Agreed Djozz.

I think Marinebeam probably have a well matched lens (diameter and focal length) which will not be easily bettered, at best equalled with very similar parts.

To progress beyond just making a clone, I think you will need a larger diameter, longer focal length lens, an altogether bigger torch. And do some fine tuning of the collar with shims.

The maths doesn’t seem difficult, at least to get an approximate idea of what might work.