Understanding Aspheric Lenses

Does anyone have enough knowledge to educate me on aspheric lenses? I had bought some of the old ones people recommended for D cell size maglights, but I realized those lenses don't work well without moving the light source as close to the lenses as possible.
I presume it is possible to get a lenses that will provided maximum flood with stock maglight emitter/bulb distances. If this all makes sense... I hope I explained it right.

Is focal length what I need to look at?

Basically I want that beautiful perfect circle flood and then a tight spot when twisted.

A diffused lens would likely work ok. When twisted to full spill all of the artifacts would be gone. When twisted to spot you would likely not get a pure pencil beam like through a clear lens though. Try smearing chap stick over the stock lens as a test. It should wipe right off.

If you like the results go to flashlight lens dot com and buy a 52mm lens called "accrylite" as it is a slightly diffused lens that really makes a nice difference in a Maglite beam while still providing nearly all light transmission through the lens. Should be about $6 or so.

The zoomy uses a transition lens where when the lens is near the LED it is like one Rx strength one way and when slid away is like an Rx strength the opposite way. To my knowledge one like that for Maglites does not exist.

Interesting, I'll have to try one of those lens.

I made a discovery last night in which I noticed that when you put in a cam style stock reflector, even at the highest position it still pushes the light carrier down a little bit. It got me to thinking that what if I were to cut the cam part of the reflector period essentially keep the same angle but just shorten it.

I'm curious if this will keep the light carrier closer to the lens and perhaps provide a better flood while still keeping the adjustment ability of the cam. I did notice if you take out the reflector and allow the lens to sit down as low as possible it gives an incredibly beautiful flood... But it has no adjustment and the lens is loose haha