DARLOT Petzval - Need info please

[kameraobskura]

http://i49.tinypic.com/1oshoj.jpg

I recently aquired two 9" lenses, one unmarked and one marked Darlot.

Darlot Opticien Paris with the AD monogram. Serial# is 28.962. I measured it to a 9" focus. Anyone have any additional info on it? Age? f?

[Steven Tribe]

Conventional wisdom has been, there is no great connection between dates and serial numbers.

Engraving style/combinations suggests after 1866. I enclose the change in engraving which appeared around 1866. This is taken from Corrado D'Agostini's book.
The problem is, that this style of engraving was continued on the more "de luxe" items right until Darlot disappeared. An "objectif d'Artiste" from the 1890's (C d'A's book) has an identical engraving (serial number 35524) to yours.

Sometimes, there is date information written on the ground glass sides of the front achromat and one of the rear pairs. This can be indian ink or pencil.