I have two of these lenses like the one you describe. They require ( and mine came with) the M2 extension tube for reproduction ratios 1:2 to 1:1. I bought the older of the two in about 1969 in Hong Kong on R&R. The M2 is not an auto ring. I am sure there is a PK something that will also work. Actually any extension tube will 'work' but the markings on the lens might not be correct. The barrel (the fixed part - chrome) has two sets of numbers representing the minimum aperature available with extension, a color depth of field indicator, and a blue set of numbers on the right that are the reproduction ratios and focus distances for use with the M2 extension tube, ie 1:2 - 24.1cm (9 1/2 ") out to 1:1 21.1 cm (8 13/32") On the focusing ring, the distances are marked in feet and meters and additionally there are small red numbers that give the reproduction ratios without the M2 ie 1:10 down to 1:2. On this lens the aperature diaphragm changes automatically when you change the focus so that the real aperature stays the same with all reproduction ratios (down to 1:2), ie it 'opens up' with decreasing focus distance. This was important in pre-TTL use since f11 at 1:20 becomes something like f 32 at 1:2. This 'feature' was supposedly deleted with the arrival of TTL metering my 'newer' lens does not do this. I have AI converted my older lens. It is a terrific copy lens. I believe it is flatter and sharper than my f2.8 60 mm Micro. I use it to make presentation slides since autofocus is not an advantage under thise circumstances. In the 'field" the f2.8 60 mm autofocus is much easier to use. Richard Richard N. Sutton, M.D. 808 Brook Ave. Wichita Falls, TX 76308 940-766-0217 fax 1: 940-691-4305 fax 2: 940-766-0730
