I do not know about this particular enlarger, but most condenser enlargers need the light source adjusted so that it is focused by the condensers through the lens. Properly adjusted it removes both uneven illumination and vignetting.
I have used several dozen enlargers from the 1940's to the late 80's and they all but one had this feature. and that was factory set.
-------------------- 63 happy photo years from amateur to professional and back to amateur