Talk:Cardinal point (optics)

message: A few things:
#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?
#The nodal points are coincident with the principal points if the lens the same medium on both sides. Probably worth adding.
#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?
#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)
replies: text: Hiatus (optics) : "By neglecting the distance between the lens' principal points, known as the hiatus, s + s' becomes the object-to-image distance. This simplification, called the thin-lens approximation, can speed up calculation when dealing with simple optical systems." . Using H for Hiatus instead of P would be like a little reminder or clue that the thin lens approximation has been used.  Which page should it #REDIRECT to ? --Redbobblehat (talk) 22:06, 11 August 2009 (UTC)

text: Yes, you're right.--Srleffler (talk) 17:40, 30 January 2021 (UTC)
thread_title: Diagrams etc.

message: Would it appear petulant to suggest that vacuum would be a better example ? --195.137.93.171 (talk) 06:31, 7 March 2008 (UTC)
replies: text: Not at all. Air (treated with the approximation n≈1) is a pretty important case in classical geometric optics, though, and needs to be addressed. I tried rephrasing the article a bit. See if you like the new text better.--Srleffler (talk) 18:00, 7 March 2008 (UTC)
replies: text:  It might be worth making it clear that nAIR is never exactly 1. The differences are non-trivial even to naked eye - twinkling stars, mirages, heat-haze, squashed setting sun. I recently came across a Nikon FAQ about why a lens focus-ring will turn beyond the infinity mark - mountaineers work in a lower refractive index due to altitude. Cynically I had thought it was due to sloppy manufacture, or a marketing ploy ("... infinity and beyond ...") akin to the guitar amps that 'go to 11'.  Plus we always noted the daily barometer reading in our optics lab notebook - I can't remember the experiment for context, but it wasn't just a token gesture. --195.137.93.171 (talk) 01:15, 8 March 2008 (UTC)
thread_title:  refractive index of 1 (e.g., air) 

message: We could do with a diagram for surface vertex, obvious as it may be. —Ben FrantzDale (talk) 20:55, 26 May 2008 (UTC)
thread_title:  Reqdiagram

message: In the subsection Cardinal point (optics)#Nodal points it said that "If the medium on both sides of the optical system is the same (e.g., air), then the front and rear nodal points coincide with the front and rear principal planes, respectively." I changed "planes" into "points" here, as having points coincide with planes sounds a bit like sorcery...
I did not change another statement in the same sentence, as it is not wrong but only incomplete. Fot the nodal points to coincide with the corresponding principal points, it is not necessary that the medium on either side is the same, but the refractive index. If the media are different but happen to have the same refractive index, the nodal points will also coincide with the corresponding principal points.
--HHahn (Talk) 12:57, 15 January 2010 (UTC)
thread_title:  If (...), nodal points coincide with principal ''points'' (not ''planes'') 

message: Your point about the incompleteness of the section on ideal optical systems is well taken.  I actually fell asleep before finishing this sorry I will fix it today.  TedEyeMD (talk) 13:19, 20 August 2010 (UTC)
replies: text: Non ideal focal systems certainly have front and rear focal points and principal points. It seems strange to assert that such systems don't have "cardinal points".--Srleffler (talk) 21:12, 22 August 2010 (UTC)
thread_title: Recent Changes August 20, 2010

message: The recommended file format for drawings and diagrams on Wikipedia is SVG. Inkscape is a free editor for these files. For more info, see How to draw a diagram with Inkscape. You upload the image at Wikipedia:Upload. Be sure to read and follow the prompts. When uploading images, you have to specify the license under which they are released. The upload page's prompts try to help you with this. For an image you drew yourself common choices would include the CCbySA license, or just releasing the image to the public domain.--Srleffler (talk) 06:25, 28 August 2010 (UTC)
thread_title: Drawings

message: There are numerous names for this addition to the gaussian model, IMO "Toepler points" is the most distinctive : 
* “Negative principal and nodal points. Negative principal (Toepler or symmetric) points are those conjugate points of a system for which the lateral magnification is – 1, i.e. at 2f in both object and images spaces from the (usual) principal points. The negative nodal points are points for which the angular magnification is unity and negative. They lie as far from the focal points as the ordinary nodal points (q.v.) but on opposite sides. Also known as Anti-principal and Anti-nodal points. See Centred optical systems.” [Gray, H.J, 1958, Dictionary of Physics. p.355]
AFAIK (from citation) they originate in Toepler, A. Bemerkungen ueber die Anzahl der Fundamentalpuncte eines beliebigen Systems von centrirten brechenden Kugelflaechen: Pogg. Ann., cxlii. (1871), pp.232-251. 
The main use of toepler points (AFAIK) is to actually measure the focal length of a lens, using the conjugate distances at unit magnification. This method is implicit in Newton's conjugate equation, but for a full description of the method (and his contraption "the focometer") see Thompson, S.P. 1912 The Trend of Geometrical Optics : "Proceedings of the Optical Convention 1912" p.297-307. 
--Redbobblehat (talk) 01:11, 11 February 2011 (UTC)
thread_title:  Toepler points 

message: Section: Principal planes and points
This section and the accompanying diagram “Various lens shapes...” do not explain the concept clearly. The diagram shows a random collection of arrows impinging on lenses from all directions, signifying nothing. I respectfully suggest that this section be rewritten with a more meaningful diagram.
--Prof. Bleent (talk) 14:41, 24 April 2015 (UTC)
replies: text: The arrows are meant to indicate the direction to each surface from its center of curvature. I agree that it's not a very good diagram.--Srleffler (talk) 04:08, 25 April 2015 (UTC)
thread_title:  Principal planes and points