Abbreviation: IF = "Internal Focusing System" (Tamron)

The abbreviation IF means "Internal Focusing System" and is seen on Tamron products.

Explanation from Tamron

Internal focusing (IF) provides numerous practical benefits to photographers including a non-rotating front filter ring that facilitates the positioning of polarizing and graduated filters, and more predictable handling because the lens length does not change during focusing. Even more important, Tamron’s Internal Focusing (IF) system provides a much closer minimum focusing distance (MFD) throughout its entire focusing range. In addition, IF improves optical performance by minimizing illumination loss at the corners of the image field, and helps to suppress other aberrations that become more troublesome at different focusing positions.

See examples of effected products

	Tamron SP AF 17-50mm f/2,8 XR Di-II LD Asph IF
	Tamron SP 200-500mm f/5-6,3 Di LD IF
	Tamron SP AF 180mm f/3,5 Di LD IF Macro

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