[Laser] Fresnel lenses

[Chris L]

Dear Paul,

All of our lenses are fresnels, both on receive and transmit. For our 167 km 
record we used fresnels 19cm by 25 cm with a focal length about 25 cm. We 
also have two receivers with fresnels 45 cm by 64 cm, focal length 60 cm - 
not used on 19th February because I took my gear down to Tasmania by 'plane 
for the record...

Details, photos, further information and several web pages are at the 
following url, and also look at the bottom of that url page for further 
information and urls:

http://www.bluehaze.com.au/modlight/index.htm

Mike VK7MJ has two of the 16 " square fresnels from 3DLens.com, they are 
apparently excellent - also he has located a source of 40 cm by 60 cm 
fresnels for about Aust$70 in Adelaide, South Australia - quite fine for 
optical comms but unfortunately with a slight blue tint which is a bit of a 
pain if you're trying to collimate from a 630 nm (red) Luxeon III.

Do NOT bother with old fresnels from 'overhead' transparency projectors. 
They are WAY too short in focal length, and are designed for close-field 
collimation, not for collimation at infinity. Most of those have no 
correction for spherical aberration. The 3DLens types do.

I will be putting up more about optics as soon as I can get access to my 
url's computer - maybe a week or two away yet.

Hope this helps....

Chris Long and Mike Groth VK7MJ.



<br><br><br>&gt;From: &quot;Paul Cianciolo&quot; 
&lt;Paulc at snet.net&gt;<br>&gt;Reply-To: Paulc at snet.net,Free Space LASER 
Communications &lt;laser at mailman.qth.net&gt;<br>&gt;To: 
&lt;laser at mailman.qth.net&gt;<br>&gt;Subject: [Laser] Fresnel 
lenses<br>&gt;Date: Sat, 11 Jun 2005 13:36:55 
-0400<br>&gt;<br>&gt;Folks,<br>&gt;<br>&gt;I wonder if anyone has used a 
10&quot; or so diameter for a receive antenna?<br>&gt;<br>&gt;The problem I 
see is the relatively short focal lengths.  This combined with<br>&gt;the a 
2.5 mm dia. detector<br>&gt;makes for a pretty wide FOV.<br>&gt;<br>&gt;The 
fresnel's have tried have not been the most well focused 
lens's.<br>&gt;<br>&gt;<br>&gt;Just curios.<br>&gt;<br>&gt;<br>&gt;  
3DLEN.COM perhaps?<br>&gt;<br>&gt;What are you guys using as a FOV for NLOS 
receivers?<br>&gt;<br>&gt;W1VLF<br>&gt;<br>&gt;PauLC<br>&gt;<br>&gt;<br>&gt;<br>&gt;<br>&gt;_______________________________________________<br>&gt;Laser 
mailing 
list<br>&gt;Laser at mailman.qth.net<br>&gt;http://mailman.qth.net/mailman/listinfo/laser<br>