Nikon 60 mm f/2.8 Auto-Focus Micro-Nikkor

The extension available is 50 mm, and the focal length at the close focus point is 55 mm.

Magnification Subject distance Correcting Lens Extension tube    
Near focus Far focus Near focus   Far focus   Focal Length diopters      
                       
1.00 0.00 4.33 in Inf   None   0.00 0    
1.50 0.46 3.61 in 7.52 in None mm 0.00 27.5 mm PK-13, M-ring
1.95 0.88 3.27 in 5.06 in None mm 0.00 52.5 mm PN-11
2.00 0.92 3.25 in 4.94 in None mm 0.00 55 mm 2 PK-13s
2.45 1.33 3.05 in 4.13 in None mm 0.00 80 mm PK-13 + PN-11
                       
1.18 0.09 3.67 in 26.25 in Nikon 3T   1.50      
1.35 0.17 3.21 in 13.58 in Nikon 4T   2.90      
                       
1.73 0.59 3.14 in 5.84 in Nikon 3T   1.50 27.5 mm PK-13, M-ring
1.94 0.71 2.80 in 4.84 in Nikon 4T   2.90 27.5 mm PK-13, M-ring
                       
2.22 1.04 2.88 in 4.24 in Nikon 3T   1.50 52.5 mm PN-11
2.47 1.20 2.59 in 3.69 in Nikon 4T   2.90 52.5 mm PN-11
                       
2.77 1.54 2.70 in 3.57 in Nikon 3T   1.50 80 mm PK-13 + PN-11
3.06 1.74 2.45 in 3.17 in Nikon 4T   2.90 80 mm PK-13 + PN-11