Rodenstock Apo-Rodagon 90 mm

Hi

I just bought a Rodenstock Apo-Rodagon 90 mm on eBay.
The lens come with a big plastic rim with a red dot an a small ring inside.
I put the lens on the lens board (Omega D2V) without this rim. It's seems that
is OK; I didn't print nothing for now. My question is why this rim? Is it something to use with another type of lens board or what? See the attached
files.

Mine came without the plastic rim – and it works very well indeed.

looks like an adaptor for using it in a camera, perhaps for reproduction.

I know there is something called helical focusing adapter for enlarger lenses. Because enlarging lens can not be focused itself, enlarger is used for focusing, when enlarging lens is used on camera one attach helical focusing adapter on enlarging lens and with it get possibility to focus lens itself. When lens is used on enlarger, it is used without that adapter. I never saw helical focusing adapter in life, only on pictures and before some time, so I can't tell for sure, but can that be that? I hope someone who know better will help, sorry...

Check this web site: http://www.linos.com/pages/no_cache...chnikccd/?sid=13388&cHash=83dc2ea03d#sid13388

Thank you Haris

I'm thinking that it is exactly what I have.

Thank you everybody.