Measuring Focal Length - 18-70mm f3.5-4.5G ED-IF AF-S DX Zoom Nikkor
Prepared 2005-11-15 (146/42926) by Bill Claff

Charts

Data was collected using a set of Kenko extension tubes. A charts of the data at 18mm and 70mm follow:

Results

The focal lengths at infinity are 18.2mm and 70.8mm.
The lens focus extension is approximately 9.4mm. This is somewhat uncertain with only 3 data points.
The lens focuses internally.
The focal lengths at nearest focus are 16.6mm and 45.8mm.

Conclusion

Note that at nearest focus the lens is actually wider (at 45.8mm) than a 50mm lens, even at maximum zoom.