The problem of correlation wavefront sensing using an extended arbitrarily structured target as a light source is studied. The principle of extended target correlation wavefront sensing employing an intensity-transmittance type of mask is analyzed. The problems of simulation and selection of a target in laboratory experiments are discussed. The methods of generating the mask images from the target structure and of preparing the experimental masks from the mask images are presented. Typical results of the mask images generated by processing the target image are given. The preliminary experiment on the extended target wavefront sensing using the intensity-transmittance type mask are made. The effects of two different intensity-type masks on wavefront sensing are compared. Experimental results that are in agreement with the theory are obtained.