Just tried one of those page bookmark fresnels after reading about this experiment over on mtbs3D, must admit the groove pitch is finer than I expected. Focal length is a bit long (200mm) though (=long box, small FOV). 120mm would probably be good. edit: the lens i tried was this one , not the one referred to in the mtbs postNot happy with the 2.5x headband lens solution after proper flight testing: FOV not wide enough (for me) and more crucially eyes started feeling strained after 10mins or so.However it spurred me into figuring out how to mod my RCV922's and now life is SWEET