So what makes a Bolex viewfinder 13x/14x?

[Todd Pinder]

Is it just the eyepiece itself? Something internal to the viewfinder? Jean-Louis? Dom?

[Dom Jaeger]

It's my understanding that most of the magnification is done by the eyepiece, but to make sure that the field of view adequately covers the groundglass the other optics are also important, especially the field and relay lenses just above the groundglass.

During a viewfinder conversion several elements are replaced, not just in the eyepiece. But Jean-Louis would know more about that than I do.

[Jean-Louis Seguin]

Every element in the viewfinder tube is upgraded not only to increase magnification but increase brightness too. First element after groundglass is different also.

[Todd Pinder]

Cheers gentlemen!