antennaboy Posted May 9, 2012 Share #1 Â Posted May 9, 2012 Advertisement (gone after registration) Hello Forum, Â I have recently read about telecentric lenses: they offer an orthographic perspective of the scene, free from natural perspective effects. Parallel lines remain parallel and don't meet at infinity. Far objects don't appear smaller than closer objects...etc.... Â Anyone knows how they do that? Do they work, intercept only certain rays from the object and use them to create an orthographic projection on the film? Â thanks, antennaboy Link to post Share on other sites More sharing options...
Advertisement Posted May 9, 2012 Posted May 9, 2012 Hi antennaboy, Take a look here ever heard of telecentric lenses?. I'm sure you'll find what you were looking for!
pico Posted May 9, 2012 Share #2  Posted May 9, 2012 Hello Forum, I have recently read about telecentric lenses: they offer an orthographic perspective of the scene, free from natural perspective effects. Parallel lines remain parallel and don't meet at infinity. Far objects don't appear smaller than closer objects...etc....  Anyone knows how they do that? Do they work, intercept only certain rays from the object and use them to create an orthographic projection on the film?  thanks, antennaboy  First, strictly speaking, there are no consumer (affordable) telecentric lenses. They are quite limited in their application and not useful to general purpose photography. Digital sensors with firmware correction might try to create similar outcomes, but to date it hasn't been complete.  How do they do it? The first set of lenses brings the image to infinity (all rays pointing to center), then there is an aperture (effectively at infinity), then the second set of lenses project the image with all rays parallel to each other and perpendicular to the subject, IOW collimated.  Sometimes, very long telephoto lenses will create a quite 'flattened' perspective that might look orthographic (or orthographic enough) to illustrate the effect. Recall straight-on photos of a group of people so that the persons behind those in the foreground seem too large. Our sense of perspective is not accustomed to such. Link to post Share on other sites More sharing options...
250swb Posted May 9, 2012 Share #3 Â Posted May 9, 2012 All true 4/3 and m4/3 lenses are telecentric in design. The 4/3 sensor requires a straight light path to gain most from it, and which is why very wide angle 'legacy' lenses show fall off in the corners, because the light hits the photosites at a very acute angle instead of square on. Â Steve Link to post Share on other sites More sharing options...
pico Posted May 9, 2012 Share #4  Posted May 9, 2012 All true 4/3 and m4/3 lenses are telecentric in design. The 4/3 sensor requires a straight light path to gain most from it, and which is why very wide angle 'legacy' lenses show fall off in the corners, because the light hits the photosites at a very acute angle instead of square on. Steve  "Telecentric in design" is not the same as telecentric. The phrase, "Telecentric in design", means "kinda, almost, wishfully telecentric", IOW good enough for quotidian, but not science. Link to post Share on other sites More sharing options...
250swb Posted May 9, 2012 Share #5 Â Posted May 9, 2012 Yes sir! Â Steve Link to post Share on other sites More sharing options...
pico Posted May 9, 2012 Share #6  Posted May 9, 2012 Yes sir! Steve  OMG, did I come off as overly strident? I hope not. I should have a professorialectomy now that I'm retired. Hope we are okay, Steve.  p Link to post Share on other sites More sharing options...
mjh Posted May 9, 2012 Share #7  Posted May 9, 2012 Advertisement (gone after registration) All true 4/3 and m4/3 lenses are telecentric in design. Olympus has always described these lenses as ‘near telecentric’ which isn’t quite the same. These are lens designs where the exit pupil is far from the rear lens but not quite at infinity, i.e. they are nearly but not quite image-space telecentric.  If a lens is object-space telecentric, i.e. its entrance pupil is infinitly far from the front lens, it creates the orthographic projection mentioned above. Link to post Share on other sites More sharing options...
sdk Posted May 10, 2012 Share #8 Â Posted May 10, 2012 Is telecentric the same as infinity optics? We have Zeiss and Nikon microscopes with infinity optics at work. They are quite good. Link to post Share on other sites More sharing options...
Richardgb Posted May 10, 2012 Share #9 Â Posted May 10, 2012 Wikipedia Telecentric lens - Wikipedia, the free encyclopedia has info as well as further links. Link to post Share on other sites More sharing options...
antennaboy Posted May 31, 2012 Author Share #10 Â Posted May 31, 2012 Hello Pico, Â if possible, let me ask some basic clarifying questions on your comments about telecentricity... Â You say that: "...The first set of lenses brings the image to infinity (all rays pointing to center), then there is an aperture (effectively at infinity), then the second set of lenses project the image with all rays parallel to each other and perpendicular to the subject, IOW collimated...." Â What does it exactly mean that the image is brought to infinity? An object emits rays in all directions. Each point on the object emits its own bundle. If an object is located at "infinity", the rays that belong to a bundle are parallel to each other. But rays that belong to different bundles are not (the are oblique), correct? Â So the first lens "straighten up" the rays from the object. What does it exactly mean that the second set of lenses project the image with all rays parallel to each other and perpendicular to the subject? Â to form an image, rays that belong to the same object point need to converge to a point image.....if they are parallel, no point image is formed... Â thanks, antennaboy Link to post Share on other sites More sharing options...
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