135 was the product code given by Kodak Eastman for the 35mm film.
35mm film has the dimentions of 24mm X 36mm, thats the physical size of the film negative.
Since this is the focal lens corrosponds to the film size. a 50mm lens is only 50mm when in respect to a 35mm film negative. But what happens when u get a smaller film neg like APS or a smaller area like a CCD sensor?
You get a crop. They will specify how much smaller, some are 1.5X smaller some are 1.3X smaller some are 1.6X smaller. that 1.somethingX is the crop factor, the number u shld multiply your lens focal length by to get the "new" focal lenght caused by a smaller than 135/35mm negative/CCD
35mm film has the dimentions of 24mm X 36mm, thats the physical size of the film negative.
Since this is the focal lens corrosponds to the film size. a 50mm lens is only 50mm when in respect to a 35mm film negative. But what happens when u get a smaller film neg like APS or a smaller area like a CCD sensor?
You get a crop. They will specify how much smaller, some are 1.5X smaller some are 1.3X smaller some are 1.6X smaller. that 1.somethingX is the crop factor, the number u shld multiply your lens focal length by to get the "new" focal lenght caused by a smaller than 135/35mm negative/CCD