5 ms·

In my high school physics class we measured the pitch between the tracks of a CD using the same principle. You just need a light source with a known wavelength,

In my high school physics class we measured the pitch between the tracks of a CD using the same principle. You just need a light source with a known wavelength, like a laser. It was a pretty cool experiment!

SamBam 3y ago
What's the pitch between tracks?
- tmearnest 3y ago
  1.6 μm
  - SamBam 3y ago
    Ah, I see. Multiple meanings of both "pitch" and "tracks" on a music CD.
anfractuosity 3y ago
That sounds a fun project :) I tried a little peeling of a CD-R under a microscope, where can see the tracks, I should try and measure the pixel distance and convert to track width - https://www.anfractuosity.com/files/cd-r.JPG https://www.anfractuosity.com/files/cd-r.JPG
- dylan604 3y ago
  what microscope are you using? i've been itching to get into microscope photography for a new hobby, but because i know myself, it'll be a fun but expensive rabbit hole. i've been deliberately putting off on researching because i also know myself and will be just as likely to be shopping than researching
  - anfractuosity 3y ago
    It's an Olympus BHM that I got cheaply from ebay. It's a trinocular metallurgical microscope, that I added an old SLR to, for that photo. I noticed the semi-silvered mirror seems rather scratch though, so might need to look at replacing that.
    - dylan604 3y ago
      are you attaching the camera directly with an adapter, or is it projecting on to whatever lens you are using? i guess i'm coming at this thinking of it in terms of astrophotography using T-adapters to connect in place of on eyepiece vs taking an image from the eyepiece
      - anfractuosity 3y ago
        In the trinocular port, there's an eyepiece, which I forget the magnification of afraid. And to that port I added this - https://www.alanwood.net/olympus/photomicro-adapter-l.html https://www.alanwood.net/olympus/photomicro-adapter-l.html and then used an OM to EF mount converter, which the Canon camera directly attached to. I've since bought a microscope imager, that provides an output over USB. But I think I need to remove the OM converter, and get a shorter adapter to successfully attach to the microscope C-Mount.
        dylan604 3y ago
        Thanks for that. I was hoping that would would be possible. I think I now know what to ask Santa for xmas!
      - dekhn 3y ago
        Either works, but trust me, the trinocular part is far superior, ergonomically. You do need to know whether you want a metalurgical scope or a compound light transmission scope. The former is good at looking at opaque samples, the latter for transparent samples (biological stuff mostly).
        dylan604 3y ago
- chankstein38 3y ago
  This is an awesome picture! Forgive me if this is a stupid question but are we seeing 0s and 1s here? Is that what the black is? Kind of the equivalent to a morse code dit (0) and dah (1)?
  - andruby 3y ago
    That not a stupid question. It's a bit (ha!) more complex. These are called pits and lands. > The pits and lands do not directly represent the 0s and 1s of binary data. Instead, non-return-to-zero, inverted encoding is used: a change from either pit to land or land to pit indicates a 1, while no change indicates a series of 0s. There must be at least two, and no more than ten 0s between each 1, which is defined by the length of the pit. This, in turn, is decoded by reversing the eight-to-fourteen modulation used in mastering the disc, and then reversing the cross-interleaved Reed–Solomon coding, finally revealing the raw data stored on the disc. https://en.wikipedia.org/wiki/Compact_disc#Physical_details https://en.wikipedia.org/wiki/Compact_disc#Physical_details These encoding types are used to improve the "tracking" of the laser head, and to keep the timing consistent. We want the medium to regularly have changes between pits and lands to synchronise the timing and speed of the disc. The encoding scheme enforces this. https://en.wikipedia.org/wiki/Non-return-to-zero#NRZI https://en.wikipedia.org/wiki/Non-return-to-zero#NRZI https://en.wikipedia.org/wiki/Eight-to-fourteen_modulation https://en.wikipedia.org/wiki/Eight-to-fourteen_modulation
    - chankstein38 3y ago
      I missed this until now, I really appreciate you tracking down links and sharing this info! Thank you! It's wild it's as complex as it is! Though it makes sense it seems way more robust

