short focal length Fresnel lenses for sale

Buy / Sell Want to Sell
1

Hi guys,

For various flashlight/dive light projects I have been looking for good fresnel lenses to focuss the light of LEDs.
I know many of you are familiar with aspheric lenses. Fresnel lenses can provide the same functionallity using a very thin lens, typically only 2mm thick.
The advantage is a very light weight plastic lens. Due to the nature of the fresnel lens, it also doesn’t stick out of flaslights like aspherics do, so you can often place it behind the standard glass lens or replace the glass lens by the fresnel lens.

People that already experimented with fresnel lenses and aspherics, probably noticed that you need lenses that have short focal length relative to their diameter, otherwise known as a low F number.

While searching for good lenses, I often ran into high shipping costs out of China mainland.
Therefore, I ordered more than I needed so I have some to spare, and I’m willing to sell them here. Some forum members here on BLF and on CPF already have some. If they want to post pictures here, that’s fine for me.

I currently have 3 types of lenses for sale:

  • 25mm diameter
  • 38mm diameter
  • 50mm diameter

The 25mm lens is very similar to the ahorton lens, but I think it is more interesting pricewise and if you don’thave a lot of space like in dive lights. I used this lens in several projects where often P60 style dropins can be used. I used them with custom made spacers which keep the lens in place and put it at the right distance from the LED.

The 38mm lens I just bought for testing, but haven’t finished the build yet so don’t have pictures of this yet.

The 50mm lens fits perfect behind the front lens of a Maglite. I just added an o-ring to push it against the lens so it wouldn’t rattle and an o-ring to seal it (since the edge of the reflector is not there anymore).

When specifying the distance to the LED, I prefer to give the distance between the lens and the heatsink, as this makes it easier to make a heatsink.
I place the 25mm lens at about 15,5mm from the heatsink, the 38mm at 18,5-19mm (haven’t measured this exaclty yet) and the 50mm lens at about 28,5-29mm depending on how far away you want to focus it.
The lens should be used with the side with the rings pointing away from the LED, otherwise the lens doesn’t work.

Prices (paypal fee included):

  • 25mm lens: 6€/lens
  • 38mm lens: 7€/lens
  • 50mm lens: 7.5€/lens

I ship them from Belgium in a standard bubble envelope
International shipping: 1.5€, for tracked shipping +5€
For these shipping costs, I can ship multiple lenses.

You can pay via Paypal at [my_username]@gmail.com where you need to replace the [my_username] by my actual username.

current stock (I’ll try to keep this up to date):

  • 25mm: out of stock
  • 38mm:7
  • 50mm: 25pcs

If many people are interested, I can order more and try getting the price a bit down.

Some pictures of these lenses and results:
25mm lens in plastic holder (not included)

result with an XML (image underexposed):

comparison between the 25mm lens with XML and the original led and optic (driver was nog changed)

50mm lens installed in a maglite:

XRE with 50mm lens in a maglite, focussed on the ceiling:

comparison between the 50mm lens and the gaggione LLC49R optic, both with XML, image is underexposed:

50mm lens installed in a greenforce PRO dive light:

If you have any questions, let me know.

Best regards,
Johan

Sales:
username: 25mm-38mm-50mm-status
MosesM: 1-1-1-shipped
Confusius: 1-1-1-shipped
djozz: 0-0-1-shipped
waehrik: 0-0-2-shipped
John Murtagh: 0-0-4/4-shipped
NVF1: 1-1-1: shipped
NV2: 0-3-2: shipped
NV3: 0-2-0: 2 shipped
cat eyes: 2-2-2 shipped
cereal_killer: 0-1-0
onetrickpony: 0-0-2
Dave_: 0-1-0

2

Awesome selection of sizes! I’ll take one of each please, can you PM me the shipping cost to Singapore?

FYI, the 38mm lenses will fit Easy2LED’s M36 housing as well, which is where I’ll be putting this in! :party:

3

PM sent
MosesM, Order is shipped

4

whats the light transmission rates of these lenses compared to an aspheric?

