The Nikon DK-17C (-3) Eyepiece Correction Lens optimises the sharpness of your camera’s viewfinder to your eyesight. Cameras without built-in adjustable eyepiece correction have a base diopter of -1 which is considered the optimal starting point for photographers with good vision. The viewfinder’s components in combination with a clear, standard eyepiece form a virtual image of the subject that is the approximate equivalent of a viewing distance of one metre.
Numerical values are minus for nearsighted users and plus for farsighted users. The base diopter value does not affect the end value, so if you require a diopter of -3, this is the correct eyepiece for you to use.
The DK-17C is suitable for all professional bodies. Due to a limited selection of DK-17C strengths, see the range of Nikon Circular Correction Eyepiece Diopters which are exactly the same size, the only difference being it has a slightly different thickness of rubber around the outside.