These finders attach to the Auto Meter IVF and allow it to make reflected-light measurements. With the Viewfinder 5 deg. the angle of acceptance is 5 deg.; with Viewfinder 10 deg. II, the angle of acceptance is 10 deg.
The meter can thus be used to accurately spot-measure exposure for parts of a subject or scene, or within the approx. angle of view of certain telephoto lenses.