OLcontest, modified light: 20cm fresnel lens thrower

[Skylight]

Very well done, djozz. Awesome build and finish.

That zoom function looks very interesting in your video. The different stencils are ingenious. That virus or the spider is going to freak out everyone who sees it.

I liked your build so much that I ordered myself a big fresnel lens. Never imagined what cool things can be done with this. 4.2 Mcd should throw incredibly far.

[PolarLi]

“Meet the Vir-O-blast C19”

This is my kind of humor Really great build!

[Scallywag]

@djozz

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).

Page Not Found - Aliexpress.com

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…

[MtnDon (Don Miller)]

Me too!

[djozz]

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]

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]

@djozz

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.