Creating a parrallel lightbeam.

Jun 2016
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A spherical lens can focus a parallel light beam onto a point
or visa-versa, rays coming out from a point into a parallel beam.

If you work it out precisely this is actually an approximation.
The approximation is un-noticeable for most practical purposes
but can become important for very strong (very fat) lenses.

Your problem is that you have light rays diverging from several points
which you want to focus through a single point
and then on (through more lenses) to produce a parallel beam.

A standard point focus lens is based on sections of spheres
A line focus lens can be constructed from sections of cylinders.
 
Aug 2019
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Watch this picture. There are more divergending beams of light, seperated from eachother.

Here is where the fresnel 'rings' come in.

Let's see how far I come!
 

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Aug 2019
30
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Ok

Nice parellel beams, or maybe they should be slightly divergend or convergend when entering the Fresnel.
 

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Apr 2017
540
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I wouldn't waste your time with Fresnel lenses ...

There is one possibility , since you are not bothered about size ...

As said earlier a bigger lens will help , but you cannot get them too big , weight , cost ...

A large parabolic reflector will do the same thing ... This is how WWII searchlights were build , with an arc light as the source ..



Modern ones are acrylic , I bought one a long time ago ... now the prices for these seem to be ridiculously high on Ebay ... up to 1 meter diameter



A cheap way would be to use mylar film (2Meters dia) on a hoop , reduce pressure on one side to make a parabola .... Or a big bowl of mercury rotating slowly ...

Whichever route you go its of utmost importance to use the most powerful , compact emitter available ...

check out this ...I didn't realize they existed!! 300W from an area about 10 x 10 mm ....

ebay.co.uk/itm/LED-light-Bead-60-90-150-180-200-300W-white-chip-For-stage-spotlight-led-beads/233294160495?hash=item36516a626f:m:mYGvfNLZFe4clwdEi8k5I5g

You will need a very good heat sink , and a lens close to the led to aim the light on the parabola .
 
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Apr 2017
540
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On second thoughts Fresnel maybe OK ....

After a few ebay searches I've come up with a good combination ... I think I might make one myself ... should cost around 100 Euros ...

the light source see link above ...

looks like this , Available in many sizes, 300 to 60 Watts

the white block in the right hand courner is described as "a high quality thermal resistance" not sure what that does ???

plastic fresnel lens 300mm dia , https://www.ebay.co.uk/itm/1PC-300mm-Dia-Round-PMMA-Plastic-Solar-Fresnel-Solar-Condensing-Lens-Focus-Large/183835438843?hash=item2acd722efb:m:mxw-vl7F58OcTgzDanyjAKw

these come with different focal lengths 200mm should capture all the light from the led which has a spread of 120 Degs

You will need a good heat sink for the led , or it will burn out ... and a good power supply , around 12V , 20A!! (car battery constantly recharged ... or li-ion)

The compact source and big lens should get fairly close to a parallel beam.

EDIT ... I just had to buy one of those leds . I went for the 200W size , cost 43 Pounds ... I already have a Fresnel lens
 
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Aug 2019
30
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Ok

Nice parellel beams, or maybe they should be slightly divergend or convergend when entering the Fresnel.

The Fresnel rings have to be placed.
This picture only shows the 'preparation' before entering the rings.
With some adjustment I get them divergend or convergendand still there are nice beams from center, half-way and edge. ( coul make it in more stages )
 
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