This is one of the biggest TIRs, 75mm
It’s only been tested with COBs up to 23mm but the LED opening seems much bigger than that.
Only problem is that when using a TIR with a large LES LED then the angle of incidence varies a lot, which may cause light leakage since total internal reflection only works at large incidence angles.
There’s one zoomie construction that I haven’t seen on a flashlight yet but found 3 lens makers that do it:
Moving lenslet array based.
Near the LED there’s a fixed TIR. The TIR has a lenslet array at the front face.
In front of the TIR there’s another lens. Its back is the exact negative of the TIR’s lenslet array; the front may be flat or refract the light in other ways.
When both lenses are very close (pretty much touching each other) - the lenslet array doesn’t do much, it’s almost like a regular TIR.
When they move out - the beam gets wider.
Pros:
fair efficiency, TIR capctures all the LED light
no need to put LED on a pole
easy to do fair waterproofing: seal at the TIR. Beam will be bad under water but submersion won’t cause damage.
short zooming movement
Cons:
current implementations don’t have AR coating which hurts efficiency
The description states PC with aluminum coating… I can only postulate that the center is not coated; helping to effect the large beam angle. And it’s a HUGE angle…
Could be either a clear or matte dome… or a fresnel + reflector setup, that’s where I’d bet my money.
With the central dome being hollow, it can’t be (single-surface) refraction towards the reflector.