Do you have any 25m 50m or 100m beamshots?
Would like to see how well these freshnel lenses throw
me to! 
Hmm, I don’t have any at the moment. I use them in dive lights where I’m interested in the beam up to maybe 5m…
I may be able to come up with some beamshots of the 25mm lens at about 20m but I’ll need to see which LED I have in a P60 pill.
I have one of your 50mm lenses. It is not build into a flashlight, but I could improvise something tonight and make a beamshot...
I made this from brown paper, it is my UF-T20 without aspheric head, fitted with the 50mm fresnel lens, I put a pill with dedomed XP-G2 3C @ 2.95A in (that both with the normal UF-T20 aspheric -32mm effective diameter- and in a smooth reflector C8 does 108klux @ 1meter throw). This improvised paper holder should work as wel as some nice dedicated adapter. The hotspot zoomed in looks fairly nice and clean, a bit different from an aspheric lens hotspot but not better or worse.
I wanted to do a beam shot of the tree from outside on my balcony, but in the middle of the night two people decided to have endless conversations and hugs and kisses right under my test tree :angry: . And even with their surely diminished perception of the world around them, a 100+ klux pencil beam right above their heads might not go unnoticed 
So I just measured the throw with the lux-meter, it is an impressive 138 klux @ 1meter (I measured at 2 meters), which is very ok for a 50mm lens, but a true aspheric 50mm lens would have performed a bit better.
Yay, they're gone, here's the tree-shot after all (tree at 25 meters), and another shot further in the grass (lamp post and sign are 92 meters away):
This may be a stupid question but is it possible to trim these down a little, I have a project light I’m working on that takes a 36mm lens, would I be as to trim about 1mm off the diameter of the 38mm lens to get it to fit or would trimming it mess it up/make it not be able to focus?
If these are still around, I’m interested in at least 2 of the 50mm, maybe other sizes as well.
Hi onetrichpony,
yes, I still have some plenty of 50mm lenses.
I have 2 38mm lenses left, but can get more if necessary.
I think I have about 10 25mm lenses left as well.
cereal_killer, about trimming the lenses, I did it once with a dremel (using a rotating sand paper thing) from 38 to 35 and it worked, but it’s a bit difficult to hold it properly and still be able to rotate it. Be carefull not to hit the front or backside though with the dremel.
The lenses are made out of PMMA so quite easy to work with.
Does cutting them change the focal length? (I ask since the different size lenses have different focal lengths).
Also a general question about them, does swapping in emitters require some focal length adjustment or as long as the die is the same distance will it always be the same length?
I’ve got to see the answer to my 1st question to say for sure but please don’t sell out of 38mm lenses before I see your answer tomorrow, I’m going to bed now, I’ll reply tomorrow.
Hi,
If you grind away the edge, this won’t change the focal length of the lens at all. You will only catch slightly less light in the lens but this won’t be noticable to the eye.
The focal length and the diameter are a bit linked since it is difficult to produce lenses under a certain F/# (ratio of the focal length and diameter). That is why the different sizes have different focal lenghts. It is for example very difficult to make a 50mm lens with only a 15mm focal length withouth getting in trouble with abberations and reflections.
As long as the distance between the bottom of the star (backside) and the LED die is the same, swapping emitters does not require a focus adjustment. Most LEDs I’ve used have silimar distances (about 2.5mm IIRC), but I don’t know how accurate that is. I never swapped emitters in my lights. I did use the same distance for an XML and XPG on 20mm stars for the 25mm lens and this was just fine.
I’ll keep the 2 lenses reserved for you for the coming days.
Regards,
Johan
As discussed in PM I’ll take one of the 38mm ones. Payment incoming (a little layer tonight).
Thanks.
edit: payment sent
PP sent for two 50 mm lenses with tracking, thanks!
That means that there is one 38mm one left, right?
I’ll take that one, then.
Cereal_Killer, OnetrickPony and Dave_,
Thanks,
your packages are ready and will be shipped on Monday.
current stock:
25mm: 9
38mm: temp. out of stock.
50mm: 35
Darn, I was just about to decide that I need 1 or 2 38mm ones…
I’m getting some more, I’ll let you know when I have them (probably in 1 or 2 weeks).
do you leave the reflector in the head when swapping the glas with a lens?
A conical reflector might be good
Please do!
I’ll keep my eye on this topic as well.
I typically don’t use a reflector when using a lens. light that hits the reflector will not go through the lens correctly and the lens will not focus the light but just image it somewhere else. this basically destroys what the refector did, namely focus the light that hits the reflector properly.
one way could be to use a reflector that is bigger than the lens and use the lens to focus the light that otherwise would not hit the reflector so also that light gets focussed. This is however quite a tricky setup since you need a way to properly mount the lens inside the reflector and properly centered.
The reason I’m offering only short focal lengths, compared to their diameters, is to capture most of the light so I would not need a reflector. In some applications you also don’t want a corrona around the hotspot. In that case, it is better to make the walls black and have a sharp spot from the lens with no light around it.
regards,
Johan