Maybe these Yajiamei lenses would work as well?
@Unheard: how did you manage to open the head and hence swap the optics?
It seemed to me it was glued and therefore impossible to open.
There’s red threadlock. Brute force and maybe heat helps.
Disappointing. 
It’s very little threadlock. Sofirn just made sure the pill won’t stuck in the battery tube when loosen the head. This problem has been reported a few times.
The pill doesn't seem to be screwed in the head, but force fit (judging from the two notches).
So you need to pull it out with a tiny screwdriver tip, correct?
Pictures of the process would be helpful 
What you see in the picture is the shell which holds and protects the optic. You have to grab the head at the threads and then unscrew the bezel.
No, it is screwed.
Don’t touch the PCB. The threaded part is actually part of the pill.
Thanks SammyHP and Unheard, it's clearer to me now. So the way to go is to:
- Remove the O-ring,
- Gently heat with a hairdryer (hot enough?) or a cigarette lighter (not too close),
- Grab the thread with plyers, inserting e.g. a rubber sheet to protect them,
- Same for the bezel.
Correct?
Yes. Before applying heat, see if you get it loose without. A lighter is very hot, not recommended.
We talked about these 45° Lens,glad you like them.
The Beam is larger but also dimmed than stock lens. For outdoor I’ll try 20° or frosted 25° white holder that need be removed 2.11€ 10% OFF|10 stücke 13mm CREE LED Objektiv 10 30 45 60 90 Grad XPE2 XPG2 XTE Epiled/Semiled 3535 3030 Emitter Plano Reflektor Kollimator|Objektive| - AliExpress
For outdoor, maybe the original optics will do. It gives a lot of throw. I recommend using a 219C at 4000K, that gives a nice beam and a larger hotspot. This is my only C01S still with original optics.
Thought the Led die size on TIR lens had no effect for the hotspot width. Good to know it does 
Also,maybe in real there is small difference betwin frosted 25° and 45 ° lens
I had to apply moderate heat, using a hair dryer, then unscrew very hard using two pliers.
Once opened, I replaced the stock optic with a 20° Shamian (frosted) from Yajiamei Optics, like I did to successfully improve the beam of my Skilhunt E3A.
No more rings, but although I don't have a way to measure it, I notice a noticeable decrease in brightness WRT the original optic, both in direct lighting and in a ceiling bounce test.
A piece of DC film on the original optic gives as good a result on the beam, without any noticeable brightness loss.
Strangely I had not noticed such a dimming effect on the E3A with the Yajiamei optic, but maybe I did not compare both options carefully enough.
Mine didn’t have a threadlocker, I can unscrew the bezel easily.
It’s not glued on my non-ano BLF version either. But it’s the one light I kinda wish had glue (I know, I could do it myself). On multiple occasions the “pill” section has gotten stuck in the battery tube (turned on) while the bezel comes off in my hands. Tears my fingers up getting the pill section back out. Come to think of it, maybe I did go ahead and put threadlocker on it last time it did that.
Clear spot TIR.
Got the light yesterday. Today the driver died. 
I didn’t do anything special, just turned the light on with the AAA that I used with it before, it blinked and died.
I contacted Sofirn already….
Had similar issues on grey C01S. Have you check rear spring?
I took it out with fine pliers and cleaned the bottom of tube with cloth and alcohol
Yes, I checked the tube. It’s fine, but I get 0V at the LED wires.