New camera building question.

So I've constructed a camera. My question is im trying to figure out the aperture of my "lens." I'm using a standard peephole you use in doors. i believe my measurements are accurate but have not tested it yet. can anyone know of what the aperture is or how i can figure it out. Thanks so much
-Dan

Aperture number is roughly the focal length divided by the actual opening diameter. You can work out the focal length by measuring from the film to around the middle of the lens when focused at infinity. A door peephole does not have an adjustable iris so just measure the diameter of the glass.


Steve.