The collimator
The preliminary design of the collimator was a Petzval lens with the very remote re-imaged pupil.
This preliminary design was optimised between the telescope and the three cameras simultaneously. The resulting lens was a compromise between the requirements for imaging quality, through put and the manufacturers requirements.
It has to attempt to keep the effects of chromatic aberration between 320nm and 900nm within reasonable bounds whilst transmitting well in the u’ band. This restricts the available glasses considerably and only N-PSK3, LLF1 and CaF2 were used in the four element design.