[Laser] receiver question (with URL removed to avoid bouncing)

[Charles Pooley]

Tim Toast  wrote:
   
  hi George
Yes, either lens would collect the same amount of
light and i suspect either one of those would be fine
as long as your detector has a field of view...
  
P.s. - I sketched this out on a piece of paper and
just measured the angles with a compass to avoid the
math, so i hope i'm not too far off :)
With the 390mm dia. 220mm FL lens, the detector needs
at least a 100 degree FOV to see the whole lens. With
the 330mm FL lens, the detector only needs to have
about a 80 degree FOV. I'm assuming that's a square
lens (550mm diagnal)
  ----------------------------------------------
  You might add a second lens, either + or -, to make it a telescope.  
Then it will tend to place a nearly parallel beam of light coming from 
a distant point source, onto the detector when the focus is adjusted.
   
  This has the advantage of allowing easy placement of a pinhole 
blocker to confine the field of view.  Also, to accomodate the placement of a 
tilted bandpass filter (tilted as a tuning measure, and to allow a 
camera to get the image from light reflected from the BPF).
   
  I plan to use  1/2 of a cheap pair of binoculars for first 
experiments, then scale up to larger area later.
   
  Charles Pooley  KD6HKU  
 (a url for the site microlaunchers dot com was here)