Another 'age' question R & J Beck lens

I bought this lens - marked R & J Beck, 11" Rect, whole Plate - with a serial number of 682 (I used to operate a Beck made MTF test rig many moons ago so I have a soft spot for their equipment). I can't seem to find any really definitive dates for when they started to make photographic lenses and this is a low serial number and so presumably an early lens from them. Can anyone point me in the right direction for dating it. (I'm hoping to have it ready to shoot with a 5" x 4" camera in just a few weeks time).

Before 1865, they were Smith, Beck & Beck. After 1895, they became R &J Beck LTD. Lenses and Cameras were a minor interest (Microscopes were the big thing!).

Indeed. As its marked R & J Beck it would appear that it was made somewhere between 1865 and 1895. From searching on the web it looks as though a lens with a serial number in the 4-5000 range is thought to have been made c. 1890 (because of the date of production of the camera it is on) so I'm assuming that Beck entered the photographic lens market some time before this. Various web searches suggest that Beck were building cameras (and presumably lenses for them) by at least 1880. The trouble is that everything is vague with nothing concrete (scanned adverts and suchlike) before about 1900 that I have found as yet.

Some further information:

From THE PHOTOGRAPHIC JOURNAL. [JAN. 28, 1887]
"Mr. CONRAD BECK exhibited some of his photographic lenses fitted with an Iris diaphragm of a most ingenious form, which, although used in microscopes twenty years ago, had only recently been applied to photographic lenses. This diaphragm consisted of a series of metal flaps fixed in the middle of the lens, working one behind another, and opening from a point to full aperture. actuated by a lever outside the lens mount, with graduated markings for retaining the size of the openings in accordance with the Society’s standards.
Mr. A. MACKIE remarked that this form of stop was introduced into photographic lenses some three years since, and was mentioned in Monckhoven’s “Photographic Optics ” about 1869.
Mr. C. BECK also stated that the Iris diaphragm was mentioned in an old edition of Newton’s “ Optics.” By its introduction into large lenses, a considerable amount of weight in metal stops was avoided.
The CHAIRMAN said that if the diaphragm itself was not new, yet Mr. Beck had carried out the principle in a very perfect way, as now shown in its adaption to the lenses exhibited by him.

[The Photographic Journal is fully digitised and searchable (http://rps.org/rps-journal/journal-archive)]

So this suggests that by January 1887, R and J Beck were fitting diaphragms to their lenses. This suggests that they had been building photographic lenses prior to 1887. As mine is a low serial number and not fitted with a diaphragm it probably pre-dates 1887. As ever, hard data is difficult to come by though.