But your link goes to what you don't want to use for correct focusing since it is pre focused instead of being able to be
adjusted so you focus on the actual grain surface of the gg where the film will actually be placed. This loupe will always
be out of focus by, at least, the thickness of the ground glass and even more if a top mounted Fresnel is used!
Always use a loupe that can be adjusted. In addition, this is an open tube design which will allow light to enter from the
sides creating flare on the gg and making focusing more difficult. A focusing loupe for a gg should have an opaque skirt.
Not a clear or translucent one.