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Old Aug 29th 2019, 10:37 AM   #11
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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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Creating a parrallel lightbeam.-optc-f.png  
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Old Aug 29th 2019, 11:08 AM   #12
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It CAN work.

The idea is ok!
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Old Aug 29th 2019, 12:24 PM   #13
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Something wrong, I see...
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Old Aug 29th 2019, 12:54 PM   #14
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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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Old Aug 29th 2019, 05:47 PM   #15
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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:mYGvfNLZFe4clwd Ei8k5I5g

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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Old Aug 29th 2019, 09:05 PM   #16
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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...8OcTgzDanyjAKw

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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Last edited by oz93666; Aug 29th 2019 at 10:33 PM.
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Old Aug 30th 2019, 01:00 AM   #17
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Originally Posted by cobaltBlue View Post
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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Old Aug 30th 2019, 02:04 AM   #18
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oz93666

Nice!
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Old Aug 30th 2019, 02:07 AM   #19
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No way!

Small circle surface instead of 22mmx22mm.

Those stage lights have indead a nice sharp spot at the podium from up to 50 meters away!

But the price...
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Old Aug 30th 2019, 02:11 AM   #20
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The led circle is even smaller than the 14.2mmmx13.2 mm!
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