and f the focal length is negative. Let F be the principal focus of the lens BAG, fig. 92.Take a point F on the axis to the right of the lens and at adistance from the lens equal to its focal length /, so that AFis equal to AF. Case (1). The object is at a, distance, less thanf. Let PQ be an object… … Fig. 92. will be found that FR and TA can be produced backwards tomeet; let them meet at p. Then p is a virtual image of P.Draw pq perpendicular to the axis; pq is the image of PQand it is virtual, erect and magnified. This will be found tobe the case whenever PQ lies between A and F. Case (2). The…
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