I found this reference by Ed Buziak on the web...
"Interestingly, when I recently published a highly detailed lens testing and evaluation feature entitled "The World's Best Enlarging Lenses" by Ctein (one of the most knowledgeable American photojournalists and one of the few remaining master printers of dye-transfers) he nominated five El-Nikkors in his "Top Twenty" listing out of over 90 enlarging lenses rigourously tested during a six-month period. They were the 50mm f/2.8, 63mm f/2.8, 105mm f/5.6, 135mm f/5.6 and Apo-El-Nikkor 105mm f/5.6... that's right, there was a 105mm Apo El-Nikkor; it was made for scientific use plus the American space program and became an instant legend according to those who were fortunate enough to use one.
In his article Ctein said, "The 105 Apo was arguably the most perfectly made enlarging lens available, and priced accordingly. There were no detectable aberrations of any type... and it was the one true Apo on the market." On another occasion in "Darkroom User" he stated, "If you need the ultimate in colour correction this lens provides it; it costs thousands of pounds, assuming you can find one! I don't own one and you probably don't need one, but I thought you should know just in case."