Homebrew PCBs

James Owens wrote:
> Hi,
> 
> I have a lens which came from a 3'x3' process camera. It is 210mm focal
> length. Is this information any use?

The gaussian form of the lens equation is: 1/f = 1/d(source) + 1/d(target),
so the film should be 315mm from the lens and the pcb printout should be
630mm from the lens.

> I used lithe film when I did my boards that way. Most photographic
> shops/suppliers have it in sheet form.