Years ago I used a Nikon F4 and F3 and loved them, but moved on and sold them. Several months ago I realized that I really wanted one of them back, and decided on an F4, and after several weeks found one in good shape at a pretty good price. It came with the standard matte/fresnel field focusing "B" screen. I loved these cameras for their versatility and ease in changing focusing screens to meet the occasion. As I use a lot of manual focus lenses as well as AF lenses, I've come to really like a brite-view split image, and I remembered having one with my previous body. So I searched the bin and realized I must have sold all of my F4 screens, but still had a selection of F3 ones, including a split image "K" screen. After some research I found that you could use some F3 screens in an F4 (it's the details nobody mentions which get you though). Anyway I looked online for a K screen for an F4----scarce as hen's teeth and waaaay to expensive when I could find them, but F3 "K" screens were plentiful and not very expensive at all. Back to the drawing board...slipped the F3 one into the F4 body and voila...it worked. Well, not perfectly, I discovered. It didn't matter whether I was using MF or AF lenses....objects at a distance didn't precisely line up in the vf when the camera said they were in focus...they were slightly off, which meant they would be slightly off at other distances as well....so precision focusing went out the window. After a couple of weeks I grabbed my micrometer and measured the focusing screen mountings of the F4 and F3 screens and discovered there was a miniscule difference in depth, and the screen lens itself was held in place in its holder with 4 screws which held a tiny "L" bracket which fit into slots in the top and bottom sides of the lenses. So I exchanged the "B" screen lens of the F4 holder with the K screen from the F3, and put the F4 holder back in the camera body. Slipped on an AF lens and focused on several structures about 4-500 feet away....the vf lineup was right on the button....same when I moved to closer objects. Did the same with a couple of MF lenses which had hard stops at infinity....same results. IT WORKED. So, for anybody out there who has an F4 and wants to use a much less expensive K screen...get one for an F3 and change it into the F4 holder.