Standard digital video displays use 640 x 480 (NTSC) or 512 x 512 (PAL) pixels to display a full screen image, while observers searching such images for small targets (or reading text) will typically operate with a screen subtense of 25 x 35 deg. Often, however, the region of interest in these images may be about 100 x 100 pixels in size, and so subtend only about 5 x 5 deg on a standard screen. In this case enlargement-that is, increasing the angular subtense-of the region of interest may well be appropriate. To obtain a larger viewing angle, the image must be zoomed, with some form of interpolation being used to generate new intermediate pixels. This paper reports on two experiments in which the effects of various methods of zooming on target acquisition are psychophysically evaluated. The results show that zooming generally enhances performance, but that for zooming factors greater than 2, smooth zooming techniques need to be used.