Adapter / ring? Rodenstock Sironar-N 210mm

[Malcao]

Just bought a Rodenstock Sironar 210mm with Prontor Press shutter on ebay.
What is this adapter / ring for? Never seen this before. Is it for mounting the lens on the lens board a bit further away or?

[B.S.Kumar]

That's a spacer ring. They're usually found on #3 lenses. It's nice to have if you're using the lens on a field camera, where the uprights on the lens panel might prevent the lens from being mounted, or the controls are obstructed.

Kumar

[John Layton]

...test and/or measure to be sure that the spacing between front and rear cells is as "factory specified."

[Malcao]

That's a spacer ring. They're usually found on #3 lenses. It's nice to have if you're using the lens on a field camera, where the uprights on the lens panel might prevent the lens from being mounted, or the controls are obstructed.

Kumar

Thank you very much for the info. as you say can be good to have.

[Malcao]

...test and/or measure to be sure that the spacing between front and rear cells is as "factory specified."

Where can I find the correct values for "factory specified" so I know if it's correct?
Or how is it possible to test?