What is this adapter on my Dallmeyer Pentac 2.9/8" for?

[schlicksbier]

I got today a Dallmeyer Pentac 2.9/8“ and was very surprised by the huge adapter on the lens. Any idea for what this brass adapter was used? The mount at the end is approx 5cm in diameter.

[Steven Tribe]

Once upon a time (post WW2) there was a shortage of affordable lenses for, especially, 35mm cameras, but a lot of cheap fast ex military large format lenses were available.
So lots of people got adapters made to use these on prewar 35mm cameras. Lathe work with brass/aluminum tubing used to be readily available and low cost!

[schlicksbier]

Once upon a time (post WW2) there was a shortage of affordable lenses for, especially, 35mm cameras, but a lot of cheap fast ex military large format lenses were available.
So lots of people got adapters made to use these on prewar 35mm cameras. Lathe work with brass/aluminum tubing used to be readily available and low cost!

So they used this to attach it on some kind of helicoid to focus it correctly?

[domaz]

So they used this to attach it on some kind of helicoid to focus it correctly?

Or maybe it was just fixed focus at infinity, a poor man's telephoto for a 35mm camera.

[LabRat]

I have seen surplus lenses with that mount, and I think some old cinema projection lenses had them...

A Pentac is fast enough for projection...

Steve K