Everyone has at least one DVD they are ashamed of buying. You know, the DVD that was 'a good idea at the time', was watched half way through and then consigned to the back of the DVD rack, 'hidden' from prying eyes. This instructable makes some use of that mistaken purchase.
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
- One extremely naff DVD, in a black, full size case
- 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
Strip the DVD case of inserts and DVD, leaving just the plastic. You will need to print out the templates from here to provide the new insert and plans for the other parts. Be sure when you print these out you do not 'fit to page' or 'zoom/scale' the image - they need to be exactly the right size. You should check that what comes out of your printer hasn't been enlarged; the DVD insert should be exactly 184mm tall.
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
Get out your dremel and cut through the outer transparent plastic, the template and the case. Make sure you do this with the case laid open, flat. You don't want to cut through the back as well. You will find the case can be quite sturdy so take care to make a neat job of it. Smooth off the edges and clean up.
Step 4: Cutting the Wedge Parts
Take your 'wedge' template and lay it over the card. I used paperclips to keep it in position while I cut around the outlines using a sharp knife and a metal rule.
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
Take the two triangular pieces and join them to the main rectangular piece using sticky tape on the 'inside' of the wedge. You should then be able to test it out by positioning the wedge along the inside edge of the DVD case, and closing the case lid. This should form a nice robust edge shape approximately 30o thick. Trim the parts as necessary to provide a snug fit.
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
Fit the DVD into the case, shiny side up. Fit the wedge in place, slit closest to the front of the case. If you want to be able to break the DVD Spectra apart for storage, fix it using a little blue tack. If you want a permanent construction then a little stickytape to fix the wedge sides in place, and a little along the top edges will make a stable wedge shaped spectrometer.
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
For very point-like light sources, such as the sun, you will find it difficult to form a good, wide, spectrum. In these cases cut a small square of material from a thin translucent bag and fix it over the front of the slit. This will spread the light so you can see the entire slit imaged as a spectrum.
Step 8: Results and Imaging
The spectra you can see with this view can be quite detailed. You can easily see the Fraunhofer lines in the Sun's spectrum, down to the level of resolving the Sodium D lines. That's pretty good for a DVD! Looking at domestic bulbs and comparing fluorescent tubes to incandescent bulbs makes it obvious why some people can say colours can look strange in fluorescent light.
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
When not in use your DVD Spectra can be broken down to fit on the DVD shelf. Open the case, take out the wedge and fold the triangular ends in. Place this inside the case using the insert clips to hold it in place.
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.