Question:
'Circle of least confusion' refers to which one of the following defects occurring in images formed by mirrors or lenses?
'Circle of least confusion' refers to which one of the following defects occurring in images formed by mirrors or lenses?
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Think of the term logically: when an image cannot form a perfect single-point focus due to spherical structural curves, the "circle of least confusion" is literally the spot where the beam is most concentrated and least "confused" or blurred.
Updated On: Jun 12, 2026
- Distortion
- Coma
- Astigmatism
- Spherical aberration
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Question:
The question asks us to identify which optical monochromatic aberration or defect in mirrors/lenses is physically associated with the concept known as the 'circle of least confusion'.
Step 2: Key Formula or Approach:
Spherical aberration occurs because marginal rays (passing near the edge of a lens/mirror) and paraxial rays (passing near the central axis) focus at different longitudinal spatial points along the principal axis. This produces a blurred region rather than a sharp point focus.
Step 3: Detailed Explanation:
Because of the variance in focal points between the marginal and paraxial light paths, a circular cross-section of the converging beam varies in size along the axis.
At a specific longitudinal position between the two focal planes, the beam cross-section forms a circle with a minimum diameter.
This minimum cross-sectional circle of the focused beam represents the position where the image is least blurred and shows the maximum possible clarity.
In optics theory, this minimal circle of distortion is explicitly defined as the
circle of least confusion, and it serves as the best possible focus compromise when spherical aberration is present.
Step 4: Final Answer:
The circle of least confusion refers directly to spherical aberration, which matches option (D).
The question asks us to identify which optical monochromatic aberration or defect in mirrors/lenses is physically associated with the concept known as the 'circle of least confusion'.
Step 2: Key Formula or Approach:
Spherical aberration occurs because marginal rays (passing near the edge of a lens/mirror) and paraxial rays (passing near the central axis) focus at different longitudinal spatial points along the principal axis. This produces a blurred region rather than a sharp point focus.
Step 3: Detailed Explanation:
Because of the variance in focal points between the marginal and paraxial light paths, a circular cross-section of the converging beam varies in size along the axis.
At a specific longitudinal position between the two focal planes, the beam cross-section forms a circle with a minimum diameter.
This minimum cross-sectional circle of the focused beam represents the position where the image is least blurred and shows the maximum possible clarity.
In optics theory, this minimal circle of distortion is explicitly defined as the
circle of least confusion, and it serves as the best possible focus compromise when spherical aberration is present.
Step 4: Final Answer:
The circle of least confusion refers directly to spherical aberration, which matches option (D).
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