Assertion: newtonian telescope's mirror | /r/HasProperty | large
Facets:
value: for wide-field photo
type: PURPOSE
value: generally
type: DEGREE
Source sentences:
text: To minimize harmful diffraction effects, the secondary, or diagonal, mirror is generally only large enough to let the central portion of the focal plane receive light from the whole primary mirror.
text: On the other hand, a secondary mirror that is too large will also adversely affect the telescope’s performance.
text: For wide-field photo, the secondary mirror should be large enough to let the whole film frame be fully illuminated, but for visual use, a secondary size of no more than 20-25 % of the primary mirror diameter is commonly preferred, in order to minimize unwanted diffraction effects.