Strange Things Around the House #2

I was sorting through a box of stuff moved from house to house recently and stumbled across this.  I am probably the only one looking at this that has a clue what it is, or why anyone would hang onto it.  

So what is it?

It is a focusing screen for a first generation Cannon F-1 35mm SLR.  At the time (about 1975) it was the top of the line professional camera that Cannon made.  I lusted over it for a couple of years, my father had an FTb, that my oldest brother bought in Asia in the early 1970's when he was in the Navy.  I liked it, but the F-1 was another world.  The shutter was titanium, a masterpiece of engineering and manufacturing.  It would do everything that could be done at that time, you could change the viewfinders, backs, add motor drives. I saved up from my summer work on the farm, one summer, did some extra aerial photography jobs and splurged on it one fall.  With it I fit in with the pros. I made a living with it for a couple of years. I don't recall why I changed out the focussing screen, maybe because you could. The camera was solid. I was known to say you use it to bang the nails in to build a house, and when you were done use it to take pictures of the house.  They don't make them like that anymore.  

Around 2000 I traded a bag full of Cannon cameras and 6 lenses on a new Nikon 35mm SLR.  I used that about three years and then went digital.  Last year I bought my first digital SLR, and now have three lenses.  

The only thing I have left of the F-1 is the focussing screen, the memories of owning the best of the best in it's day, and some amazing images I created with it.