This idea came out of my need for a workable spectrometer to gather some data. Rather than looking to buy a commercial one, it was more useful (and cheaper) to build it out of the bits I had lying around. It turns out its fairly easy to use a CD for this purpose - but most of the older related pointers seemed to require you to build a box yourself, and in any case I wanted to use a DVD to improve the resolution.
Thus the idea of taking the DVD, case and all, to construct the spectrometer was born.
Step 1: Parts List
- Stiff card
- Two knife blade refills, or the lid from an old tub of margarine
- 'DVD Spectra' Templates
- Old translucent plastic bag
- Sharp knife
- Steel rule
- Multipart rotary tool, such as a dremel
As far as the DVD is concerned the best option is a single layer DVD to ensure you get a sharp spectra. These can be found often as the old 'flippy' DVDs, the freebie DVDs given away with newspapers/magazine, or writeable DVD.
The sturdier the card, the sturdier the 'DVD Spectra' - however the harder it is to cut. By all means you can use the cornflake box, but I'd suggest something a little thicker.
Step 2: Preparing the Case
Cut down your new sleeve insert to replace the old one. You can find alternative designs here to download for different usages. When you insert your new cover you will find that the white 'eye' hole is positioned at just the right spot on the DVD case, telling you exactly where to cut.
Step 3: Cutting the Eye Hole
Step 4: Cutting the Wedge Parts
The template is such that in general you want to be cutting to the inside of the line. The shaded areas should also be removed. Those top and bottom of the larger endpiece allow the card to sit over the various bits of plastic of the case. Cut these to fit your particular case, but leave enough left and right to steady the card fit.
You will want to lightly score the indicated horizontal line. This is the line you will align your spectrometer slit with.
Step 5: Constructing the Wedge
Once you are happy with the fit, take some stickytape and wrap a little around the left and right edges of the square slit hole. This is to ensure a crisp edge to your slit, rather than having the card fibres visible in the eventual spectrum.
Fix the two blades on the inside of the slit hole in your 'wedge', lined up with the line you scored earlier. The closer you get the blades, the finer the lines in the spectrum you eventually see. However if the blades are too close little light gets through and its difficult to see anything. A hair's breadth apart seems about right.
Alternatively, if you don't want to fix razor blades inside your 'DVD Spectra' (say you are going to let your kids have access to it) you can make the slit out of a plastic lid. Just cut an even slit in a section of plastic from the lid, longer than the hole, and fit the plastic over the hole in place of the blades. Its not as good as evenly spaced blades, but the plastic ensures a crisp edge and with care you can make it even. Cardboard or paper won't work, the fibres along the cut edge get imaged into the spectrum you see.
Step 6: Fitting It Together
If you are making this to be permanently constructed, you may like to use thick tape to block any light from entering the case, except via the slit itself.
Step 7: Diffuser
Step 8: Results and Imaging
Trying to make images of these spectra tends to show up limitations in your equipment. With CCD and CMOS sensor chips you will notice that they are poor at showing the strong yellows and cyans from the naked eye spectra, and don't really stretch far into the deep reds and ultraviolets. This is mainly due to the RGB filters they use within the sensors which only respond well to strong red, green and blue.
You will also notice that most point and shoot digital cameras find it impossible to make a accurate focus on the lines in the spectra. For good results you need a camera where you can set your own close macro focus. The results you see above are from a consumer webcam fixed to the front of the DVD Spectra. Its cheap enough to have a manual focus.
Step 9: Breaking It Down
You can then close the case up and proudly display it amongst all the other DVDs - the ones you aren't ashamed of.
Acknowledgements to Jerry Xiaojin Zhu's CD spectroscope and Joachim Koppen's CD ROM spectroscope.