[Laser] Re: Fresnel lenses

[John Matz]

There are 57.3 degrees in one radian (angle measure).  Therefore one
milliradian is 0.057 degrees.  It's all to convert from one unit of angle
measurement to another.

John Matz KB9II

----- Original Message -----
From: "Paul Cianciolo" <paulc at snet.net>
To: "Free Space LASER Communications" <laser at mailman.qth.net>
Sent: Monday, June 13, 2005 4:41 PM
Subject: Re: [Laser] Re: Fresnel lenses


> Hey Tim,
>
> Thanks a bunch for the time to answer my email.
> I was never sure if the answer came out in mR or in degrees.
>
> Where does the constant 57.3 come from?  I have seen formulas  that state
FOV = detector dia/ focal length.
>
> I have a 1 watt laser diode that I want to collimate a single 5" lens.
The diode has a fiber output angle that closely matches a 5" lens I have.
>
> I have been doing some experiments with an 808nm at 150 mw if you want to
see a pix of cloud bounce at straight up I have that I can send you. Also
Have a clear sky night trace of signal return as well.
>
> Both are graphs showing noise floor and the 1 Khz square wave.  Boy does
the signal pic up when you follow the light column up and finally hit the
dot on the clouds.
>
> hi pau\
> i'm using a short focal length mirror for some NLOS
> experiments and it has a FOV of about 0.7 degrees or
> so. (247mm focal length and 3x3mm detector)
>
> here's a formula for calculating field of view:
>
> F = (57.3/FL) x D
>
> where:
> F= field size in degrees
> FL = focal length of lens or mirror in millimeters
> D = detector or film dimension in millimeters
>
> for your example:
> 57.3 / 400mm = 0.14325
> 0.14325 x 2.5mm = 0.358 degrees FOV
>
> in milliradians:
> milliradians = degrees x 17.45
> 0.358 x 17.45 = 6.247 mR FOV
>
>
> >
> >From: "Paul Cianciolo"
>
> >Subject: [Laser] Fresnel lenses
> >
> >Folks,
> >
> >I wonder if anyone has used a 10" or so diameter for
> >a receive antenna?
> >
> >The problem I see is the relatively short focal
> >lengths. This combined with the a 2.5 mm dia.
> >detector makes for a pretty wide FOV.
> >The fresnel's have tried have not been the most well
> >focused lens's.
> >Just curios.
> >3DLEN.COM perhaps?
> >What are you guys using as a FOV for NLOS receivers?
> >W1VLF
> >PauLC
> >
>
>
>
> Tim Toast
> http://www.aladal.net/toast/exp.html
>
>
>
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