Talk:Cardinal point (optics)

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[edit] Diagrams etc.

A few things:

1. I believe the principal planes are actually principal surfaces (curved) unless you're using the paraxial approximation. Worth mentioning, or leave that to another article?
2. The nodal points are coincident with the principal points if the lens the same medium on both sides. Probably worth adding.
3. What diagrams do we want? I was thinking of basically redrawing Hecht (2nd ed.) figure 6.1. Would fig 6.2 & 6.3 be useful also, or too much?
4. Any preferred labelling scheme? Hecht uses F1, F2, V1, V2, H1, H2, etc., whereas Jenkins & White use F, F', A, A', H, H'.

--Bob Mellish 17:08, 9 March 2006 (UTC)

1. Yes, the principal surfaces are actually curved, if you're not using the paraxial approximation. Perhaps that could be mentioned. The article (and most of the rest of geometric optics on Wikipedia) assumes the paraxial approximation though. I'm not sure how useful it is to consider the cardinal points at all, once one moves beyond paraxial optics.
2. It's in there already.
3. Hecht's 6.1 and 6.2 look good. I'm not so sure about 6.3.
4. No preference on numbers vs. primes. I prefer V to A for the vertices, for obvious reasons. Greivenkamp uses F, F', P, P', V, V', and N, N', which seems nice and simple. Any idea why the more conventional symbol for the principal planes is H? One of those things inherited from German, perhaps?

--Srleffler 17:53, 9 March 2006 (UTC)

1. OK, I've left it out of the diagrams for now.
2. Oops, yes, so it is. Sorry.
3. Diagrams of the first two have been added. Let me know if you want anything tweaked in them.
4. I've followed that convention. No idea about H, probably German as you say,

--Bob Mellish 01:35, 10 March 2006 (UTC)

Excellent diagrams, Bob! The dashed "virtual" extensions on the rays are good, and they pointed out to me that the definition of P and P' that I had written was unclear if not outright incorrect. --Srleffler 02:18, 10 March 2006 (UTC)

Thanks Srleffler for integrating the section I wrote about the back focal plane into this article - and improving it. --Richard Giuly 08:51, 28 July 2006 (UTC)