Abbreviation: FTM = "Full Time Manual Focus" (Tamron)

The abbreviations means "Full Time Manual Focus"

Explanation from Tamron

Full Time Manual Focus makes fine tuning easy

All Tamron lenses have high autofocus precision and are designed to capture subjects easily in almost any situation, yet sometimes a photographer wants to fine tune and make adjustments on the fly. The integration of full time manual focus offers just that: instead of fumbling with switches, photographers can switch from autofocus to manual focus by simply adjusting the focus ring. This feature helps the lens produce impressive results even in telephoto situations where the depth of field is narrow.

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tamron-usa.com