[PeterHA (Peter)]

All,
Some designs of refracting scopes (Zeiss) take a glass path like a prism star diagonal into consideration when the optics are designed.
Other designs are optimised to perform best with mirros star diagonals.

Does anyone know what Takahashi bases it's optical calculations for refractors on.
Are the Sky90, TS-102 and 120 better used with prism diagonals or with mirror diagonals?

Thanks for any help,

Regards,

Peter