This morning I spent a couple of hours measuring the entrance pupil position (often although incorrectly called the “nodal point”) of my Nikkor AF-S 10-24 f/3.5-4.5G and AF-S 50mm f/1.4G lenses. The entrance pupil is the point around which the lens should be rotated in order to eliminate parallax when shooting multiple images that will be stitched into a panorama.
I mounted the lens on my D5000, and mounted this in portrait orientation on a tripod with a panning base. I set up a vertical rod close to the camera, and used vertical bars on a window as a far target. Both targets were checked for vertical orientation using a spirit level and the camera was levelled using the tripod levelling base. The camera was positioned so that when the targets appeared in the centre of the viewfinder, they were precisely alligned. The fore/aft position of the camera was then adjusted until no parallax was detectable in the viewfinder when panning from left to right.
Results are given as the distance from the focal plane, not from the tripod mount, so that they can be applied to any camera. For the D5000, the focal plane is 5mm behind the centre axis of the tripod mounting hole.
Nikkor AF-S 50mm f/1.4G
Measured with near target at 2m, far target at 30m, focused at 30m.
Entrance pupil is 46mm in front of the focal plane.
Nikkor AF-S 10-24mm f/3.5-4.5G
Measured with near target at 1m, far target at 10, focused at 10m
At f=10mm – entrance pupil is 105mm in front of the focal plane.
At f=12mm – entrance pupilis 103mm in front of thefocal plane.
At f=15mm – entrance pupilis 103mm in front of thefocal plane.
At f=18mm – entrance pupilis 106mm in front of the focal plane.
At f=20mm – entrance pupilis 108mm in front of the focal plane.
At f=24mm – entrance pupilis 110mm in front of the focal plane.
Comments
I estimate the measurement error as being +/- 5mm. The entrance pupil of the prime lens approximately the same distance in front of the focal plane as the nominal focal length of the lens. The entrance pupil of the ultrawide zoom is about 90mm further in front of the focal plane than the nominal focal length.
