Talk:Entrance pupil

This article is rated Start-class on Wikipedia's content assessment scale. It is of interest to the following WikiProjects:

Physics Mid‑importance This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.PhysicsWikipedia:WikiProject PhysicsTemplate:WikiProject Physicsphysics Mid This article has been rated as Mid-importance on the project's importance scale. Film: Filmmaking This article is within the scope of WikiProject Film. If you would like to participate, please visit the project page, where you can join the discussion and see lists of open tasks and regional and topical task forces. To use this banner, please refer to the documentation. To improve this article, please refer to the guidelines.FilmWikipedia:WikiProject FilmTemplate:WikiProject Filmfilm This article is supported by the Filmmaking task force.

It is requested that an optical diagram or diagrams be included in this article to improve its quality. Specific illustrations, plots or diagrams can be requested at the Graphic Lab. For more information, refer to discussion on this page and/or the listing at Wikipedia:Requested images.

I'd like to see a diagram showing a cross section of a lens with dotted lines going to the image of the aperture. —Ben FrantzDale (talk) 20:35, 27 July 2008 (UTC)[reply]

" When the optical system is physically rotated about its entrance pupil, the perspective geometry of its image does not change." -- this is false. the perspective geometry depends on the objects in the field of view, not on the figure of the optics. see for example the image at http://www.handprint.com/HP/WCL/IMG/LPR/pirenne.jpg, where the perspective geometry changes from central perspective to two point perspective simply by rotating a pinhole camera around the aperture. a correct formulation might be, "the projective geometry does not change ... " etc., but that is only the trivial claim that the optical path is not distorted by rotation. i have deleted the statement. Macevoy (talk) 15:29, 20 November 2010 (UTC)[reply]

I'm not sure whether your main point is correct, but if those two images are complete (not portions of larger images) they clearly do not differ merely by rotating the camera around the center of the aperture. If they did, the building could not be centered in both images.--Srleffler (talk) 05:43, 21 November 2010 (UTC)[reply]

Indeed. I too don't follow the initial question, but the example looks like two images with the same entrance pupil but different image planes. That is, they look like the same image up to distortion by a homography. —Ben FrantzDale (talk) 15:21, 22 November 2010 (UTC)[reply]

Tilt_(view_camera)#Back_tilt.2Fswing

Look at the vignetting - the camera back has been swung about a vertical axis.

--195.137.93.171 (talk) 09:58, 15 July 2013 (UTC)[reply]

i.e. the camera is not a pinhole camera as described above, and the rotation is not a rotation of the entire optical system about its entrance pupil.--Srleffler (talk) 01:28, 16 July 2013 (UTC)[reply]

I've been looking high and low for authoritative formulae for entrance pupil position and diameter but have come up dry with equations that match ZEMAX's. Its documentation claim it is using the paraxial position and diameter, yet doesn't give an equation and my attempts to compute those values paraxially fail to agree with ZEMAX in all but the trivial cases. What's a good reference for this stuff? —Ben FrantzDale (talk) 03:22, 10 April 2014 (UTC)[reply]

"The entrance pupil [...] , it lies behind the first optical surface of the system." The pupil can be located well beyond the first optical surface, which I agree includes the fact it is behind the first optical surface, but formulated this way the sentence can mislead some readers to interpret it as that "behind the first optical surface" is its sole location. I suggest to remove "it lies behind the first optical surface of the system." or reformulate it: "[...] it lies beyond the first optical surface [...]".Kogatana (talk) 00:22, 1 February 2016 (UTC)[reply]

The full sentence reads, "The entrance pupil is usually a virtual image: it lies behind the first optical surface of the system." I don't see how to make that clearer. The main point here is that the image is usually virtual. It doesn't matter whether the pupil is just behind the first surface, or far behind it. Behind first surface = virtual.--Srleffler (talk) 06:13, 1 February 2016 (UTC)[reply]

I removed the parenthetical "(as the location is where a chief ray or its extension, depending on whether the pupil is a real or virtual image, crosses the optical axis)" from the sentence about the role of the entrance pupil in a camera lens. This insertion made the sentence pretty much incomprehensible, and provides no value to the typical reader. You cannot assume the reader knows what a chief ray is, or what you mean by an "extension" or what a real or virtual image is. The article hasn't dealt with these topics at all up to that point in the text. Inserting technical details in parentheses in a less technical sentence does not work, in general.

Even for a reader who understands these things, the parenthetical comment doesn't actually explain anything. -- Srleffler (talk) 05:19, 6 October 2023 (UTC)[reply]