Today we look at a CD-ROM under a variety of magnifications up to an ‘empty’ 2000x.
Here’s a link to the Applied Science video that I used as inspiration for my own foil separating technique:
Why use ‘empty’ 2000x?
2000x magnification is actually so-called ‘empty magnification’ because beyond 1000x we generally cannot resolve much more detail from the optical setup. By increasing the magnification beyond this point (say to 2000x, by combining a 20x eyepiece and a 100x objective) it does make the image appear larger, but no additional detail is gained.
I chose to use empty 2000x magnification in this video because it allowed me to fill the image sensor on the camera with a larger equivalent image. This allowed more pixels to be devoted to each ‘pit’ and ‘land’ on the sensor, letting you see them in more detail. The ‘pits’ and ‘lands’ were dim and small enough at 1000x that they started blending into the noise of the camera sensor, even with contrast enhancement. Although light at 2000x is even dimmer, the observed size of the ‘pits’ and ‘lands’ is large enough that they can be effectively differentiated from the back ground sensor noise. Thus, in this case empty 2000x magnification effectively results in an improved image, even though optically it is unable to resolve more detail.
- With additional research and the help of your comments, I have created a list of corrections & clarifications for this video. I will update if further changes are needed.
00:18 Technically, the metal coating we view in this video is only an imprint of the data stored on the CD-ROM. This imprint is formed from the actual data which resides as ‘pits’ and ‘lands’ in the thick plastic of the CD-ROM itself. When the metallic layer is applied over these ‘pits’ and ‘lands’ during manufacturing it creates a similar pattern on the metal sheet. Thus, when we peel this layer off we see a near identical copy of the data as it was on the CD-ROM.
10:02 The arrangement of ‘pits’ and ‘lands’ do indeed code for binary, but they don’t exactly match up to the binary that makes up the game's code. A transition from 'pit' to 'land' or 'land' to 'pit' registers as a 1 and an unchanging ‘pit’ or ‘land’ registers a 0. The arrangement of the ‘pits’ and ‘lands’ are also encoded in an error-correcting format that introduces changes that obscure the data further. In addition, there are other computational layers of abstraction in the data that must be worked through before it could be interpreted as standard game-data information. Thus, the ‘pits’ and ‘lands’ of the CD-ROM do store the 0s and 1s that make up the game, but only in an encoded, obfuscated way.
11:55 Computers in the 1980s did indeed have several MB of hard drive space. For example, the IBM Personal Computer XT, which was released in 1983 had a 10MB hard drive. However, for an average home computer that used floppy drives for storage, you could be working with as little as 170 KB of storage per disk.
12:36 See 10:02 clarification.
13:30 I say 2000x magnification, but magnification beyond 1000x is generally considered ‘empty’, meaning no additional detail can be resolved. Due to the nature of recording images from the scope however, the 2000x does actually provide a superior image to 1000x in this case. Check the description above where it says ‘Why use ‘empty’ 2000x?’ for more information.
13:31 The empty 2000x magnification is grainy in this video because of contrast enhancement that makes the elements more visible.
14:20 The ‘pits’ are generally at minimum 850 nm long, 500 nm wide and 100 nm deep. The laser that reads the ‘pits’ has a wavelength 780 nm.
14:54 See 14:20
14:56 The technical process by which the laser reads data is more amazing than the rough approximation I mention in the video.The laser beam is actually a good deal wider than the ‘pit’ size, but the wavelength is indeed 780 nm. The wavelength has little do with the width or height of the ‘pits’ but rather is tightly correlated with their depth. The laser bounces light off of the CD-ROM and into a light sensor, looking for changes in order to read data. When the laser shines on a ‘pit’ the light has to travel slightly farther (around one half of a wavelength ) which causes the light to destructively interfere with itself, making it dimmer as it bounces back to the sensor. Thus, by measuring this change in brightness, we can read the surface of the CD-ROM. A transition from 'pit' to 'land' or 'land' to 'pit' registers as a 1 and an unchanging ‘land’ or ‘pit’ registers a 0.
Have a good one!
-The Microscopic Channel