Reflective triplet optical form with external rear aperture stop for cold shielding

An all-reflecting, non-relayed optical system having an optical axis comprising:

• an off-axis concave primary mirror configured to receive radiation from objects;
• an off-axis convex secondary mirror configured to receive the radiation reflected from the primary mirror;
• an off-axis concave tertiary mirror configured to receive the radiation reflected from the secondary mirror;
• a focal plane configured to receive the radiation reflected from the tertiary mirror and for forming an image of the objects, wherein an aperture stop of the optical system is located between the tertiary mirror and the focal plane;
• and
• a cold cavity having a window coincident with the aperture stop, the cold cavity enclosing space up to and between the aperture stop and the focal plane,
• wherein the optical system is non-relayed.

A method of imaging objects in an all-reflecting, non-relayed optical system having an optical axis, the method comprising:

• reflecting radiation received from objects in a first direction relative to the optical axis utilizing a primary mirror;
• reflecting the radiation received from the first mirror in a second direction relative to the optical axis utilizing a secondary mirror;
• reflecting the radiation received from the secondary mirror in a third direction relative to the optical axis utilizing a tertiary mirror;
• forming an image of the distant objects utilizing an image plane, wherein an aperture stop of the optical system is located between the tertiary mirror and the focal plane;
• and
• providing cold shielding up to and between the aperture stop and the focal plan,
• wherein the optical system is non-relayed.