It is a Galilean telescope. The objective is a converging lens and the eyepiece is a diverging lens. It must be a wide angle version, however and have an objective with a very short focal length. If I remember rightly the magnification is the ratio of the focal length of the objective over the focal length of the eyepiece, so if the objective has a shorter focus length than the eyepiece then it will make a smaller image, but wide angle. Chris Strevens http://www.chrisscrazyideas.co.uk http://www.chrissimageshop.co.uk http://www.chrisssoftwareshop.co.uk mailto:nimbo@ukonline.co.uk -----Original Message----- From: owner-photoforum@listserver.isc.rit.edu [mailto:owner-photoforum@listserver.isc.rit.edu]On Behalf Of Don Roberts Sent: 06 May 2002 19:11 To: List for Photo/Imaging Educators - Professionals - Students Subject: Re: Not really photography but optics related 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 ============================================================
