Copal 1 protection

[luis a de santos]

I recently purchased a convertible 210mm lens in Copal 1.This has proven a very good and useful lens for me but I am concerned about exposing the Copal 1 blades when I remove the front element particularly in the field.
I have tried filters but the thread of the copal is deeper than the filter thread .
Is there a filter or something I can screw in front to protect the shutter first and second a place where I can screw in filters ?

I remember a device that Wisner use to sell called "the corrector" that was used for that purpose and to correct for aberrations when only one element was used.Is there anything like that available?.

Thanks to whoever can help me with this.

Best Luis

[Dan Fromm]

Fire the shutter on "T" and the shutter blades will retract and stay retracted. Open the diaphragm all the way and the iris blades will retract and stay retracted.

And put the front cell back in when you're done shooting with the lens converted.

[EdWorkman]

Some lens makers, back then, recommended using the single cell in front, for the very reason you stated.