Do other folks using the 72XL find a center filter necessary or desirable when u sing 4x5 format? I've been doing some testing of the 72XL at and near it's cove rage limit. The results have made me want to do a comparison with a center filt er. With tall architectural subjects, the fall-off is quite noticable on a chro me. Could someone with a 72XL center filter comments on this issue?