5

I haven’t measured it (don’t have access to an integrating sphere, not sure if lux measurements make any sense before and after the lens), but transmission of PMMA (material of the fresnel lenses) is very similar to uncoated glass. The fine structure of the fresnel lens will also give a very small amount of scattered light at the edges of each ring, but in general, this is not visible to the eye.
I think you would need an aspheric with the exact same diameter and focal length to really compare the transmission with an image on a white target to compare the intensity I think. I didn’t find any aspherics that come close to these lenses, except for the Ahorton lens. The ahorton lens gives a slightly more intense spot compared to the 25mm lens, but depending on the available space, an ahorton lens may not fit and the 25mm lens could fit.

I hope this answers your question.

Johan

6

thanks. never seen these types of lenses in flashlights before, and are pretty interesting. thanks for offering them

if you still have some in a week or two i will be in for a 50mm one

7

I'd love a 50mm fresnel lens, it will be fun!

Thanks for the offer, and convenient that it comes from Belgium .

PM in a minute!

8

If there are a lot of people interested, I can order a new batch of 20 as I did last time. I also have a bad batch (bad production run, quality issue, happens when dealing with chinese stuff I guess). Perhaps I can make some people happy with those as well. I’ll add info on these later.

9

djozz and confusius, your orders are shipped. :arrow: :email:

10

waehrik, your order has been shipped this morning.

I’ll be ordering some more of the 50mm lenses, so for those people that expressed interest, don’t worry.

11

Received the 50mm Fresnel lenses and wanted to post a couple photos of the results.

The lenses will not be used in the HD2010 used here for testing, but I wanted to see what they could do and the reflector housing gave a nice place to set the lens in.

The results are quite impressive! All beam photos below are shot at the same aperture and shutter speed for comparison. The light is running a 2800mA Nanjg driver and Cree XM-L U3

Control:

Bare Emitter:

Stock Reflector:

Fresnel:

Lens in Flashlight:

12

Thanks for sharing. The center of both pictures is saturated, so it’s difficult to tell which one is the brightest. what was your impression?
It looks to me that the fresnel lens is not exaclty in focus, so moving it a bit forward or backward if possible could improve the result even more. But it could also be the exposure time that was too long and the camera not being able to properly image the result.

I’d love to see more results of what people are doing with these lenses :slight_smile:

Johan

13

I will try to retake the pictures within the next couple days with different settings to avoid the oversaturation. I believe the original optics had the brightest spot, though the spot was quite a bit smaller than with the fresnel lens. The focus was improving as I brought it nearer to the emitter, but the shape of the flashlight prevented me from putting it any closer. Next I will be trying it in front of a 50w LED panel (its intended target), though I know the focus will be worse due to the significantly larger emitter size.

It seems that the optical efficiency of these fresnel lenses is not as good as an aspheric or good reflector arrangement due to them being made of plastic and having a lower transmittance. That may account for the slightly dimmer ceiling spot. The real interesting part though is how it keeps the beam collimated over a longer throw. I would happily give up some lumens for a nice tight spot.

14

50mm lenses will be in stock again soon. Since the new batch was a larger order, I can lower the price a bit. First post is updated accordingly.

Johan

15

50mm lenses back in stock, price lowered a bit.

Johan

16

38mm lenses also back in stock

17

Hi Cat eyes,

I updated the stock in the first post.
current stock is:

  • 25mm: 28pcs
  • 38mm: 1pcs out of stock
  • 50mm: 35pcs

paypal address: [my-username]@gmail.com
meanwhile, there’s a similar thread on CPFmarketplace, which also has some links to what other people have been doing with the lenses.
http://www.cpfmarketplace.com/mp/showthread.php?303077-WTS-Short-Focal-lenght-Fresnel-lenses&p=4785636#post4785636

best regards,
Johan

18

Hi,

I ordered some more 38mm lenses, but it may be a week or 2 before they get to me.
Do you want to wait for them?

Regards,
Johan

19

38mm lenses are back in stock

20

cat eyes, your lenses are shipped. Feel free to post results in this thread or place a link to a seperate thread.