5.2 Raw material and manufacture
The telescopes were made from cattle metatarsals. Cattle metatarsals are especially suitable because they are quite round and have a thick compacta. The length of the telescopes is about 8 to 9 cm, this is about the limit for making telescopes because the marrow cavity becomes more oval towards the epiphyses. After the removal of the epiphyses, the outer side of the diaphysis was modified on a lathe. The marrow cavity was only modified on each end to create a platform for the lenses to rest on. On both ends screw-thread was formed on the outer side for the lens caps. When the bone tube of the telescope was finished, the lenses were put in place with metal rings (Peter Louwman, pers.comm.).