The standard set by Leitz in its Leica lenses was a close-up distance of 1m or 39 inches. Spider legs and various close-up devices allowed smaller items to be recorded, right down to 1:1.
This standard was continued with the Summicron 50mm lenses until the famous lens was recalculated in Midland, Ontario by the magnificent lens designer Walter Mandler to use only six elements. The close-up distance was reduced almost a foot to 28 inches or .7m. The lens was marketed in 1969. I bought mine in 1972 along with an M4 to photograph my two daughter, the youngest of whom was born that summer just before I took the plunge.