So I’m building an aspheric lens lights, as some of you may know. I’m using a CXB3590 for the LED. Many larger zoomie flashlights have an area angled away from the PCB to the outer edge of the flashlight head. I’m guessing that it works as a semi reflector catching stray light and attempting to redirect it. I know I’ve used reflectors behind an aspheric and I did not like the results. So, do I need this angled area? Does it actually increas output OTF? Also if I go this route, what type of lens should I use as a collimating/condensing lens to focus the light to the aspheric. I have such a long focal length, I’m worried about light output being lost in the “head” on the way to the aspheric and not being directed straight out. I basically want to narrow the beam profile down on the LED prior to getting to the aspheric lens if that will have a positive effect. I just don’t want to do it to the point that my exit beam is pinpoint looking like a laser. What’s the point in a 35mm LED that makes a pin point dedomed XP-E2 type beam.
Try making a light recycling collar? Use a reflective dome to redirect all the stray light back to the LED, with an aperture large enough for the light to hit the back of the lens only. The larger the dome, the better the recycling. But, make sure to focus it properly, so you get as much effect as possible. You do need a sphere for this, not a parabolic reflector.
You don’t need the angled reflector.
- It’s usually so shallow its actually less than the emission angle from the LED. As a result very little light will actually be reflected from it resulting in virtually no effect on the beam pattern.
- The shallow angled reflector is really just decorative. It hides the star and bondwires. In my own zoomies I don’t bother.
I previously tried using deeper parabolic reflectors in small aspherics. I took small plastic reflectors from an UKE lamp module or a cheapie 2xAAA or AA incan maglite. Chopped off the bottom results in a fairly shallow reflector. Using these reflectors I got:
- flood mode gains a very large and wide hotspot in the center. The net result is that the center of the flood looks probably twice as bright. This makes for quite a useful floodbeam.
- Because the reflector sticks up slightly higher than the LED dome, flood mode isn’t nearly as wide. To get maximum flood width, modify the bezel, body, or pill so the back of the lens almost touches the top of the emitter. For an even wider flood use a dedomed emitter or XPL HI. Doing this should easily produce a flood beam at least 90 degrees wide.
- In spot mode the reflector produces an ugly donut around the spot. This looks hideous in white wall shots, but in actual use it isn’t enough to affect the usefulness of the beam.
My current personal preference is no reflector. I just leave the Noctigon and bondwires exposed.
That’s a waiven collar. It’s completely different from the almost flat conical reflector found in some larger zoomies that the original poster is talking about. A waiven collar can result in a substantial increase to throw. The disadvantage is they can be quite expensive and are supposedly very difficult to focus properly. Also, I suspect they’re difficult to use effectively in zoomies since the collar will likely interfere with flood mode.
Yeah, I know they’re significantly different. 
As you said above, the little “reflector” is just a decorative retaining ring. I’d rather have a flat black ring instead of a reflective one, because any light that is bouncing around in the head will eventually reflect off those things and out the front, where it makes the beam very ugly. The reason I suggest he make a “waivien” collar is because those will actually help to make the otherwise excess light spilled inside the head into part of the useful beam coming out the front. With the size light he’s talking about, it should be fairly easy to make one and to focus it reasonably well.
The smaller condensing lens near the LED will have an effect similar to having a shorter focal length main aspheric, it will make the spot larger. As with a shorter focal length single lens, if it catches light from angles where the LED’s output falls off, it will reduce throw.
That is only a first order analysis. If the secondary lens has a large effect, the result will also depend on what happens off axis, that is it will depend on the shapes of the two lenses. Two aspherics, either of which will produce a clear image by its self, may not be shaped right to be used in combination. You would probably have to do ray tracing calculations or try it to see what shaped beam you get. It is probably best to stick to a thin secondary lens close to the LED, to have a limited effect and make the optics close to that with only the primary lens.