Controlling Aberrations – Practical Measures in Survey Telescopes Which of the following statements correctly describe methods used to control spherical and chromatic aberrations in the optics of surveying instruments?

Introduction / Context:
Aberrations degrade image sharpness and color fidelity. Survey telescopes must deliver crisp cross-hair coincidence on fine targets, so designers employ simple yet effective optical strategies to control spherical and chromatic aberrations while keeping instruments rugged and compact.

Given Data / Assumptions:

• Standard refracting telescope architecture (objective + eyepiece).
• Desire to limit spherical blur and chromatic fringing.
• Use of classical eyepiece designs compatible with reticles.

Concept / Approach:

Spherical aberration arises when peripheral rays focus at different points than paraxial rays. Narrowing the aperture cuts peripheral rays (option a) and helps immediately. More powerfully, using a compound lens system (option b) allows designers to balance ray paths. Objectives are typically achromats—a convex lens cemented to a concave lens of different glass types—to reduce both spherical and chromatic errors (option c). Eyepieces like Huygens and Ramsden employ two plano-convex elements separated by a small gap, arranged to minimize aberrations while accommodating a reticle (option d).

Step-by-Step Solution:

Verification / Alternative check:

Optics texts and instrument manuals illustrate these exact configurations for survey telescopes to achieve adequate field performance with modest complexity.

Why Other Options Are Wrong:

Each statement is accurate; therefore, none of them should be rejected individually, making 'All of the above' correct.

Common Pitfalls:

Assuming eyepieces are single lenses; overlooking that aperture reduction also reduces brightness—designs balance sharpness and light.

Final Answer:

All of the above