Has anyone had success with a Fresnel lens? How 'bout this one...

Flashlight Modding and DIY Parts
1

Has anyone had success with a Fresnel lens? How 'bout this one...

it's from Rolyn Optics:

http://rolynoptics.thomasnet.com/item/simple-lenses/fresnel-lenses/16-7150-id-442-?&bc=100|2000002|3001008|3001006|3001005

It is 50mm dia clear aperture, 32mm focal length, 1.5mm thick (much lighter than glass), but is only rated to 80C. (might melt - but your Leds don't like that temp either)

$15.40 +shipping :(

Anyone want to try it? They also have many other lenses I've yet to try...

2

I have never seen a fresnel on a flashlight, it might be interesting.

3

I have not really seen them in flashlights, but it is sometimes used in divelights, like the ones from mbsub.

I'm also playing with some 50mm fresnel lenses and they fit nicely in a maglite without any modification. The tricky part is to position the LED so that it is nicely imaging the die at a certain distance.

4

I had NO idea that you could buy those! I thought they were made to/by specific companies for an already designed product.

@ jspeybro: How is it going with the positioning? Any progress.

I imagine that it is a lot like positioning a asperic lens but I wouldnt know really. Can you share a little more about the project and the progress (and perhaps mistakes) that you have made?

This might be wonderful for an XML thrower although to be perfect it would have to have a shorter focal length AFAIK.

5

I’ve seen people use them in maglites instead of aspherical lenses. They work ok but you lose more light through them than a standard lens because the light gets bent several times before exiting and there is always some lose at each bend.

6

I didn't think that a Fresnel bent light any more times than a solid lens. Some light is scattered if it hits the side of a ring segment, this makes it less suitable for quality imaging. But Fresnel lenses have been used in lighthouses for years... See wikipedia.org/wiki/Fresnel_lens

Oooh, now there's an idea, LED lighthouses - with mammoth LEDs cooled by seawater. Its a perfect fit!

OK, back to reality

I agree the key is focal length, and apparent LED die size has something to do with a tightly focused beam too.

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Welcome to BLF. I think I recognize you from the divelight forum at CPF as well.

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Fresnel lens are like a conventional lens cut into concentric rings. Rather than one lens bending light there are several all focusing to one point. They are not able to focus as sharply as a normal lens which is why you wont find one in a camera.

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Thanks, yes, that's me as well. Been hanging around here a little for reprogramming AMC drivers.

the losses in a fresnel lens are rather small (scattering at the edges) and in a flashlight, I don't think you will notice (perhaps a lux meter could tell but then you'll need to find an aspheric with same diameter and focal length).

I see several advantages over normal aspherics: price, weight, size, easier to mount. disadvantages are scratch resistance and strength, but for dive lights I don't see this as an issue since it will be behind another flat lens.

The smaller the F/# (function of diameter an focal length) of the lens, the better since you will be able to capture more light with the lens.

10

It seems Khatod read my post... or maybe its just coincidence.

But, I just noticed they have a Fresnel lens that looks promising!

50mm diameter, sits 10.5mm from the LED, about ±8 degree beam (±20 and ±30 degree models have shorter legs, might be the only difference). May be able to tweak the focus to get tighter/variable beam?

Khatod #PL117415

This link may or may not work:

http://www.khatod.com/cms/pl1174_series___fresnel_lenses_for_cree_xlamp_xp_e_leds-2598677-2598677.html#

If anyone gets there hands on one please post the results!

11

Here's one company selling them, with pictures

They come in several sizes. I have a few of the 4-AA size; they use a bi-pin incandescent bulb.

I did try rewiring one as 2x2AA with a 5mm LED, years ago, but it didn't work well.

You'd need a side-emitter, I think.

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@OP - Thx for the post! I've been looking for smaller lenses as they same like they'd be interesting alternatives for asphericals without providing that magnifying glass effect.

You guys might be interested in:
https://budgetlightforum.com/t/-/6566

Cheers,
Tim

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Hi Sorry for the late reply on this one. Meanwhile I've been experimenting with 3 fresnel sizes for different projects and I'm impressed. I used 50mm frensel lenses for upgrading maglites. Works very well. other than that, I've used them in several divelights with success. I have 38mm fresnel lenses that could fit some hosts but I needed to reduce the diameter to 35mm to make it fit the host I had in mind.

