What is this ??

[Joao]

Hello ! This thing came with two old British Ensign folders, it measures about 5 cm diameter (outer ring). Can someone tell me what is is for ?

Thanks
Joao

 

[axiom]

p3n15 ring

It even has "HARDCORE" engraving

 

[johannielscom]

I am selling the above set of auxilliary lenses and retaining ring on Dutch vending site Marktplaats.nl.

Yours must be part of a set like that and became separated from the auxilliare lenses.

 

[Joao]

Interesting ! I'm not familiar with that kind of system for holding lenses.
I'm grateful for your input.
Regards
Joao