28-300 set at 300mm really only 119mm?

Started Aug 8, 2012 | Discussions thread
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Jerry Jongerius
Regular MemberPosts: 311
28-300 set at 300mm really only 119mm?
Aug 8, 2012

I was always aware that focusing distance could affect focal length, but I was very surprised by just how much.

Take the "AF-S NIKKOR 28-300mm f/3.5-5.6G ED VR" lens. When set to 300mm and focused very close (say 18 3/8 inches from 'film plane' mark on camera), the resulting photo (on a D700/FX) of a ruler showed 4 1/8 inches (horizontal) visible.

A little math says that is an effective focal length of 119.35, not 300mm. I would expect an error in the math, but a quick Google search confirms that others also see similar results with that lens.

All the more interesting given the Nikon manual for that lens says "This lens is equipped with the Internal Focusing (IF) system. As the shooting distance decreases, the focal length also decreases."

So, an error in the math, or accurate?

Nikon D700
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