[rollei_list] Lens coating
- From: <dwilli10@xxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Fri, 3 Jun 2011 10:24:38 -0700
I'm actually on a real vacation and took a few books to read, including 3 by
Richard Feynman- QED, 6 Easy Pieces, and 6 Not-so-easy Pieces.
If you don't know Feynman, look him up, he was a fascinating person, a great
physicist, and a superb teacher.
Anyhow, QED is not the same as "Q.E.D", a term concluding that "It has been
proven". In this case QED is "Quantum Electro Dynamics", and the little book
is fascinating.
Most camera folks know that lens coating is sort of an impedance matching
process that cuts down reflections of light waves at lens surfaces. I always
took that point of view since it sort of relates to the radar reflection issues
I worked on when I had a real job.
Feynman takes an interesting approach. He starts with quantum light particles
and shows that when light quanta hit a glass surface about 4% of them decide to
reflect, the rest penetrate. Then he considers the second (exit or back side)
of the glass and once more about 4% of the quanta decide to reflect, the rest
pass into the air behind the glass.
Now here is the kicker, depending on the thickness of the glass the sum of the
reflection may range from 4% to 16% (why not 4 to 8% I don't grasp yet) but the
% reflection varies cyclicly with the thickness of the glass (or film) and
Newton proved that held to at least 55 meters of glass thickness.
This all sort of links back to my interest in understanding "Action at a
distance" in which quanta (or anything) can decide what to do based on what
happens to an event some distance away, linked by some unknown connection.
Lot's of articles on this and even with my schooling and experience, it's still
a mystery to me.
If you want some reading entertainment, I highly recommend this, and all his
other books, available for low cost on Amazon. He always takes a simple but
correct approach to problems and uses a lot of the little vector diagrams he is
famous for. (There is even a more recent book, published after his death, that
might be interesting reading, Perfectaly reasonable deviations from . . . . )
In his collection of lectures he proves Snell's law in 3 lines. Try that on
your own some time.
Anyhow, this message is not intended for just the lens designers in the group,
it's good reading for anyone with a curiosity about different approaches to
lens coating, and scientific writing in general. I have some recordings of
some of his lectures and he is very down to earth, with a Bronx or Boston
Accent, can;t tell the differece.
Sorry to offer a topic so far away from Camera design but I just couldn't
resist.
DAW, resting in sunny San Diego.
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