Hi there Hal, X-pro filters are for medium format & movie camera, I used to use "A" filters when most Nikkors had a standard 52 mm thread or not much bigger and they were fine - used multiple holders and dedicated hoods, stacked up 3 or 4 with ease on some lenses. Now tend to use "P" filters, with a holder but rarely the hood. Also sometimes just hold them in front by hand when using a tripod. I also use the circular screw in ND grads and solid ND - all are 77 mm thread and if lens is different, use step up or step down rings. If you are interested look at the Singh-Ray ones from the States, cost a fortune, but are very high spec and very good - they are the only people I know who make a "reverse graduated" ND filter, which I fancy but it has very limited use and cannot be justified - even by me.
