Weston was using an older system of aperture designation (US I think). In that system, 256 is equivalent to about f/64. For an 8x10 camera, that's not yet in the range where diffraction is a problem.
@OP: As Bob points out, placing your plane of sharp focus to optimize depth of field is a good way to keep diffraction at bay. If you use the near-far focus method described in the "How to Focus the View Camera" article on the home page, then a good way to check if your plane of sharp focus is optimally positioned is to find the minimum distance between near and far focus for a given subject. Keep in mind that if you use tilts/swings, the "near" and "far" focus points are not necessarily the closest or most distant, rather those that are in front of and behind the focus plane. For example, if you use front tilt to get a near object and a distant mountaintop in the plane of sharp focus, the "far" focus point will be close to the base of the mountain.
Best,
Doremus
Bookmarks