Devon Posted July 14, 2020 Share Posted July 14, 2020 I just got me an old set of Yashica auxiliary lenses from the antique store. See the image below for the included manual. Doesn't an auxiliary lens keep the same aperture in relation to it's COMBINED (taking lens + auxiliary) focal length? For the wide auxiliary lens, why does it specify "f4" for the maximum aperture? (I think the multiplication factor of the wide auxiliary lens is really .84x aside from the manual stating "0.8x".) These lenses were usually sold for the Yashica Electro 35, which came with a fixed lens: 45mm F1.7. For example: Electro 35 Lens with no adapter: Focal length: 45mm Entrance pupil diameter (aperture): 26.47mm (f1.7) Add the wide auxiliary lens: Focal length: 45 x 0.84 = 37.8mm Entrance pupil diameter (aperture): 26.47 x 0.84 = 22.23mm Divide focal length by entrance pupil: 37.8 / 22.23 = 1.7 (f.17) Electro 35 Lens WITH wide auxiliary adapter = 37.8mm f1.7 Can somebody help me understand where "f4" comes from? Is my math/thinking wrong? Quote Link to comment Share on other sites More sharing options...
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