I noticed many vintage lenses with unmounting iris aperture, especially lots of aplanats and rectilinears. My recent lens Emil Busch A-G Rathenow Rapid Aplanat 200mm f7 has also no iris aperture. This uncovered the whole rear glass and "increased" its diameter about 4-5mm. I have not estimated it yet but suppose it can give extra 1 or 2 stops lens speed... to get f/4.5-5? I did ones something similar with Kodak achromat meniscus lens from Kodak Folding 3A that originaly was f/11, but after removing the special hood (which has much smaller hole then the lens diameter) I got about f/6.3-6.8.

Do you also unmount iris to get your one lens faster?