Zeiss Mess Ikonta filter size?

[Jerevan]

I managed to snag one of these beauties at $65, in very nice condition, and I am going to do a field test within a few days with some outdated Fuji Astia. I am going do mostly BW, so does anyone know what filter size the Opton-Tessar on this camera take?

 

[elekm]

Is this the 6x6 camera? If so, it takes a 35.5mm filter that threads to the outside of the lens.

 

[Jerevan]

Yes, it is the 6x6 version. Thanks a lot for your help. Now off to find a yellow or green filter in this size.