I want a uniformly illuminated surface over an area of 60 cm square area using a wide angle lens. What should be the specification for that wide angle lens?
Sibasish, Image intensity of a lens obeys cos(theta)^4 law. Image peripheral of a wide angle lens is very dark by this reason. Theoretically, this difficulty is overcome by distortion which is described by y'=f sin (theta). Attached please find my lens design using semispherical lens with the flat surface in front, where aperture is located. If you locate 45 x 45 LED array in the object plane, you will obtain first order approximation of flat field. If you reduce power of LED's near center in the object plane, better approximation will be obtained. Shigeo
Sibasish, do you specifically ask about using a lens since you want to avoid mirrors, or would it also be feasible for you to use mirrors?
Mirrors will also do the task for the time being. So what should be the optics design?
If you use very many LEDs in a square array, you only need the mirrors. In principle, that's all for the optics, if you are fine with the emission from the LEDs. (Possibly you need an active cooling of the LEDs.) In case they also emit light in an unwanted wavelength range you need an additional optical filter in front of the LEDs. For example, I study silicon solar cells illuminated by red high-power LEDs. From a certain fraction of the the LED chip, infrared light is emitted (for whatever reason). However, since my detected signal is in the IR range, I have to block this parasitic IR emission from the red high-power LEDs, using a full-area optical filter glass in front of the LEDs. Unfortunately, this reduces the maximum power of the usable light. Have that in mind when you design your set-up!
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