Talk:Harold Hopkins (physicist)

Harold Hopkins' 4 principal contributions to optics
Harold always claimed the zoom lens, fibre optics, the theory of partial coherence and the modern (rod-lens) endoscope as his chief achievements. But: In my view, this list omits the main achievement: Harold was the first person outside France seriously to promote the idea of Fourier optics and MTF. So I have added a paragraph to that effect. Unfortunately the Wikipedia entry on MTF is sketchy to say the least - Modulation transfer function (infrared imaging) is much better. I would value the views of others. Bblandford (talk) 21:22, 7 November 2009 (UTC)
 * the invention of the zoom lens I think is due to Warmisham, USP 1947669 - the 1902 patent by Allen is not a zoom, it is a two-position lens which does not keep in focus between the ends.
 * Jeff Hecht in "City of Light" has implied that without A C S van Heel's idea of core and cladding of higher and lower index respectively, fibre optics would never have got off the ground. I have to agree with him.
 * The theory of partial coherence is a bit too esoteric for this audience.
 * The rod-lens endoscope has saved countless lives, and made Harold quite a lot of money in royalties.

Harold Hopkins the teacher
One of the most remarkable memories I have of my (and Harold's) first year at the University of Reading (1967-8) was the number and quality of postgraduates and postdocs who came from Imperial College to Reading just to hear him lecture. He told me that he never spent less than 3 hour preparing a 1 hour lecture - and that was if he had given it before. The result was, in my view, the best MSc course in Applied Optics available on the planet. We were so privileged to have had the chance to be there.

As an example of his skill, I'll never forget attending a conference on engineering uses of holography. Many of the delegates knew little about optics. The conference chairman was thrashing out some impenetrable mathematical explanation of Fourier transforms and the like. Once he had ended, at the request of one of the delegates, HHH stepped forward and drew the diagrams describng the reference wave, the diffracted wave and the reconstruction so clearly, that I can remember every detail to this day.

It is no surprise that Bud Vander Lugt (as well as other distinguished postgraduates) from the University of Michigan where off-axis holography was pioneered, chose to come to Reading for their PhDs.

--Bblandford (talk) 00:21, 28 January 2010 (UTC)

Picture
Picture?

More on rod-lens endoscopes
More should be added, the Hopkins rod-lens endoscope is a very clever trick that deserves some illustrations and description. Try this:
 * Endoscopes relay images down the scope. For a given tube diameter and length, you want to let as much light through with as few lenses as possible. You could put one thin lens in the middle of the tube, but then only a narrow cone of light from a point at one end would get through the system (only the rays subtended by that little lens at that l/2 distance). You can add more lenses, putting one at l/4 and one at 3*l/4, but that costs more money.


 * With that in mind, you want a way for the tube length to "seem" shorter. All other things being equal, if you are looking down a portion of the tube, you want the far end -- the light at the end of the tunnel -- look as big as possible. Just thinking about a tube with no curved-surface lenses in it, if you have a tube of fixed length and diameter, if you fill its entire length with a thick glass "window" with flat ends, the far end of the tube will appear closer -- it will subtend a larger angle -- because even though the surfaces aren't curved, a cone of light going in one end will refract at the air-glass interface, so the cone of light inside the "window" will be more acute. To a first order, this effect is proportional to the "optical path length" -- the length of the system in number of waves. Since the index of glass is about 1.5 versus 1.0 for air, the optical path length through 1 cm of glass is 1 cm /1.5 -- 0.66 cm -- 2/3 as long. Inversely, if you have a rod-lens endoscope and made it mostly air, for the same light throughput and same diameter and same number of elements, it would have to be shrunk to 2/3 its length.

Again, it could do with some illustrations. —Ben FrantzDale (talk) 15:33, 6 March 2013 (UTC)