A new variation on an older optical form, the three-mirror anastigmat, has been designed. Using the form off-axis in both aperture and field allows for an unobscured system that can be packaged in a small volume without any auxiliary folding mirrors. Significant extensions both in speed and in field of view have been made. Two examples are shown, i. e. , (a) a 3° x 6° field of view, f/2.6 design with 0.17 mrad resolution, and (b) a 0.5° x 10° field of view f/3.0 design with approximately 0.10-mrad resolution. Both designs have flat focal surfaces and good shielding from stray radiation. The performance of these two systems has been enhanced by tilting and decentering the mirrors by small amounts during the final optimization stages. This technique, which makes it possible to put the conic surfaces to the best optical use, is applicable because of the off-axis nature of the design.