[Laser] Re: focal length question

[Tim Toast]

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 wide
enough to 'see' the entire lens from its position.
Although the longer focal length version would give a
narrower field of view and slightly better image
quality, both of which help cut down on background
noise.
I know from photography, a shorter focal length lens
does have some advantages in some cases (faster) but i
don't know if that really applies to optical
communications as much as it does in photographing dim
stars. 

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)



Tim Toast
http://www.aladal.net/toast/exp.html

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