What Happens when you de-focus an Aspheric ?

[Doh!Nut]

As per the title
I understand that the attraction of the aspheric lens is that is takes 100% (ish) of the light and projects it forwards with no spill, the beam ends up looking like as disk that can be focussed to get great throw.

What I need to know what happens to the beam if you try to get a 10 or 20 degree beam? is is smooth or do you get a do-nut etc.

The problem I am trying to solve is I have a headlight to be used with by handlebar mounted bike light. The handlebar light gives the flood and the headlight gives more throw. The trouble is the tight hotspot does not need to be quite so tight and the light lost to spill is wasted as the other light is providing the spill.
I need a light that produces little spill and throws a nice even beam.

Cheers

 

[LukeA]

Once you get it past the point where there's not hotspot, it becomes very smooth, no hole.

 

[divine]

This thread shows an aspheric in a less than spot focus.

 

[KrisP]

I mostly use my aspherics defocused due to the nice even beam

 

[HarryN]

As noted, the beam from an optic / lens tends to be squarish when in focus, and can be defocused as much as you want.

In my testing I did not find that an aspherical lens had higher light capture than a reflector, but that testing was conducted several years ago. (and I did not publish it)

Beam customizing is somewhat trial and error for each end use / user. After you look at 10 beams from various optical arrangements, you start to have vision / memory problems. oo:

 

[Gunner12]

The light collected by the lens is only what hits the less, which I think is a good bit less then 100% of the light from the LED.

When you defocus the lens, it gives a nice round smooth beam.

For your task, maybe a 10-20 degree optic or a reflector light might work.