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Comment by bentpins | Hacker News Reader

Maybe I'm missing something but how is the image so clear? CDs don't have a mirror like surface, they reflect light in unusual ways

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The rather shallow angle probably helps a lot. On top of that the camera probably has some form of auto white balance which will counteract the tint the CD will give to the image.

Here's a quick proof of concept using a random CD and my phone's camera: https://svkt.org/~simias/up/20200914-000627_psx-cd-reflectio...

Note that the color of the reflection is not much different from a normal picture (visible at the bottom). For added difficulty I used an original PlayStation disc, that's dyed black: https://svkt.org/~simias/up/20200914-000836_psx-cd.jpeg

It's very HN that we've been trolled into debating the irrefutable, widely-known, totally obvious fact that a CD reflects light.

Everything reflects light, but not everything reflects it clear enough to read documents through. I haven't held a CD in ages, so it it's possible that folks don't remember exactly how reflective they are. ¯\_(ツ)_/¯

Didn't mean to come across as a troll, this is how I remember CDs, with rainbow diffraction. https://www.google.com/search?tbm=isch&q=cd

I think at such shallow angles it's the plastic surface that becomes reflective, not the metal layer with the pits and grooves. Hence the lack of diffraction (and hence why it works with my black PSX disc).

She's using a CD-RW with blue/purple dye. The reflection is definitely coming off the surface.

Almost everything reflects light. The discussion is on why it can be used as a mirror.

The quarter helping to hold down the CD may also contribute by blocking overhead inbound interference.

Use a pressed CD (which are good mirrors at this angle), not a blank CD (which are tinted).

I just pointed a CD at my face and it's pretty much a mirror. What unusual reflection did you expect?

Some rainbow diffraction I guess. It has been a long time since I've used a CD https://www.google.com/search?tbm=isch&q=cd

Real CDs don't look like clip art CDs. 90% of the images for "mirror" don't have reflections either.

Well I noticed it's a CD-RW which is a peculiar device, so maybe it doesn't reflect the same as normal CDs.

I think you probably haven't played around with CDs more than just to play them.

I also don't really get it. Looks too clear and sharp for a CD reflection.

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