Found this brass lens in the .50 cents box at an antique store. There are no markings on it except for the apertures. They read 16, 32, 64, 128, 256 & 512. Are those f-stops or something else entirely? The lens measures 2-1/4" x 1". The glass measures 1" is Diameter.

Like said, there are no markings on it at all, no numbers or stamps. So I have no clue. I looked through a few catalogs from the 1900's to 1920's I saw a few that came close, but nothing exact.

Would be interesting to use this somehow hoping it will cover 5x7, or at least 4x5.