Abbreviation: IF = "Internal Focusing" (Nikon)

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

Explanation from Nikon

Imagine being able to focus a lens without it changing in size. Nikonīs IF technology enables just that. All internal optical movement is limited to the interior of the nonextending lens barrel. This allows for a more compact, lightweight construction as well as a closer focusing distance. In addition, a smaller and lighter focusing lens group is employed to ensure faster focusing. The IF system is featured in most NIKKOR telephoto and selected NIKKOR zoom lenses.

See examples of effected products

Nikon AF-S 200mm f/2 G IF ED VR
Nikon AF-S 17-35mm f/2,8 IF ED
Nikon AF-S DX 12-24mm f/4 G IF-ED

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