If you own one of the very common and very excellent Russian lenses Industar-26 and Industar-61 (found on the long-lived FED 2 and later FED cameras) they are frequently found gummed-up with grease that has thickened to a sticky wax consistency. Here´s a way to fix it....
Not unlike toilet ring wax if you’ve ever had the pleasure. Common symptom: the focus feels alternately stiff and loose throughout the range like it’s rubbing on something…waxy.
So to get the most out of your lens, you’ll need to get this gunk out and replace it with fresh grease. You’ll be surprised at the difference it makes.
Luckily, it’s an easy if slighly messy task that you can do yourself!
Now, follow along with the great Matt Denton who is running this tutorial