This test shows focal length comparison on a 1.5 crop factor camera (all Nikon DX cameras) from 12mm to 500mm. All images were taken on Nikon D300 with ISO 200, f/10. The focal lengths are not 100% accurate because of different lens sizes and mounts (when short lenses such as the 50mm f/1.4 were used, the camera was mounted on the tripod, while zoom lenses had to be mounted via lens collars). The tripod was never moved (just slightly re-adjusted to focus on the top-left portion of the blue ornament). The 420 and 500mm shots are a little soft because of slight vibration and use of a teleconverter.
The shots were taken indoors because it was too cold outside :)