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Parallel beam of light out of biconvex lens f=45mm Answered

Hi,

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.

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Downunder35m

3 years ago

For LED's you get nice metal holders with a lens included.
Usually just used to make them appear much brighter in machine setups or for control purposes.
But if the lens is glued into the cap you adjust the foca point even to the point where you see the thin connecting wires on the LED chip itself in the reflected light.