Thanks for the information. Eric Renner calls people like us "techno-nerds". But I know for a fact that he knows all this stuff too but won't admit it. ----- Original Message ----- From: "Guillermo" <pen...@rogers.com> To: <pinhole-discussion@p at ???????> Sent: Wednesday, December 11, 2002 9:43 PM Subject: Re: [pinhole-discussion] What is Diffraction?
> > ----- Original Message ----- > From: <erick...@hickorytech.net> > To: <pinhole-discussion@p at ???????> > Sent: Wednesday, December 11, 2002 9:27 PM > Subject: Re: [pinhole-discussion] What is Diffraction? > > > > Here's a question that has troubled me for a long time, since we've gained > > the attention of the physicists among us. If the optimal image occurs when > > all light waves are 'in phase", which the Young article says occurs at the > > junction between the nearfield and farfield diffraction patterns (whatever > > that is), is there another point further on where the various waves again > > come into simultaneous phase sync, and thus optimal sharpness? > Theoretically > > there should be, but how far? > > Physicists analyze diffraction using either near or far field methods. > Far-field means the source of light is far relative to the aperture size, > the wave front arriving at the aperture is assumed to be flat. Near-field > is the apposite, wave front is assumed to arrive curve shaped. This, I > believe, also affects or determines how far from the aperture the near-field > diffraction reaches and how far from the aperture the far field diffraction > starts. There is a gray area in between, this area can be assumed to > separate near and far field diffractions voiding any "juncture" of them, and > as Young's article says: "here, the image is not amenable to description by > simple arguments". When you talk about "in phase" you may be thinking > about how a zoneplate works, where the aim is carefully position the edges > of the clear rings so the diffractions caused by all of those edges > positively interfere at the focal point and therefore add up their > intensity. Pinhole does not work like that. > > For my view of how zoneplates work, pls read: > http://members.rogers.com/penate/zoneplate.html > It talks a bit about the near and far field diffraction, also. > > Don't quote me on all this pls, this is just a layman's view of the topic. > > Guillermo > > > > _______________________________________________ > Post to the list as PLAIN TEXT only - no HTML > Pinhole-Discussion mailing list > Pinhole-Discussion@p at ??????? > unsubscribe or change your account at > http://www.???????/discussion/ >
