Thanks Charlie & 9ja,
The only filter I use is the UV filter, I do have a set of Lee filters (ND grad etc) with adaptor but not used them for ages.
I am delighted with the images the D810+24-120 render, they are a great combo and as I shoot usually at f5.6 I have had no problems with sharp images - I do have the auto ISO settings covering the lens reciprocal so the shutter speed is never less than the focal length used - a great addition on the D810.