OLcontest, modified light: 20cm fresnel lens thrower

Very cool :slight_smile:

Holy spotlight … Batman :wink:

Throwtest :slight_smile:

For who is into throw distance as unit (distance at which the illumination is reduced to 0.25lux AKA moonlight level), that is 4.36 km.
My Extech LT45 over-reads a bit, the Tasi 8133 makes it 4.24 Mcd but that may be under-read again. Let’s agree on rather throwy :wink:

(I do not dare to use my Mobilux classA luxmeter too much lately because the cable-connection to the sensor is rather worn-out and fixing it will require a completely new calibration as well, which will cost me 300+ euros)

Outstanding! Great work, once again!!

For the Americans, 4.36km is about 2.7 cheeseburgers per bald eagle miles

I could go for about 2.7 cheeseburger right about now!

Where did I put that bald eagle?

So much throw, nice work!

Would These parabolic reflectors be appropriate for making somthing like this ? It doesn’t look very expensive. If I understand correctly the short focal lenght means that all light would be collected (expect in center), also it would not produce chromatic aberation as opposed to the fresnel lens.

those are uncoated aluminium reflectors, good for focusing sunlight for heating up stuff, but how is the light loss, and are they optical quality? If yes, they should be fun to make a recoil thrower with :slight_smile:

I’m very impressed by the optical performance of these budget plastic fresnel lenses btw, the throw per surface area is very similar to the GT reflector. What helps is that the light source is small and centered (as opposed to projecting an image i.e. a slide which is a large source), the fresnel rims are only maximally optimised for light coming right from the focal point which is the case with a led.

Excuse my ignorance on these calculations—i see how you calculated the luminous intensity in candela, but i struggle to understand how the Luxmeter sensor area or solid angle come into play, or if they do? Does the sensor area not matter?

If the sensor area were known, would it be possible to calculate the lumens of the beam?

I measured the luxvalue in the hotspot at 12.33 meter, then calculated that back to 1 meter to get the candela-value.

I’m not sure what “solid angle” is, and the sensor area does not matter as long as it is more or less uniformly lit, as is the case because the hotspot is way larger than the aensor area.

Please excuse if this is off topic, i was puzzled by the calculation. But after a little study it makes more sense—the lightmeter is calibrated to provide a Lux value for a 1 square meter area at the sensor and not just for the tiny sensor area.

Lux is a measure of the light energy hitting a target area. The units of Lux are lumens/m², where lumens is a measure of the light energy known as luminous flux, with units of cd-sr, candela-steradians. And of course area is measured in square meters.

Steradians are a unitless measure of solid angle, symbol Ω, which is the angle from the apex (light source) subtended by the area of the target.

i was assuming the target area was just the tiny sensor area, but it is effectively a 1 square meter target area. So the solid angle Ω subtended at 12.33 meters away is Ω = Area/distance² = 1m²/(12.33m)², or the target Area = Ω ・(12.33m)²/1m²

So to convert: lux = lumens/Area = candela-steradian/ Ω ・(12.33m)²/1m² ;

and solving for candela = lux ・(12.33m)²/1m²

:+1: :slight_smile:

No matter how impressive the numbers are - the bat signal trumps everything !! :laughing: :sunglasses: :smiley: Great project djozz :+1:

First class build djozz :+1:
I had no conception what a Fresnel lens can do until your build. I’m still new here and very impressed how well this works.
Every part of this build is very clean and neat. Great build work djozz :sunglasses:

Thanks, there is still little things to be done, like a name and some beamshots, I hope to do them during the Christmas holidays.

I like this! :+1: :slight_smile:

may I suggest the Dutch thrower?
Or
Throwing Dutchman?

Awesome build!
:+1:

A box of light

DSS
= Djozz’s Star Shooter

The Flying Dutchman? :wink:

Ver licht? :stuck_out_tongue:

I had to finish it today, so here’s the final stretch.

Because the star and the batman projections were not what I wanted for this build, I tried a little spider. The shape was too difficult for the fretsaw, so I went for etching a thin copper sheet, for so long that the copper was eaten through by the FeCl3. I took a long time, and the cutout was not perfect, but the result was rather nice.

Still, this was not the final version. But here are some pictures. Both are at about 40 meters.