The Metrogon lense is an extreme wide angle and very old design. A Metrogon with a 6" focal length will cover an area 9"x9" with virtually no loss at the extreme edges. These are WWII aireal camera lenses and available in the surplus market. They are usually stopped down to f8 to minimize astigmatism. They were originally corrected for use with black and white film and the use of a yellow filter is benificial. Their main problem is the large film format (8x10 cut film), it`s expensive and not easily found at the local camera shop. You had better be able to do your own processing. I have one that I used many years ago with good results but it`s been gathering dust for at least twenty years. If you succomb to the temptation, I wish you good luck.