Optical performance of the 6.5-m off-axis new planetary telescope.

We describe an off-axis design for a 6.5-m astronomical telescope optimized for low scattered light and low emissivity. This is part of a new concept for an instrument that we call the New Planetary Telescope. We show how the geometric optical performance can equal that of an on-axis conventional telescope while the diffractive performance fundamentally surpasses conventional telescopes because of the absence of pupil obstruction. The decentered concept also allows wide-field and versatile instrumentation configurations that are not possible with more-conventional designs.