ http://www.noah.org/acidwarp/

jcl 7y ago

"Big Face Box" was a fun project I saw at a Makers Faire: https://makezine.com/2017/05/25/bigfacebox-a-simple-way-to-gigantify-your-head/ https://makezine.com/2017/05/25/bigfacebox-a-simple-way-to-g... I'm not sure where they got the plastic sheet lenses from... I know old rear-projection TVs used to have giant ones. (They had a warning on the booth: "Do not take outside". I'd hate to learn that lesson the hard way.)