OLcontest, modified light: 20cm fresnel lens thrower

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PolarLi
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“Meet the Vir-O-blast C19”

This is my kind of humor Wink Really great build!

Scallywag
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djozz wrote:

I bought it a few years ago actually, on aliexpress. They are cheap (under 10 dollar for a 20cm diameter lens) and pretty good, here is a link, I expect it to be the same quality as the ones I got. I chose 200mm focal length as a compromise between the amount of light catched by the lens, and image quality (a very short focal length lens will catch/transmit a large percentage of the light but also show a lot of image distortion at the edges which will negatively affect the beam and throw).

https://m.aliexpress.com/item/32650652778.html?spm=a2g0n.productlist.0.0...


I just wanted to thank you for this build and the fresnel lens link. I’ve ordered a few sizes to try out and I think this will really scratch my thrower itch. Who knows, one of the lenses could even end up in the next OL contest…

Old Lumens Contest 2020 - Hand-made light category

ZL SC62(w) | Jaxman E2L XP-G2 5A | Purple S2+ XPL-HI U6-3A | D4 w/ Luxeon V | RRT-01 | Purple FW3A, 4000K SST20 | Baton S1
Boruit D10 w/ Quadrupel Fet+1/Anduril | EagTac D25C Ti | DQG Slim AA Ti | Jaxman E3 | UF-T1 by CRX | Olight S15 Ti | Nitecore EX11.2
L6 XHP70.2 P2 4000K FET+7135 | Jaxman M8 | MF02 | Jaxman Z1 CULNM1.TG | Blue S2+ w/ ML Special | Thrunite T10Tv2
Supfire M6 3xXHP50.2, Sofirn C8F, Unfinished: Sofirn SP70, IYP07/Tool AAA hot-rods, Jetbeam E3S
Others: Nitecore EC23 | Nebo Twyst | Streamlight ProTac 1AA | TerraLux LightStar 100

MtnDon
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djozz
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Nice! I have two findings for these plastic fresnel lenses:

1) the focal distance should not be much shorter than the lens diameter (maybe a focal distance equal to the diameter, as I used in the viroblaster is close to optimal), otherwise the the edges of the lens makes such a bad image that it is wasted for forming a good focal image and throw is ruined.

2) their imaging is pretty good but not good enough for very small light sources: it makes a mess of my LEP flashlight (stock lens removed) and I’m not sure that a White Flat will produce a good image (bad image=bad throw). I could test that btw one of these days.

Skylight
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So leds with big die size would be better? Is it noticeable in the projection if the led has a quad die, for example a XHP70?

I have an Amutorch TC500 with fresnel lens and White Flat 1. The beam is said to throw 1000m but it is quite colored in vicinity.

Scallywag
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djozz wrote:
Nice! I have two findings for these plastic fresnel lenses:

1) the focal distance should not be much shorter than the lens diameter (maybe a focal distance equal to the diameter, as I used in the viroblaster is close to optimal), otherwise the the edges of the lens makes such a bad image that it is wasted for forming a good focal image and throw is ruined.

2) their imaging is pretty good but not good enough for very small light sources: it makes a mess of my LEP flashlight (stock lens removed) and I’m not sure that a White Flat will produce a good image (bad image=bad throw). I could test that btw one of these days.


For one of the smaller lenses I ordered, I’m thinking of trying my dedomed XM-L2 behind it. I recall for your thread (and re-read before I ordered) you mentioning the focal length a bit.

Old Lumens Contest 2020 - Hand-made light category

ZL SC62(w) | Jaxman E2L XP-G2 5A | Purple S2+ XPL-HI U6-3A | D4 w/ Luxeon V | RRT-01 | Purple FW3A, 4000K SST20 | Baton S1
Boruit D10 w/ Quadrupel Fet+1/Anduril | EagTac D25C Ti | DQG Slim AA Ti | Jaxman E3 | UF-T1 by CRX | Olight S15 Ti | Nitecore EX11.2
L6 XHP70.2 P2 4000K FET+7135 | Jaxman M8 | MF02 | Jaxman Z1 CULNM1.TG | Blue S2+ w/ ML Special | Thrunite T10Tv2
Supfire M6 3xXHP50.2, Sofirn C8F, Unfinished: Sofirn SP70, IYP07/Tool AAA hot-rods, Jetbeam E3S
Others: Nitecore EC23 | Nebo Twyst | Streamlight ProTac 1AA | TerraLux LightStar 100

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