A method of field flattening using a bundle of transparent fibers is studied in some detail. Different optical arrangements of field flatteners are proposed and their relative merits are investigated. An improved type of field flattener which also acts as two Fresnel lenses has been developed and the term “Fresnel lens type field flattener” is proposed to denote it. A gain in image quality and weight of a flight periscope system seems possible by the use of such a field flattener. The methods of alignment and fabrication of these field flatteners are described. Working models using 200 μ diameter glass fibers have been constructed which demonstrate the expected gain.