Originally posted by UncleVanya Interesting. Tell me more...
It's pretty simple, a nested set of telescoping heavy-paper or cardboard tubes thats big enough on one end to hold the 77mm close-up lens and cover the camera's mount flange on the other end makes the filter into a lens.
In theory, the 500D close-up lens (also known as a +2 diopter close-up lens) has a focal length of 500 mm which means that infinity focus occurs when the lens is 500mm from the sensor (or about 454 mm from the flange). In practice, the distances might be a little more or less which is why nested telescoping tubes are nice. Also, the focus throw will be really really long. Shifting from infinity focus to an object about 3 meters away requires extending the lens out about another 125 mm.
The image quality won't be great and the floppy home-made lens won't impress the local BIF photographers but there is a certain magical satisfaction at forming a focused image of some distant object.
You can improve IQ by painting the inside of the tube black, being really careful to mount the lens parallel to the sensor, adding a waterhouse stop just behind the lens, and adding a lens hood to cut flare.