Parallel beam of light out of biconvex lens f=45mm Answered
I would like to create an almost parallel beam of light with an LED and a biconvex lens. Therefore I have to place the LED directly in the focal point.
I thought of a setup with a PVC pipe with threading: I could glue the lens to one end and screw a cap onto the other. Then I would drill a hole in the middle of the cap and stick the LED through the hole. By screwing the cap back and forth on the PVC pipe I would be able to find the exact focal point and then fix the cap in place.
There is just one problem: Lenses are either incredibly expensive or only available as sets. The only exception I found so far are lenses for google cardboard. They sell for just a few euros on ebay.
Google cardboard lenses have a focal length of 45mm and different diameters, I would like to use a diameter of 25mm which is no problem.
Now I wonder: Is the focal length of 45mm too small ? Will I be able to get an (almost) parallel beam of light out of this setup ? The LED is no ideal point light source. Originally I wanted to get f>80mm but that is really expensive.
Anyone with experience on this kind of setup ? Tips you could share ? Can I get this to work, or will the approach be too unprecise.