My understanding of this is that there are simply two lenses. The first would invert the image and the second would invert it again making it rightside up. And I hate to disagree with authority but I have used these things mounted on body caps and on lens caps to make surreal fisheye images. Don Gregory Fraser wrote: > Thanks for the answers but I needed a little more clarification and I found > it at this web site. > http://webphysics.ph.msstate.edu/javamirror/ipmj/java/dlens/. This applet > explains your mysterious remark about this type of lens not forming an image > on film Andy. > > Thanks Bob and Andy. > > Greg > > > -----Original Message----- > > From: ADavidhazy [mailto:ANDPPH@ritvax.isc.rit.edu] > > > > > Does anybody know why the image in an apartment door > > peep-hole is not > > > inverted? Is there a tiny little penta-prism in there? > > > > The real short answer is that the image is formed by a > > negative lens system and > > is a virtual image. Such lenses form right side up and > > unreversed virtual > > images of subjects. These virtual images can be seen and > > photographed but can > > not themselves make an impression on photographic film (since they are > > "virtual" ... not "real" as images made by positive lenses are). > > > > Andy > > > > There is no little penta prism in there. The construction is similar to a > "spy glass" (Galilean telescope) in that it doesn't developed an image, you > just look through it backwards (optically speaking). Look at it like a wide > angle adaptor similar to those built for the normal lens of a cheap camera - > only for your eye. > > Regards, > Bob.. -- ============================================================ Don Roberts * Bittersweet Productions * Iowa City, IA * * And the Devil whispered behind the leaves, "It's pretty, but is it Art?". -- Rudyard Kipling ============================================================
