That is very interesting Andy. I had forgotton or did not know! It does mean that images made with a 400mm lens on 35 mm enlarged to 20 x 16 inches shoud be viewed from 18x25/35 x 0.4 meters or 7 meters. That is 20 feet (all rough mental arithemetic as I do not have a calculator here unless there is on on this pc). I do not think that happens very often as we take long lens images for their special effect as we do wide angle. Has anyone seen the 3 D TV yet? I notice some TV stations show images that are photos and the viewer is taken for a walk through the image with the changes in perpective and vignetting that you would expect from a 3 D camera. Roll up 3 D TV! I wonder if there will be a 3D camera, I have seen one based on a "bees eye" lens. I do know about the twin lens type, this one has about 10,000 lenticules. It has been known for at least 8000 years and Jesus mentions them in his parable of the lattice. I think the 3 D TV system is to be called "lattice TV". Chris. >This has been posted in the past on this list but did not include the >reference >to digital cameras and their image sensors. So here it is again for what it >is >worth. > > A Brief Comment on Perspective > >In order to view a picture with the proper perspective, we wish to preserve >the >angular relationships between the original scene and the picture. As a >result, >we should view a contact print from a film camera, or a print equal in size >to >the dimensions of the sensor in a digital camera, at a distance equal to the >image distance in the camera. > >This distance is equal to the focal length of the lens unless the lens is >focused >on a close-up subject. > >For accurate perspective an enlargement (a print larger than the contact print >or >sensor size) requires a viewing distance equal to the product of the focal >length >and the enlarging magnification. So, a magnified print from a 35mm film frame >to >5x7 inches and originally photographed with a 50mm lens should be viewed from >a >distance of about 5 inches / 1 inch where M then is 5x and so the proper >viewing >distance for perspective is 250 mm or about 10 inches. In the case of a >digital >camera with a 16x24 mm sensor from which a 5 x 7 inch print is made the >situation >is 5 inches / .66 inches and the M is then 7.5x and the viewing distance for >proper perspective is 50 x 7.5 or 375mm or about 15 inches. > >In both of the above cases the taking lens is assumed to be of 50mm focal >length. >And M stands for MAGNIFICATION or enlargement factor. > >Quoted from "Introduction to Photographic Principles" by Lewis Larmore, >Director, >Advanced Research Laboratory, Douglas Aircraft Company. Dover Publications, >Second >Edition, May 1965. Updated to include digital cameras on 06-07-09. > >Andy's extra comment: The consequence of this is that if we view a print from >the >"wrong" distance (as related to seeing a print in normal perspective) a print >will >exhibit "strong" perspective if viewed from too far a distance (usually the >case >when wide angle lenses are used) and "weak" perspective (usually the case >when >photographs with long focus or telephoto lenses are made) if viewed from too >near >a distance. > >==== if you notice any errors in the stuff above please bring to my attention >==== >andy >
