Creating a parrallel lightbeam.

Jun 2016
The maths of lenses has a couple of quirks...

To get it to focus parallel to a point,
the angle of the surface of the lens at the position at which the bending of the light beam occurs,
should be the angle of the surface of a section of a sphere.
However, this assumes that the bending of the light occurs at the centre plane of the lens.
The refraction actually takes place at the surface.

This approximation is OK for a slim lens, but starts to become problematic for thicker lenses.
This is one of the reasons why multiple (relatively slim) lenses are used rather than a single (fat) lens.
(There are other reasons, as OZ pointed out)

As you note, the Fresnel lens avoids some of these problems,
but it introduces other problems (e.g. it does not produce a nice sharp image).

It is possible to calculate alternative lens shapes that do not make the zero thickness lens approximation,
but the construction of the resulting lens shapes is difficult (and expensive).
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Aug 2019
Thanks! All make sense!

Allready decided to go for 20Watt led, with a light-source-surface, just a few mm's in diameters.Something tells me to use at least 2 lenses, because the light source is not an infinit "point". The second lens will be a Fresnel.
Aug 2019

Checked whole setup. limitations, angle of ledlight distance etc...
Ordered Fresnel, diameter 95mm, focus 100mm and 20Watt led's, 7070/12V.

Got 80mmx80mm heatsinks and fans, but probably they can be much smaller due of 20W led instead of 100W. The leds are 12V but I gonna build in a Voltage/Current indicator and adjustable powersource. Got some, they where purchased for the 100W led. Acutaly, its a dc-dc converter.

it's gonna be a 2 stage lens setup.

Want to build it ( exept powersource) inside these yellow containers:


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Aug 2019
Wainting for the optic parts, the coming time, I'll put some time in my DIY rc hobby.

Excavator testing at low speed. DIY cylinders, Arduino etc...

Feel free to move around on my youtube channel...

Kind regards. Marcel
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Aug 2019
As told before, I only want a kinda almost parellel beam.

At the end, all combined together, in summary:
- Combination of: small area and a lot of power at decent price.
- A collimator and a Fresnell-lens.
Aug 2019
Recently, i received the Fresnel-lenses.

With a particular focuslnegth and lensdiameter.

This, in right proportions for the total setup.
Sep 2019
The particularity of LED determines that it needs a guide plate to be placed in front of it. It is a PMMA plastic or ground glass with grids, This design has been added to many LED lighting fixtures.
Oct 2017
I've been on holiday for a week, so haven't been replying, so sorry for the late addition.

The name for a device responsible for making light beams parallel is the "collimator". If you go shopping specifically for collimators, you will get many hits for the kind of lenses you've been talking about. In addition to lenses, you can also get prepackaged collimator peripherals. These are usually designed with the astronomer in mind (e.g. for Newtonian telescopes), but perhaps there are more general purpose collimators available if you shop around?
Apr 2017
A colimator is just a lens (or parabolic dish )

"A collimator is a device which narrows a beam of particles or waves. To narrow can mean either to cause the directions of motion to become more aligned in a specific direction (i.e., make collimated light or parallel rays), or to cause the spatial cross section of the beam to become smaller (beam limiting device)."


Employing the device above would be no use ... (small hole in front of the light source) you would get a nice tight beam , but 99% of the light would be lost.
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