The lenses I've used the most so far are 25mm lenses which fit easily in any P60 style flashlight, but you need to make some kind of holder to put it at the right distance.

I've been using these 25mm lenses in small divelights (greenforce diamond) more than 2-4 times the light output (also replaced the led and electronics).

For positioning the lensen, I now use my lathe to make a heatsink so the led is at the right distance or make a holder (like for the 25mm lens) to position it at the right distance.

Here are some pictures for you to enjoy ;-)

25mm fresnel lens with holder:

http://s302.photobucket.com/user/jspeybro/media/Greenforce%20Mod/DSC04175.jpg.html

host for this lens:

http://s302.photobucket.com/user/jspeybro/media/Greenforce%20Mod/DSC04178.jpg.html

lens installed:

http://s302.photobucket.com/user/jspeybro/media/Greenforce%20Mod/DSC04180.jpg.html

beamshot:

http://s302.photobucket.com/user/jspeybro/media/Greenforce%20Mod/DSC04183.jpg.html

comparison between original and end result, note: XML running at only 1.5A to keep battery life usable for diving:

http://s302.photobucket.com/user/jspeybro/media/Greenforce%20Mod/GF_diamondResult.jpg.html

This is an XML with the 50mm fresnel lens at 3m from the wall on a sunny day in my living room; the ruler is 30cm long:

http://s302.photobucket.com/user/jspeybro/media/Greenforce%20Mod/XML-50mmlensat3m_zpsfb1aee61.jpg.html

50mm lens installed in a maglite, no modifications to the maglite except cutting a piece of the switch barrel that held the original light bulb. add an o-ring to prevent the lens from moving 1mm back and forth (because the reflector was removed):

http://s302.photobucket.com/user/jspeybro/media/DSC04404_zpsf2c4916e.jpg.html

maglite head twisted to widest setting:

head twisted to best focus at the ceiling (about 1.5-2m from the flashlight), LED is an XRE at 800mA:

http://s302.photobucket.com/user/jspeybro/media/DSC04407_zpsb077abce.jpg.html

comparison between XML with 50mm fresnel lens and an XML with a gagionne 45mm optic (which is one of the best TIR optics I've found). The Led with the fresnel lens came from DX, the other led from Led-tech.de:

http://s302.photobucket.com/user/jspeybro/media/DSC04454_zps1afe1247.jpg.html

50mm fresnel lens installed in a greenforce PRO head, also perfect fit, no modification required:

http://s302.photobucket.com/user/jspeybro/media/DSC04475_zpsaef3f125.jpg.html

And, best of it all, I bought quite a few of these lenses, so I have some to spare. If you want some, please PM me for now. I'll see if I can make a thread specific to these lenses if many people are interested.

Regards,

Johan

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Cool stuff. Thank you for the update. I've put this hobby on the back burner for a while though but I hope others pick up on your offer. TY again :-)

15

or you can use magnifying glasses… it works wonderful if you have flood type light ( tube light)
pretty much double the lux ( even more depending on light)

using convoy S2 XML-U2 1C at 2.8A and the ” light blaster modulator” ( had to give it a fancy name hehe…)
here’s the beamshot taken from 10’ from the wall

Convoy S2 from fasttech

“Light Blaster Modulator” in action

Lux reading at 10’ before ” Light Blaster Modulator”

Lux reading after using “Light Blaster Modulator”

so far it only works wonderful with flood type lights… heck… it even works with TK75 too ( weird beams though )

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the idea of using aspherics is to get shorter focal lenghts compared to spheric lenses (such as magnifying glass). The shorter the focal length, the more light is captured by the lens and will be projected forward. For a certain setup, when using a shorter focal length gives you also a bigger magnification, which may work as a disadvantage, but typically, this is not so much of an issue.

The down side of these aspherics is that they are quite thick compared to the diameter and also quite heavy due to the amount of glass involved.
Plastic fresnel lenses get around both issues and give you a short focal length which is comparable to aspherics, but are only 2mm thick and weigh almost nothing.

Johan

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I picked up a couple of 52mm Fresnel lenses from Johan. They produce a beam very similar to the aspherics they replaced

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who’s johan? :~

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see post #15

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Aliexpress is selling Fresnel lens Shuster s-136. Someone on YouTube just did review. Seems interesting.