Use one of those semi-large rubber bands that are stretched around lettuce or "leafy" veggies at the super-market. Stretch it around the lens diagonally. Works perfectly and does NOT interfere with operation of the lens. And, when it wears out (approximately 12 months) get another one. . .
I've been doing this for 15-20 years. Great conversation starter also. . .EVERYBODY asks: "What's that?"
PS. . .Tamron and Sigma lenses seem to have this quirky "problem". . .
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