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.
Aliases (3)
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
→
surface form: "Cassegrain telescope"
|
| usedWith |
Barlow lenses
→
field flatteners → focal reducers → |
| usesPrimaryMirror | concave primary mirror → |
| usesSecondaryMirror | convex secondary mirror → |
Referenced by (5)
Full triples — surface form annotated when it differs from this entity's canonical label.
subject surface form: "GSAOI"
this entity surface form: "Cassegrain focus of Gemini South telescope"
subject surface form: "GeMS"
this entity surface form: "Cassegrain focus of Gemini South"
this entity surface form: "Cassegrain telescope"