This unusual ‘open’ monocular can be held with one finger through he ring. The two lenses can be focused by sliding the bar open.
This is possibly French from around 1900. It is in good condition and although the smaller lenses is at a slight angle it can still work.
It can be neatly folded shut.
Ask the Dealer
I have been dealing with antiques for over 45 years. I have a special interest in medical and optical items. The earlier the better for my collection. I used to sell in Portobello Rd & Bermondsey Market, I now can be found at Newark & by appointment .