This Right-Angle Optical Viewfinder Kit from Voigtlander bundles one right-angle optical viewfinder with three attachments for it that correspond to different lens focal lengths: 15mm, 21mm and 25mm. It is designed to allow convenient, comfortable shot composition with a variety of lenses. Select the attachment that matches the focal length you want to use and screw it onto the front threads of the finder.
There is a built-in diopter correction dial at the top of the finder. This top section can rotate left or right. Look through the eyepiece at the top and you will see the view through the front of the viewfinder. The unit mounts onto a camera's standard hot shoe. It is constructed from lightweight metal.