In this contribution an Atmospheric Dispersion Corrector (ADC) developed for the FastCam project is presented. FastCam is a system based on 'lucky imaging' techniques for high spatial resolution, developed at the Instituto de Astrofisica de Canarias (IAC). The use of a system to correct the atmosphere's effects is necessary to obtain a good optics quality in order to satisfy science requirements. Two alternatives for an atmospheric dispersion corrector for the instrument FastCam have been studied. One ADC has been designed to be implemented and intended to correct that atmospherical effect at the 4.2m William Herschel Telescope (Roque de los Muchachos Observatory, La Palma) for zenithal distances larger than 15 degrees, mainly in I band. The excellent resolution reached with FastCam makes this effect to distort the images. This work presents the design of an ADC as a pre-focus system of two prisms with variable separation in order to compensate the dispersion until zenithal distances of 50°. Both are placed in a rotator to align the orientation of zenithal distorsion. The results for this ADC has been tested in lab, and in May 2008, at the WHT; our next step will be to use it at the 10.4m Gran Telescopio Canarias (GTC). Although the system is still under the final stages of its development, we want to implement it to the new instruments for high spatial resolution.