Dave writes: > Steve, we are never going to be in harmony here because we are not on the > same page. Indeed, we may not be in the same song book! You can no more > agree with me than I with you. We seem to have different definitions for > some basics. So be it. I don't agree with what you said but I really > admire the way you said it. Dave - you got me thinking .. Steve also wrote: > Diameter of pinhole = 1.56 sqrt( wavelength * focal length ) > > and if we use 500 nm for wavelength, we get: > f d > 4 mm 0.0698 mm > 8 mm 0.0987 mm > 17 mm 0.144 mm > > 699 mm 0.922 mm > 736 mm 0.946 mm > 750 mm 0.955 mm While I have done these same calcs and drawn out all the graphs for these myself and have stated the very same thing to anyone who cares to know, I decided to review what I understood and in light of Dave's POV I started questioning a few things.. the statement Steve makes: "However, for each distance from the film plane there is an optimal size of pinhole" may be semantically rearranged to "However, for each size of pinhole there is an optimal distance from the film plane" - this holds true, yes? Does this mean _focus_ or is this just semantics?* I set down and started drawing up ray diagrams and examining the effective sizes of Airy rings, calculators up all over the monitor and paper everywhere, then it struck me - I was REALLY complicating things - a lens is a device for focussing rays of light , but so is a pinhole. What was I doing? The aperture of a lens is effected by the focal length, but the focal length is NOT affected by the aperture. Why on Earth would it be any different for a pinhole? Steve's statements are as correct after my re-evaluation as they were before so the answer to my question above (*) is yes, this appears to be just semantic. Sorry Dave, I could find nothing to support your statement karl
