I've been using a Fuji Professional 4x loupe, but it's gone somewhere into abyssal storage, so I'm borrowing a friend's Rodenstock aspheric 4x loupe. I wear glasses, so looking through the loupe does not render a sharp image. Is there a way to focus the Rodenstock loupe? I was able to do it adjust focus with the Fuji loupe, but can't figure out how it's done with the Rodenstock.

Just to be clear, I'm asking about how to change the focus of the Rodenstock loupe, not focus of the camera. Thanks!