I would like to talk about the needle you have to use, to make the hole in the foil and eventually becomes your aperture.
With other words the opening where the light will come through during the extreme long exposure photography.
It is so, that if you shoot with a regular camera the opening of your lens at the time of exposure will define how much dept of field you will end up in the image after exposure.
Meaning that the wider your opening (smaller number on the lens) the less dept of field you will have.
The smaller your opening (bigger number on the lens), the more dept of field.
Dept of field means how much sharpness you will have towards the front and the back in the image.
With the opening in the foil it’s actually the same, with the difference that it is not so extreme as in a normal camera.
The ‘disadvantage’ here is that you don’t have a lens !
Meaning that the sharpness of the image here is going to be ‘relative’.
The image will never be as sharp as with a normal camera.
Although you have to bear in mind that the rule here counts equally.
That’s why I advice you to use an as tin as possible needle to make the opening in the foil. I use N° 11 whatever that may mean in knitting world… 😉