UNMOUNTING IRIS APERTURE to get faster lens

[renes]

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?

[Jimi]

BTW, renes, could you just post a photo of the Emil Busch? From the description it seems to be a twin to mine. Would be cool to see another one, just for the fun of it. :)

[renes]

Here they are.
I wanted to use it with my 6x9 but it's too long focal lenght for my needs. So if there is someone who have Emil Busch 6" aplanat (need not has iris aperture) and would like to trade it with this one, PM please.

http://img825.imageshack.us/img825/3466/91876513.jpg

http://img832.imageshack.us/img832/5955/78690069.jpg

http://img838.imageshack.us/img838/9083/94918481.jpg

[Jimi]

It's a beautiful lens, renes! Mine (I don't have any photos and the lens is in the lab unfortunately) is "unpainted" brass and probably a bit older than yours. Mine has the ROJA designation on the flange. Thanks for sharing the photos!

[papah]

I do this often, mostly with meniscus lenses. A recent one is a TTH Rapid View, which only opens to f/11; I found that the slot for the iris stop could be enlarged. Now it's at least f/7 or so, more like the Rapid View Portrait lens.

I have also added an iris to a Rodenstock Imagon, instead of the strainer-like aperture device. I had an extra aperture, which I machined out and added a purchased iris. Now, turning the strainer adjusts the aperture, and allows me to use the Imagon by controlling the softness by stopping down without the pattern in the highlights which often occur with the strainers. It is like a small Kodak Portrait Lens...