This paper presents a novel technique for depth map estimation using a sequence of images acquired at varying focus. In depth map estimation noise, illumination variations and types of extracted features significantly affect the performance of a focus measure. This paper proposes the use of SUSAN operator, to extract features, because of its structure preserving noise filtering which plays a pivotal role in depth estimation of a scene. We introduce a new focus measure based on exponentially decaying function to use neighborhood information of an extracted feature point that assigns more weight to the closer pixel points. Experiments validate superior performance of our proposed algorithm in comparison to other well-documented methods.