  In the present paper we consider quantitative estimation of the tolerances
widening in optical systems with curved detectors. The gain in image quality
allows to loosen the margins for manufacturing and assembling errors. On
another hand, the requirements for the detector shape and positioning become
more tight. We demonstrate both of the effects on example of two optical
designs. The first one is a rotationally-symmetrical lens with focal length of
25 mm, f-ratio of 3.5 and field of view equal to 72$^\circ$, working in the
visible domain. The second design is a three-mirror anastigmat telescope with
focal length of 250 mm, f-ratio of 2.0 and field of view equal to $4^\circ
\times 4^\circ$. In both of the cases use of curved detectors allow to increase
the image quality and substantially decrease the requirements for manufacturing
precision
