So, Tom -- dumb question time. As I understand it, a 1.6 ND filter lowers the light entering the lens by one and two-thirds stops. Presuming you were shooting these images at f11 with the filter, what is the difference between doing that and shooting without the filter, but with your aperture stopped down an additional one and two-thirds stops? Obviously doing the latter would increase diffraction softness in the final image (or, in some other cases, depth of field would be increased, which might be unwanted), but other than that, is there a difference?
Scott