What exactly does an aspheric lens accomplish? How do you get them to fit?

I was at thic outdoor music festival in the city 2 weeks ago, and the band was all about 70's and 80's soul, funk, R&B. The singer/band leader is almost 70, and he gets out into the audience while singing with his wireless mic. Well in the mean time, there's this city cop standing in front of us, and he has the Batman style utility belt with all these pouches and tools all over it, and he has this one 10" cylindrical object with a round top piece that looks like another wireless microphone from a distance, so I'm wondering if he's going to pull this thing out and break into song at some point, but then I walk by him and see that this thing is apparently a flashlight with a clear aspheric lens on top(not a wireless mic!).

I' had seen pictures here of a few people adding aspheric lenses to modified Maglights, etc. I just now went to 2 different lens manufacturer's websites(Optolife and another company with the initials MG, Mellow Graffiti or something), and they show pictures of these things, but dont seem to explain what they do, what all applications they are used for, etc.

So what do aspheric lenses do, and when you buy them, do they usually fit right into whatever flashlight you are installing them into? I wouldnt imagine that most of these lenses are special made for certain flashlights. They seem to just come in different sizes, but different flashlights have different bezel styles and head styles, so what if it doesnt fit and the bezel doesnt screw down onto it properly to ensure its waterproof or element proof? Is there often some "adjustments" that have to be done?

Do aspheric lenses make a dramatic improvement in flashlight beam profiles?

They are mainly to increase beam "throw" (although beam-shape may be worse ) ....

Here are some ideas and examples -

http://www.candlepowerforums.com/vb/showthread.php?312991-Ahorton-s-Hall-of-Fame

HighlanderNorth said:

Do aspheric lenses make a dramatic improvement in flashlight beam profiles?

Click to expand...

An aspheric lens makes a distinctive beam profile. It can 'project' the light source (Often an LED) out ahead of the flashlight. This means that you get a focused square-shaped beam of light, at very high intensity (High lux numbers). This lets you send a concentrated beam of light with very little spill. If you move an aspheric lens closer to an LED, it projects a smooth beam of light, with even intensity across the beam.

Some like 'em, some hate 'em. It's one way to get a WOWlight for cheap. 3 AAAs and a cree LED with an aspheric can be had for 8 bucks and look quite bright just because it will throw nicely. I have a Deft EDC, one of the top hand-held lights for pure throw. It really is a pocket spotlight. I can see human-sized targets at 200 yards at night...but I can't see anything around the tiny beam of light thrown by it.