DIGITAL PHOTOGRAMMETRIC ANALYSIS OF STEREO IMAGES OBTAINED BY ZOOM LENSES By Dr. Farrag Ali FARRAG (farrag@acc.aun.eun.eg) Assistant Professor, Civil Engineering Dept. Faculty of Engineering Assiut University, Assiut, Egypt Dr. Mostafa Abdel-Bary EBRAHIM (Ebrahim@acc.aun.eun.eg ) Lecturer, Civil Engineering Dept. Faculty of Engineering Assiut University, Assiut, Egypt ABSTRACT Close range photogrammetry has proved that it is one of the most important 3D measurements techniques. The dimension of the objects to be photographed or the conditions of the surrounding place sometimes force the photographer to use zoom lenses in order to obtain clear and geometrically accepted photographs. The main objective of this research is to find out the effect of using zoom lens (by different adjustment techniques) on the accuracy of digital close range photogrammetric applications compared with the standard lenses. A theoretical study was carried out using CAD environment in order to model the expected accuracy in case of using standard lenses under an ideal conditions (free error images). Then a number of field tests were carried out using single lenses and zoom lenses in order to find out the practicality of using zoom lenses. Two single lenses were practically examined, the first is normal angle lens (f=50mm) and the second is narrow angle lens (f=135mm). The zoom lens was practically tested at different focal length varied from 50 mm up to 150 mm. The processing of data was carried out digitally in order to gain flexibility and accuracy. The photogrammetric adjustment was carried out in two modes, with and without incorporation of additional parameters. The results of this study showed that the use of good zoom lenses has a minor effect compared with single lenses of the same focal length. Also the results of this study investigated the importance of incorporating the additional parameters during the photogrammetric solution in case of using non-metric lens especially with zoom lenses. KEY WORDS: Digital Close-Range Photogrammetry, Zoom lenses, Non-Metric Camera, Accuracy Analysis. INTRODUCTION Close range photogrammetry has been proved to be one of the precise and fast 3D measurements techniques in both, the classic applications such as the industrial, engineering, and architectural applications and in modern applications, such as GIS and mobile mapping. The dimensions of the objects to be photographed or the conditions of the surrounding place usually force the photographer to use zoom lenses in order to obtain clear and geometrically accepted photographs. In order to obtain accurate 3D information from 2D images during the potogrammetric processing, one needs the