Great, informative review, Clive.

Early in the review you mention the star diagonal prisms started waning in popularity because they do not work well with fast optical systems. But then you said nothing more about the performance of these diagonals with respect to different focal ratios. What is the fastest focal ratio that prisms can be effectively used with?

Would a star diagonal prism help with CA correction in an achromat, slower optical system?

Thanks.