Collimation definition
Collimation. (“collinear” or 'in-line) means that all optical elements of a tele- scope are centered and square to its opti- cal axis and its imaging system. Lenses must be accurately spaced; primary and secondary mirrors must be accurately separated and aligned; focal reducers, field-flatteners, field correctors and fo- cus draw tubes require accurate align- ment (centered/moving parallel to the optical axis); additionally, filter holders need to be well-centered. NOTE: the mirror grinding error on the Hubble Space Telescope (HST) primary mirror (later fixed and subsequently serviced by four Space Shuttle crews) was off as lit- tle as 4 micrometers (microns) at the edge of a 2.4 meter (94.5 inch) mirror.
Examples of Collimation in a sentence
Parameter Single-energy CT Dual-energy CT kVp 120 80/140 dual Tube current (mA) 300 375 Scan time (s) 0.5 0.6 Pitch 0.984:1 0.984:1 Collimation (mm) 40 40 Image acquisition (mm) 64 × 0.625 64 × 0.625 Scan field of view Body large (50 cm) Body large (50 cm) Kernel ‘‘Bone’’ ‘‘Detail’’ ASIR 30% Not available CTDIvol (mGy) 11.35 12.92 ASIR, adaptive statistical iterative reconstruction; CTDIvol, volumetric CT dose index.