I think french Ebay has rather more interesting items than the UK/USA sites at the moment. I couldn't resist this set of 4 alternative lenses. Two of these were "plus grande" and two were "plus petit". It is exactly the text which appears on the (often missing!) extra lenses which are mounted inside the Derogy " Foyers multiples et lentilles additionelles" - see secon image. These are Bayonet attached lenses too, but I didn't think this was part of a huge, more complicated version of this Derogy.
The lenses were marked 43 and 55 for the "petit" and 86 and 108 for the "grand". I assume the normal lens they replace is something like a "70".
I was expecting a set of single lens, but they turn out to be achromats. The numbers certainly don't represent focal length in cm. Perhaps inches. Combining the two shorter lenses I was able to produce an image at around 100cm.
The Fvalues and focal lengths are so high that I feel these must be replacement/alternative front achromats for a telescope, rather than for photography. Anyone with any insight into sophisticated French telescopes around 1870 - 1890?