Experimental results of a new approach to the problem of sharpness function maximization in adaptive optics are presented. The main difference from the ordinary method is in the forming of signals, proportional to the components of the sharpness function gradient, in an optical processor. This solution is very effective in the case of low light intensity, when the quantum effects of registration are essential. It is shown that, in this particular case, the scheme of the adaptive system is similar to curvature sensing system. The experimental system provides a 32-zonal correction of the wavefront in real atmospheric conditions for objects of various forms.