Eyepieces and Binoculars Flashcards
Also known as an ocular lens, it takes in light; and magnifies the image.
Eyepiece
If the principal focus lies in front of the field lens, then the eyepiece is
positive
If the principal focus lies between the field lens and the exit eye lens, then the eyepiece is
negative
The “power” of an eyepiece. Refers to the distance of the lens to the focal point.
Focal Length
Refers to how much of the sky is visible
Field of View
Refers to the field of view seen through the telescope
Apparent FOV
Refers to the FOV with respect to the entire night sky
True FOV
The width of the light leaving the eyepiece
Exit Pupil
The distance between the eye and the ocular lens for a comfortable view of the full FOV
Eye relief
A negative eyepiece who has the simplest design, consists of two plano-convex lenses, narrow FOV, prone to aberration,
Huygens’ Eyepiece
A positive eyepiece that has two plano-convex lenses facing each other, reduced aberration, better eye relief, and image clarity
Ramsden’s Eyepiece
A positive eyepiece that uses two sets of doublet lenses. offers a clearer view of celestial objects, reduced aberrations, moderate FOV, ideal for deep sky observations however has an uncomfortable eye relief
Plossl’s Eyepiece
Positive eyepice; Known as the achromatic Ramsden, utilizes an achromatic doublet for its 1st lens, better color correction, wider FOV, and is prone to internal reflections.
Kellner’s Eyepiece
Optimized for an ultra-wide FOV with good correction for astigmatism and other aberrations. Utilizes a negative doublet field lens with increased magnifying power, with multiple lenses to attain a long focal length.
Nagler’s Eyepiece
Narrow FOV, positive focus, optimized for minimal distortion, high contrast, and good color correction using a four-element design with a cemented convex-convex triplet achromatic lens
Orthoscopic eyepiece
Extended version of Plossl’s design, 5-eyepiece which consists of 2 doublets with a simple lens in between, has a positive focus
Erfle’s Eyepiece
Better depth perception, wider FOV, affordable, useful for wide-field deep-sky observations
Porro Prism Binoculars
Compact and lightweight, less depth perception and narrower FOV, and is not often used in astronomy
Roof Prism Binoculars
