Off-axis Explained: What it is & How it Contributes to Comatic Aberration

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Discussion Overview

The discussion centers around the concept of "off-axis" in relation to comatic aberration, exploring its definition, implications, and how it contributes to the phenomenon. Participants seek clarification on the terms "optical axis" and "off-axis," as well as diagrammatic representations of these concepts.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant seeks to understand the term "off-axis" as it relates to comatic aberration and requests a diagrammatic explanation.
  • Another participant suggests that "off-axis" refers to a line parallel to the principal axis but positioned above or below it, or at an angle to the principal axis.
  • A different participant clarifies that the "optical axis" is an imaginary line defining the centerline of the optical system, and notes that coma is zero on this axis.
  • Some participants express confusion about the relationship between the terms "optical axis" and "off-axis," questioning whether they are the same or different.
  • It is noted that rays traveling along the optical axis are not deviated, while off-axis rays are those that do not travel along this line.

Areas of Agreement / Disagreement

Participants express confusion regarding the definitions and relationships between "optical axis" and "off-axis," indicating that multiple competing views remain and the discussion is unresolved.

Contextual Notes

Some participants have not reached a consensus on the definitions of "optical axis" and "off-axis," and there are unresolved questions about their implications for understanding comatic aberration.

roshan2004
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As I was studying Comatic aberration, in the definition of coma the word off-axis is used which I couldnot understand. What does off axis means? and how does it contribute to the comatic aberration? I also want to know about off axis diagrammatically.Thanks......
 
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By "axis" I assume you mean principle axis this beng a line drawn at 90 degrees through the centre of the lens/mirror.Off axis therefore would refer to a line parallel to the principle axis but above or below it or it could refer to a line at an angle to the principle axis.
 
Last edited:
roshan2004 said:
As I was studying Comatic aberration, in the definition of coma the word off-axis is used which I couldnot understand. What does off axis means? and how does it contribute to the comatic aberration? I also want to know about off axis diagrammatically.Thanks......

Diagram and explanation...

http://www.telescope-optics.net/coma.htm

...
 
roshan2004 said:
As I was studying Comatic aberration, in the definition of coma the word off-axis is used which I couldnot understand. What does off axis means? and how does it contribute to the comatic aberration? I also want to know about off axis diagrammatically.Thanks......

As Creator's posted link states, the 'axis' refers to the "optical axis", which is an imaginary line that defines the centerline of the optical system. For rotationally symmetric elements (round lenses, etc), the optical axis passes through the center of each element.

Coma is an aberration that is identically zero on the optical axis.
 
I am still confused about optical axis and off axis.Are these terms same or different?
 
roshan2004 said:
I am still confused about optical axis and off axis.Are these terms same or different?

Principle axis,optical axis or just axis call it what you will,it is the line that passes symmetrically(at 90 degrees)through the centre of the lens/mirror.A ray passing through the optical axis of a lens will be refracted but it will not be deviated through an angle or laterally displaced,it will pass straight through.A ray traveling along the optical axis of a curved mirror will reflect back along the optical axis.Off axis refers to any ray that is not traveling along the optical axis.
 

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