As it happens I've the 1910 BJP Almanac open in front of me with looking at the Dallmeyer advertising, and the illustration shows the D series having a similar aperture mechanism, in fact by then every Dallmeyer lens appears to have an iris diaphragm aperture control.
Ian.
I think that all the "turn the barrel" diffusion patent portraits have the iris - otherwise the WHS stop might fall out!
The only exception is a 3B which I reconstructed from a complete set of lens cells! U/S irises are quite common with this design.
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