6 ms·

She's getting a surprisingly high-quality reflection from that CD. I would have thought a CD wouldn't have had enough specularity, or created too much distortio

She's getting a surprisingly high-quality reflection from that CD. I would have thought a CD wouldn't have had enough specularity, or created too much distortion to achieve that kind of quality. The only downside appears to be that you have to angle the CD, in order to reflect the keyboard plane into the webcam, which means the captured image can only be viewed at an angle. It'd be nice to have some live, post-processing to fix some issues like this. You could apply a perspective transformation to rotate the image to a head-on view, and maybe increase the contrast between black and white.

CydeWeys 6y ago
It does make you wonder why not just use a small mirror. It might be a little bit harder to suspend in place correctly depending on weight but it'll do the job perfectly.
- kumarvvr 6y ago
  A CD is readily available, dead cheap, unbreakable (if not actively trying to break it). Making a mirror would be a far more involved process.
  - nabaraz 6y ago
    That reminds me, i don't have a CD lying around.
    - saeranv 6y ago
      Haha, I don't have access to a CD either. But assuming it's partially the webcam/video software that's correcting the exposure/contrast to eke out a decent image, other common household items could be used in it's place i.e silverware, annealed glass etc.
      - CydeWeys 6y ago
        You're overthinking this. Just use a compact or hand mirror. I hacked it together in a minute flat: https://i.imgur.com/OF29Ci3.jpg https://i.imgur.com/OF29Ci3.jpg
        saeranv 6y ago
        You're right. I completely forgot about compact mirrors. They're probably way more accessible then CDs as well.
  - CydeWeys 6y ago
    Tiny cheap mirrors are also readily available (potentially more available since lots of young teachers legitimately may not have any CDs; they're a dated technology). They're a buck at dollar stores. And you're overstating how much harder it would be to prop up a tiny cheap mirror. I bet you could do it with two pencils taped together at an angle, with one taped to the back of the laptop and the other taped to the back of the mirror.
    - pessimizer 6y ago
      > Tiny cheap mirrors are also readily available Where? > potentially more available since lots of young teachers legitimately may not have any CDs I'm sure you'll pass a Walgreen's on the way to the tiny cheap mirror shop.
      - CydeWeys 6y ago
        Do you really not know what hand mirrors and compacts are? You know, how people do their make-up? Walgreen's definitely sells them (and they'll be cheaper than CDs besides working better as mirrors, too). I'm trying to interpret your post in good faith but you're making it so hard. https://smile.amazon.com/dp/B07PWD75TG/ref=cm_sw_r_cp_apa_i_MA5xFbMFYD6Y0 https://smile.amazon.com/dp/B07PWD75TG/ref=cm_sw_r_cp_apa_i_... This is one example that may well work as-is, no pencil or tape necessary. And that $5 is the inflated "shipping is factored in" Amazon price; they're cheaper in dollar stores and similar.
      - tzs 6y ago
        Craft stores such as Joann have small mirrors. I'd not be surprised if Walmart has them, too, in their craft section.
        CydeWeys 6y ago
        The most likely place to find 'em is in the cosmetics section.
        tzs 6y ago
- gwbas1c 6y ago
  The hole in the CD is used to secure it. FWIW, many CDs are also very good mirrors. I've also used commercial pressings without extensive paint to look at eclipses.
  - CydeWeys 6y ago
    The hole isn't necessary. Here's a working solution with a compact: https://i.imgur.com/OF29Ci3.jpg https://i.imgur.com/OF29Ci3.jpg
- Balgair 6y ago
  The trick is that the CD/DVD acts as a first surface mirror. I just tried it with a bit of regular mirror (second surface) taped to bits of an old lamp. It does not work well, as there are internal reflections and glare from the glass fronting. You get slight double images too. First surface mirrors can be made by taking apart kaleidoscopes and using the mirrors in them. That or dissolving the protective backing to regular mirrors with acetone. You can buy them outright as well, but they tend to be more expensive (~$20 each). A CD/DVD is much easier than the other options and I'd say that the hack is even easier than a regular mirror. https://en.wikipedia.org/wiki/First_surface_mirror https://en.wikipedia.org/wiki/First_surface_mirror
  - coolspot 6y ago
    Are you sure CD/DVD is a first-surface mirror? AFAIK The reflective layer is on the top of the disc - where logos and graphics are. From the clean side you are looking at this metallic layer through the plastic.
    - Balgair 6y ago
      Hmmm, maybe there are differences between them. The DVDs and CDs that I have access to all acts as first surface mirrors (albeit not the best ones).
      - CydeWeys 6y ago
        The CDs I have access to are mostly burnt, not factory-pressed, and they don't have nicely mirrored surfaces at all :(
      - CydeWeys 6y ago
        There are no CDs/DVDs that are first surface mirrors. There is always a protective plastic layer on the outside, same as with any normal household mirror (except it might be glass in a household mirror; regardless, you will get internal reflections). This is the structure of a CD/DVD: https://cdn4.explainthatstuff.com/layer-structure-compact-disc.png https://cdn4.explainthatstuff.com/layer-structure-compact-di... I don't know where you got this idea from that CDs/DVDs can be first surface mirrors; they aren't. If they were they'd be really bad at their job, because one of the hallmarks of first surface mirrors is that they're incredibly fragile and do not stand up to any kind of handling whatsoever. That would not work for CDs/DVDs for obvious reasons. More info and diagrams here: https://www.clir.org/pubs/reports/pub121/sec3/ https://www.clir.org/pubs/reports/pub121/sec3/
tzs 6y ago
> The only downside appears to be that you have to angle the CD, in order to reflect the keyboard plane into the webcam, which means the captured image can only be viewed at an angle The angle doesn't look like it is farther away from head-on than you would get when looking at a piece of paper sitting on your desk, which is a pretty common thing to do. I think most people are so used to reading paper at that angle that they wouldn't even notice that it isn't head-on.

