What is the filter size ? My, rough measure
of lens diameter is 42mm is this right ?

I have the Schneider-Kreuznach Xenar 135mm f4.7 lens on my Crown Special and I use a 42.5 mm (1 and 11/16") Kodak Adapter Ring to push on over the lens, and then I can use Series VII (7) filters and a lens hood.

The filter I use the most in shooting scenics is the Wratten K2 medium yellow which helps to separate the clouds from the sky and gives a "snap" to the contrast.

I also use a lens hood which helps to reduce glare on the lens surface which could produce flare inside the lens and lower contrast.

my Xenar uses 40.5mm filters that screw right in. I got a polariser, a 38 wratten and a deep red from calumet many years ago. now.

Hey, I've just registered with this site to have an opportunity to ask your forum a Xenar 4,7/135 question:
What is this lens exactly?
I have been using it on my Crown Graphic but I have never seen any lens charts for it, or specifications even. Does anyone know about Schneider-Kreuznach Xenar 1:4,7/135 specs, like hyperfocal distance chart, etc?

tis a tessar formula, just like the Ektar, Optar, Paragon, the Kodak anastigmat and of course the B&L Zeiss Tessar.

ACCURATE Depth of Field charts depend
on the size of the end result. For instance if I were only doing contact prints, the circle of confusion at which I would decide it's no longer acceptably sharp would be much larger than if I were blowing up 4x5s to 40x50, hence the DOF chart would show a greater depth of field for contact prints than for 10x enlargements.

DOF charts are easy enough to make on your own. Tell me what size negative and what size your end photo will be and I'll set you into motion. All you need is a calculator or slide rule and some not paper.