The initial aim of the work presented in this thesis was to increase the soft x-ray quantum detection efficiency of a tandem-pair microchannel plate detector by the use of a CsI deposition photocathode. This aim was achieved. The coating technique and initial measurements are presented herein. After showing the use of such photocathodes, we investigated their stability and reproducibility. The effects of storage in poor vacuum, high vacuum and desiccated air are presented as is the stability of CsI photocathodes under prolonged X-ray bombardment. One consequence of the use of CsI is that a degree of energy resolution can be conferred upon a microchannel plate detector. We present further research in this field, including measurements performed on detectors with eight micron diameter channels. A feature of microchannel plate operation that is undesirable is the phenomenon of gain degradation. We performed a series of lifetests on a number of microchannel plate detectors.