4 ms·

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 doe

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/
    - Balgair 6y ago
      I'm holding it in my hand right now. It's a DVD copy of Empire Strikes Back. It may not be a 'mirror', but the reflection starts right at the surface. Yes, it is rainbowy.
CydeWeys 6y ago
I just tried it with a freebie compact from a makeup store and a single piece of tape (definitely simpler than these tape/pencil/coin shenanigans), and it worked better than I've been able to get any CD to work while taking literally less than a minute to set up properly. Proof: https://i.imgur.com/OF29Ci3.jpg https://i.imgur.com/OF29Ci3.jpg I'm really struggling to see how the pencil/CD/coin solution is better. I wouldn't be surprised if more teachers have compacts readily available than CDs. I think the whole CD thing is going viral because it falls into the "clever lifehack" bucket, i.e. it is optimized for hackiness virality while not actually being the best/simplest solution to the problem. But a simple compact taped to a laptop screen isn't as interesting of a "hack", and thus doesn't go viral. (Also -- conveniently -- the layer of glass/plastic on compacts is super thin, basically just barely enough to prevent the aluminum or whatever from oxidizing and from you getting the mirrored surface all fingerprinty, so it doesn't seem to cause noticeable internal reflection problems. And it's thinner than the layer of plastic on CDs, which are NOT first surface mirrors, which is easily provable by scratching the bottom of the CD and noting that you're scratching the plastic and not the reflective material directly.)
- flycaliguy 6y ago
  It’s better because it’s a surprisingly universally applicable solution.
  - CydeWeys 6y ago
    Actually, I think my solution is more universally workable. You're overestimating how many teachers will have suitably reflective CDs on hand and underestimating how many will have small mirrors on hand.

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/
  - Balgair 6y ago
    I'm holding it in my hand right now. It's a DVD copy of Empire Strikes Back. It may not be a 'mirror', but the reflection starts right at the surface. Yes, it is rainbowy.

CydeWeys 6y ago

I just tried it with a freebie compact from a makeup store and a single piece of tape (definitely simpler than these tape/pencil/coin shenanigans), and it worked better than I've been able to get any CD to work while taking literally less than a minute to set up properly. Proof: https://i.imgur.com/OF29Ci3.jpg https://i.imgur.com/OF29Ci3.jpg I'm really struggling to see how the pencil/CD/coin solution is better. I wouldn't be surprised if more teachers have compacts readily available than CDs. I think the whole CD thing is going viral because it falls into the "clever lifehack" bucket, i.e. it is optimized for hackiness virality while not actually being the best/simplest solution to the problem. But a simple compact taped to a laptop screen isn't as interesting of a "hack", and thus doesn't go viral. (Also -- conveniently -- the layer of glass/plastic on compacts is super thin, basically just barely enough to prevent the aluminum or whatever from oxidizing and from you getting the mirrored surface all fingerprinty, so it doesn't seem to cause noticeable internal reflection problems. And it's thinner than the layer of plastic on CDs, which are NOT first surface mirrors, which is easily provable by scratching the bottom of the CD and noting that you're scratching the plastic and not the reflective material directly.)

flycaliguy 6y ago
It’s better because it’s a surprisingly universally applicable solution.
- CydeWeys 6y ago
  Actually, I think my solution is more universally workable. You're overestimating how many teachers will have suitably reflective CDs on hand and underestimating how many will have small mirrors on hand.