Infrared mark

[6x6x9]

Hi!
I have Carl Zeiss Jena Pancolar 1.8/50 lens and it has a depth of field scale on it like following: 22 16 11 8 4 l 4 8 11 16 22. That vertical line in the middle of the scale is red coloured and number 4 next to it as well. Since I'm planning to shoot infrared for the first time, my question is: Is that "red 4" an infrared, focus compensation mark?
Thanks for your opinions!

 

[Ole]

That seems likely. Could be useful if you shoot Kodak HIE with a strong IR filter, I guess...

For all other IR films, and "weaker" filters like red, the IR focus mark will give you out-of-focus images.

 

[6x6x9]

Thank you, Ole!
Yes, the setup will be: HOYA R72 > Pancolar MC 1.8/50 > Kodak HIE IR.