I have a lens that is a bit tough to turn the aperture ring and also there is no focal length listed on it. The black finish on it is coming off and it looks like brass underneath. The lens is a Bausch & Lomb - Zeiss - Tessar 4X5 lens. Does anyone know the focal length and how i can loosen up the aperture ring? Also is there anything i could expect from the lens or is it just an average older lens? Im hoping for a vintage look to the images and i want to build a board for it and mount it on my Speed Graphic. Thanks!