If you had the camera set to AF then i am not suprised it didn`t work. Was there a lot of snow about. Reflections mess up the AF system. Your camera doesn`t require air to operate and therfore the moderately thin air at 4,300 will not effect it. However the tempreture will make a difference on the optics. James Grove On the great bug hunt - Beta testing Windows 2000 JPG Photography Pumori `99 M.Blanc `96 Elbrus `95 http://www.jpgservices.ndirect.co.uk Fax : 0121 602 0857 >> When I was in Bolivia last month, my 85/1.4D would not focus to >> infinity (using my F5). This happened at 4,300 m altitude. Can the >> thinnner air and its (very slightly) different optical properties >> explain this?