THE DIAPHRAGM SHUTTER - MODEL OF 1891
Bausch & Lomb Optical Company, Rochester, New York 1890-1908
In 1890, this new model was introduced as "The Diaphragm Shutter", which is how it's mostly referred to in factory advertisements. As a shutter option in many camera ads though, it's mostly referred to as an "Iris Diaphragm" which is the term used by most collectors today. The "diaphragm" name originates from the shutter's leaves which also serve as the aperture by advancing to a preset opening as the shutter is tripped.
The Diaphragm Shutter is easily identified by the two vertically mounted valves on the front of the shutter, one to release the action pneumatically and the other to regulate speed, together with its unique linkage. Speeds are selected by rotating the dial at top front, with the aperture opening being set by rotating the dial at the rear. The lever below the speed dial is used to select either time or instantaneous exposures. The exposure is then made after cocking the lever on top between the speed and aperture dials, using either the manual release or pneumatically with a squeeze bulb attached. Some Diaphragm Shutters are not equipped with a manual release, but you'll find them on about half of those encountered today.
I've referred to this shutter as The Diaphragm Shutter - Model of 1891, adding the "Model of 1891" to distinguish it chronologically among Bausch & Lomb's earliest shutters. The Diaphragm was designed in 1890 (patent filed July 2, 1890) with the earliest examples probably being produced later that year prior to the issuance of Patent No. 444,083 on January 6, 1891. The shutter's design was shared by Edward Bausch, George Hommel and Andreas Wollensak. In 1899, Andreas Wollensak, together with his brother John and financier Stephen Rauber, went on to form Rauber & Wollensak:
Source: U.S. Patent and Trademark Office
The most frequently encountered model of Bausch & Lomb's earliest shutters, the Diaphragm is typically found on self-casing cameras by various manufacturers and prominently featured on the Folding Kodak (satchel) series.
Several variations exist, one of the changes being the speed dial's design. Speed dials on the earliest versions are marked for speed only, with no other information:
Early "Pat. Pending." version
On those examples that were made in 1890 or early 1891 prior to the patent's issuance, the shutter's casing is engraved with "Bausch & Lomb Optical Co.", Pat. Pending." and the serial number, appearing beneath the lens or barrel:
After the issuance of the January 6, 1891 patent, the patent's date now appears in place of "Pat. Pending.":
Later on, the Bausch & Lomb Optical Company name along with the company's address and the January 6, 1891 patent date, appears on the speed dial. Sometimes the words "Diaphragm Shutter" can also be found on the speed dial. The serial number is contained on a small brass plate attached to the lower casing. It's this later speed dial version that is most often seen today:
Some versions mounted on the Folding Kodak series were engraved "Eastman Kodak Co.":
Lens board from a No. 5 Folding Kodak (satchel-style)
The same shutter engraving below from 1891, depicting the early version speed dial and engraved casing, was used in advertising through at least 1899, well after later versions came into existence:
From Scovill's The American Annual of Photography and Photographic Times Almanac for 1891
Variations also exist in the shutter's mounting system. Most examples encountered are equipped with a standard threaded mounting flange, affixed to the lens board with screws. Some examples found on Kodak's "satchel" series (Folding Kodak), attach with a breech-style mount allowing removal of the shutter with a simple twist. The Eastman Kodak Company name on this example along with the shutter's serial number is found on a nickel-plated brass tag:
Breech-mount often found on Eastman's Folding Kodak (satchel)
One of the least encountered variations is one where the shutter's rear element is integrated with the mounting flange. When the flange is removed, the rear lens element goes with it.
In addition to brass, the Diaphragm Shutter was also available in aluminum which increased the price substantially. Although this aluminum version could be found on many self-casing cameras, it was specific equipment on Blair's Century Hawk-Eye, 6-1/2 x 8-1/2, Folding, and the original model of Manhattan Optical Company's Wizard Camera. Both the earliest and latest versions of the speed dial have been found on aluminum models as well.
Diaphragm Shutter aluminum version
Diaphragm Shutter aluminum version with early speed dial
In comparison to the Bausch & Lomb Time and Instantaneous models that preceded it, the Diaphragm Shutter is seen quite frequently today. It seems to have made its final appearance in the Poco and Premo Catalogues for 1902, lasting till 1908 at least and appearing in Ralph J. Golsen's catalogue believed dated for that year.
With an impressive 18-year run, it was Bausch & Lomb's longest-lived shutter at that point.