Cassegrain focus
E17448
Cassegrain focus is a telescope optical configuration in which light is reflected by a secondary mirror back through a hole in the primary mirror to form a compact, accessible focal point behind the primary.
All labels observed (8)
How this entity was disambiguated
This entity first appeared as the object of triple T147060 — resolving that mention is where its identity was fixed. The disambiguator weighed these candidate entities and picked the highlighted one (or “None”, minting a new entity). This is how homonymy is resolved: the same surface form can point to different entities.
NED1
Entity disambiguation (via context triple)
gpt-5-mini-2025-08-07
Target entity: Cassegrain focus Context triple: [Ritchey–Chrétien reflector, hasSecondaryMirrorPosition, Cassegrain focus]
-
A.
Ritchey–Chrétien reflector
A Ritchey–Chrétien reflector is a specialized type of reflecting telescope that uses hyperbolic primary and secondary mirrors to produce a wide, coma-free field of view ideal for professional astronomical imaging.
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B.
Warsaw Telescope
The Warsaw Telescope is a 1.3-meter optical telescope at Las Campanas Observatory in Chile, widely used for large-scale astronomical surveys such as the OGLE project.
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C.
du Pont Telescope
The du Pont Telescope is a 2.5-meter optical telescope at Chile’s Las Campanas Observatory used for a wide range of astronomical imaging and spectroscopic research.
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D.
Baade Telescope
The Baade Telescope is one of the twin 6.5-meter Magellan optical telescopes used for cutting-edge astronomical research in Chile.
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E.
Optica
Optica is a leading scientific society dedicated to advancing the study and application of optics and photonics worldwide.
- F. None of above. chosen
- G. Unsure - the case is ambiguous/there is not enough information to decide.
NED2
Entity disambiguation (via description)
gpt-5-mini-2025-08-07
Target entity: Cassegrain focus Target entity description: Cassegrain focus is a telescope optical configuration in which light is reflected by a secondary mirror back through a hole in the primary mirror to form a compact, accessible focal point behind the primary.
-
A.
Ritchey–Chrétien reflector
A Ritchey–Chrétien reflector is a specialized type of reflecting telescope that uses hyperbolic primary and secondary mirrors to produce a wide, coma-free field of view ideal for professional astronomical imaging.
-
B.
Warsaw Telescope
The Warsaw Telescope is a 1.3-meter optical telescope at Las Campanas Observatory in Chile, widely used for large-scale astronomical surveys such as the OGLE project.
-
C.
du Pont Telescope
The du Pont Telescope is a 2.5-meter optical telescope at Chile’s Las Campanas Observatory used for a wide range of astronomical imaging and spectroscopic research.
-
D.
Baade Telescope
The Baade Telescope is one of the twin 6.5-meter Magellan optical telescopes used for cutting-edge astronomical research in Chile.
-
E.
Optica
Optica is a leading scientific society dedicated to advancing the study and application of optics and photonics worldwide.
- F. None of above. chosen
Statements (44)
| Predicate | Object |
|---|---|
| instanceOf |
optical configuration
ⓘ
telescope focus configuration ⓘ |
| advantage |
accessible focal plane at back of telescope
ⓘ
compact telescope tube ⓘ convenient mounting of instruments at rear of telescope ⓘ long effective focal length in short physical tube ⓘ |
| benefitFor |
photometric instruments at rear focus
ⓘ
spectrographs mounted at rear focus ⓘ |
| commonIn |
catadioptric telescopes
ⓘ
reflecting telescopes ⓘ |
| componentOf |
Dall–Kirkham telescope design
ⓘ
Maksutov–Cassegrain telescope design ⓘ Ritchey–Chrétien reflector ⓘ
surface form:
Ritchey–Chrétien telescope design
Schmidt–Cassegrain telescope design ⓘ classical Cassegrain telescope design ⓘ |
| contrastWith |
Coudé focus
ⓘ
Newtonian focus ⓘ prime focus ⓘ |
| enables |
mounting of heavy cameras at rear cell
ⓘ
use of diagonal mirrors for comfortable viewing ⓘ |
| feature |
folded optical path
ⓘ
secondary mirror located near primary focus ⓘ |
| formsFocalPoint | behind the primary mirror ⓘ |
| hasFocalPlane | behind primary mirror cell ⓘ |
| historicalPeriod | 17th century origin ⓘ |
| lightPath |
light reflects from primary mirror to secondary mirror
ⓘ
light reflects from secondary mirror back through a central hole in the primary mirror ⓘ |
| locatedAt | back end of the telescope tube ⓘ |
| namedAfter | Laurent Cassegrain ⓘ |
| opticalEffect | increases effective focal ratio compared to primary mirror alone ⓘ |
| requires | central perforation in primary mirror ⓘ |
| requiresAlignment |
primary mirror
ⓘ
secondary mirror ⓘ |
| typicalUse |
amateur compound telescopes
ⓘ
medium to large professional telescopes ⓘ |
| usedFor |
astrophotography
ⓘ
instrument mounting in professional observatories ⓘ visual astronomy ⓘ |
| usedIn |
Cassegrain focus
self-linksurface differs
ⓘ
surface form:
Cassegrain telescope
|
| usedWith |
Barlow lenses
ⓘ
field flatteners ⓘ focal reducers ⓘ |
| usesPrimaryMirror | concave primary mirror ⓘ |
| usesSecondaryMirror | convex secondary mirror ⓘ |
How these facts were elicited
The pipeline generated the facts above by prompting gpt-5.1 with this entity's name + description and the instruction below.
Instruction
You are a knowledge base construction expert. Given a subject entity and a description of it, return factual statements that you know for the subject as a JSON list of dictionaries(triples), where keys must be "subject", "predicate" and "object". The number of facts may be very high, between 25 to 50 or more, for very popular subjects. For less popular subjects, the number of facts can be very low, like 5 or 10. # Requirements - If you don't know the subject at all, return an empty list. - If the subject is not a named entity, return an empty list. - Include at least one triple where predicate is "instanceOf". - Do not get too wordy. - Separate several objects into multiple triples with one object.
Input
Subject: Cassegrain focus Description of subject: Cassegrain focus is a telescope optical configuration in which light is reflected by a secondary mirror back through a hole in the primary mirror to form a compact, accessible focal point behind the primary.
Referenced by (9)
Full triples — surface form annotated when it differs from this entity's canonical label.
this entity surface form:
Cassegrain telescope
subject surface form:
GeMS
this entity surface form:
Cassegrain focus of Gemini South
subject surface form:
GSAOI
this entity surface form:
Cassegrain focus of Gemini South telescope
this entity surface form:
Cassegrain reflector
this entity surface form:
Cassegrain configuration
subject surface form:
GMOS-N
this entity surface form:
Cassegrain focus of Gemini North
this entity surface form:
Gemini North Cassegrain focus