Optics system is usually designed as such criteria that quantify optical performance are satisfied. However, this is not enough to maximize the performance of the imaging system overall. We think optical design in a broader sense should be required since we have been experienced a variety of design and development of real space optics. In this paper, we emphasize the required "optical design" is to design "characteristic values" of imaging system overall. For the mater, all the characteristic values need to be optimized dynamically and simultaneously, though optical design is a coupled problem with many optical, mechanical and thermal parameters. We suggest a practical design concept and method with some actual achievements, to which the proposed concept and method have been applied.