I came across some NOS (still sealed in the packaging) Nikon focusing screens for a F4 and F3 in some gear I traded for today. The F4 screen is a type K standard screen which is not the standard screen the F4 came with from the factory the F4 came equipped with the Type B as it was sold. The F3 screen is the Type S which is similar to a Type K except it is setup for use with the data back I believe for the F3. Both of these screens are some of the more rare screens and I have not been able to find a value for them in their respective camera accessories. I was planning on getting rid of them but I was trying to get an idea of how to value them if anyone can give me an idea it would be helpful. I have not found any of either type on ebay or the usual places on the web I would normally use as a reference. All help is appreciated .