What specific physical characteristic of reflecting telescopes introduces a measurable reduction in image contrast compared to a pure refractor design?

Answer

The necessity of a smaller secondary mirror placed in the light path

Reflectors use a secondary mirror to redirect light to the eyepiece. This component obstructs a tiny fraction of incoming light and slightly reduces the overall image contrast.

What specific physical characteristic of reflecting telescopes introduces a measurable reduction in image contrast compared to a pure refractor design?

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