I want to communicate 2.7 miles from a peak on a mountain. I will be using a very bright LED and some type of photo-element (photo multiplier tube, avalanche photo diode etc.) to receive the amplitude modulated signal.
One problem I have is: what optics will I use to receive the signal to "zoom in" to the light?
So in short... Where can I get the optics which the people there ↑↑↑ used. I do not want to buy a telescope because of the expense and then my project won't be considered D.I.Y.
I will be starting out at the night time, and probably not doing any day experiments for a while.
Im sorry if this question is considered off topic, I thought it should fit this site at least because it has to do with communications, and optical is above 275Ghz which is on the chart.