Hi all Ok, I just asked the man....
Way back in days of yore (before computers, never mind digital!) Someone thought "what lens shall I put on my camera?" so being a clever victorian type chappy he worked it out. Given a viewing distance of 10 inches the human eye has a sharp (circular) field of view about 10 inches across (funny that a 8x6 whole plate fits bang into that circle, huh!) Some of you may have spotted the 10inch diagonal and 10 inch distance thing happening there. -------------------- Cutting out a whole load of math -------------------- Having the focal length=format diagonal gives the same field of view (when the print is viewed at normal viewing distance) as the eye has, so the perspective looks 'normal'. Hope that makes it clearer than mud! For source reading try: Ray, Sidney F. Applied Photographic Optics 3rd ed. p280 I keep a copy here if anyone wants a read ;-) Surely a good knowledge of the fundamentals helps us all be PROfessional And DIGital cameras still have lenses. I googled this subject and came up with nothing useful, But I'm very lucky to have a prime source at living at home! Merry chrimbo! Alex Ray > >> Janne please tell me why the standard focal length is the same as the >> diameter of the film =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
