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

[roshan2004]

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......

 

[Dadface]

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.

 

[Creator]

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

...

 

[Andy Resnick]

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.

 

[roshan2004]

I am still confused about optical axis and off axis.Are these terms same or different?

 

[Dadface]

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.