OLcontest, modified light: 20cm fresnel lens thrower

A couple of years ago I made a 36cm fresnel lens thrower, from wood, featuring a dedomed XM-L2.

It did/still does over 5Mcd, which is great, but it is rather bulky. And because of the short focal distance I think that the outer part of the lens has a lot of distortion and contributes relatively little to the center of the hotspot. So now I try to make one a bit more compact and usable (i.e. without being really water proof, it will be usable in slightly rainy conditions), with a 20cm lens, and a bit longer focal distance: also 20cm. The hotspot will be smaller, but expect also optically better. And I move on to a more modern led: a SBT90.2 .The aim is to reach 2Mcd.

I’m not sure if this build can be done within the rules of the OL handbuild competition, because, as in my former build, one of the parts is a commercial flashlight, although it is only used as switch+battery tube, with the head removed. If it complies I’m happy to join with this build.

Edit: after inquiring, this build is fitting into the modified light category, so it will enter the OL-competition as a slightly modified Yootoo SD2 :slight_smile:

These are the parts to start with. The plate is 20cm/20cm/3mm aluminium and the heatsink is a 13cm passive heatsink made for a 65W COB. I’m still waiting for a SBT90.2 on a Noctigon from Hank. And lots of wood is not on the picture either.

Whoa, that’s something.

Do you have data about how does the previous build compare to the current (as planned) regarding LED light emitting surface and power?

The SBT90.2 should have a bit higher surface brightness than the dedomed XM-L2, but I expect also a bit better optical performance from this lens, and also the larger surface area of the die may be a bit more forgiving for the poor quality of fresnel lenses. But there is a lot of guessing involved, my fuzzy conclusion is 2Mcd but it can go either way.

The output of the SBT90.2 is also much higher as the dedomed XM-L2, about 4 times, but with the smaller lens at increased distance, the amount of light exiting the lamp will not that much higher.

After a lot of measuring (the heatsink must be centered pretty perfectly on the alu plate to get the led centered behind the lens) I made some holes in the 20cm x 20cm x 3mm aluminium plate, 4mm small holes with a drill and two bigger holes with a fretsaw (IMO the fretsaw is the ultimate handbuild tool :sunglasses: )

It fits.

That is all for today.

Do I recognize an Amutorch Yootoo SD2? Very interested how that plan is coming together.
FWIW, I do remember a sketch of a big thrower with the batteries placed behind/around the reflector.

Yes, an SD2, I have two of them spare because they did not fit the boost driver I was planning to mod them with :frowning:
Now it is a convenient 21700 battery compartment with added switch.

And yes, this is still my favorite setup for a big thrower since the first plans for the BLF-GT. Who knows it will be picked up some day by a manufacturer.

Forgot, the tools of today:

Not shown: drill press

Nice start djozz. Looking forward to the rest of the build. :+1:

Thanks Steve!

Today small progress: a mount for the lens made from plywood. Tools: pencil, ruler, drawing compasses, drill, fretsaw, wood glue.

The effective diameter of the lens will be 196mm.

Awesome! I bet it will be a crazy thrower.

Do your students know you are building this? So the above is two pieces of wood glued together to get the step?

No, they do not know that I build searchlights. But they do know that I build stuff myself every now and then, before summer I built a wind tunnel from wood and polycarbonate panels for physics demonstrations (to make wind I used a 10 inch 12V 80W car radiator fan from aliexpress).

Yes, two pieces glued together, I think that I will glue the lens in the slot from the outside after everything else is finished, and keep the lens clean. In fact I have two identical fresnel lenses (they are cheap), one for during the build to check the workings, and one for the finished lamp.

Nice project and thanks for showing ……

Also nice to see “creativity hard at work ……”.



I’m here for the fun :smiley:

Welcome MB, here is some fun :slight_smile: .

To check the potential of the lens, I clamped it in with a FT03-mini (harddriven SST-40 with dome) behind it. I measured the throw at 6.99 meter from the fresnel lens and got 2.16 Mcd (at 30 seconds). So the potential is there, the domeless SBT90.2 should even do a bit better, and if it doesn’t I can always go SST-40 and have the runtime and less heat.

That is fun indeed! :smiley:
I admire your creativity and work! An SBT will blow it, not in the “explosive” way! You’ll soon rename your city to Amster…daaaamn :o when that beam hits the sky :wink:

Thanks Martin, and others. The creativity was already 4 years ago, it is more of a rebuild with improvements based on what I learned back then. I like that you do not need to be a fancy flashlight manufacturer to make a superthrower, this thing will look extremely homebuilt :smiley: . But I must admit that the cost of the parts add up, I’m over 100 dollar already, the led+board+heatsink+alu plate+SD2 were 92 dollar, I can’t remember the cost of the lens, but it was about 10 dollar. Maybe 8 dollar worth of plywood, and a dollar for a handle, so maybe 120 dollar. That is what I paid for the Lumintop/BLF GT a year ago so homebuilding is fun but does not really pay off :person_facepalming:

Well see it like this .... you're now or soon will be ..... the owner of (another) homebuild world exclusive ! ....

... and in "my eyes" that's basically priceless !

Also the "material cost" is probably only a fraction of what the "manual creativity" would have cost ....

... that is if "someone would have payed you to do it" ?



PS> Let me know when you plan to use it so I can close the curtains first ......

A really nice build djozz. :slight_smile:
Hope the judges let it in.
If no….you have good chances to win the mod category. :slight_smile:

Cool :+1:
Modified light category? :slight_smile: