The Gregorian telescope employs a concave secondary mirror that reflects the image back through a hole in the primary mirror.

Gallery
Tutorial
TRAIL: Webel SysML Parsing Analysis example: Optical telescopes from Wikipedia: Structure and port-based light flow model
Section
Topic level
INTERMEDIATE
UML keywords
Generalization
Property::redefinedProperty
Property::subsettedProperty
SysML keywords
Block
Keywords
Slide kind
SysML Block Definition Diagram (BDD)
The target snippets are:
Wikipedia: 'The Gregorian telescope ... employs a concave secondary mirror that reflects the image back through a hole in the primary mirror. This produces an upright image'
Wikipedia: 'The Gregorian telescope consists of two concave mirrors; the primary mirror (a concave paraboloid) collects the light and brings it to a focus before the secondary mirror (a concave ellipsoid) where it is reflected back through a hole in the centre ...'
Click on the image to view it full size
The diagram also includes an embedded captioned figure:
Wikipedia: 'Diagram of the lightpath through a Gregorian telescope.'
Image author: Krishnavedala; Copyright licence: Creative Commons CC BY-SA 4.0
The following in fact describes a "classic" Gregorian reflector with a concave parabolic mirror:
The Gregorian telescope consists of two concave mirrors; the primary mirror (a concave paraboloid) collects the light and brings it to a focus before the secondary mirror (a concave ellipsoid)
Modern large Gregorian telescopes (such as the Giant Magellan Telescope) are aplanatic, and instead use an ellipsoid primary as explained at telescope-optics.net. Thus there is an intermediate abstract block GregorianReflector (which always has an ellipsoid secondary) and specific variants ClassicGregorianReflector and AplanaticGregorianReflector with different primary mirrors.

However, there is a very important property of the primary; it has a hole in it! From the point of view of the light flow model, light flows into the spatial region of the hole in the primary mirror then out of it, represented by the abstraction HoledMirror with additional ports for iHoleLight and oHoleLight. The ClassicGregorianReflector has a HoledParabolicMirror as primary and the AplanaticGregorianReflector has a HoledEllipsoidMirror as primary.

Up next
The Newtonian telescope has flat secondary mirror and a paraboloid or spherical primary mirror
Notes
[CAPABILITY, FEATURE, TOOL]{INFORMATIVE} MagicDraw/Cameo supports embedding images in diagrams
[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.
Snippets (quotes/extracts)
 The Gregorian telescope ... employs a concave secondary mirror that reflects the image back through a hole in the primary mirror. This produces an upright image
 There are several large modern telescopes that use a Gregorian configuration such as the Vatican Advanced Technology Telescope, the Magellan telescopes, the Large Binocular Telescope, and the Giant Magellan Telescope.
 The Gregorian telescope consists of two concave mirrors; the primary mirror (a concave paraboloid) collects the light and brings it to a focus before the secondary mirror (a concave ellipsoid) where it is reflected back through a hole in the centre ...
 Diagram of the lightpath through a Gregorian telescope.
 The overall focal ratio of the complete telescope will be f/8 and the optical prescription is an aplanatic Gregorian telescope.
Visit also
Visit also (backlinks)
Related slides (includes other tutorials)
Related slides (backlinks, includes other tutorials)