I resisted posting for two days, lol, I am going to give it one more try with the intent to clarify things for forum readers, especially those new to optical lens for flashlight use :). It’s very confusing, so bear with me. The OP’s thread actually started here: " Brighter light without changing the driver!! & Prototype is done!! :) ( picture heavy)": Brighter light without changing the driver!! & Prototype is done!! :) ( picture heavy) It was using a lens that looks like a long EFL fresnel lens directly on top of the flashlight, don’t know why all the photos were gone, but anyways, my comments started there & followed here when OP started a new thread with what looked like the same device. All my comments, when I said it won’t wk, stated it’s for long EFL lens, where the focal length is much longer than the distance between led & the lens. Scaru’s test that confirmed my statements probably used long EFL fresnel lens, more inline with OP’s initial experiments. This optical principle only partially apply to Medium EFL lens depends on where is the placement of led in relation to the lens focal point. and depends on the size of original reflector., thus the throw of original flashlight, in relation to the size of added lens. What’s further complicating this thread is that it looks like mixing of original long EFL lens now with devices with medium EFL lens as well as telescopes, without separating the various lens as well as lens vs telescope & using them to support each other. I think we pretty much figured out which shots are from telescope, I am going to focus on the remaining confusion, what’s happening when Medium EFL lens are used? When OP place a 3" medium EFL lens, mounted in a tube 8" away from the flashlight, if the lens has an EFL of 8" or so, this basically create an Aspherical flashlight, just not as efficient as typical aspherical flashlight, which use short EFL lens, so that it can be placed very close to led to collect a bigger angle of light spread. The lens placed far away like 8", only collect a small angle of beam coming from the led. None the less, if the led is placed at the focal point of a medium EFL lens, it’ll have the same effect as typical aspherical flashlight and increase throw. As we all know, the throw of Aspheric flashlight is based on the diameter of the lens, thus OP was able to make it throw much further by using a 3" lens over a small reflector flashlight. May be OP can measure the EFL & confirm that he is actually placing the led at the focal point for his later single lens device, i.e actually making an aspheric flashlight? If this is the case, it’s possible to explain why it works better in a floody light but not so much in a thrower. A floody light typically have very small reflector, most of the light comes out as spill, the lens collect the spill & turns it into parallel beam, in the mean time, diverge the original parallel beam from reflector so that the throw from reflector is lost. because the large lens works much more efficiently than a small reflector, the net effect is much increased throw. The gain is much greater than the loss. On the other hand, a thrower flashlight usually has a large reflector, TN31 3", SR90, SR95 UT 3.5", they are able to collect majority of the light & send them out as parallel beam to have great throw to begin with. With the lens of similar diameter,3" for example, if the led is placed at the focal point, the lens will still collect the spill & turn it into throw, but in the mean time, diverge & mess-up the original throw from the reflector, because the original throw may be greater, the lens may not provide improvement, especially a low quality lens placed 8" away. In a nuts shell, There are total of at least three type of optical systems experimented by the OP, improve throw or not will depend on the EFL of the lens, the placement of led, and the original reflector size in relation to the diameter of added lens. 1. Long EFL lens placed in front of a flashlight: Will not increase throw, it’s not practical to place led at the focal point as its to long. 2. Medium EFL lens, with flashlight led placed at or near EFL: Will increase throw, rather than a shocking new discovery, it’s just a less practical & less efficient form of aspheric flashlight setup, non the less, follow the same principle. 3. Telescope placed in front of a flashlight: Will increase throw. Not practical but I do find it interesting, especially if it has a really big front lens. I do want to apologize for using the elephant story to make my point, even if its out of frustration triggered by wild claims & great confusion, it was inappropriate for me to do so.
and Happy New Year!! :party: