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How Galileo made his telescopes August 3, 2009

Posted by aquillam in Astronomy.
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Galileo’s lone surviving in-tact telescope paid a visit to the Franklin institute this year.  The telescope is there until September 7, when it will return to Italy.Until then it is part of an exhibit on Galileo and the age of the Medici, and there is another special exhibit related to telescopes and optics right outside the exit.  Included in that exhibit was a display on how Galileo assembled his telescopes.


Objective end of the telescope assembly

The display case showing how the telescope was assembled has two cut-aways, one unfinished (the lower one) and one finished. There are 3 basic pieces to the telescope: the objective, the eyepiece and the tube.

The tube is a series of wood strips glued to a black felt liner and formed into a tube.  It doesn’t show up well on these images, but the outside of the unfinished tubes looked almost as if they had pinstripes. This was the felt showing between the tiny gaps in the strips of wood. Incidentally, they didn’t say what kind of wood Galileo used.  The model was pale and very fine grained, and I suspect was made of something good for modeling, like poplar.

When the tube was completed, it was covered with leather that was tooled and dyed.  The leather would help add stability and structure to the tube, and give it a smoother more attractive outer appearance.


Cut away showing construction of the eyepiece end of the telescope.

The eyepiece and objective have similar  construction. Again, a tube is constructed by gluing wood strips to black felt. You can actually see the “pinstripe” appearance of the eyepiece in this second image. The cell that holds the lenses is larger in diameter than the tube, and is mounted to a smaller diameter tube that will slip inside the main tube. This probably allows the lens to slide in and out, to obtain a good focus.

The eyepiece lens is sanwiched between two aperature stops, which then fits into the front of the lens holder.  The objective is a little different. It has it’s own cell, about an inch long and two different diameters (see the topmost image). The lens sits in the wider section between two aperature stops and held in place with a metal tension ring. The narrower end fits into the cell. You can see how this looks in the last picture.


The objective end of the assembled models. Note the serperate lens carrier for the objective in the finished model.



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