[Laser] BPW34 field of view rating (for N5GUI)

[George Vastianos]

From: <TWOSIG at aol.com>
> I would like to start with some comments on the field of view rating of 60
> degrees on the BPW34 sensor.  If you hold that sensor face toward a steady
> light source you can measure its output.  If you then tilt the sensor 60
degrees
> it will will measure half, not because the sensor is only half a
sensitive
> to photons from that direction, but because it is only intercepting  half
as
> many photons from the source.

As far as I know the "tilt" verb is related to elevation right??? so if we
tilt up
+60 degrees we have half output from the sensor (-3dB). Now if we tilt down
-60 degrees we have again half output (-3dB). So finaly the angle between
the two
lowcuts of -3dB is 2*60=120 degrees Right????? Based on this idea I was
talking
about 120 degrees in my previous postings. I think we are talking about the
same
thing. In case that Iam wrong or I misunderstood something in your message
please let me know...

> The sensor will still receive and convert photons from angles greater than
> 60 degrees.  The field of view calculations on the fresnel lens on the
other
> hand are "hard" transitions from angles that have light passing through
the
> lens to angles that are beyond the edges of the lens.

Yes I agree about that

> The bottom line is that the BPW34 sensor will work with either of the
> fresnel lenses that you described.  What I think is more important is that
you
> realize that the lenses are not "perfect".  Depending on how well  you
mount them,
> the light from your signal source will create a fuzzy spot  rather than a
> tiny point of light near the focal plane.  As long as that  fuzzy spot
falls
> entirely on the sensor, it will do its job of converting  photons to
electricity.
> The size of the BPW34 will make your job of focus  and alignment easer
than
> if you used a smaller sensor.
>
> It will also allow the system to receive more noise.  The sensor  active
area
> is, if I remember correctly, about 3.5mm square.  If you  use a 300mm
focal
> length lens, it will "see" an area about 12 milliradians  across, or about
half
> again the diameter of the full Moon.

About the noise you mean that will happen because only a small part of the
sensor area will be covered by the light of our signal???? I think our goal
is to "see"
as wider "picture" we can...in order to increase the posibilities of
grabbing the remote
small spot... so since we try see "wide" we will get more qrm...right?

> The necessary field of view of the  sensor calculations:    Worst case is
the
> corner.   Assuming that you are going to use the 180mmX260mm lens with
focal
> length  300mm,   start by calculating the diagonal. Square root of (
180X180 +
>  260X260) is about 316.23mm.  The tangent of the angle you want is half of
> that divided by the focal length.    Roughly 27.8  degrees.   Full field
of
> view is less than 56 degrees.  Certainly  not a problem for the BPW34.

Yeap! you are 100% right about the diagonal 316.23mm....

Thanks for your respomce