[Laser] (no subject)

[Kerry Banke]

Art - I did get a chance last evening to sand off the lens on an SFH-203 
detector and polish it.   There was a definite improvement in sensitivity 
as well as narrowed field of view as you had stated.  I didn't get a chance 
to make  quantitative measurements last night  but I will do that just for 
the record.  The focus had been mushy as one might expect from a miss match 
and is now more definitive.  The aiming is of course more critical but that 
will be helpful in eliminating interference from other nearby sources.   I 
had been meaning to run that experiment for some time & appreciate your 
comments which spurred me on to finally doing it.
  - Kerry N6IZW -



>Kerry,
>
>The units that come in plastic LED type packages are NOT good. If you want 
>to use the bare diode without an external lens, they are fine.
>
>When using them with an external lens to collect more light, they are not 
>good. The problem is that the package does not focus the light on the 
>photodiode unless the light striking the package is parallel. SO, the 
>losses are quite large when used with an external collector lens because 
>the focal point will then fall quite short of the photodiode surface itself.
>
>Years ago, I worked out a procedure to correct the problem though. I 
>ground the bubble lens away till it was flat, then polished the front 
>surface (with Comet and water on a small piece of glass). Having a front 
>face that is flat and relatively smooth made a lot of difference when used 
>with an external lens.
>
>Regards,
>
>Art
>
>
>
>
>
>
>_______________________________________________
>Laser mailing list
>Laser at mailman.qth.net
>http://mailman.qth.net/mailman/listinfo/laser