Stiff focusing ring on a Biotar 58/2...? No problem!!!
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Stiff focus ring in Carl Zeiss T* 50mm 1:1.7 C/Y RE-lube with #10 grease - YouTube
Buying a Used Lens: Inspection and Testing Guide for Photographers • Points in Focus Photography
Stiff focus ring In Nikon Lens Series E 100mm 1:2.8 - YouTube
Canon nFD 28mm f2 Gritty Focus Ring & Stiff Aperture Ring. Easy to clean/fix? : r/AnalogRepair
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Nikon Non-AI 28mm f3.5 Nikkor-H Lens with Hood | eBay
Re: Used Sigma UC Zoom 70-210mm focus ring very stiff/grinding and autofocus motor getting stuck: Third Party Lens Talk Forum: Digital Photography Review
How to fix your Canon 16 - 35mm L Series lens, stuck or loose focus ring - YouTube