Optics: real images vs virtual images and focus points

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Tutorial
TRAIL: Webel SysML Parsing Analysis example: Optical telescopes from Wikipedia: Structure and port-based light flow model
Section
Topic level
INTERMEDIATE
SysML keywords
Block
Keywords
Slide kind
SysML Block Definition Diagram (BDD)
The main target snippets are:
Wikipedia: 'A real image is the collection of focus points actually made by converging rays, while a virtual image is the collection of focus points made by extensions of diverging rays. '
Wikipedia: 'A real image ... is an image which is located in the plane of convergence for the light rays that originate from a given object.'
Wikipedia: 'a virtual image is found by tracing real rays that emerge from an optical device (lens, mirror, or some combination) backward to perceived or apparent origins of ray divergences.'
Wikipedia: 'Because the rays never really converge, a virtual image cannot be projected onto a screen. In contrast, a real image can be projected on the screen as it is formed by rays that converge on a real location. '
Wikipedia: 'In ray diagrams ... real rays of light are always represented by full, solid lines; perceived or extrapolated rays of light are represented by dashed lines.'
Wikipedia: 'A real image occurs where rays converge, whereas a virtual image occurs where rays only appear to diverge.'
Click on the image to view it full size
Embedded figures are used here to reinforce understanding:
Wikipedia: 'Top: The formation of a real image using a convex lens. Bottom: The formation of a real image using a concave mirror. In both diagrams, f is the focal point, O is the object, and I is the image.'
Image author: Krishnavedala ; Copyright licence: Creative Commons CC0 1.0 Universal Public Domain Dedication
Wikipedia: 'Top: The formation of a virtual image using a diverging lens. Bottom: The formation of a virtual image using a convex mirror. In both diagrams, f is the focal point, O is the object and I is the image, shown in grey ...'
Image author: Krishnavedala ; Copyright licence: Creative Commons CC0 1.0 Universal Public Domain Dedication

The block Image gets mutually exclusive value properties isReal:Boolean and isVirtual:Boolean, where the main image:OpticalImage of the OpticalTelescope has a constraint {isReal} and the image viewedImage:OpticalImage has a constraint {isVirtual} (this will be justified by some later snippets).

The following new elements in the model help tie together the observed object, the light rays, and the image. From the point of view of an «optical» system an observed Object is composed of one or more point:ObjectLightPoint[1..*], each of which may be associated with one or more lightRay:LightRay[1..*]. An Image is now defined as having a 1-to-1 Association with an Object (so 'object' is not used here in the sense of many "objects" in a view, i.e. it means an the entire image view, not a star in an image of a cluster).

We are told that:

Wikipedia: 'In optics, an image is defined as the collection of focus points of light rays coming from an object.'
Wikipedia: 'In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge.'

So OpticalImage has one or more focusPoint:FocusPoint[1..*], which in turn has one or more lightRay:LightRay[1..*]. There are some constraints in a concise "mock OCL" (without full use of OCL forAll or forAny) to say that the lightPoint (on the object) of a lightRay of a FocusPoint must be the same as that of the FocusPoint, and that the 'object' of the OpticalImage must be the same as that of the 'lightPoint' of every 'focusPoint'.

We are warned that:

Wikipedia: 'Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by aberrations of the imaging optics.'

This is for now represented by a reference property blurCircle:BlurCircle on FocusPoint.

Up next
An object infinitely far from the optical system forms an image at the rear focal plane
Notes
[DISPLAY, STYLE, TIP]{SUGGESTED} Webel Parsing Analysis: If the dashed-line "anchors" from your «snippet» ElementGroup symbols to elicited elements make a «pa» Parsing Analysis Diagram (PAD) too hard to read, try making them light grey using symbol properties.
[POLICY, STYLE]{STRICT} Webel «pa» Parsing Analysis Diagrams (PADs) are "scratchpads" used to elicit model elements traceably from text Snippets (extracts from source Documents). While BDDs are a good initial choice, most types of SysML diagram can be used as a «pa» diagram.
[POLICY, STYLE]{STRICT} Webel Parsing Analysis «pa» diagrams are NOT intended as final presentation diagrams! They serve merely to traceably elicit model elements, which may then be shown in other (typically much tidier) presentation diagrams elsewhere.
[CAPABILITY, FEATURE, TOOL]{INFORMATIVE} MagicDraw/Cameo supports embedding images in diagrams
Snippets (quotes/extracts)
 In optics, an image is defined as the collection of focus points of light rays coming from an object.
 A real image is the collection of focus points actually made by converging rays, while a virtual image is the collection of focus points made by extensions of diverging rays.
 A real image occurs where rays converge, whereas a virtual image occurs where rays only appear to diverge.
 a virtual image is found by tracing real rays that emerge from an optical device (lens, mirror, or some combination) backward to perceived or apparent origins of ray divergences.
 Because the rays never really converge, a virtual image cannot be projected onto a screen. In contrast, a real image can be projected on the screen as it is formed by rays that converge on a real location.
 A real image ... is an image which is located in the plane of convergence for the light rays that originate from a given object.
 In ray diagrams ... real rays of light are always represented by full, solid lines; perceived or extrapolated rays of light are represented by dashed lines.
 In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge.
 Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by aberrations of the imaging optics.
 Top: The formation of a real image using a convex lens. Bottom: The formation of a real image using a concave mirror. In both diagrams, f is the focal point, O is the object, and I is the image.
 Top: The formation of a virtual image using a diverging lens. Bottom: The formation of a virtual image using a convex mirror. In both diagrams, f is the focal point, O is the object and I is the image, shown in grey ...
Visit also
Visit also (backlinks)
Related slides (includes other tutorials)
Related slides (backlinks, includes other tutorials)
External links
https://en.wikipedia.org/wiki/File:Real_image.svg
https://en.wikipedia.org/wiki/Virtual_image#/media/File:Virtual_image.svg