Trevor : not trying to argue here, i'm just a little confused: : the 1.5 factor comes into play because the size of the sensor is different than the film plane on a 35mm camera, as the film plane on a mamiya is different than a 35mm format camera. the 1.5 is the multiplier applied to the *actual* focal length - in this case 80mm - to give a 35mm equivalent. what this means is that a 35mm lens (format unspecified) x 1.8 = 63mm it's not actually a 63mm lens, but it will have the same field of view (NOT anything to do with the imae circle size) as a 63mm would. ..on a 35mm camera :) now lets pretend we have three lenses of 35mm and these lenses came from a 16mm camera, a 35mm camera and a 645 camera. they all have different image circle sizes and they all have different angles of view when shot using the format they were designed for 35mm x 1.8 63mm hmmm that's pretty close to the 'normal' focal length for 35mm AND no surprise, the real focal length (35mm) is close to the 'normal' focal length for the 16mm camera, to use the example above ;) Essentially, the coverage and angle of view on a 80mm mamiya lens is vastly different than the angle of view and coverage of an 80mm lens for a 35mm format camera. On the 645 format, an 80mm lens is a normal perspective lens, on a 35mm format an 80mm lens is a telephoto. Are you saying that the 80mm mamiya lens on a dslr sensor is going to be 120mm? yes! :) My math is coming from frame diagonal ratios Further, how invalidated would the focusing ring indicators be? that depends on the film registration distance and this is different for each camera/brand/format. Chances are if it's a well designed adapter then they've taken that into account and you should maintain infinity focus.. t's OK Trevor - *equivalent focal lengths* are deceptive and confusing. Best thing to do is to get used to the *actual* focal lengths and how they relate to the various formats. 80mm =extreme wide angle (on 5x7 / 4x5) 80mm = moderae wide (on 6x9) 80mm ='normal (on 66) 80mm =moderate tele (on 35mm) 80mm =tele (on 16mm) 80mm = long tele (on 110) it's all relative but the focal length remains the same ;) k
