The nikon dk 17c 0 eyepiece correction lens enables you to optimise the sharpness of your slr viewfinder in conjunction with your own eyesight cameras without in built adjustable eyepiece correction have base diopter value of 1 which is thought to be the optimal starting point for slr users with good vision the components of the cameras viewfinder combined with a clear standard eyepiece form a virtual image of the subject that is the approximate equivalent of a viewing distance of one me