SamBam 3y ago

What's the pitch between tracks?

tmearnest 3y ago
1.6 μm
- SamBam 3y ago
  Ah, I see. Multiple meanings of both "pitch" and "tracks" on a music CD.

anfractuosity 3y ago

That sounds a fun project :) I tried a little peeling of a CD-R under a microscope, where can see the tracks, I should try and measure the pixel distance and convert to track width - https://www.anfractuosity.com/files/cd-r.JPG https://www.anfractuosity.com/files/cd-r.JPG

dylan604 3y ago
what microscope are you using? i've been itching to get into microscope photography for a new hobby, but because i know myself, it'll be a fun but expensive rabbit hole. i've been deliberately putting off on researching because i also know myself and will be just as likely to be shopping than researching
- anfractuosity 3y ago
  It's an Olympus BHM that I got cheaply from ebay. It's a trinocular metallurgical microscope, that I added an old SLR to, for that photo. I noticed the semi-silvered mirror seems rather scratch though, so might need to look at replacing that.
  - dylan604 3y ago
    are you attaching the camera directly with an adapter, or is it projecting on to whatever lens you are using? i guess i'm coming at this thinking of it in terms of astrophotography using T-adapters to connect in place of on eyepiece vs taking an image from the eyepiece
    - anfractuosity 3y ago
      In the trinocular port, there's an eyepiece, which I forget the magnification of afraid. And to that port I added this - https://www.alanwood.net/olympus/photomicro-adapter-l.html https://www.alanwood.net/olympus/photomicro-adapter-l.html and then used an OM to EF mount converter, which the Canon camera directly attached to. I've since bought a microscope imager, that provides an output over USB. But I think I need to remove the OM converter, and get a shorter adapter to successfully attach to the microscope C-Mount.
      - dylan604 3y ago
        Thanks for that. I was hoping that would would be possible. I think I now know what to ask Santa for xmas!
    - dekhn 3y ago
      Either works, but trust me, the trinocular part is far superior, ergonomically. You do need to know whether you want a metalurgical scope or a compound light transmission scope. The former is good at looking at opaque samples, the latter for transparent samples (biological stuff mostly).
      - dylan604 3y ago
chankstein38 3y ago
This is an awesome picture! Forgive me if this is a stupid question but are we seeing 0s and 1s here? Is that what the black is? Kind of the equivalent to a morse code dit (0) and dah (1)?
- andruby 3y ago
  That not a stupid question. It's a bit (ha!) more complex. These are called pits and lands. > The pits and lands do not directly represent the 0s and 1s of binary data. Instead, non-return-to-zero, inverted encoding is used: a change from either pit to land or land to pit indicates a 1, while no change indicates a series of 0s. There must be at least two, and no more than ten 0s between each 1, which is defined by the length of the pit. This, in turn, is decoded by reversing the eight-to-fourteen modulation used in mastering the disc, and then reversing the cross-interleaved Reed–Solomon coding, finally revealing the raw data stored on the disc. https://en.wikipedia.org/wiki/Compact_disc#Physical_details https://en.wikipedia.org/wiki/Compact_disc#Physical_details These encoding types are used to improve the "tracking" of the laser head, and to keep the timing consistent. We want the medium to regularly have changes between pits and lands to synchronise the timing and speed of the disc. The encoding scheme enforces this. https://en.wikipedia.org/wiki/Non-return-to-zero#NRZI https://en.wikipedia.org/wiki/Non-return-to-zero#NRZI https://en.wikipedia.org/wiki/Eight-to-fourteen_modulation https://en.wikipedia.org/wiki/Eight-to-fourteen_modulation
  - chankstein38 3y ago
    I missed this until now, I really appreciate you tracking down links and sharing this info! Thank you! It's wild it's as complex as it is! Though it makes sense it seems way more robust