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!