Thank you every one for that I understand now, and will do some sums. Poisson du Jour, I dont quite agree with you, it isnt naff. I have been bumbling along with trial and error with my pinholes for too long now. I Like experimenting, but its better to learn from experiments. I also like the concept of 'not knowing for certain', and anti- precious that comes with a pinhole camera but I dont want to waste time and paper. Someone who can, has worked out the sums so that I can use the calculations,and they have put their labour of love on line for free. I do like to use recycled containers for my cameras and it amuses me, that the biscuit tin, and the hole made with a sewing needle, now has a calculation on it.