Hi. There's a question that has given some variables which am not sure how to compute to some previous lens/optics equations. These are not the actual variable values by the way. If a projector (square pixel SXGA) has a diagonal size of 5 mm which uses a screen of 1 m in which the distances vary from 1 to 2 m, how would the focal length range be calculated? Would you just calculate the focal length at 2 m, then 1 m then take these values away giving the range? And would the 1/f = 1 / u + 1 / v equation be used? It is the diagonal size and horizontal size that am not sure about. Thanks.