CydeWeys 6y ago

It does make you wonder why not just use a small mirror. It might be a little bit harder to suspend in place correctly depending on weight but it'll do the job perfectly.

kumarvvr 6y ago
A CD is readily available, dead cheap, unbreakable (if not actively trying to break it). Making a mirror would be a far more involved process.
- nabaraz 6y ago
  That reminds me, i don't have a CD lying around.
  - saeranv 6y ago
    Haha, I don't have access to a CD either. But assuming it's partially the webcam/video software that's correcting the exposure/contrast to eke out a decent image, other common household items could be used in it's place i.e silverware, annealed glass etc.
    - CydeWeys 6y ago
      You're overthinking this. Just use a compact or hand mirror. I hacked it together in a minute flat: https://i.imgur.com/OF29Ci3.jpg https://i.imgur.com/OF29Ci3.jpg
      - saeranv 6y ago
        You're right. I completely forgot about compact mirrors. They're probably way more accessible then CDs as well.
- CydeWeys 6y ago
  Tiny cheap mirrors are also readily available (potentially more available since lots of young teachers legitimately may not have any CDs; they're a dated technology). They're a buck at dollar stores. And you're overstating how much harder it would be to prop up a tiny cheap mirror. I bet you could do it with two pencils taped together at an angle, with one taped to the back of the laptop and the other taped to the back of the mirror.
  - pessimizer 6y ago
    > Tiny cheap mirrors are also readily available Where? > potentially more available since lots of young teachers legitimately may not have any CDs I'm sure you'll pass a Walgreen's on the way to the tiny cheap mirror shop.
    - CydeWeys 6y ago
      Do you really not know what hand mirrors and compacts are? You know, how people do their make-up? Walgreen's definitely sells them (and they'll be cheaper than CDs besides working better as mirrors, too). I'm trying to interpret your post in good faith but you're making it so hard. https://smile.amazon.com/dp/B07PWD75TG/ref=cm_sw_r_cp_apa_i_MA5xFbMFYD6Y0 https://smile.amazon.com/dp/B07PWD75TG/ref=cm_sw_r_cp_apa_i_... This is one example that may well work as-is, no pencil or tape necessary. And that $5 is the inflated "shipping is factored in" Amazon price; they're cheaper in dollar stores and similar.
    - tzs 6y ago
      Craft stores such as Joann have small mirrors. I'd not be surprised if Walmart has them, too, in their craft section.
      - CydeWeys 6y ago
        The most likely place to find 'em is in the cosmetics section.
        tzs 6y ago
gwbas1c 6y ago
The hole in the CD is used to secure it. FWIW, many CDs are also very good mirrors. I've also used commercial pressings without extensive paint to look at eclipses.
- CydeWeys 6y ago
  The hole isn't necessary. Here's a working solution with a compact: https://i.imgur.com/OF29Ci3.jpg https://i.imgur.com/OF29Ci3.jpg
Balgair 6y ago
The trick is that the CD/DVD acts as a first surface mirror. I just tried it with a bit of regular mirror (second surface) taped to bits of an old lamp. It does not work well, as there are internal reflections and glare from the glass fronting. You get slight double images too. First surface mirrors can be made by taking apart kaleidoscopes and using the mirrors in them. That or dissolving the protective backing to regular mirrors with acetone. You can buy them outright as well, but they tend to be more expensive (~$20 each). A CD/DVD is much easier than the other options and I'd say that the hack is even easier than a regular mirror. https://en.wikipedia.org/wiki/First_surface_mirror https://en.wikipedia.org/wiki/First_surface_mirror
- coolspot 6y ago
  Are you sure CD/DVD is a first-surface mirror? AFAIK The reflective layer is on the top of the disc - where logos and graphics are. From the clean side you are looking at this metallic layer through the plastic.
  - Balgair 6y ago
    Hmmm, maybe there are differences between them. The DVDs and CDs that I have access to all acts as first surface mirrors (albeit not the best ones).
    - CydeWeys 6y ago
      The CDs I have access to are mostly burnt, not factory-pressed, and they don't have nicely mirrored surfaces at all :(
    - CydeWeys 6y ago
      There are no CDs/DVDs that are first surface mirrors. There is always a protective plastic layer on the outside, same as with any normal household mirror (except it might be glass in a household mirror; regardless, you will get internal reflections). This is the structure of a CD/DVD: https://cdn4.explainthatstuff.com/layer-structure-compact-disc.png https://cdn4.explainthatstuff.com/layer-structure-compact-di... I don't know where you got this idea from that CDs/DVDs can be first surface mirrors; they aren't. If they were they'd be really bad at their job, because one of the hallmarks of first surface mirrors is that they're incredibly fragile and do not stand up to any kind of handling whatsoever. That would not work for CDs/DVDs for obvious reasons. More info and diagrams here: https://www.clir.org/pubs/reports/pub121/sec3/ https://www.clir.org/pubs/reports/pub121/sec3/

tzs 6y ago

> The only downside appears to be that you have to angle the CD, in order to reflect the keyboard plane into the webcam, which means the captured image can only be viewed at an angle The angle doesn't look like it is farther away from head-on than you would get when looking at a piece of paper sitting on your desk, which is a pretty common thing to do. I think most people are so used to reading paper at that angle that they wouldn't even notice that it isn't head-on.