I am making the holes in a hard black paper. But I will try using aluminium from soda can.

I just made a 0.5mm pinhole. Very close to 0.422mm. I will test tomorrow but I am sure it will be good and sharp.

Thank you all for the information and help. I love it more than my brand cameras.

Now I am thinking about to load 4 sheets of paper in the camera. Maybe place a black thick paper between each of them just to make sure tha the light is not going to get though the first paper and expose the seccond one behing it. Like this I can go to the city or woods, and after each exposure I can put the exposed paper behind of those not exposed yet. Of course I woud do this changing in a change dark bag.

Do you think it woud work? Or any of you have a better idea to reload and take more than one shot without have to go back home to reload the camera?