• The current circle of confusion diameter used by most camera and lens makers is c = 1/1500 the diagonal of the image rectangle on film. The circle of confusion for the 35mm format is generally taken as 0.029mm.

Using circle of confusion diameter 0.029mm, the hyperfocal distance for a 50mm lens at f/8 on the 35mm format is 10.8 meters = 35.5 feet.

A 50mm lens on the 35mm format at f/5.8 would achieve hyperfocal focus at 34 feet with a circle of confusion diameter of 0.042mm.

In particular, if the maker had chosen a circle of confusion diameter of 0.042mm as “good enough”, then the markings make sense.

On page 17 of the Kodak Retina 1b manual (First version PDF), the last example gives a 22-foot hyperfocal distance at f/8. You have to read it carefully to see that this is the actual focusing distance being used (“The depth of field then extends from 11 feet to infinity.”)

This leads to a circle of confusion diameter of 0.047mm.

http://www.cameramanuals.org/kodak_p..._retina_ib.pdf