[Laser] Fresnel comparisons

[Clint Turner]

After intermittently working on it for a number of years, I have put 
online a page that compares a number of typical molded Fresnel lenses 
against each other while providing some empirical measurements of some 
of the qualities of the lenses.

The page is here:

http://www.modulatedlight.org/optical_comms/fresnel_lens_comparison.html

Specifically, the "blur circles" of a specific lens has been measured.  
It is hoped that enough lenses have been tested to give an idea as to 
what might be typical of these types of lenses as well as providing some 
information on techniques that may be applied to make further such 
measurements.

This information is important in that it has implications as to the 
minimum size of detector (or aperture for a detector) that one would 
use.  This "minimum" size could also be applied to the apparent size of 
an emitter and whether or not it was the size of the emitter or the 
quality of the lens that dictated the minimum attainable divergence for 
that lens - a factor that could then be used to give an idea as to the 
minimum field-of-view of an optical receiver using a given lens/detector 
combination.  In order to keep it to a reasonable length, the deeper 
implications of much of what is covered is not discussed.  Also, while 
it briefly touches on the subjects of optimally matching an 
emitter/detector to a given lens and forming a complete system, it does 
not provide an in-depth discussion on that topic as that will 
(hopefully) be a topic of future writings.

73,

Clint
KA7OEI