Considerations Detector Matching and Baffling

At any focal position, the distance measured along the optical axis within which the images remain acceptably defined is referred to as the depth of focus. The detector should be adjusted to the most sharply focused position in this region however, it is more common to adjust the focus (e.g., by moving the secondary) to sharpen the images at the detector. Certain instruments containing reimaging 

TABLE II Basic Image Aberrations Occurring in Telescopes 

Spherical aberration Light focuses at different places along the optical axis as a function of radial position in the aperture. 

Coma Image size (magnification) varies with radial position in the focal region. Off-axis flaring. 

Field curvature Qff-axis images are not focused on the ideal surface, usually a plane. 

---