From: pireddag@hotmail.com   
      
   On 2017-10-04 03:55, malna.polya@gmail.com wrote:   
   > Hi All,   
   >   
   > I am working on a project: we have a light sensor with only around 40   
   degrees field of view. Our goal is to measure the strength of the sunlight   
   without introducing too much of a bias based on the time of the day - when the   
   sun shines at a different    
   angle. We want to keep the sensor stationary.   
   >   
   > I was thinking about using a set of lenses to change the angle of the rays   
   but I am stuck, since one lens would only focus the parallel rays of different   
   angles to different points in the focal plane - and our sensor has a fairly   
   small surface area.   
   >   
   > Some of the diffusers I have found were only changing the angles with up to   
   10 degrees which is not enough, since we want to measure from -75 to 75   
   degrees.   
   >   
   > Another concern is to find a solution which doesn't filter out much of the   
   light spectrum.   
   >   
   > Does anyone have any ideas on how to solve this challenge?   
   >   
   > Thank you in advance!   
   >   
      
      
   Other posters have more experience and might comment on this, but I have   
   got a feeling that the theorem of conservation of etendue makes what you   
   want impossible. If you want to decrease the angular spread of a source   
   (and this is what you want to do: a source emitting at different angles   
   for different times is the same as a source emitting at different angles   
   at the same time for what regards the theorem) then you have to increase   
   the area which the light crosses. I think this is what is happening in   
   the solution with a set of lenses.   
      
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