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In this paper we show that the sensitivity function of a scalar feedback sl-stem must satisfy an integral constraint when the open-loop transfer function is strictly-proper and contains a time delay. The integral constraint is identical to the classical Bode sensitivity integral, s,hich holds provided the open-loop gain has greater than a one-pole rolloff. The design implications of the two constraints are somewhat different, however, and this difference is discussed. The relation between open-loop phase and a conflict explored.

We present a new method of calibrating adaptive optics systems that greatly reduces the required calibration time or, equivalently, improves the signal-to-noise ratio. The method uses an optimized actuation scheme with Hadamard patterns and does not scale with the number of actuators for a given noise level in the wavefront sensor channels. It is therefore highly desirable for high-order systems and/or adaptive secondary systems on a telescope without a Gregorian focal plane. In the latter case, the measurement noise is increased by the effects of the turbulent atmosphere when one is calibrating on a natural guide star.

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